SUMMARY We investigated the effect of i.v. dipyridamole, a potent small-vessel coronary vasodilator, on myocardial infarct size in conscious dogs. Dipyridamole, ,ug/kg; 15 dogs) or saline (15 dogs) was infused for 6 hours beginning 10 minutes after acute permanent occlusion of the mid-circumflex coronary artery. After sacrifice, 48 hours after occlusion, stereoscopic postmortem angiography was used to define the mass DRUGS that dilate the coronary arteries are often categorized by their predominant site of action, the large epicardial conductance arteries or the small, precapillary (arteriolar) resistance vessels. Large-vessel dilators, such as nitrates or slow-channel calcium blockers, have been shown to reduce ischemic injury during coronary artery occlusion by increasing collateral flow,1-5 reducing myocardial oxygen demands6' 7 or both; small-vessel dilators have produced variable results. In some studies these agents have produced a deleterious effect by diverting flow away from ischemic myocardium toward nonischemic regions -a socalled coronary steal. This problem has been associated in the dog with the presence of occlusive lesions in more than one coronary artery.8 In other reports, hypotension resulting from the systemic effects of these small-vessel dilators has led to reduced coronary perfusion pressure and diminished collateral flow.This study was designed to determine whether dipyridamole, a prototype coronary arteriolar dilator, could augment collateral blood flow and reduce ultimate infarct size in conscious dogs with permanent coronary artery occlusion. By using a model with a single coronary artery occlusion and by using dipyridamole in small doses that produced minimal From Circulation 64, No. 5, 1981. decreases in blood pressure, we hypothesized that beneficial effects on myocardial salvage would be found.
Methods
InstrumentationThirty-eight dogs, 18-24 kg, were instrumented under pentobarbital general anesthesia. A left thoracotomy was performed and an occluder snare placed around the left circumflex coronary artery just past the first large marginal branch, 2-3 cm from the aorta. The snare consisted of a silk thread that was attached to a plastic tube at one end and looped around the coronary artery before exiting through the same plastic tube. Polyethylene catheters were placed in the right external jugular vein, right common carotid artery and left atrium. The distal ends of these catheters and the tube containing the snare thread were externalized at the back of the neck through a subcutaneous tunnel. Penicillin (1 million units) and Streptomycin (1 g) were given intramuscularly after surgery and the catheters were filled with heparinized saline.