Effects of Pinacidil on Myocardial Blood Flow and Infarct Size After Acute Left Anterior Descending Coronary Artery Occlusion and Reperfusion in Awake Dogs With and Without a Coexisting Left Circumflex Coronary Artery Stenosis

To determine whether partial stenosis of a second major coronary artery promoted vasodilator-induced coronary steal and increased infarct size after acute coronary artery occlusion, we produced acute myocardial infarction by 4-h left anterior descending coronary artery occlusion and 20-h reperfusion in awake dogs with and without a mild to moderate stenosis (33–72%) of the proximal left circumflex coronary artery. Dogs were randomized to receive intravenous (i.v.) normal saline or pinacidil, a new antihypertensive agent with a marked coronary dilator property, beginning 40 min after onset of coronary artery occlusion and continuing throughout the occlusion and the first hour of reperfusion. Pinacidil was titrated to decrease mean aortic pressure 25 mm Hg, which resulted in an increase in heart rate (HR), cardiac output (CO), and left ventricular (LV) dP/dt and LVdP/dt/P. Saline infusion had no effects. Blood flows to ischemic and remote myocardium did not differ between dogs with and without coronary stenosis. Pinacidil increased blood flow threefold in normal myocardium, but had no effect on infarct zone myocardial blood flow or infarct size (58 ± 4% of region at risk vs. 56 ± 4% in animals receiving normal saline) in dogs without coronary stenosis. In contrast, similar administration of pinacidil in dogs with coronary stenosis reduced infarct size zone myocardial blood flow and increased infarct size (69 ± 3% vs. 55 ± 5% in the saline group, p < 0.05). The data indicate that although neither myocardial blood flow nor infarct size is affected by a mild to moderate stenosis of a second major coronary artery, administration of an effective vasodilator during acute myocardial infarction can potentially further reduce infarct zone myocardial blood flow and increase infarct size.