DE: Coronary hemodynamic effects of increasing ventricular rate in the unanesthetized dog. Circ Res 22: 753

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 opti-mum range for cardiac output and aortic pressure from 52-77 to 115-156 beats/min. ADDITIONAL KEY WORDS heart block cardiac output beta-receptor blockade reactive hyperemia coronary blood flow • Hemodynamic studies both in the anes-thetized dog and man have shown that aortic pressure and cardiac output fall above an optimum ventricular rate (1-3). There is also suggestive evidence that adrenergic receptor activity is of importance in the response of the systemic circulation to increases in ven-tricular rate (4). Studies on the effects of increasing ventricular rate on coronary blood flow in the anesthetized dog have, however, given conflicting results (5-10). Because of this variability and because of possible differences between conscious and anes-thetized animals, we have used implanted electro-magnetic flow transducers to study this problem in the unanesthetized dog