Electrocardiographic correlates of spontaneous termination of ventricular tachycardia in patients with coronary artery disease.

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Abstract
BACKGROUND: In vitro studies have reported that beat-to-beat variance in tachycardia cycle length and in conduction and repolarization properties can result in spontaneous termination of reentrant arrhythmias. The purpose of this study was to define the ECG patterns associated with spontaneous termination of ventricular tachycardia in humans late after myocardial infarction. METHODS AND RESULTS: The QRS durations, QT intervals, and cycle lengths were measured on a beat-to-beat basis during episodes of sustained and spontaneously terminating ventricular tachycardias (VT) induced at antiarrhythmic drug-free and drug-assessment electrophysiological studies. Twenty-six patients were studied. Four categories of inducible ventricular tachycardia were studied: inducible sustained ventricular tachycardia in an antiarrhythmic drug-free state, spontaneously terminating ventricular tachycardia in an antiarrhythmic drug-free state, sustained ventricular tachycardia on antiarrhythmic therapy, and spontaneously terminating ventricular tachycardia on antiarrhythmic therapy. The ECG patterns that were statistically related to spontaneous termination of ventricular tachycardia included impingement of the QTP interval on the tachycardia cycle length (P < .001) both in the presence and absence of drugs, transient shortening of QRS just before termination, and paradoxical prolongation of QTP after abrupt shortening of ventricular tachycardia cycle length. In addition, greater beat-to-beat variances in tachycardia cycle lengths, QT intervals, and QRS durations were statistically associated with spontaneously terminating ventricular tachycardia. These ECG patterns did not occur during sustained episodes of ventricular tachycardia during the antiarrhythmic drug-free state or during ineffective antiarrhythmic drug therapy. CONCLUSIONS: A dynamic interplay between QRS duration, QT interval, and cycle length of tachycardia and their variances are associated with spontaneous termination of ventricular tachycardia in humans late after infarction. This study of ECG changes associated with spontaneous termination of ventricular tachycardia provides insight into potential mechanisms of antiarrhythmic drug efficacy.