Prolonged QT, atrioventricular block, and sudden death in the newborn: an electrophysiologic evaluation

Clinical presentation and genetic characterization of early-onset atrial fibrillation in patients affected by long QT syndrome: A single-center experience

INTRODUCTION

Early-onset atrial fibrillation (AF) has already been observed in approximately 2% of patients with genetically proven long QT syndrome (LQTS). This frequency is higher than population-based estimates of early-onset AF. However, the concomitant expression of AF in LQTS is likely underestimated. The purpose of this study was to examine the clinical presentation, genetic background, and outcomes of a cohort of patients with LQTS and early-onset AF referred to a single tertiary center.

METHODS

Twenty-seven patients diagnosed with congenital LQTS were included in the study based on the documentation of early-onset (age ≤50 years) clinical or subclinical AF episodes in all available medical records, including standard electrocardiograms, wearable monitor or cardiac implantable electronic devices.

RESULTS

Seventeen patients experienced clinical AF during the follow-up period. Subclinical AF was detected in 10 patients through insertable or wearable cardiac monitors. In our series, the mean heart rate during AF episodes was found to be relatively low despite the patients' young age and the low or minimal effective doses of beta-blockers used for QTc interval control. All patients exhibiting LQTS and early-onset AF were genotype positive, carrying mutations in the KCNQ1 (66%), KCNH2, KCNE1, and SCN5A genes. Notably, most of these patients carried the same p.(R231C) mutation in the KCNQ1 gene (59%) and were from the same families, suggesting concurrent expression of familial AF and LQTS.

CONCLUSION

LQTS patients are prone to developing clinical and subclinical AF, even at a younger age. The occurrence of early-onset AF in the LQTS population could be more frequent than previously assumed. AF should be considered as a potential dysrhythmia related to LQTS. Our study emphasizes the importance of carefully researching clinical and/or subclinical episodes of AF through strict heart rhythm monitoring in the LQTS population.

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.

Rare Cause of Infranodal Block

The patient exhibits multiple features suggestive of Timothy syndrome, which is a multisystem autosomal-dominant condition with findings that include prolonged QT interval, hand and foot abnormalities, dysmorphic facial features, and mental retardation. A 2:1 infranodal atrioventricular block may occasionally be seen in the setting of severely prolonged QT interval. Functional nature of atrioventricular block is demonstrated by resumption of 1:1 conduction with changes in heart rate.

Large-scale elucidation of drug response pathways in humans

Elucidating signaling pathways is a fundamental step in understanding cellular processes and developing new therapeutic strategies. Here we introduce a method for the large-scale elucidation of signaling pathways involved in cellular response to drugs. Combining drug targets, drug response expression profiles, and the human physical interaction network, we infer 99 human drug response pathways and study their properties. Based on the newly inferred pathways, we develop a pathway-based drug-drug similarity measure and compare it to two common, gold standard drug-drug similarity measures. Remarkably, our measure provides better correspondence to these gold standards than similarity measures that are based on associations between drugs and known pathways, or on drug-specific gene expression profiles. It further improves the prediction of drug side effects and indications, elucidating specific response pathways that may be associated with these drug properties. Supplementary Material for this article is available at www.liebertonline.com/cmb.

Long QT syndrome and life threatening arrhythmia in a newborn: molecular diagnosis and treatment response

Intrauterine and neonatal manifestations of congenital long QT syndrome are associated with a high cardiac risk, particularly when atrioventricular block and excessive QT prolongation (> 600 ms(1/2)) are present. In a female newborn with these features, treatment with propranolol and mexiletine led to complete reduction of arrhythmia that was maintained 1.5 years later. High throughput genetic analysis found a sodium channel gene (LQT3) mutation. Disappearance of the 2:1 atrioventricular block and QTc shortening (from 740 ms(1/2) to 480 ms(1/2)), however, was achieved when mexiletine was added to propranolol. This effect was considered to be possibly genotype related. Early onset forms of long QT syndrome may benefit from advanced genotyping.

Compound heterozygosity for mutations (W156X and R225W) in SCN5A associated with severe cardiac conduction disturbances and degenerative changes in the conduction system

Cardiac conduction defects associate with mutations in SCN5A, the gene encoding the cardiac Na+ channel. In the present study, we characterized a family in which the proband was born in severe distress with irregular wide complex tachycardia. His older sister died at 1 year of age from severe conduction disease with similarly widened QRS-complexes. Mutational analysis of SCN5A in the proband demonstrated compound heterozygosity for a nonsense mutation (W156X), inherited from the father, and a missense mutation (R225W), inherited from the mother. Genotyping on DNA extracted from tissue from the deceased sibling revealed the same SCN5A genotype. Injection of cRNA encoding the W156X mutation in Xenopus oocytes did not produce any current. The R225W substitution neutralizes the third Arg residue within the voltage-sensing segment of domain I. Expression studies showed that this mutation leads to a severe reduction in I(Na) and is also associated with gating changes. Histological examination of the heart from the deceased sibling revealed changes consistent with a dilated type of cardiomyopathy and severe degenerative abnormalities of the specialized conduction system. The occurrence of compound heterozygosity for these two mutations implies that the proband carries solely severely dysfunctional cardiac Na+ channels. This explains his severe phenotype and that of his deceased sister who had been a carrier of the same genotype. The morphological changes within the heart of the deceased sibling may have occurred secondary to the Na+ channel abnormality and contributed to the severity of the disorder in this individual.

Homozygous SCN5A mutation in long-QT syndrome with functional two-to-one atrioventricular block

Heterozygous mutations in genes encoding cardiac ionic channel subunits KCNQ1, HERG, SCN5A, KCNE1, and KCNE2 are causally involved in the dominant form of long-QT syndrome (LQTS) while homozygous mutations in KCNQ1 and KCNE1 cause LQTS with or without congenital deafness. In addition, two homozygous HERG mutations have been associated with severe LQTS with functional atrioventricular conduction anomalies in young children. A 2:1 atrioventricular block (AVB) with a major QTc prolongation (526 ms) was evidenced in a 5-year-old boy referred for syncope and seizure. LQTS was diagnosed and beta-blocking therapy initiated leading to normal atrioventricular conduction. Electrophysiological study provided support that location of the AVB was infra-Hisian. DNA analysis was performed in the proband and in asymptomatic family members. A novel missense mutation, V1777M, in the early C-terminal domain of SCN5A was identified. The proband was homozygous while the parents and two siblings were heterozygous carriers. Homozygote and heterozygote expression of the mutant channels in tsA201 mammalian cells resulted in a persistent inward sodium current of 3.96+/-0.83% and 1.49+/-0.47% at -30 mV, respectively, which was dramatically reduced in the presence of tetrodotoxin. This study provides the first evidence for a homozygous missense mutation in SCN5A and suggests that LQTS with functional 2:1 AVB in young children, a severe phenotype associated with bad prognosis, may be caused by homozygous or heterozygous compound mutations not only in HERG but also in SCN5A. The full text of this article is available at http://www.circresaha.org.

Arrhythmias in the congenital long QT syndrome: how often is torsade de pointes pause dependent?

OBJECTIVE

To determine the frequency and predictors of pause dependent torsade de pointes among patients with the congenital long QT syndrome and spontaneous ventricular tachyarrhythmias.

DESIGN

The literature on the "congenital long QT" was reviewed. Articles with illustrations demonstrating the onset of spontaneous polymorphic ventricular arrhythmias in the absence of arrhythmogenic drugs were included.

RESULTS

Illustrations of 62 spontaneous episodes of torsade de pointes among patients with congenital long QT syndrome were found in the literature. The majority (74%) of documented arrhythmias were "pause dependent"; 82% of these pauses were longer than the basic cycle length by > 100 ms. Age and sex correlated with the mode of arrhythmia initiation. Arrhythmias in infants (</= 3 years old) were not pause dependent, while female sex correlated with pause dependent torsade. Using multivariate analysis, age was the only independent predictor of the mode of onset of torsade de pointes.

CONCLUSION

Available data suggest that the majority of spontaneous arrhythmias in the congenital long QT syndrome are pause dependent. Torsade de pointes that is not preceded by pauses appears to be limited to patient subgroups with severe forms of the disease, like symptomatic infants. These findings have important implications regarding the use of cardiac pacing for arrhythmia prevention.

The long QT syndrome with impaired atrioventricular conduction: a malignant variant in infants

INTRODUCTION

The long QT syndrome (LQTS) is occasionally complicated by impaired AV conduction, mostly 2:1 AV block. This form of LQTS can manifest before birth or during neonatal life, and it is more sporadic than familial. It is usually an isolated disorder, although it can be accompanied by a variety of cardiovascular and other anomalies. In spite of different treatment modes, mortality is high.

METHODS AND RESULTS

The reported case presented not only with 2:1 AV conduction, but also with Wenckebach episodes with impaired right and left bundle branch conduction, and decremental conduction in the His-Purkinje axis. We also observed sinus pauses and accelerated AV junctional escape beats.

CONCLUSION

Our findings, and similar observations by others, suggest involvement of the sinus node and the distal conduction system in this form of the LQTS. Several histologic studies have documented abnormalities within the conduction system, including apoptosis. Because of the rare occurrence and poor prognosis of the LQTS with impaired AV conduction, international guidelines for diagnosis and treatment are needed. Development of an internal cardiac defibrillator for this young age group is necessary.

High-rate atrial pacing as an innovative bridging therapy in a neonate with congenital long QT syndrome

INTRODUCTION

The neonatal presentation of the long QT syndrome is rare, although it is frequently accompanied by life-threatening arrhythmias. Infants may not survive childhood despite traditional management with beta-adrenergic blockade and pacing.

METHODS AND RESULTS

This case describes a newborn with a long QT interval, T wave alternans, intermittent 2:1 AV block, ventricular arrhythmias, and a family history of sudden death. After failing medical therapy, conventional VVI and DDD pacing were unsuccessful due to prolonged ventricular refractoriness and proarrhythmia. At 2 months of life, the child was treated with high-rate (180 ppm) atrial pacing to produce intentional 2:1 AV block. Following an episode of possible syncope at 16 months of age, an automatic implantable cardioverter defibrillator (ICD) was added. Finally, as recently reported, acutely induced hyperkalemia led to both a marked decrease in QTc and functional improvement in repolarization (consistent 1:1 AV conduction at rates to 180 beats/min). Spironolactone and dietary potassium were added and have produced the same effects chronically.

CONCLUSIONS

High-rate atrial pacing with 2:1 AV block is presented as a novel and "bridging" therapy for neonatal long QT syndrome and 2:1 AV block with ventricular arrhythmias. Definitive therapy with ICD implantation was then possible when patient size was substantially increased. The electrophysiologic response to intentional elevation of the serum potassium suggests a genetic defect in an inward potassium channel and demonstrates a possible therapy of long QT syndrome in some future patients.

Prenatal findings in patients with prolonged QT interval in the neonatal period

OBJECTIVE

To describe prenatal abnormalities of cardiac rhythm in patients with prolonged QT interval in the neonatal period.

DESIGN

A retrospective analysis of the results of fetal echocardiography and the outcome in patients with prolonged QT interval in the neonatal period who had been referred for prenatal evaluation.

SETTING

Two university hospitals.

PATIENTS

Nine patients with prolonged QT interval in the neonatal period who had been referred for prenatal evaluation. Fetal echocardiograms were obtained from 24 to 40 weeks of gestation. Indications were fetal bradycardia (five patients), a family history of long QT syndrome (two patients), and complex arrhythmias (two patients).

RESULTS

Seven fetuses had persistent sinus bradycardia without ventricular arrhythmias (heart rates 70-120 beats/ min). Five patients were treated with propranolol, after the diagnosis had been established by postnatal electrocardiogram (ECG). One of these patients died suddenly at the age of 3 weeks, after the treatment had been stopped because of profound bradycardia. One of the remaining two patients who did not receive propranolol had a syncope at the age of 6 weeks. Two fetuses presented with frequent runs of ventricular tachycardia and intermittent bradycardia caused by intermittent, functional second degree atrioventricular block. Both patients died on the first day of life despite treatment with propranolol and transvenous temporary pacing.

CONCLUSIONS

Sinus bradycardia in an otherwise normal fetus may be a symptom of long QT syndrome. Postnatal ECGs and a family examination are strongly recommended in these children. In fetuses with frequent runs of ventricular tachycardia and intermittent second degree atrioventricular block long QT syndrome should be suspected prenatally. These high risk patients should be delivered in centres with a paediatric cardiology unit.

Long reflections on the QT interval: the sixth annual Gordon K. Moe Lecture

This review of accumulated knowledge about the long QT syndromes begins with an iteration of the original papers and then proceeds to a broader historic reflection that includes my personal work as well as many studies by others. Next come reflections upon the current status of knowledge on the subject, combined with comments about remaining challenges and questions grouped as follows: (1) morphologic abnormalities of the cardiac conduction system and their pathophysiologic significance in the long QT syndromes; (2) cardioneuropathy in the pathogenesis of long QT syndromes; (3) variability of QT prolongation, including consideration of peripheral and central dysautonomic conditions with certain diagnostic and therapeutic implications; (4) some caveats about the popular use of left cervical sympathectomy to treat symptomatic individuals with long QT syndrome, emphasizing hazards for future electrical instability of the heart; (5) consideration of genetic influences in the long QT syndromes, a field holding great promise as well as fraught with many puzzling dilemmas; and (6) apoptosis and the pathogenesis of the long QT syndromes, based upon personal observations previously made with electron microscopic studies of the sinus node and now including new immunohistochemical evidence expanding the relevance of this novel view-point. These intentionally provocative presentations are made to stimulate physicians and other scientists to consider these several different perspectives in planning future studies aimed at better understanding of one of the most challenging medical entities facing cardiology today.