Changes in Ischemic Blood Flow Distribution

The effects of equipotent fl3-receptor-blocking doses of propranolol, metoprolol and sotalol on distal coronary pressure, stenosis resistance and regional myocardial blood flow (endo/epi) were studied in anesthetized dogs with a severe noncircumferential stenosis of the left circumflex coronary artery. No significant differences between the three blockers were observed for overall hemodynamics and regional myocardial blood flow. After drug treatment, subendocardial blood flow (0.47 ± 0.05 to 0.78 ± 0.05 ml/min/g) and endo/epi (0.67 ± 0.04 to 1.18 ± 0.04) increased significantly (p < 0.05) in the ischemic region. These changes were associated with a marked increase in distal coronary perfusion pressure and a decrease in heart rate. Resistance across the stenosis decreased significantly (p < 0.05) after,-receptor blockade (3.2 ± 0.3 to 1.4 ± 0.2 units). Atrial pacing to control heart rate only partially attenuated these changes. These results suggest that a favorable redistribution of ischemic blood flow after blockade is the result of an increase in distal diastolic pressure-time index and an autoregulation-induced increase in distal bed vascular resistance due to a decrease in myocardial oxygen demand associated with blockade. The latter effect also resulted in a decrease in the dynamic severity of a proximal coronary stenosis.