Effects of sotalol and vagal stimulation on ischemic myocardial blood flow distribution in the canine heart.

The purpose of the present study was to compare the effect of equivalent decreases in heart rate produced by sotalol and bilateral vagal stimulation on regional myocardial blood flow and coronary perfusion pressure distal to a severe stenosis of the left circumflex coronary artery in anesthetized dogs. Tissue blood flow was measured with radioactive microspheres (15 mu). Vagal stimulation or beta adrenergic blockade produced by sotalol (1.0 mg/kg i.v.) reduced heart rate approximately 35 beats/min. This decrease in rate was accompanied by nearly equivalent increases (P less than 0.05) in diastolic perfusion time and subendocardial blood flow and in the ischemic region. Both interventions also significantly increased the oxygen supply-demand balance (distal diastolic pressure time index divided by the tension time index) in the ischemic region. These values returned to control after cessation of vagal stimulation or during atrial pacing to predrug heart rate. Coronary perfusion pressure distal to the stenosis increased significantly only in the sotalol-treated group. These results suggest that a decrease in heart rate and increase in diastolic perfusion time are important factors in the favorable redistribution of ischemic myocardial blood flow and increase in the oxygen supply-demand balance observed after beta adrenergic blockade with sotalol or after vagal stimulation. Whether these beneficial actions are solely due to the prolonged diastolic perfusion period or to reduced oxygen demand and a return to autoregulation in the ischemic area cannot be determined with certainty.