QRS PROLONGATION AS AN INDICATOR OF RISK OF ISCHEMIA-RELATED VENTRICULAR-TACHYCARDIA AND FIBRILLATION INDUCED BY EXERCISE

The majority of patients with serious ventricular arrhythmias induced by exercise have ischemic heart disease. These arrhythmias, however, d evelop only in a minority of the patients with coronary artery disease . The aim of this study was to investigate whether patients with ventr icular tachycardia or fibrillation produced by exercise-induced ischem ia exhibit any premonitory electrocardiographic indicators of arrhythm ia propensity and whether arrhythmia suppression by myocardial revascu larization abolished these changes. High-quality exercise electrocardi ograms (50 mm/sec) from 30 case patients with ventricular tachycardia and fibrillation produced by exercise-induced ischemia were studied be fore and after surgical revascularization. These results were compared with those obtained from 30 control patients matched for age, sex, he art disease, and preoperative exercise capacity. The resting and peak exercise electrocardiograms were examined separately in a blinded mann er with respect to QRS duration, ST-segment depression, and JT interva ls. Patients with bundle branch block patterns were excluded. The QRS duration at rest was similar in case and control patients preoperative ly and increased significantly with exercise in both groups. However, the QRS prolongation was larger in the case group, in which it was 11 +/- 3 msec compared with 4 +/- 2 msec in the control group (p = 0.043) . QRS prolongation greater than or equal to 15 msec predicted ischemia -related ventricular arrhythmias in 73% of the patients. After surgica l revascularization, there was no QRS prolongation with exercise in ei ther group. In both groups, the QRS prolongation was associated with s ignificant ST-segment depression, which was larger in the case patient s. After revascularization, the ST-segment depressions at peak exercis e were smaller in both groups. The rate adaption of the JT-apex and JT -end intervals was similar in the case and control group both before a nd after surgery. The current findings confirm that QRS prolongation i s a specific characteristic of ischemia. Furthermore, they indicate th at the prolongation is greater in patients exhibiting ischemia-related ventricular tachycardia and fibrillation and that arrhythmia suppress ion by surgical revascularization is associated with a normalization o f these changes. QRS prolongation greater than or equal to 15 msec, in the absence of bundle branch block, may be a useful indicator of risk of ischemic ventricular tachycardia or fibrillation related to exerci se.