Comparative electrocardiographic and myocardial blood flow effects of rapid atrial pacing and dipyridamole infusion in dogs with chronic coronary artery occlusion.

Altering regional myocardial flow by the use of potent vasodilators as well as increasing oxygen demand by exercise have been employed as diagnostic methods for detecting coronary arterial obstruction. We sought to define the relative capabilities of these two methods to produce abnormal ECG patterns and to alter myocardial blood flow after Ameroid constriction of the left circumflex coronary artery. Atrial pacing to rates of 210 beats/min was performed, followed by intravenous administration of 0.25 and 0.50 mg/kg of dipyridamole. ECGs were recorded to construct body surface isopotential distributions. Flow was measured by serial injections of radiolabelled microspheres. In 15 animals studied after 3 to 5 weeks of Ameroid constriction, pacing increased epicardial flow by 19.14 +/- 7.11% but reduced endocardial flow by 35.69 +/- 12.32%, with a significant reduction (to less than 0.67) in the endocardial/epicardial flow ratio in 12 (80%) dogs; both endocardial and epicardial flows were significantly lower in the ischemic than in the nonischemic bed. Ten dogs developed abnormal ST segment responses of subendocardial ischemia. In contrast, dipyridamole produced a dose-dependent rise in both endocardial (25.33 +/- 8.54% and 55.80 +/- 9.22% after 0.25 and 0.5 mg/kg, respectively) and epicardial (29.13 +/- 7.49% and 66.33 +/- 7.64% after 0.25 and 0.5 mg/kg, respectively) flows without a significant fall in the transmural ratio. These increases were, however, significantly less than those observed in nonischemic bed flow, resulting in a transventricular gradient of blood flow. No dog developed abnormal ECG patterns after dipyridamole infusion. Thus pacing produces both a transmural and a transventricular gradient in blood flow, whereas vasodilation causes only a transventricular flow abnormality.(ABSTRACT TRUNCATED AT 250 WORDS)