Effects of heptanol, class Ic, and class III drugs on reentrant ventricular tachycardia: Importance of the excitable gap for the inducibility of double-wave reentry

Abstract

Background: Double-wave reentry (DWR) can be a mechanism for acceleration of ventricular tachycardia (VT) with a large excitable gap (EG). The purpose of this study was to determine the effects of heptanol, class Ic, and class III drugs on the inducibility of DWR. Methods and Results: In 11 Langendorff- perfused rabbit hearts, a thin ring of anisotropic left ventricular epicardium was created by a cryoprocedure. VT with a revolution time of 180±26 milliseconds and an EG of 106±8 milliseconds was induced by incremental pacing. During control, entrainment with 10 stimuli at a 99±15- millisecond interval terminated VT in seven hearts. In four hearts VT was accelerated from 205±24 to 115±14 milliseconds by introduction of a second circulating wave in the ring. In the seven VTs that could not be accelerated, 0.5 μmol/L Org7797 (class Ic) and 1.0 mmol/L heptanol (uncoupling agent) prolonged the cycle length of VT by 32% and 37%, respectively. Because the refractory period (RP) only increased by 11%, the EG prolonged by 71% and the ratio between EG and RP was increased from 0.66 to 1.00. Under these conditions, DWR could be induced in all seven hearts. In the four VTs that could be accelerated during control, administration of the class III drug D- sotalol (35 μmol/L) only slightly slowed VT by 6%. Because the RP was prolonged by 15%, the ratio between the EG and the RP decreased from 0.76 to 0.63. Entrainment now failed to accelerate VT in two of four hearts, whereas in the two other hearts, double-wave reentry self-terminated within eight cycles. Conclusions: Drugs that increase the ratio of EG and RP enhance the susceptibility to acceleration of VT, whereas drugs that decrease this ratio prevent induction of sustained double-wave reentry.