Effects of verapamil in ventricular tachycardias. An experimental and clinical study

To determine the effect of verapamil in ventricular tachycardias, we performed an experimental and clinical study. Experimental ventricular tachycardias (VT) were produced in dog hearts with minute aconitine crystals introduced into the periphery of a left ventricular area, damaged by intramural injection of 1.0-1.5 ml phenol. The response of these tachycardias to 0.2 mg/kg verapamil was analyzed. Verapamil was infused into the superior vena cava over 15-20 min. Leads II, aVL, intraventricular right and left unipolar records, as well as one of the superior vena cava, were registered under control conditions, in the presence of VT, and after application of verapamil. Recordings were obtained at constant intervals, waiting for the recovery of sinus rhythm (SR) and the posterior reappearance of tachycardia. Experiments were performed for 6 to 8 h under continuous infusion of Hartmann's solution. Throughout these periods, variations in systemic systolic pressure were recorded. From 75 animals submitted to this treatment, 30 (40%) recovered transiently the SR, whereas the drug exerted no antiarrhythmic effect in 19 (25%), and arterial systolic pressure fell importantly in 10 (13%) animals. In two more groups, of 15 dogs each, the VT response to verapamil was compared with the response to lidocaine and flecainide. Endovenous verapamil (5-10 mg) was administered to 10 patients, coursing with VT and having a structurally normal heart, after this arrhythmia was induced by electrical stimulation. The response to verapamil was satisfactory in nine patients (90%), in which VT originated in the septal and apical regions of the left ventricle. Verapamil seems to be effective in experimental and clinical ventricular tachycardias related to calcium-dependent potentials, in which the sustaining mechanism could either be triggered activity or reentry.