Factors that determine the occurrence of reperfusion arrhythmias

The determinants of reperfusion arrhythmias were investigated in 63 open-chest dogs undergoing a 25-minute coronary artery occlusion followed by reperfusion. Heart rate correlated positively with the occurrence of reperfusion ventricular tachycardia (VT) and ventricular fibrillation (VF). Collateral flow during ischemia (radioactive microspheres) exhibited a strong negative correlation with the incidence of both VT and VF upon reperfusion. Importantly, a sensitive coupling was present, whereby small differences in flow were associated with large differences in rhythm disorders. The rise in intramyocardial CO2 tension (another index of severity of ischemia) was greater in dogs exhibiting reperfusion VT (p less than 0.001) and VF (p less than 0.08); however, this variable was significantly correlated with collateral flow (r = -0.57, p less than 0.01). The size of the occluded coronary bed, determined by postmortem perfusion, was not consistently related to VT; within a given range of occluded bed sizes, the incidence of VT was inversely related to collateral flow. Thus, reperfusion-induced VT is relatively independent of the size of the occluded bed, and is determined primarily by the degree of myocardial hypoperfusion. In contrast, VF did not develop with occluded beds less than 25% of the left ventricular mass; above this critical occluded bed size, its incidence was inversely related to collateral perfusion. Reperfusion VF is therefore determined by the association of a large occluded bed with a poor collateral flow. This study identifies and systematically analyzes three major determinants of reperfusion arrhythmias: (1) the severity of antecedent ischemia, estimated either from the degree of flow reduction or the rise in intramural CO2 tension; (2) the amount of ischemic/reperfused myocardium; and (3) the heart rate. In addition to conceptual interest and clinical implications, the findings have important implications for the design of future studies aimed at evaluating antiarrhythmic interventions in experimental models.