Relationship between incidence of early ventricular arrhythmias, ischemic zone size, and coronary collateral flow in the dog.

The relationship between early ventricular arrhythmias (EVA), the size of the ischemic zone and the depth of the ischemia was examined. Myocardial ischemia was induced by occlusion of the left anterior descending coronary artery (LAD) in open chest of dogs for 6 minutes. The depth of ischemia was varied in each dog by simply occluding the branch (which results in normal collateral flow to the segment), or by occluding it and collecting retrograde flow from the distal segment. The later condition causes a very low collateral perfusion but no change in the size of the ischemic segment. EVA was observed in only 59% of simple occlusion cases, but occurred in 90% of the retrograde flow cases over the 6 minute study period. Serious arrhythmias (ventricular tachycardia or ventricular fibrillation (VF)) occurred in only 9% of simple occlusions but in 50% of retrograde flow diversions. Serious arrhythmias occurred 64% of the time when both the size of the ischemic zone exceeded 10 grams and when the flow density was less than 0.1 mL/min/g. No serious arrhythmias occurred when myocardium at risk was under 10 grams, and flow was over 0.1 mL/min/g. Serious arrhythmias occurred in only 13% of the animals having collateral flow in excess of 0.1 mL/min/g and an ischemic zone in excess of 10 grams. We conclude that EVA is both proportional to the size of the ischemic zone and inversely related to residual blood flow.