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

Regional differences of the aftereffects of high intensity DC stimulation w ere 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 (IV S). Ten-millisecond monophasic DC stimulation (S-2, 20-120 V) was applied t o the signal recording spots during the early plateau phase of the action p otential induced by basic stimuli (S-1, 2.5 Hz). There was a Linear relatio nship between St voltage and the S-2 field intentisy (FI). S-1 caused posts hock additional depolarization, giving rise to a prolongation of the shocke d 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 potenti al wets inhibited, and subsequent postshock S-2 action potentials for 1-5 m inutes 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 postsho ck action potential configuration in RVep were significantly greater than t hose observed in LVep and IVS when compared at the same levels of St intens ity. In RVep, 12 of 20 shocks of 120 V resulted in a prolonged refractorine ss to S-1 (> 1 s), and the arrest was often followed by oscillation of memb rane potential. Ventricular tachycardia or fibrillation ensued from the osc illation in five cases. No such long arrest or serious arrhythmias were eli cited in LVep and NS. These results suggest that RVep is more susceptible t han LVep and IVS for arrhythmogenic aftereffects of high intensity DC stimu lation.