Distribution of action potential durations in the canine left ventricle

The distribution of action potential durations (APD) in the left ventricle were investigated and compared to the spatial orientation of the maximum T vector (MaxTv). Eight dogs with similar vectorcardiographic spatial orientations of MaxTv were used. Action potentials were recorded from 42 to 64 sites on each isolated endocardial and epicardial specimen with glass microelectrodes. Preparations included the entire left ventricular free wall. The APD50 and APD90 had similar distributions, but the APD90 distribution was less uniform in all 8 dogs. On the endocardium, APDs were longest between the roots of the papillary muscles, and progressively shorter toward the upper edge (base) where the shortest APDs were found. On the epicardium, APDs were longest in the lower lateral region, and gradually shortened, approximately concentrically, toward the anterior and posterior bases. APDs were longer in the endocardium than in the corresponding epicardium. Maximum APD endocardial-epicardial differences were found in the lower lateral region of the ventricular free wall. Results agree with reports of ventricular recovery properties in vivo, and partly account for the spatial orientation of the MaxTv. This study adds new details, and delineates the longest and shortest distributions of APDs.