BACKGROUND Patients with a history of class Ia drug-induced torsade de pointes have been treated with chronic amiodarone without recurrence of torsade de pointes despite comparable prolongation of the QT interval. We hypothesized that in such patients, class Ia drugs cause nonhomogeneous prolongation of cardiac repolarization times, whereas amiodarone causes homogeneous prolongation of cardiac ...

QT-RR hysteresis is characterized by longer QT intervals at a given RR interval while heart rates are increasing during exercise and shorter QT intervals at the same RR interval while heart rates are decreasing during recovery. It has been attributed to a lagging QT response to different directional changes in RR interval during exercise and recovery. Twenty control subjects (8 males, age 51 ± ...

Common Cause of Short QT Interval To the Editor: I read with interest the recent report by Gaita et al1 of short-QT syndrome as a familial cause of sudden death. The authors enumerated other factors that shorten QT interval, such as increased heart rate, hyperthermia, hypercalcemia, hyperkalemia, acidosis, and altered autonomic tone.1 I would like to add another important and common, but undera...

The electrocardiogram was recorded for 100 seconds in 50 patients with atrial fibrillation to determine the relations between QT intervals and both the mean and instantaneous ventricular rates. The mean ventricular rate was 94 beats per minute with a mean QT interval of 357 ms. The mean QTc, corrected beat by beat with Bazett's formula, was 444 ms--longer than reported for sinus rhythm. Between...

OBJECTIVES To introduce a nomogram of the normal QT interval at various heart rates measured from 24 hour Holter ECG recordings in healthy subjects with respect to age and sex and to use the nomogram to characterise dynamic changes in QT interval in patients with idiopathic ventricular fibrillation (IVF) and the long QT syndrome (LQT). METHODS The study group consisted of 422 subjects: 249 he...

Historically, the heart rate corrected QT (QTc) interval has been the standard method to assess for impaired ventricular repolarization, particularly for drug development. However, QTc does not reflect changes in autonomic state or QT-RR hysteresis which can also affect the interpretation of arrhythmogenic risk. With the advent of more accurate algorithms to automatically measure the QT interva...

We examined the relationship between changes in heart rate and the measured QT interval of the electrocardiogram in healthy subjects after exercise and during breath holding, hyperventilation, the dive reflex, the Valsalva maneuver, and the cold-pressor test. The tachycardia of exercise was accompanied by the familiar shortening of the QT interval, but substantial heart rate changes encountered...

The goal of the present study was to examine the utility of the conscious dog model by assessing the QT-interval-prolonging potential of ten positive compounds that have been reported to induce QT interval prolongation in clinical use and seven negative compounds considered not to have such an effect. Three doses of test compounds or vehicle were administered orally to male beagle dogs (n=4), a...

One of the major reasons of drug withdrawal or drug label revision is the drug induced sudden cardiac death associated with a prolongation of the QT interval in the electrocardiogram (ECG). When the QT interval is prolonged, there is an increased risk of ventricular tachyarrhythmia, including the life threatening form torsade de pointes. The QT interval of the ECG is a measure of the duration o...