Factors that determine the occurrence of arrhythmias during acute myocardial ischemia

To elucidate the determinants of arrhythmias during acute myocardial ischemia, a 25-minute coronary artery occlusion was performed in 101 open-chest dogs. Heart rate correlated positively with the number of premature ventricular complexes (PVCs) and the occurrence of ventricular tachycardia (VT) and fibrillation (VF). The size of the occluded coronary bed was positively correlated with the occurrence of VF, but exhibited only a weak association with PVCs and VT. Coronary collateral flow exhibited a strong negative correlation with all forms of arrhythmias. Importantly, a sensitive coupling was present, whereby small differences in flow were associated with large differences in rhythm disorders. VT occurred in all ranges of occluded bed size examined, but within any given range, its incidence was inversely related to collateral flow. Thus, VT is relatively independent of occluded bed size, and is determined primarily by the degree of myocardial hypoperfusion. In contrast, even in the presence of low flows, VF did not develop with occluded beds less than 28% of left ventricular mass; above this critical occluded bed size, the incidence of VF was inversely related to collateral perfusion. VF is therefore determined by the association of a large occluded bed with a poor collateral function. This study identifies and systematically analyzes three major determinants of arrhythmias during acute myocardial ischemia: the heart rate, the amount of ischemic myocardium, and the severity of myocardial flow reduction. The finding that these factors account for most of the variability in the occurrence of malignant tachyarrhythmias has important methodological and clinical implications.