Mechanism of action and efficacy of verapamil and beta-blockers in exercise-induced ventricular tachycardia

To determine the antiarrhythmic efficacy of beta-blockers (beta-B) and verapamil (V) in exercise-induced ventricular tachycardia (Ex-VT), nine patients with reproducible Ex-VT (in two consecutive exercise tests) were studied by means of electrophysiologic study (EPS) in basal conditions and serial exercise testing after beta-B (metoprolol 25 mg tid to 100 mg qid; oxprenolol 40 mg tid) and/or V (80-160 mg tid). Ejection fraction was normal in four cases and depressed in five. Of these nine patients, four developed Ex-VT during chronic amiodarone treatment, which was continued. During EPS, VT was induced at a critical atrial pacing rate in one case, and with the extrastimulus technique in four. Ventricular tachycardia was not inducible with either technique in four patients. Five of the six patients on beta-B and none of the seven on V developed Ex-VT, although they achieved the same or higher work-loads as compared to the basal exercise tests. In the case with rate-dependent VT, beta-B and V prevented VT at work-loads, sinus rates and double products significantly higher than those obtained in basal conditions. In the others, maximal heart rate and double product were lower on beta-B and showed a wide variability on V. V and beta-B appeared to be highly effective in preventing Ex-VT, in patients with normal heart as well as in those with greatly depressed ejection fraction. Both of the drugs appeared to suppress re-entry or triggered activity in the patient with rate-dependent Ex-VT.(ABSTRACT TRUNCATED AT 250 WORDS)