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	<front>
		<journal-meta>
			<journal-id journal-id-type="publisher-id">rac</journal-id>
			<journal-title-group>
				<journal-title>Revista argentina de cardiología</journal-title>
				<abbrev-journal-title abbrev-type="publisher">Rev Argent Cardiol</abbrev-journal-title>
			</journal-title-group>
			<issn pub-type="ppub">0034-7000</issn>
			<issn pub-type="epub">1850-3748</issn>
			<publisher>
				<publisher-name>Sociedad Argentina de Cardiología</publisher-name>
			</publisher>
		</journal-meta>
		<article-meta>
			<article-id pub-id-type="doi">10.7775/rac.es.v93.i2.20883</article-id>
			<article-id pub-id-type="publisher-id">00005</article-id>
			<article-categories>
				<subj-group subj-group-type="heading">
					<subject>ORIGINAL ARTICLE</subject>
				</subj-group>
			</article-categories>
			<title-group>
				<article-title>Características genéticas y clínicas de los pacientes con genotipo asociado al síndrome QT largo congénito. Experiencias durante un seguimiento a largo plazo</article-title>
				<trans-title-group xml:lang="en">
					<trans-title>Genetic and Clinical Characteristics of Patients with Congenital Long QT Syndrome- Genotype. Experiences During Long-Term Follow-Up</trans-title>
				</trans-title-group>
			</title-group>
			<contrib-group>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0002-3476-4055</contrib-id>
					<name>
						<surname>SETTEPASSI</surname>
						<given-names>PAOLA</given-names>
					</name>
					<xref ref-type="aff" rid="aff1b"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0001-7341-7032</contrib-id>
					<name>
						<surname>HYUN</surname>
						<given-names>SOK YOO</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0009-0004-9186-6527</contrib-id>
					<name>
						<surname>MUSCHIETTI</surname>
						<given-names>FLORENCIA</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0009-0008-5212-0828</contrib-id>
					<name>
						<surname>ETCHEVERRY</surname>
						<given-names>DANIEL</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0003-1380-1571</contrib-id>
					<name>
						<surname>GARRO</surname>
						<given-names>HUGO</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0002-5923-2039</contrib-id>
					<name>
						<surname>PAOLUCCI</surname>
						<given-names>ANALIA</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0001-5941-1064</contrib-id>
					<name>
						<surname>PRINCIPATO</surname>
						<given-names>MARIO</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
					<xref ref-type="fn" rid="fn1"><sup>MTSAC</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0003-3076-9745</contrib-id>
					<name>
						<surname>CARBAJALES</surname>
						<given-names>JUSTO</given-names>
					</name>
					<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
					<xref ref-type="fn" rid="fn1"><sup>MTSAC</sup></xref>
				</contrib>
				</contrib-group>
				<aff id="aff1">
					<label>1</label>
					<institution content-type="original">Hospital General de Agudos José María Ramos Mejía, Ciudad Autónoma de Buenos Aires, Argentina.</institution>
					<institution content-type="normalized">Hospital General de Agudos José María Ramos Mejía</institution>
					<addr-line>
						<named-content content-type="city">Ciudad Autónoma de Buenos Aires</named-content>
					</addr-line>
					<country country="AR">Argentina</country>
				</aff>
				<aff id="aff1b">
					<label>1</label>
					<institution content-type="original">Hospital General de Agudos José María Ramos Mejía, Ciudad Autónoma de Buenos Aires, Argentina.</institution>
					<institution content-type="normalized">Hospital General de Agudos José María Ramos Mejía</institution>
					<addr-line>
						<named-content content-type="city">Ciudad Autónoma de Buenos Aires</named-content>
					</addr-line>
					<country country="AR">Argentina</country>
					<email>paosettepassi@gmail.com</email>
				</aff>
			<author-notes>
				<corresp id="c1">
					<label>Correspondencia</label>: Paola Settepassi. E-mail: <email>paosettepassi@gmail.com</email>
				</corresp>
				<fn fn-type="other" id="fn2">
					<p>Este trabajo resultó ganador del Premio a la investigación SAC: Cardiólogo Investigador Joven en el 50 Congreso Argentino de Cardiología</p>
				</fn>
				<fn fn-type="conflict" id="fn3">
					<p>Declaración de conflicto de intereses Los autores declaran no tener conflicto de intereses. (Véase formularios de conflictos de interés de los autores en la Web).</p>
				</fn>
			</author-notes>
			<!--<pub-date date-type="pub" publication-format="electronic">
				<day>16</day>
				<month>05</month>
				<year>2025</year>
			</pub-date>
			<pub-date date-type="collection" publication-format="electronic">
				<season>Mar-Apr</season>
				<year>2025</year>
			</pub-date>-->
			<pub-date pub-type="epub-ppub">
				<season>Mar-Apr</season>
				<year>2025</year>
			</pub-date>
			<volume>93</volume>
			<issue>2</issue>
			<fpage>117</fpage>
			<lpage>123</lpage>
			<history>
				<date date-type="received">
					<day>05</day>
					<month>12</month>
					<year>2024</year>
				</date>
				<date date-type="accepted">
					<day>17</day>
					<month>02</month>
					<year>2025</year>
				</date>
			</history>
			<permissions>
				<license license-type="open-access" xlink:href="https://creativecommons.org/licenses/by-nc/4.0/" xml:lang="es">
					<license-p>Este es un artículo publicado en acceso abierto bajo una licencia Creative Commons</license-p>
				</license>
			</permissions>
			<abstract>
				<title>RESUMEN</title>
				<sec>
					<title>Introducción:</title>
					<p> El síndrome de intervalo QT largo (SQTL) congénito es una canalopatía hereditaria con un gran espectro genético pero una manifestación fenotípica en común, el intervalo QT prolongado. Sin embargo, la presentación clínica y la historia natural es muy variable. </p>
				</sec>
				<sec>
					<title>Objetivos:</title>
					<p> Definir el perfil de las características genéticas y clínicas de los pacientes con SQTL congénito durante un seguimiento a largo plazo.</p>
				</sec>
				<sec>
					<title>Material y métodos:</title>
					<p> Estudio de cohorte retrospectiva de pacientes con genotipo de SQTL congénito. Se definió la incidencia de eventos serios en el seguimiento. Las variables cuantitativas se expresan como mediana y rango intercuartilo (RIC) y las cualitativas como frecuencia y porcentaje.</p>
				</sec>
				<sec>
					<title>Resultados:</title>
					<p> El 30% de los pacientes tenían el genotipo de SQTL1, el 65% el de SQTL2 y 5% el de SQTL3. El 57% tenía la mutación <italic>missense</italic>, el 11% <italic>nonsense</italic> y el 32% <italic>frameshift</italic>. El intervalo QT corregido fue de 481 ± 22 mseg. El 66% manifestó el fenotipo, pero solo el 32% de manera permanente. El 39% tuvo episodios sincopales. El paro cardíaco fue la primera manifestación en el 7%. El 11% tuvo recurrencia de síncope aún luego de terapia farmacológica y el 5% padeció muerte súbita. Siete pacientes recibieron un cardiodesfibrilador implantable (CDI). De ellos, el 29% tuvo choques por taquicardia o fibrilación ventricular (TV/FV) y el 58% complicaciones asociadas a los dispositivos. </p>
				</sec>
				<sec>
					<title>Conclusiones:</title>
					<p> La mayoría de los pacientes tenían el genotipo de SQTL1 o SQTL2, el fenotipo intermitente y una buena respuesta al tratamiento. La edad temprana del implante y la elevada tasa de complicaciones asociadas al largo plazo exigen una evaluación personalizada al momento de indicar el CDI. </p>
				</sec>
			</abstract>
			<trans-abstract xml:lang="en">
				<title>ABSTRACT</title>
				<sec>
					<title>Background: </title>
					<p>Congenital long QT syndrome (LQTS) is an inherited channelopathy with a broad genetic spectrum but with a common phenotypic manifestation, the prolonged QT interval. However, its clinical presentation and natural history are highly variable.</p>
				</sec>
				<sec>
					<title>Objectives: </title>
					<p>The aim of this study was to define the genetic and clinical characteristics of patients with congenital LQTS during a long-term follow-up.</p>
				</sec>
				<sec>
					<title>Methods: </title>
					<p>Retrospective cohort study of patients with congenital LQTS genotype. The incidence of serious events at follow-up was defined. Quantitative variables are expressed as median and interquartile range (IQR) and qualitative variables as frequency and percentage.</p>
				</sec>
				<sec>
					<title>Results: </title>
					<p>Forty-four patients were included. Thirty percent of patients had LQTS1 genotype, 65% LQTS2 genotype and 5% LQTS3 genotype; 57% of cases carried the <italic>missense</italic> mutation, 11% the <italic>nonsense</italic> mutation and 32% the <italic>frameshift</italic> mutation. The corrected QT interval was 490 msec (IQR 462-498). The phenotype was present in 66% of patients, but it remained permanently only in 32%. Syncopal episodes occurred in 39% of patients. Cardiac arrest was the first manifestation in 7% of cases. Syncope recurred in 11% of patients even after pharmacological therapy, and 5% suffered sudden death. Seven patients received an implantable cardiodesfibrillator (ICD). Among them, 29% received shocks due to ventricular tachycardia or ventricular fibrillation (VT/VF) and 58% presented device-related complications.</p>
				</sec>
				<sec>
					<title>Conclusions: </title>
					<p>Most patients had the LQTS1 or LQTS2 genotype, the intermittent phenotype, and a good response to treatment. Implantation at an early age and the high rate of complications during long-term follow-up require careful evaluation when indicating an ICD.</p>
				</sec>
			</trans-abstract>
			<kwd-group xml:lang="es">
				<title>Palabras clave:</title>
				<kwd>Síndrome QT largo</kwd>
				<kwd>Muerte súbita</kwd>
				<kwd>Síncope</kwd>
				<kwd>Mutación genética</kwd>
				<kwd>Cardiodesfibrilador implantable</kwd>
			</kwd-group>
			<kwd-group xml:lang="en">
				<title>Key words:</title>
				<kwd>Long QT syndrome</kwd>
				<kwd>Sudden death</kwd>
				<kwd>Syncope</kwd>
				<kwd>Genetic mutation</kwd>
				<kwd>Cardiodesfibrilador implantable</kwd>
			</kwd-group>
			<counts>
				<fig-count count="2"/>
				<table-count count="2"/>
				<equation-count count="0"/>
				<ref-count count="22"/>
				<page-count count="7"/>
			</counts>
		</article-meta>
	</front>
	<body>
		<sec sec-type="intro">
			<title>INTRODUCCIÓN</title>
			<p>El SQTL congénito se caracteriza por la prolongación del potencial de acción del miocardio ventricular debido al aumento de las corrientes de entrada de sodio y calcio (<italic>INa</italic> e <italic>ICa</italic>
 <sub>
 <italic>L</italic>
</sub> ) o la disminución de las corrientes de salida de potasio (<italic>IKs</italic>, <italic>IKr</italic> e <italic>IK1</italic>). Hasta el momento se identificaron mutaciones en 20 genes diferentes que codifican los canales iónicos cardíacos y/o proteínas moduladoras que intervienen de manera directa o indirecta en la formación de estas corrientes. (<xref ref-type="bibr" rid="B1">1</xref>)</p>
			<p>Con una prevalencia en la población general de 1 en 2000 individuos, ya no es una situación excepcional ver a un paciente con un intervalo QT prolongado en una consulta médica cotidiana para práctica de deporte, escolaridad o prelaboral. (<xref ref-type="bibr" rid="B2">2</xref>)</p>
			<p>Con el avance de la tecnología informática e ingeniería genética, se han identificado centenares de variantes en cada uno de los genes involucrados en el SQTL que, a través de diferentes tipos de mutaciones alteran el funcionamiento de los canales iónicos de los miocitos. La mayoría de las mutaciones muestran un patrón de herencia autosómico dominante. De esta manera, los individuos nacen con la mutación causal de la enfermedad y conviven con ella a lo largo de toda su vida. </p>
			<p>Todos los individuos afectados presentan una manifestación fenotípica en común, la prolongación de la duración de la repolarización ventricular. Sin embargo, la existencia de una amplia variabilidad clínica entre los pacientes plantea interrogantes sobre los factores epigenéticos que modulan su expresión fenotípica. Aun cuando los pacientes nacen con el genotipo patogénico, el fenotipo puede no manifestarse nunca, evidenciarse tardíamente o en algunos casos, sólo hacerlo de manera intermitente, expresándose sólo en determinados días y pudiendo permanecer por periodos prolongados de tiempo totalmente asintomáticos. Así mismo, el riesgo de padecer eventos cardíacos adversos puede variar entre los portadores de la misma variante genética y aún en la misma persona, dependiendo de la situación a la que fue expuesta. (<xref ref-type="bibr" rid="B3">3</xref>)</p>
			<p>En este trabajo, hemos evaluado las características clínicas y genéticas de nuestros pacientes con diagnóstico de SQTL mediante un estudio genético con secuenciación masiva en paralelo y un seguimiento clínico a largo plazo por más de 10 años, pudiendo así valorar, tanto la historia natural de la enfermedad, como la aparición de eventos cardiacos adversos (síncope, taquiarritmia ventricular y/o muerte súbita cardíaca), la respuesta al tratamiento farmacológico y/o dispositivos antiarrítmicos implantables, y las complicaciones asociadas a ellos.</p>
		</sec>
		<sec sec-type="materials|methods">
			<title>MATERIAL Y MÉTODOS</title>
			<p>Se diseñó un estudio retrospectivo seleccionando a los individuos con sospecha de síndrome QT largo congénito que concurren al Hospital General de Ramos Mejía. Se utilizaron los siguientes criterios de inclusión: hombres y mujeres con edad de 5 a 70 años; sospecha clínica de SQTL congénito (un intervalo QTc ≥480 milisegundos en el ECG o puntuación de Schwartz ≥3); identificación de una variante patogénica de SQTL congénito en estudio genético. Se excluyó a aquellos con alguno de los siguientes criterios: SQTL adquirido por medicamentos; negación a firmar el consentimiento informado; menores de 18 años, sin consentimiento de los progenitores o tutores legales; hallazgo negativo de estudio genético. De cada uno de ellos, se obtuvieron registros de ECG de 12 derivaciones simultáneas. Los intervalos QTc fueron corregidos en función de la frecuencia cardíaca mediante la fórmula de Bazett (QTc = QT/√RR, en segundos). </p>
			<p>Para el análisis de secuencias y las pruebas de deleción/duplicación se utilizó el método de secuenciación masiva en paralelo (NGS) con un panel de más de 150 genes para arritmias y miocardiopatías (ABCC9, ACADVL, ACTC1, ACTN2, AGL, ALMS1, ALPK3, BAG3, BRAF, CACNA1C, CACNA1D, CALM1, CALM2, CALM3, CASQ2, CBL, CDH2, CPT2, CRYAB, CSRP3, DES, DMD, DNAJC19, DOLK, DSC2, DSG2, DSP, ELAC2, EMD, EYA4, FHL1, FKRP, FKTN, FLNC, GAA, GATA4, GATA5, GJA5, GLA, HCN4, HRAS, JUP, KCNE1, KCNH2, KCNJ2, KCNQ1, KRAS, LAMP2, LMNA, LZTR1, MAP2K1, MAP2K2, MRAS, MTO1, MYBPC3, MYH7, MYL2, MYL3, MYL4, MYLK3, NF1, NKX2-5, NRAS, PCCA, PCCB, PKP2, PLN, PPA2, PPCS, PPP1CB, PRKAG2, PTPN11, RAF1, RASA1, RBM20, RIT1, RYR2, SCN5A, SDHA, SGCD, SHOC2, SLC22A5, SOS1, SOS2, SPRED1, TAZ, TBX20, TCAP, TMEM43, TMEM70, TNNC1, TNNI3, TNNI3K, TNNT2, TPM1, TRDN, TRPM4, TTN, TTR, VCL, A2ML1, AKAP9, ANK2, ANKRD1, CACNA2D1, CACNB2, CALR3, CAV3, CHRM2, CTF1, CTNNA3, DTNA, FHL2, GATA6, GATAD1, GPD1L, HAND1, ILK, JPH2, KCNA5, KCND3, KCNE2, KCNE3, KCNE5, KCNJ5, KCNJ8, KCNK3, KIF20A, KLF10, LAMA4, LDB3, LRRC10, MAP3K8, MED12, MYH6, MYLK2, MYOM1, MYOZ2, MYPN, NEBL, NEXN, NPPA, PDLIM3, PLEKHM2, PRDM16, RANGRF, RASA2, RRAS, SCN10A, SCN1B, SCN2B, SCN3B, SCN4B, SLMAP, SNTA1, TMPO, TXNRD2), desarrollado por Invitae® (1400 16th Street, San Francisco, CA 94103, EE. UU.). El ADN genómico obtenido de la muestra de sangre periférica se enriqueció para las regiones objetivo mediante un protocolo basado en hibridación y se secuenció con tecnología Illumina®. Todas las regiones objetivo se secuenciaron con una profundidad ≥50x o se complementaron con análisis adicionales. Las lecturas se alinearon con una secuencia de referencia (GRCh37) y los cambios de secuencia se identificaron e interpretaron en el contexto de una única transcripción clínicamente relevante. El enriquecimiento y el análisis se centraron en la secuencia codificante de las transcripciones indicadas, 20 pb de la secuencia intrónica flanqueante y otras regiones genómicas específicas que se demostró que eran causantes de la enfermedad en el momento del diseño del ensayo. Las variantes detectadas se evaluaron consultando las siguientes bases de datos: dbSNP de NCBI (<italic>National Center for Biotechnology Information</italic>, https://www.ncbi.nlm.nih.gov/snp/), ExAC (<italic>Exome Aggregation Consortium</italic>, https://exac.broadinstitute.org), gnomAD (<italic>Genome Aggregation Database</italic>, https://gnomad.broadinstitute.org/) y OMIM (<italic>Online Mendelian Inheritance in Man</italic>, https://omim.org/). La patogenicidad de las variantes fue estimada mediante tres tipos diferentes de software de predicción: SIFT (https://sift.bii.a-star.edu.sg/), PolyPhen-2 (https://genetics.bwh.harvard.edu/pph2/) y Align-GVGD (https://bio.tools/align-gvgd/).</p>
			<p>Las variantes se clasificaron como patogénica o probablemente patogénica, de significado incierto, probablemente benigna o benigna utilizando un sistema de puntuación de evidencia basado en el consenso del Colegio Americano de Genética Médica y Genómica y la Asociación de Patología Molecular. (<xref ref-type="bibr" rid="B4">4</xref>) Los resultados se clasificaron como positivos, negativos, portadores o inciertos según la clasificación de la variante identificada y el patrón de herencia de la afección asociada.</p>
			<sec>
				<title>Análisis estadístico</title>
				<p>Las variables cuantitativas fueron expresadas en promedio ± desviación estándar (DE). Las variables cualitativas fueron expresadas como porcentajes (%). </p>
			</sec>
			<sec>
				<title>Consideraciones éticas</title>
				<p>El estudio se realizó de acuerdo con las normas éticas de la Declaración de Helsinki, y el protocolo del estudio fue aprobado por el Comité de Ética del Hospital General de Agudos Dr. José María Ramos Mejía, Ciudad Autónoma de Buenos Aires, Argentina.</p>
			</sec>
		</sec>
		<sec sec-type="results">
			<title>RESULTADOS</title>
			<p>Cuarenta y cuatro pacientes con diagnóstico genético de SQTL fueron seguidos durante 46 meses (RIC 35-175). De ellos, 26 (59%) eran mujeres. La edad promedio fue de 35 ± 17 años. Treinta y cinco pacientes (80%) refirieron antecedentes de muerte súbita (MS) en familiares de primer y segundo grado. </p>
			<p>De los pacientes, 13 (30%) correspondieron al genotipo de SQTL tipo 1 (gen KCNQ1), 29 (65%) al de SQTL tipo 2 (gen KCNH2) y 2 (5%) al de SQTL tipo 3 (gen SCN5A). La mutación puntual <italic>missense</italic> (con cambio de sentido) fue identificada en 25 pacientes (57%). Cinco pacientes (11%) eran portadores de una mutación <italic>nonsense</italic> (sin sentido). En 14 pacientes (32%) se halló una mutación <italic>frameshift</italic> (con cambio de marco de lectura). El intervalo QT corregido fue de 481 ± 22 mseg. En 29 pacientes (66%) se observó la manifestación fenotípica de SQTL (QTc &gt;480 mseg). Sin embargo, sólo 14 individuos (32%) manifestaban el fenotipo de manera permanente (<xref ref-type="table" rid="t1">Tabla 1</xref>). </p>
			<p>
				<table-wrap id="t1">
					<label>Tabla 1</label>
					<caption>
						<title>Características genéticas y clínicas</title>
					</caption>
					<table frame="hsides" rules="groups">
						<colgroup>
							<col span="4"/>
						</colgroup>
						<thead>
							<tr style="border: 0; background-color:#ab0534;color:#ffffff;">
								<th align="left" colspan="4">Variable </th>
							</tr>
						</thead>
						<tbody>
							<tr style="background-color: #e3aea9;">
								<td align="left">KCNQ1 (SQTL1)</td>
								<td align="center">13</td>
								<td align="center">30%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">KCNH2 (SQTL2)</td>
								<td align="center">29</td>
								<td align="center">65%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">SCN5A (SQTL3)</td>
								<td align="center">2</td>
								<td align="center">5%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left"><italic>Nonsense</italic></td>
								<td align="center">5</td>
								<td align="center">11%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left"><italic>Missense</italic></td>
								<td align="center">25</td>
								<td align="center">57%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left"><italic>Frameshift</italic></td>
								<td align="center">14</td>
								<td align="center">32%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Familiar con MS</td>
								<td align="center">35</td>
								<td align="center">80%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Síncopes</td>
								<td align="center">17</td>
								<td align="center">39%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Paro cardíaco</td>
								<td align="center">3</td>
								<td align="center">7%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">QTc (mseg)</td>
								<td align="center">490 (RIC 462-498)</td>
								<td align="center"> 
 </td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">QTc ≥480 mseg.</td>
								<td align="center">29</td>
								<td align="center">66%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Fenotipo permanente</td>
								<td align="center">14</td>
								<td align="center">32%</td>
							</tr>
						</tbody>
					</table>
					<table-wrap-foot>
						<fn id="TFN1">
							<p>Las variables cualitativas se presentan como frecuencia y porcentaje, las cuantitativas como media y desviación estándar</p>
						</fn>
					</table-wrap-foot>
				</table-wrap>
			</p>
			<p>Episodios sincopales fueron observados en 17 individuos (39%), en especial durante la adolescencia. El paro cardíaco fue la primera manifestación clínica en 3 pacientes (7%). La edad en la que comenzaron a manifestar los síntomas fue de 20 ± 8 años. </p>
			<p>El 93% recibió tratamiento con betabloqueantes (un 72% con propranolol). Dos pacientes (5%) con diagnóstico de SQTL tipo 3 fueron tratados con un bloqueante sódico (flecainida). Cinco pacientes (11%) tuvieron recurrencia del síncope aún luego de terapia farmacológica instaurada. Dos individuos con SQTL tipo 2 (5%) padecieron MS nocturna a los 17 y 66 años. </p>
			<p>Por otro lado, siete pacientes requirieron del implante de un cardiodesfibrilador (CDI) a la edad de 22 ± 6 años. De ellos, el 29% tuvo choques por taquicardia o fibrilación ventricular (TV/FV) y el 58% presentó complicaciones asociadas a los dispositivos implantables (infección o desplazamiento/fractura de catéter) durante el seguimiento de 161 meses (RIC 83-229) (<xref ref-type="table" rid="t2">tabla 2</xref>). </p>
			<p>
				<table-wrap id="t2">
					<label>Tabla 2</label>
					<caption>
						<title>Tratamiento y eventos cardíacos adversos durante el seguimiento.</title>
					</caption>
					<table frame="hsides" rules="groups">
						<colgroup>
							<col span="3"/>
						</colgroup>
						<thead>
							<tr style="border: 0; background-color:#ab0534;color:#ffffff;">
								<th align="left" colspan="3">Seguimiento </th>
							</tr>
						</thead>
						<tbody>
							<tr style="background-color: #e3aea9;">
								<td align="left">Betabloqueantes</td>
								<td align="center">41</td>
								<td align="center">93%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Bloqueantes sódicos</td>
								<td align="center">2</td>
								<td align="center">5%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Recurrencia de síncope</td>
								<td align="center">5</td>
								<td align="center">11%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">MS</td>
								<td align="center">2</td>
								<td align="center">5%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Implante CDI</td>
								<td align="center">7</td>
								<td align="center">16%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Edad de implante</td>
								<td align="center">18 (RIC 16+26) </td>
								<td align="center"> </td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Recambio del CDI (n° dispositivos/ paciente)</td>
								<td align="center">2,1</td>
								<td align="center"> </td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Choque x TV/FV</td>
								<td align="center">2</td>
								<td align="center">29%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Infección asociada a CDI</td>
								<td align="center">2</td>
								<td align="center">29%</td>
							</tr>
							<tr style="background-color: #e3aea9;">
								<td align="left">Desplazamiento o fractura de catéter</td>
								<td align="center">2</td>
								<td align="center">29%</td>
							</tr>
						</tbody>
					</table>
					<table-wrap-foot>
						<fn id="TFN2">
							<p>CDI: cardiodesfibrilador implantable; FV: fibrilación ventricular; MS: muerte súbita; TV: taquicardia ventricular </p>
						</fn>
						<fn id="TFN3">
							<p>Las variables cualitativas se presentan como frecuencia y porcentaje, las cuantitativas como media y desviación estándar</p>
						</fn>
						<fn id="TFN4">
							<p>Los porcentajes de choque, infecciòn y desplazamiento del catèter se refieren a los 7 pacientes que recibieron CDI </p>
						</fn>
					</table-wrap-foot>
				</table-wrap>
			</p>
		</sec>
		<sec sec-type="discussion">
			<title>DISCUSIÓN</title>
			<p>El SQTL congénito descrito por Jervell y Lange-Nielsen en 1957 y por Romano y Ward en 1964 es una canalopatía hereditaria que se caracteriza por una alteración en la repolarización ventricular y se manifiesta por una prolongación anormal en la duración de intervalo QTc. Predispone a la aparición de las taquiarritmias ventriculares potencialmente letales (<italic>torsade de pointes</italic> y/o fibrilación ventricular) que suele ocurrir por el aumento del tono adrenérgico tras los estímulos auditivos, el ejercicio físico o estrés emocional. (<xref ref-type="bibr" rid="B5">5</xref>,<xref ref-type="bibr" rid="B6">6</xref>)</p>
			<p>En los últimos 25 años, 20 genes fueron asociados con el SQTL congénito. Sin embargo, un análisis reciente clasificó nuevamente a varios de estos genes como de evidencia limitada o controvertida. (<xref ref-type="bibr" rid="B7">7</xref>) Este enfoque dejó siete genes con evidencia definitiva o sólida de causalidad (KCNQ1, KCNH2, SCN5A, CALM1, CALM2, CALM3 y TRDN). Todos estos genes codifican canales iónicos involucrados en la repolarización cardíaca o proteínas que regulan o modulan la función del canal iónico. </p>
			<p>El 90% de los individuos con genotipo de SQTL son portadores de mutaciones en uno de los 3 genes principales de la enfermedad: el KCNQ1 (SQTL tipo 1), el KCNH2 (SQTL tipo 2) y el SCN5A (SQTL tipo 3), que codifican a las subunidades alfa de los canales iónicos Kv7.1 (<italic>IKs</italic>), Kv11.1 (<italic>IKr</italic>) y Nav1.5 (<italic>INa</italic>), respectivamente (<xref ref-type="fig" rid="f1">Figura 1</xref>). (<xref ref-type="bibr" rid="B8">8</xref>,<xref ref-type="bibr" rid="B9">9</xref>)</p>
			<p>
				<fig id="f1">
					<label>Figura 1</label>
					<caption>
						<title>Canales iónicos involucrados en SQTL tipo 1, tipo 2 y tipo 3. El gen KCNQ1 codifica a la subunidad alfa del canal de potasio voltaje dependiente Kv7.1 (responsable de corriente rectificadora <italic>IKs</italic>). El gen KCNH2 codifica a la subunidad alfa del canal de potasio voltaje dependiente Kv11.1 (responsable de corriente rectificadora <italic>IKr</italic>). El canal de sodio voltaje dependiente Nav1.5 (responsable de corriente <italic>INa</italic>) es codificado por gen SCN5A.</title>
					</caption>
					<graphic xlink:href="1850-3748-rac-93-02-117-gf1.jpg"/>
				</fig>
			</p>
			<p>Aproximadamente el 40% de las mutaciones corresponden a mutaciones sin sentido (<italic>nonsense</italic>), que consisten en una mutación puntual en una secuencia de ADN que da como resultado un codón de terminación prematura), o a mutaciones de cambio de marco de lectura (<italic>frameshift</italic>) causadas por la inserción o deleción de nucleótidos en una secuencia de ADN, lo que genera un marco de lectura completamente diferente del original. Estas mutaciones alteran la síntesis proteica y generan subunidades alfa defectuosas de los canales iónicos. El 60% restante, son mutaciones con cambio de sentido, de sentido erróneo o contrasentido (<italic>missense</italic>), donde un solo cambio de nucleótido altera un codón de un aminoácido (<xref ref-type="fig" rid="f2">Figura 2</xref>). Estas mutaciones pueden alterar la permeabilidad del poro, la activación/desactivación o el tráfico intracelular de los canales iónicos. (<xref ref-type="bibr" rid="B10">10</xref>)</p>
			<p>
				<fig id="f2">
					<label>Figura 2</label>
					<caption>
						<title>Ejemplo de tipos de mutaciones. <italic>Missense</italic>: mutación puntual de ADN que cambia un aminoácido. <italic>Nonsense</italic>: mutación puntual de ADN que introduce un codón de terminación prematura. <italic>Frameshift</italic>: inserción o deleción de ADN con cambio de marco de lectura. Modificada de: Nerbonne JM, Kass RS. Molecular physiology of cardiac repolarization Physiol Rev 2005;85:1205-53. <ext-link ext-link-type="uri" xlink:href="https://10.1152/physrev.00002.2005">https://10.1152/physrev.00002.2005</ext-link>
						</title>
						<p>Secuencia de ADN: A: adenina; T: timina; C: citosina; G: guanina. Secuencia de aminoácidos: Ser: serina; Val: valina; Pro: prolina; Tyr: tirosina; Thr: treonina; Leu: leucina; Stop: codón de terminación prematura.</p>
					</caption>
					<graphic xlink:href="1850-3748-rac-93-02-117-gf2.jpg"/>
				</fig>
			</p>
			<p>En nuestro estudio, los pacientes mostraron un perfil genético similar a los estudios mencionados. El 95% de los pacientes eran portadores del genotipo SQTL tipo 1 (KCNQ1) o de SQTL tipo 2 (KCNH2). Las variantes genéticas predominantes se debieron a mutaciones puntuales <italic>missense</italic> con cambio de un sólo aminoácido en la secuencia proteica. </p>
			<p>Con frecuencia, el carácter intermitente de la manifestación del fenotipo de SQTL dificulta el diagnóstico de los pacientes. En nuestro estudio, la mayoría de los pacientes (66%) manifestó el fenotipo de SQTL (QTc &gt;480 mseg) pero sólo un tercio tuvo el fenotipo permanente. Estos resultados fueron comparables a los resultados del estudio de Yoo et al., en el cual los pacientes con SQTL mostraron oscilaciones significativas del intervalo QT en diferentes mediciones realizadas y sólo el 20% mantuvo el fenotipo permanente. (<xref ref-type="bibr" rid="B11">11</xref>) Estos hallazgos sugieren que para el diagnóstico de SQTL congénito, los pacientes deben ser evaluados de manera minuciosa y contínua mediante ECG seriados, ECG de esfuerzo o registro dinámico con monitoreo Holter de manera periódica. En estas circunstancias, el estudio genético para identificar la variante patogénica responsable se torna crucial para detectar a los pacientes con SQTL congénito de manera precisa y precoz. </p>
			<p>A menudo, los individuos con SQTL suelen manifestar el fenotipo y padecer episodios sincopales y/o muerte súbita a edades tempranas. La mortalidad de los pacientes con SQTL oscila entre 1 a 2% en 5 años. (<xref ref-type="bibr" rid="B12">12</xref>) Los betabloqueantes son efectivos, especialmente en el SQTL1 en cual la TV/FV es gatillada por el esfuerzo. El incumplimiento del tratamiento y el uso de fármacos que prolongan el intervalo QT son responsables principales de fracasos terapéuticos. (<xref ref-type="bibr" rid="B13">13</xref>,<xref ref-type="bibr" rid="B14">14</xref>) En el SQTL2 y el SQTL3, los eventos arrítmicos letales suelen desencadenarse en reposo o ante estímulo auditivo o emocional. (<xref ref-type="bibr" rid="B15">15</xref>,<xref ref-type="bibr" rid="B16">16</xref>) Entre los individuos con un cardiodesfibrilador implantable (CDI), la tasa de eventos recurrentes es de aproximadamente el 3% a 28% en 5 años. (<xref ref-type="bibr" rid="B17">17</xref>,<xref ref-type="bibr" rid="B18">18</xref>)</p>
			<p>Existe aún la tendencia a considerar innecesaria la identificación del genotipo de los pacientes con SQTL, una vez efectuado el diagnóstico mediante los criterios clínicos. Esta conducta imposibilita el inicio del cribado en cascada de la familia afectada. Considerando que la respuesta a los fármacos (betabloqueantes <italic>vs</italic> bloqueantes sódicos) y los estímulos que actúan como gatillo arritmogénico (esfuerzo, auditivo o emocional) son muy diferentes entre los genotipos, el desconocimiento de la causa genética dificulta brindar una terapia adecuada a los pacientes. Las consecuencias podrían resultar en la ocurrencia de muertes que podrían evitarse, en especial, entre los individuos con genotipo positivo y fenotipo negativo. De esta manera, la biología molecular ya no debe considerarse como campo exclusivo de investigación sino una herramienta médica esencial y cotidiana. (<xref ref-type="bibr" rid="B19">19</xref>)</p>
			<p>En nuestro estudio, el implante de CDI fue indicado entre la segunda y tercera década de la vida. El motivo principal fue la ocurrencia de síncopes recurrentes aún con terapia betabloqueante (prevención primaria). Las 2 mujeres (una con SQTL1 y otra SQTL2) que recibieron un CDI para prevención secundaria tuvieron terapias adecuadas por TV/FV luego de transcurrir 2 a 6 años del implante. Por otro lado, la tasa de complicaciones asociadas a los dispositivos (infección o desplazamiento/fractura de catéter durante el seguimiento a largo plazo) fue elevada. Según las guías vigentes, el implante de CDI está indicado para fines de prevención secundaria (en individuos que padecieron un paro cardíaco reanimado, clase I) y primaria (en aquellos con síncopes recurrentes bajo tratamiento betabloqueante, clase IIa). (<xref ref-type="bibr" rid="B20">20</xref>) Evidentemente, la decisión de implantar el CDI salva la vida de los pacientes de alto riesgo de MS cardíaca. Sin embargo, en el SQTL congénito, al igual que en otras canalopatías hereditarias, la edad muy temprana de diagnóstico e implante de los dispositivos y la elevada tasa (más de 20% en 5 a 10 años) de complicaciones asociadas (infección, perforación miocárdica, desplazamiento, desgaste y/o fractura del catéter, consecuencias psicológicas, etc) que ocurren a lo largo de la vida de los pacientes, sugieren que la decisión de indicar el CDI sea basada en una evaluación minuciosa y cautelosa. (<xref ref-type="bibr" rid="B21">21</xref>,<xref ref-type="bibr" rid="B22">22</xref>)</p>
		</sec>
		<sec sec-type="conclusions">
			<title>CONCLUSIONES</title>
			<p>El perfil genético de nuestros pacientes coincide con lo reportado en la literatura. La identificación del genotipo permite pesquisar a los portadores asintomáticos que no expresan el fenotipo de manera permanente, logrando así un diagnóstico preciso y tratamiento precoz mediante la estrategia de cribado en cascada de los familiares. La mayoría de los pacientes responden favorablemente a los betabloqueantes. Sin embargo, existe un grupo de alto riesgo (TV/FV previas) que requiere el implante de un CDI para prevención de MS. La edad temprana del implante y la elevada tasa de complicaciones asociadas al largo plazo exigen una evaluación personalizada y minuciosa al momento de indicarlo. </p>
		</sec>
	</body>
	<back>
		<ref-list>
			<title>BIBLIOGRAFÍA / REFERENCES</title>
			<ref id="B1">
				<label>1</label>
				<mixed-citation>Schwartz PJ, Ackerman MJ, George AL, Wilde AA, . Impact of genetics on the clinical management of channelopathies. J Am Coll Cardiol 2013;62:169-80. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/j.jacc.2013.04.044">https://doi.org/10.1016/j.jacc.2013.04.044</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Ackerman</surname>
							<given-names>MJ</given-names>
						</name>
						<name>
							<surname>George</surname>
							<given-names>AL</given-names>
						</name>
						<name>
							<surname>Wilde</surname>
							<given-names>AA</given-names>
						</name>
					</person-group>
					<article-title>Impact of genetics on the clinical management of channelopathies</article-title>
					<source>J Am Coll Cardiol</source>
					<year>2013</year>
					<volume>62</volume>
					<fpage>169</fpage>
					<lpage>180</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/j.jacc.2013.04.044">https://doi.org/10.1016/j.jacc.2013.04.044</ext-link>
				</element-citation>
			</ref>
			<ref id="B2">
				<label>2</label>
				<mixed-citation>Schwartz PJ, Stramba-Badiale M, Crotti L, Pedrazzini M, Besana A, Bosi G, . Prevalence of the congenital long-QT syndrome. Circulation 2009;120:1761-7. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.109.863209">https://doi.org/10.1161/CIRCULATIONAHA.109.863209</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Stramba-Badiale</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Crotti</surname>
							<given-names>L</given-names>
						</name>
						<name>
							<surname>Pedrazzini</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Besana</surname>
							<given-names>A</given-names>
						</name>
						<name>
							<surname>Bosi</surname>
							<given-names>G</given-names>
						</name>
					</person-group>
					<article-title>Prevalence of the congenital long-QT syndrome</article-title>
					<source>Circulation</source>
					<year>2009</year>
					<volume>120</volume>
					<fpage>1761</fpage>
					<lpage>1767</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.109.863209">https://doi.org/10.1161/CIRCULATIONAHA.109.863209</ext-link>
				</element-citation>
			</ref>
			<ref id="B3">
				<label>3</label>
				<mixed-citation>Acunzo RS (2003). Las taquicardias ventriculares multiformes y los síndromes de intervalo QT prolongado. En MV Elizari y PA Chiale (Eds.). Arritmias cardíacas. Fundamentos celulares, moleculares, diagnóstico y tratamiento. (pp. 671-698). Editorial Panamericana.</mixed-citation>
				<element-citation publication-type="book">
					<person-group person-group-type="author">
						<name>
							<surname>Acunzo</surname>
							<given-names>RS</given-names>
						</name>
					</person-group>
					<year>2003</year>
					<chapter-title>Las taquicardias ventriculares multiformes y los síndromes de intervalo QT prolongado</chapter-title>
					<person-group person-group-type="editor">
						<name>
							<surname>Elizari</surname>
							<given-names>MV</given-names>
						</name>
						<name>
							<surname>Chiale</surname>
							<given-names>PA</given-names>
						</name>
					</person-group>
					<source>Arritmias cardíacas. Fundamentos celulares, moleculares, diagnóstico y tratamiento</source>
					<fpage>pp. 671</fpage>
					<lpage>pp. 698</lpage>
					<publisher-name>Editorial Panamericana</publisher-name>
				</element-citation>
			</ref>
			<ref id="B4">
				<label>4</label>
				<mixed-citation>Richards S, Aziz N, Bale S, Bick D, Das S, Gastier-Foster J, ; ACMG Laboratory Quality Assurance Committee. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med 2015;17:405-24.<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1038/gim.2015.30">https://doi.org/10.1038/gim.2015.30</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Richards</surname>
							<given-names>S</given-names>
						</name>
						<name>
							<surname>Aziz</surname>
							<given-names>N</given-names>
						</name>
						<name>
							<surname>Bale</surname>
							<given-names>S</given-names>
						</name>
						<name>
							<surname>Bick</surname>
							<given-names>D</given-names>
						</name>
						<name>
							<surname>Das</surname>
							<given-names>S</given-names>
						</name>
						<name>
							<surname>Gastier-Foster</surname>
							<given-names>J</given-names>
						</name>
					</person-group>
					<person-group person-group-type="author">
						<collab>ACMG Laboratory Quality Assurance Committee</collab>
					</person-group>
					<article-title>Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology</article-title>
					<source>Genet Med</source>
					<year>2015</year>
					<volume>17</volume>
					<fpage>405</fpage>
					<lpage>424</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1038/gim.2015.30">https://doi.org/10.1038/gim.2015.30</ext-link>
				</element-citation>
			</ref>
			<ref id="B5">
				<label>5</label>
				<mixed-citation>Jervell A, Lange-Nielsen F. Congenital deaf-mutism, functional heart disease with prolongation of the Q-T interval and sudden death. Am Heart J 1957;54:59-68. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/0002-8703(57)90079-0">https://doi.org/10.1016/0002-8703(57)90079-0</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Jervell</surname>
							<given-names>A</given-names>
						</name>
						<name>
							<surname>Lange-Nielsen</surname>
							<given-names>F</given-names>
						</name>
					</person-group>
					<article-title>Congenital deaf-mutism, functional heart disease with prolongation of the Q-T interval and sudden death</article-title>
					<source>Am Heart J</source>
					<year>1957</year>
					<volume>54</volume>
					<fpage>59</fpage>
					<lpage>68</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/0002-8703(57)90079-0">https://doi.org/10.1016/0002-8703(57)90079-0</ext-link>
				</element-citation>
			</ref>
			<ref id="B6">
				<label>6</label>
				<mixed-citation>Romano C, Gemme G, Pongiglione R. Rare cardiac arrhythmias of the pediatric age. I. Repetitive paroxysmal tachycardia. Minerva Pediatr 1963;15:1155-64.</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Romano</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Gemme</surname>
							<given-names>G</given-names>
						</name>
						<name>
							<surname>Pongiglione</surname>
							<given-names>R</given-names>
						</name>
					</person-group>
					<article-title>Rare cardiac arrhythmias of the pediatric age. I. Repetitive paroxysmal tachycardia</article-title>
					<source>Minerva Pediatr</source>
					<year>1963</year>
					<volume>15</volume>
					<fpage>1155</fpage>
					<lpage>1164</lpage>
				</element-citation>
			</ref>
			<ref id="B7">
				<label>7</label>
				<mixed-citation>Adler A, Novelli V, Amin AS, Abiusi E, Care M, Nannenberg EA, . An international, multicentered, evidence-based reappraisal of genes reported to cause congenital long QT syndrome. Circulation 2020;141:418-28. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.119.043132">https://doi.org/10.1161/CIRCULATIONAHA.119.043132</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Adler</surname>
							<given-names>A</given-names>
						</name>
						<name>
							<surname>Novelli</surname>
							<given-names>V</given-names>
						</name>
						<name>
							<surname>Amin</surname>
							<given-names>AS</given-names>
						</name>
						<name>
							<surname>Abiusi</surname>
							<given-names>E</given-names>
						</name>
						<name>
							<surname>Care</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Nannenberg</surname>
							<given-names>EA</given-names>
						</name>
					</person-group>
					<article-title>An international, multicentered, evidence-based reappraisal of genes reported to cause congenital long QT syndrome</article-title>
					<source>Circulation</source>
					<year>2020</year>
					<volume>141</volume>
					<fpage>418</fpage>
					<lpage>428</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.119.043132">https://doi.org/10.1161/CIRCULATIONAHA.119.043132</ext-link>
				</element-citation>
			</ref>
			<ref id="B8">
				<label>8</label>
				<mixed-citation>Giudicessi JR, Ackerman MJ. Genotype- and phenotype-guided management of congenital long QT syndrome. Curr Probl Cardiol 2013;38:417-55. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/j.cpcardiol.2013.08.001">https://doi.org/10.1016/j.cpcardiol.2013.08.001</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Giudicessi</surname>
							<given-names>JR</given-names>
						</name>
						<name>
							<surname>Ackerman</surname>
							<given-names>MJ</given-names>
						</name>
					</person-group>
					<article-title>Genotype- and phenotype-guided management of congenital long QT syndrome</article-title>
					<source>Curr Probl Cardiol</source>
					<year>2013</year>
					<volume>38</volume>
					<fpage>417</fpage>
					<lpage>455</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/j.cpcardiol.2013.08.001">https://doi.org/10.1016/j.cpcardiol.2013.08.001</ext-link>
				</element-citation>
			</ref>
			<ref id="B9">
				<label>9</label>
				<mixed-citation>Napolitano C, Priori SG, Schwartz PJ, Bloise R, Ronchetti E, Nastoli J, . Genetic testing in the long QT syndrome: development and validation of an efficient approach to genotyping in clinical practice. JAMA 2005;94:2975-80. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1001/jama.294.23.2975">https://doi.org/10.1001/jama.294.23.2975</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Napolitano</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Priori</surname>
							<given-names>SG</given-names>
						</name>
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Bloise</surname>
							<given-names>R</given-names>
						</name>
						<name>
							<surname>Ronchetti</surname>
							<given-names>E</given-names>
						</name>
						<name>
							<surname>Nastoli</surname>
							<given-names>J</given-names>
						</name>
					</person-group>
					<article-title>Genetic testing in the long QT syndrome: development and validation of an efficient approach to genotyping in clinical practice</article-title>
					<source>JAMA</source>
					<year>2005</year>
					<volume>94</volume>
					<fpage>2975</fpage>
					<lpage>2980</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1001/jama.294.23.2975">https://doi.org/10.1001/jama.294.23.2975</ext-link>
				</element-citation>
			</ref>
			<ref id="B10">
				<label>10</label>
				<mixed-citation>Bohnen MS, Peng G, Robey SH, Terrenoire C, Iyer V, Sampson KJ, . Molecular Pathophysiology of Congenital Long QT Syndrome. Physiol Rev 2017;97:89-134. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1152/physrev.00008.2016">https://doi.org/10.1152/physrev.00008.2016</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Bohnen</surname>
							<given-names>MS</given-names>
						</name>
						<name>
							<surname>Peng</surname>
							<given-names>G</given-names>
						</name>
						<name>
							<surname>Robey</surname>
							<given-names>SH</given-names>
						</name>
						<name>
							<surname>Terrenoire</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Iyer</surname>
							<given-names>V</given-names>
						</name>
						<name>
							<surname>Sampson</surname>
							<given-names>KJ</given-names>
						</name>
					</person-group>
					<article-title>Molecular Pathophysiology of Congenital Long QT Syndrome</article-title>
					<source>Physiol Rev</source>
					<year>2017</year>
					<volume>97</volume>
					<fpage>89</fpage>
					<lpage>134</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1152/physrev.00008.2016">https://doi.org/10.1152/physrev.00008.2016</ext-link>
				</element-citation>
			</ref>
			<ref id="B11">
				<label>11</label>
				<mixed-citation>Yoo HS, Sommi A, Konopka I, Principato M, Pizzarelli N, Tepper R, . Variaciones espontáneas en la duración de los intervalos QTc en pacientes con síndromes de intervalo QT largo hereditarios. Rev Argent Cardiol 2017;85:410-4.</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Yoo</surname>
							<given-names>HS</given-names>
						</name>
						<name>
							<surname>Sommi</surname>
							<given-names>A</given-names>
						</name>
						<name>
							<surname>Konopka</surname>
							<given-names>I</given-names>
						</name>
						<name>
							<surname>Principato</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Pizzarelli</surname>
							<given-names>N</given-names>
						</name>
						<name>
							<surname>Tepper</surname>
							<given-names>R</given-names>
						</name>
					</person-group>
					<article-title>Variaciones espontáneas en la duración de los intervalos QTc en pacientes con síndromes de intervalo QT largo hereditarios</article-title>
					<source>Rev Argent Cardiol</source>
					<year>2017</year>
					<volume>85</volume>
					<fpage>410</fpage>
					<lpage>414</lpage>
				</element-citation>
			</ref>
			<ref id="B12">
				<label>12</label>
				<mixed-citation>Moss AJ, Zareba W, Hall WJ, Schwartz PJ, Crampton RS, Benhorin J, . Effectiveness and limitations of beta-blocker therapy in congenital long-QT syndrome. Circulation 2000;101:616-23. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/01.CIR.101.6.616">https://doi.org/10.1161/01.CIR.101.6.616</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Moss</surname>
							<given-names>AJ</given-names>
						</name>
						<name>
							<surname>Zareba</surname>
							<given-names>W</given-names>
						</name>
						<name>
							<surname>Hall</surname>
							<given-names>WJ</given-names>
						</name>
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Crampton</surname>
							<given-names>RS</given-names>
						</name>
						<name>
							<surname>Benhorin</surname>
							<given-names>J</given-names>
						</name>
					</person-group>
					<article-title>Effectiveness and limitations of beta-blocker therapy in congenital long-QT syndrome</article-title>
					<source>Circulation</source>
					<year>2000</year>
					<volume>101</volume>
					<fpage>616</fpage>
					<lpage>623</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/01.CIR.101.6.616">https://doi.org/10.1161/01.CIR.101.6.616</ext-link>
				</element-citation>
			</ref>
			<ref id="B13">
				<label>13</label>
				<mixed-citation>Priori SG, Napolitano C, Schwartz PJ, Grillo M, Bloise R, Ronchetti E, . Association of long QT syndrome loci and cardiac events among patients treated with beta-blockers. JAMA. 2004;292:1341-4. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1001/jama.292.11.1341">https://doi.org/10.1001/jama.292.11.1341</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Priori</surname>
							<given-names>SG</given-names>
						</name>
						<name>
							<surname>Napolitano</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Grillo</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Bloise</surname>
							<given-names>R</given-names>
						</name>
						<name>
							<surname>Ronchetti</surname>
							<given-names>E</given-names>
						</name>
					</person-group>
					<article-title>Association of long QT syndrome loci and cardiac events among patients treated with beta-blockers</article-title>
					<source>JAMA</source>
					<year>2004</year>
					<volume>292</volume>
					<fpage>1341</fpage>
					<lpage>1344</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1001/jama.292.11.1341">https://doi.org/10.1001/jama.292.11.1341</ext-link>
				</element-citation>
			</ref>
			<ref id="B14">
				<label>14</label>
				<mixed-citation>Vincent GM, Schwartz PJ, Denjoy I, Swan H, Bithell C, Spazzolini C, . High efficacy of beta-blockers in long-QT syndrome type 1: contribution of noncompliance and QT-prolonging drugs to the occurrence of beta-blocker treatment &quot;failures&quot;. Circulation 2009;119:215-21. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.108.772533">https://doi.org/10.1161/CIRCULATIONAHA.108.772533</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Vincent</surname>
							<given-names>GM</given-names>
						</name>
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Denjoy</surname>
							<given-names>I</given-names>
						</name>
						<name>
							<surname>Swan</surname>
							<given-names>H</given-names>
						</name>
						<name>
							<surname>Bithell</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Spazzolini</surname>
							<given-names>C</given-names>
						</name>
					</person-group>
					<article-title>High efficacy of beta-blockers in long-QT syndrome type 1: contribution of noncompliance and QT-prolonging drugs to the occurrence of beta-blocker treatment &quot;failures&quot;</article-title>
					<source>Circulation</source>
					<year>2009</year>
					<volume>119</volume>
					<fpage>215</fpage>
					<lpage>221</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.108.772533">https://doi.org/10.1161/CIRCULATIONAHA.108.772533</ext-link>
				</element-citation>
			</ref>
			<ref id="B15">
				<label>15</label>
				<mixed-citation>Wilde AA, Jongbloed RJ, Doevendans PA, Düren DR, Hauer RN, van Langen IM, . Auditory stimuli as a trigger for arrhythmic events differentiate HERG-related (LQTS2) patients from KVLQT1-related patients (LQTS1). J Am Coll Cardiol 1999;33:327-32. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/S0735-1097(98)00578-6">https://doi.org/10.1016/S0735-1097(98)00578-6</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Wilde</surname>
							<given-names>AA</given-names>
						</name>
						<name>
							<surname>Jongbloed</surname>
							<given-names>RJ</given-names>
						</name>
						<name>
							<surname>Doevendans</surname>
							<given-names>PA</given-names>
						</name>
						<name>
							<surname>Düren</surname>
							<given-names>DR</given-names>
						</name>
						<name>
							<surname>Hauer</surname>
							<given-names>RN</given-names>
						</name>
						<name>
							<surname>van Langen</surname>
							<given-names>IM</given-names>
						</name>
					</person-group>
					<article-title>Auditory stimuli as a trigger for arrhythmic events differentiate HERG-related (LQTS2) patients from KVLQT1-related patients (LQTS1)</article-title>
					<source>J Am Coll Cardiol</source>
					<year>1999</year>
					<volume>33</volume>
					<fpage>327</fpage>
					<lpage>332</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/S0735-1097(98)00578-6">https://doi.org/10.1016/S0735-1097(98)00578-6</ext-link>
				</element-citation>
			</ref>
			<ref id="B16">
				<label>16</label>
				<mixed-citation>Schwartz PJ, Priori SG, Spazzolini C, Moss AJ, Vincent GM, Napolitano C, . Genotype-phenotype correlation in the long-QT syndrome: gene-specific triggers for life-threatening arrhythmias. Circulation 2001;103:89-95. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/01.CIR.103.1.89">https://doi.org/10.1161/01.CIR.103.1.89</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Priori</surname>
							<given-names>SG</given-names>
						</name>
						<name>
							<surname>Spazzolini</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Moss</surname>
							<given-names>AJ</given-names>
						</name>
						<name>
							<surname>Vincent</surname>
							<given-names>GM</given-names>
						</name>
						<name>
							<surname>Napolitano</surname>
							<given-names>C</given-names>
						</name>
					</person-group>
					<article-title>Genotype-phenotype correlation in the long-QT syndrome: gene-specific triggers for life-threatening arrhythmias</article-title>
					<source>Circulation</source>
					<year>2001</year>
					<volume>103</volume>
					<fpage>89</fpage>
					<lpage>95</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/01.CIR.103.1.89">https://doi.org/10.1161/01.CIR.103.1.89</ext-link>
				</element-citation>
			</ref>
			<ref id="B17">
				<label>17</label>
				<mixed-citation>Schwartz PJ, Ackerman MJ. The long QT syndrome: a transatlantic clinical approach to diagnosis and therapy. Eur Heart J 2013;34:3109-16. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1093/eurheartj/eht089">https://doi.org/10.1093/eurheartj/eht089</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Ackerman</surname>
							<given-names>MJ</given-names>
						</name>
					</person-group>
					<article-title>The long QT syndrome: a transatlantic clinical approach to diagnosis and therapy</article-title>
					<source>Eur Heart J</source>
					<year>2013</year>
					<volume>34</volume>
					<fpage>3109</fpage>
					<lpage>3116</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1093/eurheartj/eht089">https://doi.org/10.1093/eurheartj/eht089</ext-link>
				</element-citation>
			</ref>
			<ref id="B18">
				<label>18</label>
				<mixed-citation>Schwartz PJ, Spazzolini C, Priori SG, Crotti L, Vicentini A, Landolina M, . Who are the long-QT syndrome patients who receive an implantable cardioverter defibrillator and what happens to them? Data from the European long-QT syndrome implantable cardioverter-defibrillator (LQTS ICD) Registry. Circulation 2010;122:1272-82. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.110.950147">https://doi.org/10.1161/CIRCULATIONAHA.110.950147</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
						<name>
							<surname>Spazzolini</surname>
							<given-names>C</given-names>
						</name>
						<name>
							<surname>Priori</surname>
							<given-names>SG</given-names>
						</name>
						<name>
							<surname>Crotti</surname>
							<given-names>L</given-names>
						</name>
						<name>
							<surname>Vicentini</surname>
							<given-names>A</given-names>
						</name>
						<name>
							<surname>Landolina</surname>
							<given-names>M</given-names>
						</name>
					</person-group>
					<article-title>Who are the long-QT syndrome patients who receive an implantable cardioverter defibrillator and what happens to them? Data from the European long-QT syndrome implantable cardioverter-defibrillator (LQTS ICD) Registry</article-title>
					<source>Circulation</source>
					<year>2010</year>
					<volume>122</volume>
					<fpage>1272</fpage>
					<lpage>1282</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1161/CIRCULATIONAHA.110.950147">https://doi.org/10.1161/CIRCULATIONAHA.110.950147</ext-link>
				</element-citation>
			</ref>
			<ref id="B19">
				<label>19</label>
				<mixed-citation>Schwartz PJ. Practical issues in the management of the long QT syndrome: focus on diagnosis and therapy. Swiss Med Wkly 2013;143:13843. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.4414/smw.2013.13843">https://doi.org/10.4414/smw.2013.13843</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Schwartz</surname>
							<given-names>PJ</given-names>
						</name>
					</person-group>
					<article-title>Practical issues in the management of the long QT syndrome: focus on diagnosis and therapy</article-title>
					<source>Swiss Med Wkly</source>
					<year>2013</year>
					<volume>143</volume>
					<elocation-id>13843</elocation-id>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.4414/smw.2013.13843">https://doi.org/10.4414/smw.2013.13843</ext-link>
				</element-citation>
			</ref>
			<ref id="B20">
				<label>20</label>
				<mixed-citation>Zeppenfeld K, Tfelt-Hansen J, de Riva M, Winkel BG, Behr ER, Blom NA, . 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J 2022;43:3997-4126. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1093/eurheartj/ehac262">https://doi.org/10.1093/eurheartj/ehac262</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Zeppenfeld</surname>
							<given-names>K</given-names>
						</name>
						<name>
							<surname>Tfelt-Hansen</surname>
							<given-names>J</given-names>
						</name>
						<name>
							<surname>de Riva</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Winkel</surname>
							<given-names>BG</given-names>
						</name>
						<name>
							<surname>Behr</surname>
							<given-names>ER</given-names>
						</name>
						<name>
							<surname>Blom</surname>
							<given-names>NA</given-names>
						</name>
					</person-group>
					<article-title>2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death</article-title>
					<source>Eur Heart J</source>
					<year>2022</year>
					<volume>43</volume>
					<fpage>3997</fpage>
					<lpage>4126</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1093/eurheartj/ehac262">https://doi.org/10.1093/eurheartj/ehac262</ext-link>
				</element-citation>
			</ref>
			<ref id="B21">
				<label>21</label>
				<mixed-citation>Miyazaki S, Uchiyama T, Komatsu Y, Taniguchi H, Kusa S, Nakamura H, . Long-term complications of implantable defibrillator therapy in Brugada syndrome. Am J Cardiol 2013;111:1448-51. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/j.amjcard.2013.01.295">https://doi.org/10.1016/j.amjcard.2013.01.295</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Miyazaki</surname>
							<given-names>S</given-names>
						</name>
						<name>
							<surname>Uchiyama</surname>
							<given-names>T</given-names>
						</name>
						<name>
							<surname>Komatsu</surname>
							<given-names>Y</given-names>
						</name>
						<name>
							<surname>Taniguchi</surname>
							<given-names>H</given-names>
						</name>
						<name>
							<surname>Kusa</surname>
							<given-names>S</given-names>
						</name>
						<name>
							<surname>Nakamura</surname>
							<given-names>H</given-names>
						</name>
					</person-group>
					<article-title>Long-term complications of implantable defibrillator therapy in Brugada syndrome</article-title>
					<source>Am J Cardiol</source>
					<year>2013</year>
					<volume>111</volume>
					<fpage>1448</fpage>
					<lpage>1451</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1016/j.amjcard.2013.01.295">https://doi.org/10.1016/j.amjcard.2013.01.295</ext-link>
				</element-citation>
			</ref>
			<ref id="B22">
				<label>22</label>
				<mixed-citation>Lewandowski M, Sterlinski M, Maciag A, Syska P, Kowalik I, Szwed H, . Long-term follow-up of children and young adults treated with implantable cardioverter-defibrillator: the authors' own experience with optimal implantable cardioverter-defibrillator programming. Europace 2010;12:1245-50. <ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1093/europace/euq263">https://doi.org/10.1093/europace/euq263</ext-link>
				</mixed-citation>
				<element-citation publication-type="journal">
					<person-group person-group-type="author">
						<name>
							<surname>Lewandowski</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Sterlinski</surname>
							<given-names>M</given-names>
						</name>
						<name>
							<surname>Maciag</surname>
							<given-names>A</given-names>
						</name>
						<name>
							<surname>Syska</surname>
							<given-names>P</given-names>
						</name>
						<name>
							<surname>Kowalik</surname>
							<given-names>I</given-names>
						</name>
						<name>
							<surname>Szwed</surname>
							<given-names>H</given-names>
						</name>
					</person-group>
					<article-title>Long-term follow-up of children and young adults treated with implantable cardioverter-defibrillator: the authors' own experience with optimal implantable cardioverter-defibrillator programming</article-title>
					<source>Europace</source>
					<year>2010</year>
					<volume>12</volume>
					<fpage>1245</fpage>
					<lpage>1250</lpage>
					<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1093/europace/euq263">https://doi.org/10.1093/europace/euq263</ext-link>
				</element-citation>
			</ref>
		</ref-list>
		<fn-group>
			<fn fn-type="other" id="fn1">
				<label>1</label>
				<p>Miembro Titular de la Sociedad Argentina de Cardiología</p>
			</fn>
		</fn-group>
	</back>
	<!--<sub-article article-type="translation" id="s1" xml:lang="en">
		<front-stub>
			<article-categories>
				<subj-group subj-group-type="heading">
					<subject>ORIGINAL ARTICLE</subject>
				</subj-group>
			</article-categories>
			<title-group>
				<article-title>Genetic and Clinical Characteristics of Patients with Congenital Long QT Syndrome- Genotype. Experiences During Long-Term Follow-Up</article-title>
			</title-group>
			<contrib-group>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0002-3476-4055</contrib-id>
					<name>
						<surname>SETTEPASSI</surname>
						<given-names>PAOLA</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0001-7341-7032</contrib-id>
					<name>
						<surname>HYUN</surname>
						<given-names>SOK YOO</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0009-0004-9186-6527</contrib-id>
					<name>
						<surname>MUSCHIETTI</surname>
						<given-names>FLORENCIA</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0009-0008-5212-0828</contrib-id>
					<name>
						<surname>ETCHEVERRY</surname>
						<given-names>DANIEL</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0003-1380-1571</contrib-id>
					<name>
						<surname>GARRO</surname>
						<given-names>HUGO</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0002-5923-2039</contrib-id>
					<name>
						<surname>PAOLUCCI</surname>
						<given-names>ANALIA</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0001-5941-1064</contrib-id>
					<name>
						<surname>PRINCIPATO</surname>
						<given-names>MARIO</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
					<xref ref-type="fn" rid="fn1"><sup>MTSAC</sup></xref>
				</contrib>
				<contrib contrib-type="author">
					<contrib-id contrib-id-type="orcid">0000-0003-3076-9745</contrib-id>
					<name>
						<surname>CARBAJALES</surname>
						<given-names>JUSTO</given-names>
					</name>
					<xref ref-type="aff" rid="aff2"><sup>1</sup></xref>
					<xref ref-type="fn" rid="fn1"><sup>MTSAC</sup></xref>
				</contrib>
				<aff id="aff2">
					<label>1</label>
					<institution content-type="original">Hospital General de Agudos José María Ramos Mejía, Ciudad Autónoma de Buenos Aires, Argentina.</institution>
					<addr-line>
						<city>Ciudad Autónoma de Buenos Aires</city>
					</addr-line>
					<country>Argentina</country>
				</aff>
			</contrib-group>
			<author-notes>
				<corresp id="c2">
					<label>Correspondence:</label> Paola Settepassi. E-mail: <email>paosettepassi@gmail.com</email>
				</corresp>
				<fn fn-type="other" id="fn4">
					<p>This work won the SAC Research Award: ‘Young Cardiologist Researcher at the 50th Argentinean Congress of Cardiology.</p>
				</fn>
				<fn fn-type="conflict" id="fn5">
					<label>Conflicts of interest</label>
					<p> None declared. (See authors' conflict of interests forms on the web).</p>
				</fn>
			</author-notes>
			<abstract>
				<title>ABSTRACT</title>
				<sec>
					<title>Background: </title>
					<p>Congenital long QT syndrome (LQTS) is an inherited channelopathy with a broad genetic spectrum but with a common phenotypic manifestation, the prolonged QT interval. However, its clinical presentation and natural history are highly variable.</p>
				</sec>
				<sec>
					<title>Objectives: </title>
					<p>The aim of this study was to define the genetic and clinical characteristics of patients with congenital LQTS during a long-term follow-up.</p>
				</sec>
				<sec>
					<title>Methods: </title>
					<p>Retrospective cohort study of patients with congenital LQTS genotype. The incidence of serious events at follow-up was defined. Quantitative variables are expressed as median and interquartile range (IQR) and qualitative variables as frequency and percentage.</p>
				</sec>
				<sec>
					<title>Results: </title>
					<p>Forty-four patients were included. Thirty percent of patients had LQTS1 genotype, 65% LQTS2 genotype and 5% LQTS3 genotype; 57% of cases carried the <italic>missense</italic> mutation, 11% the <italic>nonsense</italic> mutation and 32% the <italic>frameshift</italic> mutation. The corrected QT interval was 490 msec (IQR 462-498). The phenotype was present in 66% of patients, but it remained permanently only in 32%. Syncopal episodes occurred in 39% of patients. Cardiac arrest was the first manifestation in 7% of cases. Syncope recurred in 11% of patients even after pharmacological therapy, and 5% suffered sudden death. Seven patients received an implantable cardiodesfibrillator (ICD). Among them, 29% received shocks due to ventricular tachycardia or ventricular fibrillation (VT/VF) and 58% presented device-related complications.</p>
				</sec>
				<sec>
					<title>Conclusions: </title>
					<p>Most patients had the LQTS1 or LQTS2 genotype, the intermittent phenotype, and a good response to treatment. Implantation at an early age and the high rate of complications during long-term follow-up require careful evaluation when indicating an ICD.</p>
				</sec>
			</abstract>
			<kwd-group xml:lang="en">
				<title>Key words:</title>
				<kwd>Long QT syndrome</kwd>
				<kwd>Sudden death</kwd>
				<kwd>Syncope</kwd>
				<kwd>Genetic mutation</kwd>
				<kwd> Cardiodesfibrilador implantable</kwd>
			</kwd-group>
		</front-stub>
		<body>
			<sec sec-type="intro">
				<title>INTRODUCTION</title>
				<p>Congenital long QT syndrome (LQTS) is characterized by prolongation of the ventricular myocardial action potential due to increased sodium and calcium inward currents (INa and ICa<sub>L</sub>) or decreased potassium outward currents (IKs, IKr and IK1). So far, mutations in 20 different genes encoding cardiac ion channels and/or modulatory proteins directly or indirectly involved in the genesis of these currents have been identified. (<xref ref-type="bibr" rid="B1">1</xref>)</p>
				<p>With a prevalence in the general population of 1 in 2000 individuals, it is no longer an exceptional situation to see a patient with a prolonged QT interval in daily medical consultation for sports, schooling or pre-employment. (<xref ref-type="bibr" rid="B2">2</xref>)</p>
				<p>With the advance of computer technology and genetic engineering, hundreds of variants have been identified in each of the genes involved in LQTS that, through different types of mutations, alter the function of myocyte ion channels. Most mutations show an autosomal dominant inheritance pattern. Thus, individuals are born with the mutation causing the disease and live with it throughout their lives. </p>
				<p>All affected individuals have a common phenotypic manifestation, the prolongation of ventricular repolarization duration. However, the existence of a broad clinical variability among patients raises questions about the epigenetic factors that modulate their phenotypic expression. Even when patients are born with the pathogenic genotype, the phenotype may never manifest itself, become evident late or, in some cases, only do so intermittently, expressing itself only on certain days, and remaining totally asymptomatic for prolonged periods of time. Similarly, the risk of suffering adverse cardiac events may vary among carriers of the same genetic variant and even in the same person, depending on the situation to which he/she has been exposed. (<xref ref-type="bibr" rid="B3">3</xref>)</p>
				<p>In this study, we have evaluated the clinical and genetic characteristics of patients diagnosed with LQTS by means of a genetic study with massive parallel sequencing and long-term clinical follow-up for more than 10 years, thus allowing the assessment of both the natural history of the disease and the occurrence of adverse cardiac events (syncope, ventricular tachyarrhythmia and/or sudden cardiac death), the response to pharmacological treatment and/or implantable antiarrhythmic devices, and their associated complications.</p>
			</sec>
			<sec sec-type="methods">
				<title>METHODS</title>
				<p>A retrospective study was designed selecting individuals with suspected congenital LQTS attending Hospital General de Ramos Mejía. The following inclusion criteria were used: men and women aged 5 to 70 years; clinical suspicion of congenital LQTS (QTc interval ≥480 milliseconds on the ECG or Schwartz score ≥3); and identification of a pathogenic variant of congenital LQTS in a genetic study. Those with any of the following criteria were excluded: LQTS acquired by medication; refusal to sign the informed consent; patients under 18 years of age, without parental or legal guardian consent; and negative genetic study. Simultaneous 12-lead ECG recordings were obtained from each patient. QT intervals were corrected for heart rate (QTc) using Bazett's formula (QTc = QT/√RR, in seconds). </p>
				<p>For sequence analysis and deletion/duplication testing, massive parallel sequencing (NGS) was used with a panel of more than 150 genes for arrhythmias and cardiomyopathies (ABCC9, ACADVL, ACTC1, ACTN2, AGL, ALMS1, ALPK3, BAG3, BRAF, CACNA1C, CACNA1D, CALM1, CALM2, CALM3, CASQ2, CBL, CDH2, CPT2, CRYAB, CSRP3, DES, DMD, DNAJC19, DOLK, DSC2, DSG2, DSP, ELAC2, EMD, EYA4, FHL1, FKRP, FKTN, FLNC, GAA, GATA4, GATA5, GJA5, GLA, HCN4, HRAS, JUP, KCNE1, KCNH2, KCNJ2, KCNQ1, KRAS, LAMP2, LMNA, LZTR1, MAP2K1, MAP2K2, MRAS, MTO1, MYBPC3, MYH7, MYL2, MYL3, MYL4, MYLK3, NF1, NKX2-5, NRAS, PCCA, PCCB, PKP2, PLN, PPA2, PPCS, PPP1CB, PRKAG2, PTPN11, RAF1, RASA1, RBM20, RIT1, RYR2, SCN5A, SDHA, SGCD, SHOC2, SLC22A5, SOS1, SOS2, SPRED1, TAZ, TBX20, TCAP, TMEM43, TMEM70, TNNC1, TNNI3, TNNI3K, TNNT2, TPM1, TRDN, TRPM4, TTN, TTR, VCL, A2ML1, AKAP9, ANK2, ANKRD1, CACNA2D1, CACNB2, CALR3, CAV3, CHRM2, CTF1, CTNNA3, DTNA, FHL2, GATA6, GATAD1, GPD1L, HAND1, ILK, JPH2, KCNA5, KCND3, KCNE2, KCNE3, KCNE5, KCNJ5, KCNJ8, KCNK3, KIF20A, KLF10, LAMA4, LDB3, LRRC10, MAP3K8, MED12, MYH6, MYLK2, MYOM1, MYOZ2, MYPN, NEBL, NEXN, NPPA, PDLIM3, PLEKHM2, PRDM16, RANGRF, RASA2, RRAS, SCN10A, SCN1B, SCN2B, SCN3B, SCN4B, SLMAP, SNTA1, TMPO, TXNRD2), developed by Invitae® (1400 16th Street, San Francisco, CA 94103, USA). USA). Genomic DNA obtained from a peripheral blood sample was enriched for target regions using a hybridization-based protocol and sequenced using Illumina® technology. All target regions were sequenced to a depth ≥50× or supplemented with additional analyses. Readings were aligned to a reference sequence (GRCh37) and sequence changes were identified and interpreted in the context of a single clinically relevant transcript. Enrichment and analysis were focused on the coding sequence of the indicated transcripts, 20 base pairs (bp) of flanking intronic sequence, and other specific genomic regions shown to be disease-causing at the time of assay design. Detected variants were evaluated by probing the following databases: dbSNP from NCBI (National Center for Biotechnology Information, https://www.ncbi.nlm.nih.gov/snp/), ExAC (Exome Aggregation Consortium, https://exac.broadinstitute.org), gnomAD (Genome Aggregation Database, https://gnomad.broadinstitute.org/) and OMIM (Online Mendelian Inheritance in Man, https://omim.org/). The pathogenicity of variants was estimated using three different types of prediction software: SIFT (https://sift.bii.a-star.edu.sg/), PolyPhen-2 (https://genetics.bwh.harvard.edu/pph2/) and Align-GVGD (https://bio.tools/align-gvgd/).</p>
				<p>Variants were classified as pathogenic or probably pathogenic, of uncertain significance, and probably benign or benign using an evidence scoring system based on the consensus of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. (<xref ref-type="bibr" rid="B4">4</xref>) Results were classified as positive, negative, carriers or uncertain, according to the classification of the identified variant and the inheritance pattern of the associated condition.</p>
				<sec>
					<title>Statistical analysis</title>
					<p>Quantitative variables are expressed as median and interquartile range (IQR) and qualitative variables as frequency and percentage.</p>
				</sec>
				<sec>
					<title>Ethical considerations</title>
					<p>The study was conducted in accordance with the ethical standards of the Declaration of Helsinki, and the study protocol was approved by the Ethics Committee of Hospital General de Agudos Dr. José María Ramos Mejía, Autonomous City of Buenos Aires, Argentina.</p>
				</sec>
			</sec>
			<sec sec-type="results|conclusions">
				<title>RESULTS</title>
				<p>Forty-four patients with a genetic diagnosis of LQTS were followed-up for 46 months (IQR35-175). Among them, 26 (59%) were women, and median age was 30 years (IQR 20-49). Thirty-five patients (80%) reported a history of sudden cardiac death (SCD) in first- and second-degree relatives. </p>
				<p>From the total number of patients, 13 (30%) corresponded to the LQTS type 1 genotype (KCNQ1 gene), 29 (65%) to LQTS type 2 (KCNH2 gene) and 2 (5%) to LQTS type 3 (SCN5A gene). The missense point mutation was identified in 25 patients (57%), five patients (11%) carried a nonsense mutation and a frameshift mutation was found in 14 patients (32%). The corrected QT interval was 490 msec (IQR 462-498). The phenotypic manifestation of LQTS (QTc &gt;480 msec) was observed in 29 patients (66%). However, only 14 individuals (32%) manifested a permanent phenotype (<xref ref-type="table" rid="t3">Table 1</xref>). </p>
				<p>
					<table-wrap id="t3">
						<label>Table 1</label>
						<caption>
							<title>Genetic and clinical characteristics (n=44)</title>
						</caption>
						<table frame="hsides" rules="groups">
							<colgroup>
								<col span="3"/>
							</colgroup>
							<thead>
								<tr style="border: 0; background-color:#ab0534;color:#ffffff;">
									<th align="left" colspan="3">Variable </th>
								</tr>
							</thead>
							<tbody>
								<tr style="background-color: #e3aea9;">
									<td align="left">KCNQ1 (SQTL1)</td>
									<td align="center">13</td>
									<td align="center">30%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">KCNH2 (SQTL2)</td>
									<td align="center">29</td>
									<td align="center">65%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">SCN5A (SQTL3)</td>
									<td align="center">2</td>
									<td align="center">5%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Nonsense</td>
									<td align="center">5</td>
									<td align="center">11%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Missense</td>
									<td align="center">25</td>
									<td align="center">57%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Frameshift</td>
									<td align="center">14</td>
									<td align="center">32%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Relative with SCD</td>
									<td align="center">35</td>
									<td align="center">80%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Syncope</td>
									<td align="center">17</td>
									<td align="center">39%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Cardiac arrest</td>
									<td align="center">3</td>
									<td align="center">7%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">QTc (msec)</td>
									<td align="center">490 (IQR 462-498)</td>
									<td align="center"> </td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">QTc ≥480 msec.</td>
									<td align="center">29</td>
									<td align="center">66%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Permanent phenotype</td>
									<td align="center">14</td>
									<td align="center">32%</td>
								</tr>
							</tbody>
						</table>
						<table-wrap-foot>
							<fn id="TFN5">
								<p>SCD: sudden cardiac death.</p>
							</fn>
							<fn id="TFN6">
								<p>Qualitative variables are presented as frequency and percentage, and quantitative variables as median and interquartile range (IQR) </p>
							</fn>
						</table-wrap-foot>
					</table-wrap>
				</p>
				<p>Syncopal episodes were observed in 17 individuals (39%), especially during adolescence. Cardiac arrest was the first clinical manifestation in 3 patients (7%). The age at which symptoms began to be manifest was 17 years (IQR 14-25). </p>
				<p>Ninety-three percent of cases were treated with beta-blockers (72% with propranolol), and 2 patients (5%) with a diagnosis of LQTS type 3 were treated with a sodium channel blocker (flecainide). Five patients (11%) had recurrence of syncope even after drug therapy. Two individuals with LQTS type 2 (5%) suffered nocturnal SCD at 17 and 66 years of age. </p>
				<p>On the other hand, 7 patients required an implantable cardiodefibrillator (ICD) at 18 years of age (IQR 16-26). Of these, 29% received shocks due to tachycardia or ventricular fibrillation (VT/VF) and 58% had complications associated with implantable devices (infection or catheter displacement/fracture) during the 161 month (IQR 83-229) follow-up (<xref ref-type="table" rid="t4">Table 2</xref>). </p>
				<p>
					<table-wrap id="t4">
						<label>Table 2</label>
						<caption>
							<title>Treatment and adverse cardiac events during follow-up. (n=44)</title>
						</caption>
						<table frame="hsides" rules="groups">
							<colgroup>
								<col span="3"/>
							</colgroup>
							<thead>
								<tr style="border: 0; background-color:#ab0534;color:#ffffff;">
									<th align="left" colspan="3">Follow-up</th>
								</tr>
							</thead>
							<tbody>
								<tr style="background-color: #e3aea9;">
									<td align="left">Beta-blockers</td>
									<td align="center">41</td>
									<td align="center">93%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Sodium channel blockers</td>
									<td align="center">2</td>
									<td align="center">5%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Recurrence of syncope</td>
									<td align="center">5</td>
									<td align="center">11%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">SCD</td>
									<td align="center">2</td>
									<td align="center">5%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">ICD Implant</td>
									<td align="center">7</td>
									<td align="center">16%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Implant age</td>
									<td align="center">18 (IQR 16-26)</td>
									<td align="center"> </td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">ICD replacement (number of devices/patient)</td>
									<td align="center">2.1</td>
									<td align="center"> </td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">ICD shock due to VT/VF</td>
									<td align="center">2</td>
									<td align="center">29%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">ICD-associated infection</td>
									<td align="center">2</td>
									<td align="center">29%</td>
								</tr>
								<tr style="background-color: #e3aea9;">
									<td align="left">Displacement or fracture of catheter</td>
									<td align="center">2</td>
									<td align="center">29%</td>
								</tr>
							</tbody>
						</table>
						<table-wrap-foot>
							<fn id="TFN7">
								<p>ICD: implantable cardioverter-defibrillator; SCD: sudden cardiac death; VF: ventricular fibrillation; VT: ventricular tachycardia. </p>
							</fn>
							<fn id="TFN8">
								<p>Qualitative variables are presented as frequency and percentage and quantitative variables as median and interquartile range (IQR). Percentages of shock, infection and catheter displacement refer to the 7 patients who received ICDs. </p>
							</fn>
						</table-wrap-foot>
					</table-wrap>
				</p>
			</sec>
			<sec sec-type="discussion">
				<title>DISCUSSION</title>
				<p>Congenital LQTS described by Jervell and Lange-Nielsen in 1957 and Romano and Ward in 1964 is an inherited channelopathy characterized by an alteration in ventricular repolarization and manifested by an abnormal prolongation in QTc interval duration. It predisposes to the onset of potentially lethal ventricular tachyarrhythmias (torsade de pointes and/or ventricular fibrillation) that usually occur due to increased adrenergic tone following auditory stimuli, physical exercise or emotional stress. (<xref ref-type="bibr" rid="B5">5</xref>,<xref ref-type="bibr" rid="B6">6</xref>)</p>
				<p>Over the past 25 years, 20 genes have been associated with congenital LQTS. However, a recent analysis reclassified several of these genes as having limited or controversial evidence. (<xref ref-type="bibr" rid="B7">7</xref>) This approach has left seven genes with definite or strong evidence of causality (KCNQ1, KCNH2, SCN5A, CALM1, CALM2, CALM3, and TRDN). All these genes encode ion channels involved in cardiac repolarization or proteins that regulate or modulate ion channel function. </p>
				<p>Ninety percent of individuals with LQTS genotype carry mutations in one of the 3 major disease genes: KCNQ1 (LQTS type 1), KCNH2 (LQTS type 2), and SCN5A (LQTS type 3), which encode the alpha subunits of the Kv7.1 (IKs), Kv11.1 (IKr), and Nav1.5 (INa) ion channels, respectively (<xref ref-type="fig" rid="f3">Figure 1</xref>). (<xref ref-type="bibr" rid="B8">8</xref>,<xref ref-type="bibr" rid="B9">9</xref>)</p>
				<p>
					<fig id="f3">
						<label>Fig. 1</label>
						<caption>
							<title>Ion channels involved in LQTS type 1, type 2 and type 3. The KCNQ1 gene encodes the alpha subunit of the voltage-dependent potassium channel Kv7.1 (responsible for the slow delayed rectifier current, IKs) and the KCNH2 gene encodes the alpha subunit of the voltage-dependent potassium channel Kv11.1 (responsible for the rapid delayed rectifier current, IKr). The voltage-dependent sodium channel Nav1.5 (responsible for INa current) is encoded by the SCN5A gene. Modified from: Nerbonne JM, Kass RS. Molecular physiology of cardiac repolarization. Physiol Rev 2005;85:1205-53. <ext-link ext-link-type="uri" xlink:href="https://10.0.4.128/physrev.00002.2005">https://10.1152/physrev.00002.2005</ext-link>
							</title>
						</caption>
						<graphic xlink:href="1850-3748-rac-93-02-117-gf3.jpg"/>
					</fig>
				</p>
				<p>Approximately 40% of mutations correspond to nonsense mutations (consisting of a point mutation in the DNA sequence resulting in a premature termination codon), or frameshift mutations caused by the insertion or deletion of nucleotides in a DNA sequence, which generates a reading frame completely different from the original. These mutations alter protein synthesis and generate defective alpha subunits of ion channels. The remaining 60% are missense mutations, where a single nucleotide change alters an amino acid codon (<xref ref-type="fig" rid="f4">Figure 2</xref>). These mutations can alter pore permeability, activation/deactivation or intracellular trafficking of ion channels. (<xref ref-type="bibr" rid="B10">10</xref>)</p>
				<p>
					<fig id="f4">
						<label>Fig. 2</label>
						<caption>
							<title>Types of mutations. Missense: DNA point mutation that changes an amino acid. Nonsense: DNA point mutation that introduces a premature termination codon. Frameshift: insertion or deletion of DNA with a change of the reading frame. Modified from: Nerbonne JM, Kass RS. Molecular physiology of cardiac repolarization. Physiol Rev 2005;85:1205-53. <ext-link ext-link-type="uri" xlink:href="https://10.1152/physrev.00002.2005">https://10.1152/physrev.00002.2005</ext-link>
							</title>
							<p>DNA sequence: A: adenine; T: thymine; C: cytosine; G: guanine. Amino acid sequence: Ser: serine; Val: valine; Pro: proline; Tyr: tyrosine; Thr: threonine; Leu: leucine; Stop: premature termination codon.</p>
						</caption>
						<graphic xlink:href="1850-3748-rac-93-02-117-gf4.jpg"/>
					</fig>
				</p>
				<p>In our study, patients showed a genetic profile similar to the aforementioned studies. Ninety-five percent of the patients were carriers of the LQTS type 1 (KCNQ1) or LQTS type 2 (KCNH2) genotypes. The predominant genetic variants were due to missense point mutations with a single amino acid change in the protein sequence</p>
				<p>Frequently, the intermittent nature of the LQTS phenotype manifestation hinders patient diagnosis. In our study, most patients (66%) manifested the LQTS phenotype (QTc &gt;480 msec) but only one third had the permanent phenotype. These results were comparable to those of the study by Yoo et al. in which patients with LQTS showed significant QT interval oscillations in different measurements and only 20% maintained the permanent phenotype. (<xref ref-type="bibr" rid="B11">11</xref>) These findings suggest that to achieve the diagnosis of congenital LQTS, patients should be thoroughly and continuously evaluated by serial ECG, stress ECG or dynamic recording with Holter monitoring on a periodic basis. In these circumstances, genetic testing to identify the responsible pathogenic variant becomes crucial for the early and accurate detection of patients with congenital LQTS. </p>
				<p>Individuals with LQTS often manifest the phenotype and suffer syncopal episodes and/or sudden death at an early age. Mortality in patients with LQTS ranges from 1% to 2% at 5 years. (<xref ref-type="bibr" rid="B12">12</xref>) Beta-blockers are effective, especially in LQTS1 in which VT/VF is triggered by exertion. Non-compliance with treatment and the use of drugs that prolong the QT interval are mainly responsible for therapeutic failures. (<xref ref-type="bibr" rid="B13">13</xref>,<xref ref-type="bibr" rid="B14">14</xref>) In LQTS2 and LQTS3, lethal arrhythmic events are usually triggered at rest or by auditory or emotional stimuli. (<xref ref-type="bibr" rid="B15">15</xref>,<xref ref-type="bibr" rid="B16">16</xref>) Among individuals with ICD, the rate of recurrent events is approximately 3% to 28% within 5 years. (<xref ref-type="bibr" rid="B17">17</xref>,<xref ref-type="bibr" rid="B18">18</xref>)</p>
				<p>There is still a tendency to consider it unnecessary to identify the genotype of patients with LQTS, once the diagnosis has been made using clinical criteria. This conduct makes it impossible to initiate cascade screening of the affected family. Considering that the response to drugs (beta-blockers vs. sodium channel blockers) and the stimuli that act as arrhythmogenic triggers (exercise, auditory or emotional) are very different between genotypes, the lack of knowledge of the genetic cause makes it difficult to provide adequate therapy to patients. The consequences could result in avoidable deaths, especially among genotype-positive and phenotype-negative individuals. Thus, molecular biology should no longer be considered as an exclusive field of research but as an essential, everyday medical tool. (<xref ref-type="bibr" rid="B19">19</xref>)</p>
				<p>In our study, ICD implantation was indicated between the second and third decade of life. The main reason was the occurrence of recurrent syncope even with beta-blocker therapy (primary prevention). The 2 women (one with LQTS1 and the other with LQTS2) who received an ICD for secondary prevention had adequate therapy for VT/VF 2 to 6 years after implantation. On the other hand, the rate of device-associated complications (infection or catheter displacement/fracture during long-term follow-up) was high. According to current guidelines, ICD implantation is indicated for secondary prevention (in individuals who have suffered resuscitated cardiac arrest, class I) and primary prevention (in those with recurrent syncope under beta-blocker treatment, class IIa). (<xref ref-type="bibr" rid="B20">20</xref>) Clearly, the decision to implant an ICD is life-saving in patients at high risk of SCD. However, in congenital LQTS, as in other hereditary channelopathies, the very early age of diagnosis and device implantation and the high rate (more than 20% in 5 to 10 years) of associated complications (infection, myocardial perforation, displacement, catheter wear and/or fracture, psychological consequences, etc.) that occur throughout the life of the patients, suggest that the decision to indicate an ICD should be based on a thorough and cautious evaluation. (<xref ref-type="bibr" rid="B21">21</xref>,<xref ref-type="bibr" rid="B22">22</xref>)</p>
			</sec>
			<sec sec-type="conclusions">
				<title>CONCLUSIONS</title>
				<p>The genetic profile of our patients coincides with that reported in the literature. The identification of the genotype allows us to screen for asymptomatic carriers who do not express the phenotype permanently, thus achieving an accurate diagnosis and early treatment through the cascade screening strategy of relatives. Most patients respond favorably to beta-blockers. However, there is a high-risk group (previous VT/VF) that requires ICD implantation to prevent SCD. The early age of implantation and the high rate of associated long-term complications require a personalized and thorough evaluation at the time of implantation.</p>
			</sec>
		</body>
	</sub-article>-->
</article>