Ionic Mechanisms of Regional Action Potential Heterogeneity in the Canine Right Atrium

Abstract—Atrial action potential heterogeneity is a major determinant of atrial reentrant arrhythmias, but the underlying ionic mechanisms are poorly understood. To evaluate the basis of spatial heterogeneity in canine right atrial repolarization, we isolated cells from 4 regions: the crista terminalis (CT), appendage (APG), atrioventricular ring (AVR) area, and pectinate muscles. Systematic action potential (AP) differences were noted: CT cells had a “spike-and-dome” morphology and the longest AP duration (APD; value to 95% repolarization at 1 Hz, 270±10 ms [mean±SEM]); APG and pectinate muscle cells had intermediate APDs (180±3 and 190±3 ms, respectively; P<0.001 versus CT for each), with APG cells having a small phase 1; and AVR cells had the shortest APD (160±4 ms, P<0.001 versus other regions). The inward rectifier and the slow and ultrarapid delayed rectifier currents were similar in all regions. The transient outward K+ current was significantly smaller in APG cells, explaining their small phase 1 ...