Regional differences in arrhythmogenic aftereffects of high intensity DC stimulation in the ventricles

Regional differences of the aftereffects of high intensity DC stimulation were investigated in isolated rabbit hearts stained with a voltage-sensitive dye (di-4-ANEPPS). Optical action potential signals were recorded from the epicardial surface of the right and left ventricular free wall (RVep, LVep) and from the right endocardial surface of the interventricular septum (IVS). Ten-millisecond monophasic DC stimulation (S-2, 20-120 V) was applied to the signal recording spots during the early plateau phase of the action potential induced by basic stimuli (S-1, 2.5 Hz). There was a Linear relationship between St voltage and the S-2 field intentisy (FI). S-1 caused postshock additional depolarization, giving rise to a prolongation of the shocked action potential. With S-2 greater than or equal to 40 V (Fi greater than or equal to similar to 20 V/cm), terminal repolarization of action potential wets inhibited, and subsequent postshock S-2 action potentials for 1-5 minutes were characterized by a decrease in the maximum diastolic potential and a decrease in the amplitude and a slowing of their upstroke phase. The higher the S-1 voltage, the larger the aftereffects. The changes in postshock action potential configuration in RVep were significantly greater than those observed in LVep and IVS when compared at the same levels of St intensity. In RVep, 12 of 20 shocks of 120 V resulted in a prolonged refractoriness to S-1 (> 1 s), and the arrest was often followed by oscillation of membrane potential. Ventricular tachycardia or fibrillation ensued from the oscillation in five cases. No such long arrest or serious arrhythmias were elicited in LVep and NS. These results suggest that RVep is more susceptible than LVep and IVS for arrhythmogenic aftereffects of high intensity DC stimulation.