Comparative effect of verapamil and nitroglycerin on collateral blood flow

The effects of intracoronary verapamil and nitroglycerin on collateral blood flow were compared under conditions where coronary perfusion pressure was held constant with a servopump and the systemic effects of the drugs were minimal. Both drugs were infused into 12 anesthetized dogs after occlusion of the left anterior descending coronay artery (LAD) and regional myocardial blood flow (MBF) was measured using micropheres. Before the LAD occlusion, the myocardium not perfused by the LAD was labeled to permit calculation of the fraction of tissue normally perfused in the LAD samples and corrections for collateral flow. The central ischemic zone contained 2.5 ± 0.3% normally perfused myocardium and a 4-mm border zone contained 26.8 ± 4.3% normal myocardium. This border zone contained 10% of the total tissue supplied by the LAD. The MBF in the central ischemic zone increased from 0.101 ± 0.019 to 0.113 ± 0.022 ml/min/g after verapamil infusion (NS) and to 0.149 ± 0.024 ml/min/g after nitroglycerin (p <0.01). Uncorrected MBF in the border zone increased significantly after infusion of both verapamil (0.469 ± 0.085 ml/min/g, p <0.01) and nitroglycerin (0.398 ± 0.056, O <0.05). When corrections were made for interdigitating normal tissue in the border zone, only the MBF after nitroglycerin was significantly increased. Thus, nitroglycerin significantly increased the collateral blood flow to ischemic tissue in the central ischemic and border zones, but verapamil did not.