Arrhythmia phenotype during fetal life suggests long-QT syndrome genotype: risk stratification of perinatal long-QT syndrome

2023 HRS expert consensus statement on the management of arrhythmias during pregnancy

This international multidisciplinary expert consensus statement is intended to provide comprehensive guidance that can be referenced at the point of care to cardiac electrophysiologists, cardiologists, and other health care professionals, on the management of cardiac arrhythmias in pregnant patients and in fetuses. This document covers general concepts related to arrhythmias, including both brady- and tachyarrhythmias, in both the patient and the fetus during pregnancy. Recommendations are provided for optimal approaches to diagnosis and evaluation of arrhythmias; selection of invasive and noninvasive options for treatment of arrhythmias; and disease- and patient-specific considerations when risk stratifying, diagnosing, and treating arrhythmias in pregnant patients and fetuses. Gaps in knowledge and new directions for future research are also identified.

Systematic review of long QT syndrome identified during fetal life

Fetal long QT syndrome (LQTS) may present with sinus bradycardia, functional 2:1 atrioventricular block (AVB), and ventricular arrhythmias (ventricular tachycardia [VT]/torsades de pointes [TdP]) and lead to fetal or postnatal death. We performed a systematic review and individual participant data meta-analysis of 83 studies reporting outcomes of 265 fetuses for which suspected LQTS was confirmed postnatally and determined risk of adverse perinatal and postnatal outcomes using logistic and stepwise logistic regression. A longer fetal QTc was more predictive of death than any other antenatal factor (receiver operating characteristic [ROC] area under the curve [AUC] 0.85; 95% confidence interval [CI] 0.66-1.00). Risk of death was significantly increased with fetal QTc >600 ms. Neither fetal heart rate nor heart rate z-score predicted death (ROC AUC 0.51; 95% CI 0.31-0.71; and ROC AUC 0.59; 95% CI 0.37-0.80, respectively). The combination of antenatal VT/TdP or functional 2:1 AVB and lack of family history of LQTS was also highly predictive of death (ROC AUC 0.82; 95% CI 0.76-0.88). Our data provide clinical screening tools to enable prediction and intervention for fetuses with LQTS at risk of death.

Fetal Arrhythmia Diagnosis and Pharmacologic Management

One of the most successful achievements of fetal intervention is the pharmacologic management of fetal arrhythmias. This management usually takes place during the second or third trimester. While most arrhythmias in the fetus are benign, both tachy‐ and bradyarrhythmias can lead to fetal hydrops or cardiac dysfunction and require treatment under certain conditions. This review will highlight precise diagnosis by fetal echocardiography and magnetocardiography, the 2 primary means of diagnosing fetuses with arrhythmia. Additionally, transient or hidden arrhythmias such as bundle branch block, QT prolongation, and torsades de pointes, which can lead to cardiomyopathy and sudden unexplained death in the fetus, may also need pharmacologic treatment. The review will address the types of drug therapies; current knowledge of drug usage, efficacy, and precautions; and the transition to neonatal treatments when indicated. Finally, we will highlight new assessments, including the role of the nurse in the care of fetal arrhythmias. The prognosis for the human fetus with arrhythmias continues to improve as we expand our ability to provide intensive care unit–like monitoring, to better understand drug treatments, to optimize subsequent pregnancy monitoring, to effectively predict timing for delivery, and to follow up these conditions into the neonatal period and into childhood. Coordinated initiatives that facilitate clinical fetal research are needed to address gaps in knowledge and to facilitate fetal drug and device development.

Resuscitated Sudden Cardiac Arrest of a Neonate with Congenital LQT Syndrome-Associated Torsades de Pointes: A Case Report and Literature Review

Sudden infant death syndrome (SIDS), the most common cause of infant death in developed countries, is attributed to diverse trigger factors. Malignant cardiac dysrhythmias are potentially treatable etiologies, and congenital long QT syndrome (LQTS) is the most common cardiac ionic channelopathy confronted. β-Blockers or class Ib agents are the drugs of choice for the control of arrhythmias, and an implantable cardioverter defibrillator (ICD) should be considered for secondary prevention in survivors of lethal cardiac death. We report the case of a 4-day old neonate, later genetically confirmed as LQT type 3 (LQT3), who survived a pulseless torsades de pointes (TdP) attack and was successfully treated with propranolol, mexiletine, and ICD implantation.

Case Report: Biventricular Noncompaction Cardiomyopathy With Pulmonary Stenosis and Bradycardia in a Fetus With KCNH2 Mutation

Background: Left ventricular noncompaction (LVNC) is a rare cardiomyopathy, long QT syndrome (LQTS) is a rare ion channel disease, and simultaneous occurrence of both is even rarer. Further clinical reports and studies are needed to identify the association between LVNC and LQTS and the underlying mechanism.

Methods and Results: A 26-year-old primigravida was referred at 25 weeks gestation for prenatal echocardiography due to fetal bradycardia detected during the routine ultrasound examination. The echocardiographic findings were consistent with biventricular noncompaction cardiomyopathy (BVNC) with pulmonary stenosis and suspected LQTS. After detailed counseling, the couple decided to terminate the pregnancy, and subsequent postmortem examination confirmed BVNC and pulmonary stenosis. Then, A trio (fetus and the parents) whole-exome sequencing (WES) and copy number variation sequencing (CNV-seq) were performed. CNV-seq identified no aneuploidy or pathogenic CNV. A de novo missense variant in KCNH2 (NM_000238.3:c.1847A > G,p.Tyr616Cys) was identified by WES. This KCNH2 missense mutation was classified as pathogenic according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology variant interpretation guidelines.

Conclusion: We report the first prenatal case of KCNH2 mutation presenting with LVNC combined with bradycardia and second-degree 2:1 atrioventricular block. Importantly, this case reminds clinicians to systematically search ion channel gene mutations in patients with LVNC and arrhythmia.

Induced Pluripotent Stem Cell-Derived Cardiomyocytes with SCN5A R1623Q Mutation Associated with Severe Long QT Syndrome in Fetuses and Neonates Recapitulates Pathophysiological Phenotypes

Simple Summary

In this study, the induced pluripotent stem cell-derived cardiomyocyte model from a patient with long QT syndrome harboring a heterozygous Nav1.5 R1623Q mutation exhibited prolonged field potential duration corrected by Fridericia’s formula (FPDcF, analogous to QTcF). FPDcF was shortened with mexiletine treatment and increased the frequency of arrhythmia-like EAD events following E4031, an I_kr blocker, administration. These characteristics partly reflect the patient phenotypes. As the R1623Q mutation is related to severe congenital LQT syndrome in fetuses and neonates, the effect of the neonatal variants on the electrophysiological properties of the R1623Q mutant was examined using an automated patch-clamp system. Our results demonstrated that both R1623Q and neonatal R1623Q delayed inactivation of I_Na and increased late Na current. We speculated that neonatal Nav1.5 ameliorates QTc prolongation. Developmental switching of neonatal/adult Nav1.5 isoforms might play a role in the mechanisms underlying severe long QT syndrome in fetuses and neonates.

Abstract

The SCN5A R1623Q mutation is one of the most common genetic variants associated with severe congenital long QT syndrome 3 (LQT3) in fetal and neonatal patients. To investigate the properties of the R1623Q mutation, we established an induced pluripotent stem cell (iPSC) cardiomyocyte (CM) model from a patient with LQTS harboring a heterozygous R1623Q mutation. The properties and pharmacological responses of iPSC-CMs were characterized using a multi-electrode array system. The biophysical characteristic analysis revealed that R1623Q increased open probability and persistent currents of sodium channel, indicating a gain-of-function mutation. In the pharmacological study, mexiletine shortened FPDcF in R1623Q-iPSC-CMs, which exhibited prolonged field potential duration corrected by Fridericia’s formula (FPDcF, analogous to QTcF). Meanwhile, E4031, a specific inhibitor of human ether-a-go-go-related gene (hERG) channel, significantly increased the frequency of arrhythmia-like early after depolarization (EAD) events. These characteristics partly reflect the patient phenotypes. To further analyze the effect of neonatal isoform, which is predominantly expressed in the fetal period, on the R1623Q mutant properties, we transfected adult form and neonatal isoform SCN5A of control and R1623Q mutant SCN5A genes to 293T cells. Whole-cell automated patch-clamp recordings revealed that R1623Q increased persistent Na⁺ currents, indicating a gain-of-function mutation. Our findings demonstrate the utility of LQT3-associated R1623Q mutation-harboring iPSC-CMs for assessing pharmacological responses to therapeutic drugs and improving treatment efficacy. Furthermore, developmental switching of neonatal/adult Nav1.5 isoforms may be involved in the pathological mechanisms underlying severe long QT syndrome in fetuses and neonates.

Defining the normal QT interval in newborns: the natural history and reference values for the first 4 weeks of life

AIMS

Evaluation of the neonatal QT interval is important to diagnose arrhythmia syndromes and evaluate side effects of drugs. We aimed at describing the natural history of the QT interval duration during the first 4 weeks of life and to provide reference values from a large general population sample.

METHODS AND RESULTS

The Copenhagen Baby Heart Study is a prospective general population study that offered cardiac evaluation of newborns. Eight-lead electrocardiograms were obtained and analysed with a computerized algorithm with manual validation. We included 14 164 newborns (52% boys), aged 0-28 days, with normal echocardiograms. The median values (ms, 2-98%ile) for the corrected intervals QTc (Bazett), QTc (Hodges), QTc (Fridericia), and QTc (Framingham) were 419 (373-474), 419 (373-472), 364 (320-414), and 363 (327-405). During the 4 weeks, we observed a small decrease of QTcFramingham, and an increase of QTcHodges (both P < 0.01), while QTcBazett and QTcFridericia did not change (P > 0.05). Applying published QT interval cut-off values resulted in 5-25% of the newborns having QT prolongation. Uncorrected QT intervals decreased linearly with increasing heart rate (HR). Sex and infant size did not affect the QT interval and the gestational age (GA) only showed an effect when comparing the extreme low- vs. high GA groups (≤34 vs. ≥42 weeks, P = 0.021).

CONCLUSION

During the 4 weeks QTcFramingham and QTcHodges showed minor changes, whereas QTcBazett and QTcFridericia were stable. The QT interval was unaffected by sex and infant size and GA only showed an effect in very premature newborns. Reference values for HR-specific uncorrected QT intervals may facilitate a more accurate diagnosis of newborns with abnormal QT intervals.

The combined novel KCNQ1 frameshift I145Sfs*92 and nonsense W392X variants caused Jervell and Lange-Nielsen syndrome in a Chinese infant presenting with sustained foetal bradycardia

AIMS

We report clinical and molecular analysis of an infant presenting with foetal bradycardia and clinical outcome of Jervell and Lange-Nielsen syndrome (JLNS).

METHODS AND RESULTS

Clinical, electrocardiogram (ECG), and echocardiographic data were collected from members in a three-generation family. Whole exomes were amplified and sequenced for proband. The identified variants were verified in the remaining members. The pathogenicity of candidate variants was predicted using multiple software programmes. A 28-year-old non-consanguineous Chinese woman at 23 weeks' gestation presenting with sustained foetal bradycardia of 100 b.p.m. Immunological disorders and infection were excluded. The infant was delivered at 37 weeks' gestation with 2700-g birthweight. QTc was prolonged in both ECG and Holter recording. Hearing tests confirmed bilateral sensorineural hearing loss. Genetic testing demonstrated that the infant carried a novel frameshift c.431delC (p.I145Sfs*92) and a novel nonsense c.1175G>A (p.W392X) compound variants of KCNQ1 inherited from mother and father, respectively, in autosomal recessive inheritance. Only relative II-5 carrying heterozygous KCNQ1-I145Sfs*92 variant had prolonged QTc, while the other carriers did not have prolonged QT, suggesting an autosomal dominant inheritance of LQT1 phenotype with incomplete penetrance in the family.

CONCLUSION

We report the novel frameshift KCNQ1-I145Sfs*92 and nonsense KCNQ1-W392X compound variants in autosomal recessive inheritance that caused JLNS presenting as sustained foetal bradycardia for the first time. Meanwhile, KCNQ1-I145Sfs*92 heterozygous variant demonstrated LQT1 phenotype in autosomal dominant inheritance with incomplete penetrance.

Management of Long QT Syndrome in Women Before, During, and After Pregnancy

Congenital long QT syndrome (LQTS) is a primary genetic and electrical disorder that increases risk for torsades de pointes, syncope, and sudden death. Post-pubertal women with LQTS require specialized multidisciplinary management before, during, and after pregnancy involving cardiology and obstetrics to reduce risk for cardiac events in themselves and their fetuses and babies. The risk of potentially life-threatening events is lower during pregnancy but increases significantly during the 9-month postpartum period. Treatment of women with LQTS with a preferred β-blocker at optimal doses along with close monitoring are indicated throughout pregnancy and during the high-risk postpartum period.

Genotype Predicts Outcomes in Fetuses and Neonates With Severe Congenital Long QT Syndrome

OBJECTIVES

This study sought to determine the relationship between long QT syndrome (LQTS) subtype (LTQ1, LTQ2, LTQ3) and postnatal cardiac events (CEs).

BACKGROUND

LQTS presenting with 2:1 atrioventricular block or torsades de pointes in the fetus and/or neonate has been associated with risk for major CEs, but overall outcomes and predictors remain unknown.

METHODS

A retrospective study involving 25 international centers evaluated the course of fetuses/newborns diagnosed with congenital LQTS and either 2:1 atrioventricular block or torsades de pointes. The primary outcomes were age at first CE after dismissal from the newborn hospitalization and death and/or cardiac transplantation during follow-up. CE was defined as aborted cardiac arrest, appropriate shock from implantable cardioverter-defibrillator, or sudden cardiac death.

RESULTS

A total of 84 fetuses and/or neonates were identified with LQTS (12 as LQT1, 35 as LQT2, 37 as LQT3). Median gestational age at delivery was 37 weeks (interquartile range: 35 to 39 weeks) and age at hospital discharge was 3 weeks (interquartile range: 2 to 5 weeks). Fetal demise occurred in 2 and pre-discharge death in 1. Over a median of 5.2 years, there were 1 LQT1, 3 LQT2, and 23 LQT3 CEs (13 aborted cardiac arrests, 5 sudden cardiac deaths, and 9 appropriate shocks). One patient with LQT1 and 11 patients with LQT3 died or received cardiac transplant during follow-up. The only multivariate predictor of post-discharge CEs was LQT3 status (LQT3 vs. LQT2: hazard ratio: 8.4; 95% confidence interval: 2.6 to 38.9; p < 0.001), and LQT3, relative to LQT2, genotype predicted death and/or cardiac transplant (p < 0.001).

CONCLUSIONS

In this large multicenter study, fetuses and/or neonates with LQT3 but not those with LQT1 or LQT2 presenting with severe arrhythmias were at high risk of not only frequent, but lethal CEs.

Successful trans-maternal nadolol pharmacotherapy in a fetus presenting with long QT syndrome type 2 complicated by torsade de pointes

Fetuses with congenital long QT syndrome (LQTS) may experience life-threatening arrhythmias, such as torsade de pointes (TdP), and/or functional atrioventricular block. However, trans-maternal pharmacotherapy for these cases is rarely reported and management practices have yet to be established. The fetus of a mother with genetically-confirmed LQTS type 2 (LQT2) presented with complex arrhythmias, diagnosed via magnetocardiography as ventricular arrhythmias (including TdP), at 28 weeks of gestation. After initiation of trans-maternal nadolol administration at 15 mg/d initial dosage and 30 mg/d subsequent dosage, the frequency of fetal ventricular arrhythmias decreased and almost disappeared within several days. The mother gave birth to the baby at full term without significant complications in either the mother or fetus. This is the first report that demonstrates the efficacy and safety of trans-maternal administration of nadolol for treatment of symptomatic LQT2 fetuses with TdP. <Learning objective: Prenatal diagnosis of congenital long QT syndrome (LQTS) is challenging, but characteristic arrhythmias, including sinus bradycardia, intermittent atrioventricular block and torsade de pointes (TdP), as well as family history of LQTS, can be clues to the diagnosis. If TdP is diagnosed in the fetus, trans-maternal administration of anti-arrhythmic drugs, such as beta-blockers, sodium channel blockers, and magnesium, could be effective to restore sinus rhythm and avoid intrauterine fetal death.>.

Fetal diagnosis of KCNQ1-variant long QT syndrome using fetal echocardiography and magnetocardiography

A pregnant woman with KCNQ1 variant long QT syndrome (LQTS) underwent fetal magnetocardiography (fMCG) after atrioventricular (AV) block was noted during fetal echocardiogram-atypical for LQTS type 1. Concern for fetal LQTS on fMCG prompted monitoring of maternal labs, change of maternal beta blocker therapy, and frequent fetal echocardiograms. Collaboration between obstetricians, neonatologists, and pediatric cardiologists ensured safe delivery. Beta blocker therapy was initiated after birth, and postnatal evaluation confirmed genotype and phenotype positive LQTS in the infant. Our experience suggests diagnosis and evaluation of fetal LQTS can alter antenatal management to reduce risk of poor fetal and postnatal outcomes.

Mothers with long QT syndrome are at increased risk for fetal death: findings from a multicenter international study

BACKGROUND

Most fetal deaths are unexplained. Long QT syndrome is a genetic disorder of cardiac ion channels. Affected individuals, including fetuses, are predisposed to sudden death. We sought to determine the risk of fetal death in familial long QT syndrome, in which the mother or father carries the long QT syndrome genotype. In addition, we assessed whether risk differed if the long QT syndrome genotype was inherited from the mother or father.

OBJECTIVE

This was a retrospective review of pregnancies in families with the 3 most common heterozygous pathogenic long QT syndrome genotypes in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3), which occur in approximately 1 in 2000 individuals. The purpose of our study was to compare pregnancy and birth outcomes in familial long QT syndrome with the normal population and between maternal and paternal carriers of the long QT syndrome genotype. We hypothesized that fetal death before (miscarriage) and after (stillbirths) 20 weeks gestation would be increased in familial long QT syndrome compared with the normal population and that the parent of origin would not affect birth outcomes.

STUDY DESIGN

Our study was a multicenter observational case series of 148 pregnancies from 103 families (80 mothers, 23 fathers) with familial long QT syndrome (60 with LQT1, 29 with LQT2, 14 with LQT3) who were recruited from 11 international centers with expertise in hereditary heart rhythm diseases, pediatric and/or adult electrophysiology, and high-risk pregnancies. Clinical databases from these sites were reviewed for long QT syndrome that occurred in men or women of childbearing age (18-40 years). Pregnancy outcomes (livebirth, stillbirth, and miscarriage), birthweights, and gestational age at delivery were compared among long QT syndrome genotypes and between maternal vs paternal long QT syndrome-affected status with the use of logistic regression analysis.

RESULTS

Most offspring (80%; 118/148) were liveborn at term; 66% of offspring (73/110) had long QT syndrome. Newborn infants of mothers with long QT syndrome were delivered earlier and, when the data were controlled for gestational age, weighed less than newborn infants of long QT syndrome fathers. Fetal arrhythmias were observed rarely, but stillbirths (fetal death at >20 weeks gestation) were 8 times more frequent in long QT syndrome (4% vs approximately 0.5%); miscarriages (fetal death at ≤20 weeks gestation) were 2 times that of the general population (16% vs 8%). The likelihood of fetal death was significantly greater with maternal vs paternal long QT syndrome (24.4% vs 3.4%; P=.036). Only 10% of all fetal deaths underwent postmortem long QT syndrome testing; 2 of 3 cases were positive for the family long QT syndrome genotype.

CONCLUSION

This is the first report to demonstrate that mothers with long QT syndrome are at increased risk of fetal death and to uncover a previously unreported cause of stillbirth. Our results suggest that maternal effects of long QT syndrome channelopathy may cause placental or myometrial dysfunction that confers increased susceptibility to fetal death and growth restriction in newborn survivors, regardless of long QT syndrome status.

Deep Mutational Scan of an SCN5A Voltage Sensor

BACKGROUND

Variants in ion channel genes have classically been studied in low throughput by patch clamping. Deep mutational scanning is a complementary approach that can simultaneously assess function of thousands of variants.

METHODS

We have developed and validated a method to perform a deep mutational scan of variants in SCN5A, which encodes the major voltage-gated sodium channel in the heart. We created a library of nearly all possible variants in a 36 base region of SCN5A in the S4 voltage sensor of domain IV and stably integrated the library into HEK293T cells.

RESULTS

In preliminary experiments, challenge with 3 drugs (veratridine, brevetoxin, and ouabain) could discriminate wild-type channels from gain- and loss-of-function pathogenic variants. High-throughput sequencing of the pre- and postdrug challenge pools was used to count the prevalence of each variant and identify variants with abnormal function. The deep mutational scan scores identified 40 putative gain-of-function and 33 putative loss-of-function variants. For 8 of 9 variants, patch clamping data were consistent with the scores.

CONCLUSIONS

These experiments demonstrate the accuracy of a high-throughput in vitro scan of SCN5A variant function, which can be used to identify deleterious variants in SCN5A and other ion channel genes.

Left Ventricular Isovolumetric Relaxation Time Is Prolonged in Fetal Long-QT Syndrome

BACKGROUND

Long-QT syndrome (LQTS), an inherited cardiac repolarization disorder, is an important cause of fetal and neonatal mortality. Detecting LQTS prenatally is challenging. A fetal heart rate (FHR) less than third percentile for gestational age is specific for LQTS, but the sensitivity is only ≈50%. Left ventricular isovolumetric relaxation time (LVIRT) was evaluated as a potential diagnostic marker for fetal LQTS.

METHODS AND RESULTS

LV isovolumetric contraction time, LV ejection time, LVIRT, cycle length, and FHR were measured using pulsed Doppler waveforms in fetuses. Time intervals were expressed as percentages of cycle length, and the LV myocardial performance index was calculated. Single measurements were stratified by gestational age and compared between LQTS fetuses and controls. Receiver-operator curves were performed for FHR and normalized LVIRT (N-LVIRT). A linear mixed-effect model including multiple measurements was used to analyze trends in FHR, N-LVIRT, and LV myocardial performance index. There were 33 LQTS fetuses and 469 controls included. In LQTS fetuses, the LVIRT was prolonged in all gestational age groups (P<0.001), as was the N-LVIRT. The best cutoff to diagnose LQTS was N-LVIRT ≥11.3 at ≤20 weeks (92% sensitivity, 70% specificity). Simultaneous analysis of N-LVIRT and FHR improved the sensitivity and specificity for LQTS (area under the curve=0.96; 95% confidence interval, 0.82-1.00 at 21-30 weeks). N-LVIRT, LV myocardial performance index, and FHR trends differed significantly between LQTS fetuses and controls through gestation.

CONCLUSIONS

The LVIRT is prolonged in LQTS fetuses. Findings of a prolonged N-LVIRT and sinus bradycardia can improve the prenatal detection of fetal LQTS.

Mechanisms of death in structurally normal stillbirths

Objectives To investigate mechanisms of in utero death in normally formed fetuses by measuring amniotic fluid (AF) biomarkers for hypoxia (erythropoietin [EPO]), myocardial damage (cardiac troponin I [cTnI]) and brain injury (glial fibrillary acidic protein [GFAP]), correlated with risk factors for fetal death and placental histopathology. Methods This retrospective, observational cohort study included intrauterine deaths with transabdominal amniocentesis prior to induction of labor. Women with a normal pregnancy and an indicated amniocentesis at term were randomly selected as controls. AF was assayed for EPO, cTnI and GFAP using commercial immunoassays. Placental histopathology was reviewed, and CD15-immunohistochemistry was used. Analyte concentrations >90th centile for controls were considered "raised". Raised AF EPO, AF cTnI and AF GFAP concentrations were considered evidence of hypoxia, myocardial and brain injury, respectively. Results There were 60 cases and 60 controls. Hypoxia was present in 88% (53/60), myocardial damage in 70% (42/60) and brain injury in 45% (27/60) of fetal deaths. Hypoxic fetuses had evidence of myocardial injury, brain injury or both in 77% (41/53), 49% (26/53) and 13% (7/53) of cases, respectively. Histopathological evidence for placental dysfunction was found in 74% (43/58) of these cases. Conclusion Hypoxia, secondary to placental dysfunction, was found to be the mechanism of death in the majority of fetal deaths among structurally normal fetuses. Ninety-one percent of hypoxic fetal deaths sustained brain, myocardial or both brain and myocardial injuries in utero. Hypoxic myocardial injury was an attributable mechanism of death in 70% of the cases. Non-hypoxic cases may be caused by cardiac arrhythmia secondary to a cardiac conduction defect.

Fetal arrhythmias: Diagnosis and management

This article reviews important features for improving the diagnosis and management of fetal arrhythmias. The normal fetal heart rate ranges between 110 and 160 beats per minute. A fetal heart rate is considered abnormal if the heart rate is beyond the normal ranges or the rhythm is irregular. The rate, duration, and origin of the rhythm and degree of irregularity usually determine the potential for hemodynamic consequences. Most of the fetal rhythm disturbances are the result of premature atrial contractions (PACs) and are of little clinical significance. Other arrhythmias include tachyarrhythmias (heart rate in excess of 160 beats/min) such as atrioventricular (AV) reentry tachycardia, atrial flutter, and ventricular tachycardia, and bradyarrhythmias (heart rate <110 beats/min) such as sinus node dysfunction, complete heart block (CHB) and long QT syndrome (which is associated with sinus bradycardia and pseudo-heart block).

An Overview of Diagnosis and Management Strategies for Long QT Syndrome

Significant clinical, research, genetic, and therapeutic advances in the diagnosis and management of long QT syndrome (LQTS) have made the treatment of this channelopathy one of the most exciting and enlightening bench-to-bed success stories in the field of cardiology. Cascade screening identifies affected family members, and pre-symptomatic therapy saves lives. Here, we present a case of LQTS in a child and a review of the diagnostic and treatment strategies that have been introduced to date in the modern era.

Early somatic mosaicism is a rare cause of long-QT syndrome

Somatic mosaicism, the occurrence and propagation of genetic variation in cell lineages after fertilization, is increasingly recognized to play a causal role in a variety of human diseases. We investigated the case of life-threatening arrhythmia in a 10-day-old infant with long QT syndrome (LQTS). Rapid genome sequencing suggested a variant in the sodium channel Na_V1.5 encoded by SCN5A, NM_000335:c.5284G > T predicting p.(V1762L), but read depth was insufficient to be diagnostic. Exome sequencing of the trio confirmed read ratios inconsistent with Mendelian inheritance only in the proband. Genotyping of single circulating leukocytes demonstrated the mutation in the genomes of 8% of patient cells, and RNA sequencing of cardiac tissue from the infant confirmed the expression of the mutant allele at mosaic ratios. Heterologous expression of the mutant channel revealed significantly delayed sodium current with a dominant negative effect. To investigate the mechanism by which mosaicism might cause arrhythmia, we built a finite element simulation model incorporating Purkinje fiber activation. This model confirmed the pathogenic consequences of cardiac cellular mosaicism and, under the presenting conditions of this case, recapitulated 2:1 AV block and arrhythmia. To investigate the extent to which mosaicism might explain undiagnosed arrhythmia, we studied 7,500 affected probands undergoing commercial gene-panel testing. Four individuals with pathogenic variants arising from early somatic mutation events were found. Here we establish cardiac mosaicism as a causal mechanism for LQTS and present methods by which the general phenomenon, likely to be relevant for all genetic diseases, can be detected through single-cell analysis and next-generation sequencing.

The natural history of fetal long QT syndrome

INTRODUCTION

Fetal magnetocardiography (fMCG), the magnetic analog of ECG, has provided invaluable insight into the mechanisms of fetal arrhythmias. In the past 15years, we have evaluated over 300 fetuses with arrhythmia by fMCG. We review the unique characteristics and natural history of the long QT syndrome (LQTS) rhythms.

METHODS

We reviewed the fMCGs of subjects referred with suspected LQTS based on either a positive family history or echo diagnosis of the LQTS rhythms (sinus bradycardia, ventricular tachycardia, or 2:1 AV conduction) to the Biomagnetism laboratory in the Department of Medical Physics, UW-Madison. We recorded fMCGs using a 37-channel (Magnes, 4D Neuroimaging, Inc., San Diego, CA) superconducting quantum interference device (SQUID) biomagnetometer, housed in a magnetically-shielded room for 1200-6000s. Signal processing was used to remove maternal interference. Cardiac intervals (R-R, p, QRS, QT) were measured and compared to published normals. We correlated fetal heart rate (FHR) patterns and effects of fetal movement on FHR and rhythm using actocardiography.

RESULTS

Thirty-nine fetuses were studied at a mean of 28 (19-38) weeks of gestation. All had structurally normal hearts. One was on amiodarone for suspected supraventricular tachycardia and hydrops. Five had serial fMCGs. Isolated sinus bradycardia with a QTc >490ms was found in 35: 33 had a KCNQ1 mutation There was one false positive and one false negative LQTS diagnosis. Four fetuses had torsades de pointes (TdP) and 3 had periods of 2:1 conduction and either KCNH2 or SCN5A mutations. TdP was rarely initiated with a preceding long-short pattern and did not degenerate into ventricular fibrillation. One fetus with TdP died in utero, 2 with fetal TdP had postnatal cardiac arrest.

CONCLUSION

Fetal LQTS is diagnosed by an fMCG QTc >490ms with an 89% sensitivity and specificity. TdP are seen with uncharacterized, KCNH2 or SCN5A R1623q mutations. Fetal TdP occurs when QTc ≥620ms. Identifying fetal LQTS and defining its rhythms by fMCG risk stratifies postnatal management.

Comorbid Epilepsy and Developmental Disorders in Congenital Long QT Syndrome With Life-Threatening Perinatal Arrhythmias

OBJECTIVES

Given the association of long QT syndrome (LQTS) and neurological disorders, we speculated that the more severe LQTS phenotype, perinatal LQTS, would exhibit more frequent comorbid neurodevelopmental anomalies than LQTS without perinatal arrhythmias (nonperinatal LQTS).

BACKGROUND

Congenital LQTS with life-threatening perinatal arrhythmias (perinatal LQTS) has a poor life prognosis.

METHODS

Twenty-one consecutive LQTS patients diagnosed before 1 year of age at our institution and 3 previously reported perinatal LQTS patients with neurological seizures were enrolled. In total, the clinical course was evaluated in 24 patients.

RESULTS

Among 21 infantile LQTS patients, 5 of 6 with perinatal LQTS (83%) were diagnosed with epilepsy and 4 (67%) with developmental disorders, but none with nonperinatal LQTS were. The total development quotient by Kinder Infant Development Scale scores was 17 to 72 (median 67) in 5 epileptic perinatal LQTS. In the 8 perinatal LQTS patients with neurological disorders, including 3 previously reported cases, epileptic seizures occurred at 2 days to 2.5 years of age and 5 had developmental disorders. Mutations in these 8 patients were located in the transmembrane loop of KCNH2, and D3/S4-S5 linker, D4/S4, or the D4/S6 segment of SCN5A.

CONCLUSIONS

A high comorbidity of neurodevelopmental anomalies was observed in perinatal LQTS. Mutations in patients with neurological comorbidities were in loci linked to LQTS with a severe cardiac phenotype. These observations indicate the possibility that neurological disorders in perinatal LQTS are manifested as neurological phenotypes associated with severe cardiac phenotypes, while we could not completely exclude another possibility that those were caused by a brain perfusion injury.

Fetal and Neonatal Arrhythmias

Cardiac arrhythmias are an important aspect of fetal and neonatal medicine. Premature complexes of atrial or ventricular origin are the main cause of an irregular heart rhythm. The finding is typically unrelated to an identifiable cause and no treatment is required. Tachyarrhythmia most commonly relates to supraventricular reentrant tachycardia, atrial flutter, and sinus tachycardia. Several antiarrhythmic agents are available for the perinatal treatment of tachyarrhythmias. Enduring bradycardia may result from sinus node dysfunction, complete heart block and nonconducted atrial bigeminy as the main arrhythmia mechanisms. The management and outcome of bradycardia depend on the underlying mechanism.

Pediatric Cohort With Long QT Syndrome - KCNH2 Mutation Carriers Present Late Onset But Severe Symptoms

BACKGROUND

In children with long QT syndrome (LQTS), risk factors for cardiac events have been reported, but age-, gender- and genotype-related differences in prognosis remain unknown in Asian countries.

METHODS AND RESULTS

The study examined clinical prognosis at age between 1 and 20 years in 496 LQTS patients who were genotyped as either of LQT1-3 (male, n=206). Heterozygous mutations were observed in 3 major responsible genes:KCNQ1in271,KCNH2in 192, andSCN5Ain 33 patients. LQTS-associated events were classified into 3 categories: (1) syncope (n=133); (2) repetitive torsade de pointes (TdP, n=3); and (3) cardiopulmonary arrest (CPA, n=4). The risk of cardiac events was significantly lower in LQT1 girls than boys≤12 years (HR, 0.55), whereas LQT2 female patients ≥13 years had the higher risk of cardiac events than male patients (HR, 4.60). Patients in the repetitive TdP or CPA group included 1 LQT1 female patient, 1 LQT2 male patient, and 5 LQT2 female patients. All LQT2 patients in these groups had TdP repeatedly immediately after the antecedent event. In addition, all 5 female LQT2 patients in these groups had the event after or near puberty.

CONCLUSIONS

Female LQT2 children might have repeated TdP shortly after prior events, especially after puberty. (Circ J 2016; 80: 696-702).

The beginnings of long QT syndrome

PURPOSE OF REVIEW

The purpose of this study is to update the perinatal cardiologist and obstetrical care provider on the presentation and management of the fetus with long QT syndrome (LQTS).

RECENT FINDINGS

LQTS is a known cause of sudden death in childhood, adolescence and young adulthood that presents during fetal life, but is often not recognized. Torsades de pointes (TdP) ±2° atrioventricular block (AVB) are not always attributed to LQTS, although the most common LQTS rhythm, a fetal heart rate of less than third percentile for gestational age (GA), is not recognized as abnormal because it does not meet the standard obstetrical criteria for bradycardia. Early recognition and appropriate treatment can be life saving for the fetus and unsuspecting LQTS family members. Fetal rhythm phenotype and postnatal QTc can predict postnatal rhythm and suggest genotype: bradycardic fetuses usually have KCNQ1 mutation, while those with TdP and/or a postnatal QTc more than 500 ms have SCN5A, KCNH2 or uncharacterized mutations.

SUMMARY

The fetus with repeated heart rates of less than third percentile of GA and those with TdP ±2° AVB are likely to manifest the same rhythm after birth and have an LQTS mutation.

We only find what we look for: fetal heart rate and the diagnosis of long-QT syndrome

Long QT syndrome (LQTS), an inherited channelopathy, is a common cause of arrhythmic death in infants, children and young adults. Although many LQTS genes have been identified, most (~75%) of LQTS mutations are found in KCNQ1, KCNH2 or SCN5A. In most cases, treatment for LQTS is successful and modifies the risk of life-threatening arrhythmias; thus, making the correct diagnosis is important. The diagnosis of LQTS is made by the measurement of a prolonged QT interval on the standard ECG; family history or characteristic arrhythmia features are used to strengthen the diagnosis and genetic testing confirms the diagnosis.

Life-Threatening QT Prolongation in a Preterm Infant

Introduction Temporary QT-interval prolongation following intracranial hemorrhage and hydrocephalus has been repeatedly reported in adults. Case We report a case of excessive QT prolongation with sudden bradycardia resulting in 2:1 atrioventricular conduction in a preterm infant most likely associated with a congenital hydrocephalus. Pathomechanisms are discussed. Conclusion Congenital hydrocephalus predisposes to excessive QT prolongation in preterm infants.

Molecular diagnosis of long QT syndrome at 10 days of life by rapid whole genome sequencing

BACKGROUND

The advent of clinical next generation sequencing is rapidly changing the landscape of rare disease medicine. Molecular diagnosis of long QT syndrome (LQTS) can affect clinical management, including risk stratification and selection of pharmacotherapy on the basis of the type of ion channel affected, but results from the current gene panel testing requires 4-16 weeks before return to clinicians.

OBJECTIVE

A term female infant presented with 2:1 atrioventricular block and ventricular arrhythmias consistent with perinatal LQTS, requiring aggressive treatment including epicardial pacemaker and cardioverter-defibrillator implantation and sympathectomy on day of life 2. We sought to provide a rapid molecular diagnosis for the optimization of treatment strategies.

METHODS

We performed Clinical Laboratory Improvement Amendments-certified rapid whole genome sequencing (WGS) with a speed-optimized bioinformatics platform to achieve molecular diagnosis at 10 days of life.

RESULTS

We detected a known pathogenic variant in KCNH2 that was demonstrated to be paternally inherited by follow-up genotyping. The unbiased assessment of the entire catalog of human genes provided by WGS revealed a maternally inherited variant of unknown significance in a novel gene.

CONCLUSION

Rapid clinical WGS provides faster and more comprehensive diagnostic information at 10 days of life than does standard gene panel testing. In selected clinical scenarios such as perinatal LQTS, rapid WGS can provide more timely and clinically actionable information than can a standard commercial test.

Modeling inherited cardiac disorders

Advances in the understanding and treatment of cardiac disorders have been thwarted by the inability to study beating human cardiac cells in vitro. Induced pluripotent stem cells (iPSCs) bypass this hurdle by enabling the creation of patient-specific iPSC-derived cardiomyocytes (iPSC-CMs). These cells provide a unique platform to study cardiac diseases in vitro, especially hereditary cardiac conditions. To date, iPSC-CMs have been used to successfully model arrhythmic disorders, showing excellent recapitulation of cardiac channel function and electrophysiologic features of long QT syndrome types 1, 2, 3, and 8, and catecholaminergic polymorphic ventricular tachycardia (CPVT). Similarly, iPSC-CM models of dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) have shown robust correlation of predicted morphologic, contractile, and electrical phenotypes. In addition, iPSC-CMs have shown some features of the respective phenotypes for arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C), LEOPARD syndrome, Pompe's disease, and Friedriech's ataxia. In this review, we examine the progress of utilizing iPSC-CMs as a model for cardiac conditions and analyze the potential for the platform in furthering the biology and treatment of cardiac disorders.