Effects of dipyridamole on collateral flow and regional myocardial function in conscious dogs with newly developed collaterals.

Studies were conducted on six conscious dogs instrumented for measurement of subendocardial segment lengths in the area perfused by the left anterior descending coronary artery (LAD) and left circumflex coronary artery (LCCA), LCCA flow, and left ventricular pressure. Externally inflatable occluders were placed around the proximal LAD and LCCA. Collateral channels sufficient for the resting metabolic demands in the occluded LCCA perfusion territory were induced by repeated, brief LCCA occlusions. Dogs were then subjected to two consecutive brief periods of LAD occlusion. Dipyridamole (0.25 mg/kg) was injected intravenously 3 min prior to the second LAD occlusion. The collateral blood flow from the LCCA to the occluded LAD area was measured as the stepwise decrease in LCCA flow upon release of the LAD occlusion. During LAD occlusion after dipyridamole treatment collateral blood flow velocity decreased to 3.8 +/- 1.1 cm/s (+/- standard error) compared with a value of 4.9 +/- 0.9 cm/s measured during LAD occlusion without dipyridamole treatment. Percentage systolic segment shortening in the collateral dependent zone significantly deteriorated from 14.3 +/- 5.2 to 9.7 +/- 5.0% (p less than 0.05). Electrocardiograms taken simultaneously from endocardial ultrasonic transducers in the ischemic segment revealed significant increases in ST-segment level from 4.2 +/- 0.6 to 5.4 +/- 0.6 mV. These findings indicate that dipyridamole adversely affects the extent of myocardial ischemia in the collateral-dependent zone.