Effects of atrial pacing and dipyridamole administration on coronary hemodynamics of collateralized myocardial regions in stable angina pectoris

Great cardiac vein blood flow by thermodilution and great cardiac vein oxygen saturation were measured in 14 patients with stable exertional angina and an angiographic pattern of complete occlusion of the proximal left anterior descending artery retrogradely filled by collateral vessels supplying still viable myocardium. Measurements were obtained under control conditions, at peak atrial pacing and after dipyridamole administration (0.56 mg/kg intravenously over 4 minutes). Both stress tests induced ischemic electrocardiographic changes in all patients, but dipyridamole administration resulted in greater ST-segment depression in 11 patients (1.6 ± 0.5 vs 2.4 ± 1.6 mm, p <0.05) and transient ST-segment elevation in 3 patients. Dipyridamole provoked ischemia at a lower value of rate-pressure product (145.3 ± 30.6 vs 202.9 ± 36.6 beats/min · mm Hg · 10^-2, p <0.0005) and anterior region myocardial oxygen consumption (9.32 ± 4.76 vs 11.39 ± 3.91 ml/min, p <0.05), despite a greater increase in great cardiac vein flow (139.4 ± 45 vs 93 ± 27.4 ml/min, p <0.0025) and a greater decrease in the calculated index of anterior region coronary resistance (0.87 ± 0.27 vs 1.46 ± 0.43 mm Hg/ml/min, p <0.0005). Moreover, great cardiac vein oxygen saturation increased more significantly during dipyridamole-induced ischemia than at peak pacing (63 ± 12 vs 35 ± 8%, p <0.0005). These data show that dipyridamole administration induces more profound electrocardiographic signs of myocardial ischemia than atrial pacing in patients with stable angina and an occluded left anterior descending artery retrogradely filled by collateral vessels. The vasodilation induced by the drug markedly exceeds that induced by pacing, despite lower values of myocardial oxygen consumption.