Electrophysiological Effects of Acute Dilatation in the Isolated Rabbit Heart Cycle Length–Dependent Effects on Ventricular Refractoriness and Conduction Velocity

Background Acute ventricular dilatation has important electrophysiological effects: Dilatation shortens action potential duration and refractoriness without an apparent effect on conduction velocity. These effects have been implicated as a potential mechanism of arrhythmias in patients with congestive failure. Because the influence of cycle length on these phenomena has not been studied, we examined the effects of dilatation during ventricular pacing at cycle lengths from 1000 to 150 ms. Methods and Results Thin epicardial layers were created in isolated, perfused rabbit left ventricles (n=7). A fluid filled latex balloon was secured in the left ventricle to dilate the left ventricle. Mapping was performed with 248 epicardial electrodes. Longitudinal conduction velocity (76±1 cm/s; mean±SEM) and transverse conduction velocity (26±1 cm/s) were not influenced by dilatation at any cycle length. In contrast, the effects of dilatation in decreasing left ventricular effective refractory period (ERP) were signif...