EFFECT OF NITROGLYCERIN AND DIPYRIDAMOLE ON REGIONAL LEFT-VENTRICULAR BLOOD-FLOW DURING CORONARY-ARTERY OCCLUSION

Coronary vasodilators reportedly increase, decrease or have no effect upon blood flow to ischemic myocardium. Consequently, the effects of 2 different types of dilators, nitroglycerin (TNG) and dipyridamole, were studied with radioactive microspheres in open-chested dogs after coronary artery ligation. Given as a bolus i.v. injection, 0.4 mg TNG increased blood flow to nonischemic areas of myocardium and preserved flow to ischemic regions, despite a fall in blood pressure. Five min later blood pressure and nonischemic flow were back to base line, and a small selective increase in flow to ischemic myocardium was found (0.15-0.18 ml/min per g, P < 0.05). During an 0.2 mg/min infusion of TNG, and after 1 mg/kg i.v. dipyridamole, ischemic flow was maintained in the face of a 20-30% reduction in blood pressure. In this setting, nonischemic flow was unchanged during TNG and doubled after dipyridamole. With the addition of methoxamine in both dilator groups, blood pressure returned to base line, while flow to ischemic areas increased above base-line values (TNG, 0.16-0.20 ml/min per g, P < 0.01; dipyridamole, 0.18-0.31 ml/min per g, P < 0.05). Epicardial ST segment elevations increased during TNG infusion and were unchanged after dipyridamole, but with addition of methoxamine, ST segments became less elevated in both drug groups, concomitant with the observed increase in collateral blood flow. Both types of coronary vasodilators, when used in conjunction with methoxamine to support blood pressure, apparently reduce collateral resistance, increase collateral flow and reduce epicardial ST-segment elevations.