Long term electrophysiological abnormalities resulting from experimental myocardial infarction in cats

Chronic electrophysiological abnormalities in cats surviving experimental myocardial infarction (MI) were recorded 1 week to 6 months following single-stage ligation of multiple distal tributaries of the left coronary artery system. Sixteen of 32 long-term MI cats (50%) had a propensity to ventricular ectopic activity (VEA), as established by at least one of three criteria : (1) spontaneous VEA on electrocardiogram (ECG) prior to death (8 of 32 cats; 25%); (2) accelerated ventricular escape rhythms during vagal stimulation (7 of 21; 33%); and (3) rapid automatic activity of the isolated left ventricle in tissue bath (11 of 32; 34%). Cellular electrophysiological abnormalities in surviving subendocardial tissue overlying the MI scar were recorded in 29 of 32 preparations (91%). Focal areas of action potential (AP) abnormalities were interspersed between areas of normal activity. AP abnormalities were of three types: (1) prolongation of AP duration; (2) shortening of AP duration; and (3) low amplitude action potentials. Type 1 abnormalities were recorded most commonly between 1 week and 1 month after MI, and rarely were recorded later. Type 2 abnormalities began to appear 1 1/2 months after MI and were most common at 3-6 months. Type 3 abnormalities were recorded at any stage. At 3 months after MI and beyond, surviving cells were histologically normal, despite continued AP abnormalities and propensity to VEA. The data demonstrate a persistence of deranged cellular electrophysiology for up to 6 months after MI.