Differences in the aging-associated trends of the monophasic action potential duration and effective refractory period of the right and left atria of the rat

Abstract

Background: The incidence of atrial fibrillation (AF) increases with aging, but the aging-associated electrophysiological changes of atrial myocardium are poorly understood. Methods and Results: Based on the hypothesis that aging of the atrium enhances AF susceptibility, 30 Wistar rats were divided into 3 age groups: adult, middle-aged, and aged (n=20 per group). Their hearts were isolated and perfused by Langendorff apparatus. Monophasic action potential duration at 90% repolarization (MAPD90) and effective refractory period (ERP) at the basic stimulation cycle length (BCL: 400 ms), and MAPD 90 at other different stimulation cycle lengths in each age group were measured. At the BCL, the MAPD90 of the right atrial myocardium was prolonged from the adult to the aged group, that of the left atrial myocardium was prolonged from the adult to middle-aged group, and the MAPD 90 of the left atrial myocardium in the aged group were shorter than that in the adult and middle-aged groups. The ERP of the atrial myocardium showed the same ageassociated trend as MAPD90. As the stimulation frequency increased, the MAPD90 of both the left and right atrial myocardium shortened correspondingly in the adult and middle-aged groups, but in the aged group the MAPD90 of the right atrial myocardium shortened markedly more than that of the left atrial myocardium. Conclusions There are different aging-associated electrophysiological changes in the right and left atrium, and the older heart is more vulnerable to developing the substrate for AF.