Coronary Hemodynamic Effects of Increasing Ventricular Rate in the Unanesthetized Dog

In five unanesthetized dogs with surgical heart block, increasing ventricular rate from 50--75 to 250--300 beats/min demonstrated an optimum ventricular rate of 130 to 185, above which aortic pressure and cardiac output fell. In contrast, coronary blood flow continued to rise to a ventricular rate of 250 to 300 beats/min. Stroke systolic coronary flow was well maintained over the entire range of ventricular rates studied, while stroke diastolic coronary flow fell with an increase of ventricular rate. A reactive hyperemic response following release of a 1- to 10-second coronary artery occlusion at a ventricular rate of 250 to 300 suggests that the fall in aortic pressure and cardiac output which occurred at these rates may not be due to an insufficiency of total coronary blood flow. Beta-receptor activity did not appear to play a significant role in the hemodynamic adjustment to increases in ventricular rate within the optimum range for cardiac output and aortic pressure from 52--77 to 115--156 beats/min.