Comparison of Verapamil and Diltiazem in the Suppression of Idiopathic Ventricular Tachycardia

This study examines the efficacy of verapamil and diltiazem in the suppression of idiopathic ventricular tachycardia (VT). Eight patients (mean age 29.8 +/- 12.3 years, two males and six females) with VT, without any underlying cardiac abnormality on clinical examination and noninvasive investigation, were studied. The inducibility of the clinical VT was examined by treadmill exercise testing and programmed ventricular stimulation (PVS). In six patients, VT was inducible by exercise testing and in the remaining two by PVS. Following baseline testing, verapamil (120-mg thrice daily) and diltiazem (60-mg thrice daily) were administered in random order, allowing 5 half-lives for the drug to load before evaluation. Two patients had complete suppression of the VT and the remaining six patients demonstrated a partial response to both calcium antagonists. In the patients with a partial response, the duration of the longest run of VT was reduced (baseline 96.0, 34.2 SEM); verapamil 19.2 (7.5); diltiazem 45.3 (21.4 beats), whereas, there was no change in the rate of VT (baseline 199.7 (8.0); verapamil 184.5 (11.4); diltiazem 201.0 (9.5 beats/min). No proarrhythmic effect was observed with either of the drugs in these patients. We conclude that idiopathic VT can be suppressed in some patients by calcium antagonists. In patients with a partial response, the length of run of the VT can be reduced, but the rate is unaffected. Verapamil and diltiazem do not differ in their ability to suppress VT in individual patients.