EFFECTS OF ALMOKALANT, A CLASS-III ANTIARRHYTHMIC AGENT, ON SUPRAVENTRICULAR, REENTRANT TACHYCARDIAS

The aim of the present study was to investigate the effects of almokal ant on sustained reentrant supraventricular tachycardias. Reentrant ta chycardias were induced, using transesophageal atrial stimulation, in 82 patients with atrioventricular reentrant tachycardia (n = 54) or AV nodal reentrant tachycardia (n = 28). After a baseline procedure duri ng which the tachycardia was induced and over-drive terminated, the ta chycardia was reinduced and studied during 12 minutes of infusion of e ither placebo or almokalant, aiming at plasma concentrations of 20, 50 , 100, and 150 nmol/l. Each patient was studied at two dose levels dur ing the same procedure. There was an increase in the RR interval durin g tachycardia of 6% at 100 nmol/l (p = 0.001 vs. baseline tachycardia) . The QT interval during tachycardia increased by 5% (p = 0.001) at 50 nmol/l and by 10% (p = 0.001) at 100 nmol/l. Bundle branch block duri ng tachycardia developed in 13% during almokalant infusion, aiming at 20 nmol/l, in 25% at 50 nmol/l, in 50% at 100 nmol/l, and in 33% at 15 0 nmol/l. Rapid baseline tachycardia, increasing almokalant dose, and an increasing number of induced tachycardias correlated with the appea rance of bundle branch block. In six patients with AV nodal reentrant tachycardia, 2:1 AV block occurred, in all cases preceded by bundle br anch block. The QT prolongation during sustained tachycardia was large r in patients who were non-inducible at the same plasma concentration level than in the inducible patients. Almokalant caused bundle branch block and 2:1 AV block during sustained supraventricular tachycardia. These findings emphasize the importance of studying drug effects at ra tes in the range of clinical tachycardias that expose the conduction s ystem to the limits of its refractoriness.