Nonuniform action potential durations at different sites in canine left ventricle.

Publisher Website
Google Scholar
Abstract
The action potential duration (APD) of isolated ventricular muscle fibers was studied. Action potentials were recorded from 4 different sites (endocardium and epicarium at the apex and the base) in the canine left ventricle by microelectrode techniques. Action potentials from endocardial and corresponding epicardial specimens, and the differential potential between them were recorded simultaneously. The APD at 60 and 90% repolarization (APD60 and APD90) were measured during superfusion with normal (K+ = 2.7 mM) and altered (K+ = 5.4 mM) Tyrode''s solutions. The distributions of APD agreed with previous descriptions from in vivo studies. Endo-epicardial APD gradients were different between the apex and the base, and apicobasal APD gradients were different between endocardium and epicardium. The shapes of the differential potentials in normal and altered Tyrode''s solutions were similar to the ECG T wave form in normal and in mild hyperkalemia. Nonhomogeneous APD may be due to the inherent characteristics of cardiac muscle and the nonuniform endo-epicardial APD gradient helps to account for the genesis of the ECG T wave form.