T wave alternans in idiopathic long QT syndrome

Objectives. The study evaluates the association between T wave alternans and the risk of cardiac events (syncope, aborted cardiac arrest or cardiac death) in a large population of patients with idiopathic long QT syndrome.Background. T wave alternans is an infrequently recorded electrocardiographic (ECG) finding in patients with delayed repolarization, and its clinical significance is not clear.Methods. A total of 4,656 ECG recordings in 2,442 patients enrolled in the International Long QT Syndrome Registry were reviewed for episodes of T wave alternans. To determine the risk associated with T wave alternans, independent of corrected QT interval (QTc) duration, patients with T wave alternans were matched for QTc value (every 0.025 s^1/2) to patients with long QT syndrome without T wave alternans.Results. T wave alternans was identified in 39 patients (25 of whom had a QTc interval >0.50 s^1/2). A strong association between QTc prolongation and T wave alternans was observed (odds ratio 1.23 per 0.01-s^1/2unit increase in QTc, p < 0.0001). Conditional logistic regression analyses with adjustment for age, gender, status and QTc value revealed that T wave alternans did not make a significant independent contribution to the risk of cardiac events. The risk of experiencing a major cardiac event was primarily related to length of QTc.Conclusions. T wave alternans, a marker of electrical instability and regional heterogeneity of repolarization, identifies a high risk subset of patients with prolonged repolarization. Patients with T wave alternans have an increased risk of cardiac events, but this risk is primarily related to the magnitude of repolarization delay (QTc prolongation). T wave alternans does not make an independent contribution to the risk of cardiac events after adjustment for QTc length.     

Congenital long QT syndrome inducing 2:1 atrioventricular block: early detection in fetal life

A case is reported of congenital long QT interval associated with fixed 2:1 atrioventricular block. The bradycardia was detected at 16 weeks of gestational age. The atrioventricular block was due to an extremely delayed ventricular repolarization. Early detection of bradycardia in fetal life and the demonstration of a normal positive correlation between QT duration and ventricular rate suggest that, in this case, the syndrome may be due to an anomaly of the myocardial cells rather than to imbalance of the sympathetic nervous system.     

A case of congenital long QT syndrome associated with T wave alternans]

A case was presented in which a rare T wave alternans occurred in association with congenital long QT syndrome. A 71-year-old woman, who had experienced several syncopal attacks per year for the previous forty years, was admitted for further evaluation of the syncope. She had a family history of sudden death (sister) and QT prolongation (son). Electrocardiogram showed a corrected QT interval of 0.68 seconds. Treadmill exercise-tolerance test revealed both T wave alternans immediately after exercise and torsades de pointes 150 seconds after exercise. The syncope was induced by the mental excitation. A prolonged corrected QT interval reduced from 0.70 seconds to 0.58 seconds by the correction of her serum potassium and magnesium. The effect of propranolol, verapamil, phenytoin or mexiletine on T wave alternans and ventricular arrhythmia was evaluated by the treadmill exercise-tolerance test. The treatment with propranolol was most effective.     

Relationship between the QT indices and the microvolt-level T wave alternans in cardiomyopathy.

The relationship between the QT indices and microvolt-level T wave alternans (TWA) is unknown in cardiomyopathy, so the present study examined 86 patients with cardiomyopathy who experienced TWA during exercise testing (EXT). The QT interval (QT), duration from the Q wave to the peak of the T wave (QTp), duration from the peak to the end of the T wave and the dispersion of these parameters were measured by 12-lead electrocardiogram at rest and during EXT. In dilated cardiomyopathy (DCM), TWA was positive (TWA+) in 19 patients and negative (TWA-) in 17. No significant difference was observed between the TWA+ and TWA- groups in any parameter. In hypertrophic cardiomyopathy (HCM), TWA was positive in 24 patients and negative in 12. Max QTc, max QTpc and mean QTpc during EXT in the TWA+ group were significantly longer than those in the TWA- group. The sensitivity of TWA for ventricular tachycardia (VT) was high in DCM and HCM, and that of max QTc >500 ms during EXT for VT was high in HCM (93%). TWA is a useful predictor for VT in DCM and HCM, and prolonged max QTc during exercise has a prognostic value in HCM. Repolarization abnormality during exercise plays an important role in the genesis of VT in cardiomyopathy.     

Non-sustained microvolt level T-wave alternans in congenital long QT syndrome types 1 and 2

Background

Patients with long QT syndrome (LQTS) are predisposed to polymorphic ventricular tachycardia (VT) during adrenergic stimulation. Microvolt T-wave alternans (MTWA) is linked to vulnerability to VT in structural heart disease. The prevalence of non-sustained MTWA (NS-MTWA) in LQTS is unknown.

QT间期延长患者电风暴的临床特点、治疗策略及微伏级T波电交替的预警价值

电风暴（electrical storm，ES）是由于心室电活动极度不稳定所导致的最危重的恶性心律失常，是心脏性猝死的重要原因。本文旨在观察QT间期（QTc）延长患者发作ES的临床特点，B受体阻滞剂防治Es的疗效，并探讨微伏级T波电交替（MTWA）做为一种预警性心电图，对QTc延长伴Es患者的潜在应用价值。     

The QT syndromes: long and short

This Seminar presents the most recent information about the congenital long and short QT syndromes, emphasising the varied genotype-phenotype association in the ten different long QT syndromes and the five different short QT syndromes. Although uncommon, these syndromes serve as a Rosetta stone for the understanding of inherited ion-channel disorders leading to life-threatening cardiac arrhythmias. Ionic abnormal changes mainly affecting K(+), Na(+), or Ca(2+) currents, which either prolong or shorten ventricular repolarisation, can create a substrate of electrophysiological heterogeneity that predisposes to the development of ventricular tachyarrhythmias and sudden death. The understanding of the genetic basis of the syndromes is hoped to lead to genetic therapy that can restore repolarisation. Presently, symptomatic individuals are generally best treated with an implantable cardioverter defibrillator. Clinicians should be aware of these syndromes and realise that drugs, ischaemia, exercise, and emotions can precipitate sudden death in susceptible individuals.     

Amiodarone-induced 2 to 1 atrioventricular block in association with prolongation of the QT interval

The potential for development of 2 to 1 atrioventricular conduction in children with prolongation of the QT interval has been previously reported secondary to electrolytic disturbances. We report here a child who developed 2 to 1 atrioventricular conduction with prolongation of the QT interval following treatment with amiodarone for refractory supraventricular tachycardia. We highlight the importance of electrocardiographic monitoring to assess for those at risk of amiodarone toxicity, which may be manifested by prolongation of the QT interval and the simultaneous loss of atrioventricular conduction, and of equal importance the need for prompt conversion to an alternative anti-arrhythmic agent.     

Homozygotous mutation of the SCN5A gene responsible for congenital long QT syndrome with 2/1 atrioventricular block

Long QT syndrome is characterized by a prolongation of the QT interval on the surface ECG. This clinically and genetically heterogeneous cardiac disease is potentially lethal due to ventricular polymorphic tachyarrhythmias leading to syncope or sudden death. It is transmitted according to different mendelian modes due to mutations in several genes coding for cardiac ion channels. Heterozygous mutations in KCNQ1, HERG, SCN5A, KCNE1 and KCNE2 genes are responsible for the dominant form without deafness whereas homozygous mutations in KCNQ1 and KCNE1 are responsible for the recessive form (Jervell and Lange-Nielsen syndrome) associated with congenital deafness. We report the case of a 5 year-old boy referred for syncope with a prolongation of the QTc interval (526 ms) and a 2/1 Atrio-Ventricular (AVB) block on the surface ECG. Under beta-blocking therapy, the sinus rate decreased and the 2/1 AVB disappeared. Electrophysiological study evidenced an infra-hisian block and a unipolar ventricular endocardial pacemaker was implanted. A V1777M missense mutation was identified in the C-terminal part of SCN5A, cardiac sodium channel gene, at the homozygous state in the proband and at the heterozygous state in both parents and 2 sibblings. Only the proband had a severe phenotype with syncope and AV conduction anomalies. All other genetically affected subjects were asymptomatic. This study provides evidence for the involvement of homozygous LQT3 forms in "functional" AVB.     

Intra-His bundle block in 2:1 atrioventricular block

Intra-hisian atrioventricular (AV) block is not a common phenomenon, but it is important for the development of advanced or complete AV block. We observed a 77-year-old female patient with the 2:1 AV block due to an intra-hisian block. In this case we tried to detect the block site, but an alternating pattern of the AH conduction was noted on the His-electrogram in the electrophysiological study (EPS). The cause of the confusing finding might have been the instability of the catheter to record a His potential. We could detect a splitting of the His-electrogram with an intra-hisian block after minimal manipulation of the catheter. The authors’ observations suggest that catheter stability is important for a precise recording in the EPS and radiofrequency catheter ablation procedure.     

Functional atrioventricular conduction block in an elderly patient with acquired long QT syndrome: elucidation of the mechanism of block

The long QT syndrome (LQTS) is occasionally complicated by impaired atrioventricular (AV) conduction. This form of LQTS can manifest before birth or during neonatal life, and no previous report has demonstrated LQTS complicated by impaired AV conduction in elderly patient. This case report describes an elderly patient with an acquired form of LQTS who developed ventricular fibrillation that was successfully defibrillated during admission to the hospital. Electrophysiologic study demonstrated that HV interval was 38 milliseconds and QT interval was 635 milliseconds during sinus rhythm cycle length of 1167 milliseconds. 1:1 AV conduction was maintained to a pacing cycle length of 545 milliseconds with an AH interval of 144 milliseconds, HV interval of 44 milliseconds, and right ventricular monophasic action potential duration of 360 milliseconds. However, 2:1 HV block developed at a pacing cycle length of 500 milliseconds. Intravenous administration of mexiletine decreased the cycle length of developing HV block to 360 milliseconds.     

Congenital and acquired long QT syndromes

Exploration into the underlying genetic causes of congenital long QT syndrome (LQTS) has opened the door to our understanding of repolarization disorders. Expression of LQTS mutations has led to an improved understanding of the mechanisms of arrhythmogenesis, clinical diagnostic tools and channel specific therapy. Further insight into the mechanisms underlying the more common acquired LQTS is emerging from gene and channel studies that have used the congenital syndrome as a springboard for directing research to improve understanding. This review summarizes the clinical, genetic and electrophysiological understanding of congenital and acquired LQTS.     

T波电交替与室性心律失常

随着心电滤波、放大以及分析技术水平的提高,那些肉眼不能观察到、微伏级水平的T波电交替(TWA)现象得以深入的研究.业已证实,这种微小的TWA与恶性室性心律失常[单形/多形室性心动过速(室速)、尖端扭转型室速、心室颤动(室颤)]、心脏性猝死之间有着极为密切的联系,因而可作为室性心律失常的预测指标,TWA形成机制仍聚焦于心肌动作电位时程,心率(刺激频率)和细胞内钙循环.     

Inherited arrhythmic disorders: long QT and Brugada syndromes

Inherited arrhythmic disorders comprise a group of syndromes with unique genetic abnormalities and presentations but with very similar clinical outcomes and complications, the most terrifying of which are life-threatening arrhythmias and sudden cardiac death. Advances in molecular biology have enabled us to define and pinpoint many such disorders, which were previously labeled as idiopathic, to specific genes on various chromosomes. The current trend in the management of these potentially deadly disorders is to use pharmacotherapy (antiarrhythmic agents) and defibrillators for the prevention of sudden death; however, targeted therapy at a molecular level appears to be the path of the future. Herein, we review long QT and Brugada syndromes and focus on the genetics, pathophysiology, and clinical manifestations of these inherited arrhythmogenic disorders that affect patients with structurally normal hearts.