Effects of tocainide studied with programmed electrical stimulation of the heart in patients with reentrant tachyarrhythmias

Abstract

The electrophysiologic effects of tocainide were studied with programmed electrical stimulation of the heart in two patients with atrioventricular (A-V) nodal tachycardia, five patients with reentrant tachycardia involving an accessory pathway and two patients with paroxysmal ventricular tachycardia. The measurements were made before and after a 15 minute perfusion of tocainide at a dose of 0.75 mg/kg per min in the first seven patients and of 0.5 mg/kg per min in the last two. At the end of perfusion, the drug plasma level ranged from 2.0 to 10.2 μg/ml (mean 6). During the subsequent 60 minutes, the plasma level decreased extremely slowly, its mean value remaining constantly between 3 and 4 μg/ml. Tocainide failed to achieve statistically significant effects on the functional properties of the A-V node. However, an increase of A-H time (two patients), prolongation of nodal refractory period (one patient) and lengthening of the cycle length producing a second degree A-V block (four patients) were observed in isolated cases. The H-V interval increased by 20 msec in three of the eight cases in which its measurement was not hampered by the constant presence of a preexcitation wave. No systematic effect on the refractory periods of the atrial and ventricular muscle was noted. In six patients, tocainide was perfused during sustained episodes of tachycardia (A-V nodal tachycardia, two patients; circus movement tachycardia using an accessory pathway, three patients; and paroxysmal ventricular tachycardia, one patient). Sinus rhythm was restored in all six patients. The drug prevented reinitiation of tachycardia in four of the eight patients in whom it could easily be triggered during the control period; it lengthened the tachycardia cycle length in the remaining four. No side effects were noted. These results, obtained with low plasma levels of tocainide, allow one to consider this drug a promising antiarrhythmic agent.