Shortening of the Short Refractory Periods in Short QT Syndrome

2013

Journal of the American College of Cardiology, 2006

Almost 50 years after the first description of congenital long QT syndrome (LQTS), where QT interval prolongation was recognized as the hallmark of a new pathologic entity associated with sudden cardiac death (1), the simple linear measurement of QT interval still stands as the strongest independent predictor of cardiac events in LQTS patients. Prolonged corrected QT interval (QTc) was a powerful independent risk factor for cardiac event (syncope or cardiac arrest) since the initial analysis of patients enrolled in the International LQTS Registry (2-3). Subsequent analyses confirmed that finding (4-10). Incremental changes of QT interval carried higher risk for sudden death, and a cutoff of QTc Ͼ500 ms consistently identified higher-risk patients. Most analyses of the International LQTS Registry were based on QT interval measured on the first available electrocardiogram (ECG) (6-8). This was done to avoid possible selection bias, because symptomatic patients tended to have more ECG recordings than asymptomatic subjects, and to limit possible effects of concomitant therapies, which were less likely to be present in the earliest ECG. See page 1047 The study by Goldenberg et al. (11) in this issue of the Journal first evaluated possible incremental benefit of follow-up ECG on risk stratification. Its main results were that maximum QTc, rather than baseline QTc, was better correlated with risk of cardiac events during follow-up and that an increased number of ECG tracings may improve risk stratification. The major clinical implications are that serial ECG tracings should be routinely obtained during clinical follow-up of LQTS patients and that changes of QT interval duration may be monitored to evaluate the effect of therapies in LQTS patients.

2010

Background. The interval from the R wave to the maximum amplitude of the T wave (RTm) contains the heart rate dependency of ventricular repolarization.

European Heart Journal, 1998

The long QT syndrome is mainly defined by QT interval prolongation (QTc >0·44s). However, data obtained in genotyped patients showed that resting QTc measurement alone may be inaccurate for ascertaining the phenotype. The aim of this study was to evaluate the diagnostic performance of QT interval rate-dependence in untreated chromosome 11-linked patients.

Circulation, 1992

BACKGROUND The interval from the R wave to the maximum amplitude of the T wave (RTm) contains the heart rate dependency of ventricular repolarization. METHODS AND RESULTS A computer algorithm was developed to quantify the RTm and preceding RR intervals for each of more than 50,000 beats on 24-hour ambulatory electrocardiographic (Holter) recordings to evaluate the dynamic relation between repolarization duration and cycle length. The relation of RTm to the preceding RR interval (RTm/RR slope) was determined by the best-fit linear regression equation between these two parameters. Eleven normal subjects and 16 patients with long QT syndrome (LQTS) were investigated. Six of the normal subjects had Holter recordings obtained before and after beta-blocker therapy. beta-Blockers were associated with a significant (p = 0.005) reduction in the RTm/RR slope from 0.13 +/- 0.02 to 0.10 +/- 0.02. The mean value of the RTm/RR slope was significantly (p = 0.003) larger in the LQTS patients (0.21 ...

Circulation, 1990

The long QT syndrome is electrocardiographically characterized by a prolonged QT interval and by several other, more subtle, ST-T-U wave abnormalities, most of which have not been quantified. To determine the possible usefulness of several new electrocardiographic characteristics in identifying patients with known long QT syndrome, logistic regression models were applied to a data base of seven new, relatively independent, electrocardiographic repolarization variables. These were measured on digitized 12-lead electrocardiograms of 315 normal subjects and 37 patients with the long QT syndrome (members of well-identified long QT syndrome families, QTc greater than 0.44 second, 27% symptomatic), who ranged in age from 17 to 60 years. Electrocardiographic variables that independently differentiated (p less than 0.001) patients with long QT syndrome from normal subjects included quantitative measures of repolarization: early duration, rate, T wave symmetry, late phenomena, and heterogene...

Pacing and clinical electrophysiology : PACE, 1991

Sympathetic stimulation is well known to contribute to the genesis of QTU prolongation and ventricular tachyarrhythmias in patients with congenital long QT syndrome. In this study, we performed exercise treadmill testing, isoproterenol infusion (1-2 micrograms/min), and right atrial pacing (cycle length 500 msec) in 11 patients with congenital long QT (LQT) syndrome (LQT group) and in 12 age- and sex-matched controls (control group). The responses of the corrected QT (QTc; Bazett's method) interval and the TU wave complex were evaluated. The QTc interval was prolonged from 482 +/- 63 msec1/2 to 548 +/- 28 msec1/2 by exercise in the LQT group (n = 11; P less than 0.005), and this was associated with fusion of the T waves with enlarged U waves, whereas the QTc interval did not increase with exercise in the control group (n = 12; 402 +/- 19 msec1/2 vs 409 +/- 22 msec1/2). The QTc interval was also prolonged from 466 +/- 50 msec1/2 to 556 +/- 33 msec1/2 by isoproterenol in the LQT g...

Journal of the American College of Cardiology, 1987

A permanent pacemaker was inserted in eight patients with the long QT syndrome. All had recurrent syncope or seizures, six had documented torsade de pointes and four had aborted sudden death. Among the eight patients, permanent pacing was instituted in three who were unsuccessfully treated with both a beta-adrenergic blocking agent and left cardiothoracic sympathectomy, and in two who proved refractory or intolerant to betablockers. Another three patients had pacemaker implantation and long-term beta-blocker therapy because of spontaneousatrioventricular (AV) blockin one, aborted sudden death in one and patient preference in one.

Cardiac Electrophysiology Clinics, 2012

The incidence of long QT syndrome (LQTS) is approximately 1 in 2500, but 25% to 50% of patients may demonstrate a normal or borderline long QT interval. The rate of life-threatening arrhythmias in patients with LQTS with normal corrected QT intervals is very low (approximately 0.13% per year) but higher (>10-fold) than that in unaffected family members. Avoidance of QT-prolonging medications and routine therapy with highly efficacious b-blockers significantly reduce life-threatening arrhythmia. Therefore, identification of the index case and affected family members is critical. Comprehensive clinical history taking, rest and provocative electrocardiographic testing, and targeted genetic testing assists in diagnosing patients with LQTS with normal or borderline QT intervals.

The American Journal of Cardiology, 1991