Cellular electrophysiology of coronary artery ligation in chronic pressure overload

Abstract

We evaluated ischemia-induced cellular electrophysiologic abnormalities in chronic pressure overload ventricular myocardium in vitro. Left ventricular systolic hypertension was induced in cats via partial supracoronary aortic constriction (overload); at 1 1/2-3 months, resulting pressure overload was accompanied by ventricular hypertrophy (25-35% by weight) and patchy endocardial fibrosis. Two hours of subsequent acute myocardial ischemia (ischemia) was imposed on overload (ischemia/overload) via total occlusion of distal branches of the left coronary artery system. Spontaneous premature depolarizations in vitro were increased in ischemia/overload compared to control, ischemia or overload alone; bursts of spontaneous, repetitive depolarizations were also unique to these preparations. Multiple site recordings of endocardial transmembrane action potentials overlying the borders (interface) of fibrotic areas in ischemia/overload demonstrated numerous electrophysiologic abnormalities, including several not observed in control, ischemia or overload. Unique to the border areas of ischemia/overload preparations was the presence of maintained but depressed resting potential without action potentials; also, the incidence of depolarizations at the onset of the plateau phase was highest in these preparations. In non-fibrotic areas, electrophysiologic properties including resting potential and action potential amplitude and rate of rise were diminished in ischemia/overload compared to ischemia or overload preparations. These data demonstrate that acute myocardial ischemia in the setting of chronic pressure overload leads to additional cellular electrophysiologic abnormalities compared to ischemia or overload alone.