AJP - Heart and Circulatory Physiology, Vol 239, Issue 5 621-H627, Copyright © 1980 by American Physiological Society
Effect of heart rate on myocardial blood flow in dogs with left ventricular hypertrophy
T. R. Vrobel, W. S. Ring, R. W. Anderson, R. W. Emery and R. J. Bache
Because of the previous suggestion that subendocardial perfusion may be
inadequate in the hypertrophied heart, this study was carried out to
examine the response of transmural myocardial blood flow to pacing induced
tachycardia in dogs with chronic left ventricular hypertrophy. Myocardial
hypertrophy, produced by banding the ascending aorta of puppies at 5-6 wk
of age, resulted in an 87% average increase in relative left ventricular
mass compared with the control dogs. Myocardial blood flow was examined
during ventricular pacing at heart rates of 100, 200, and 250 beats/min
using radionuclide-labeled microspheres. Mean blood flow per unit
myocardial mass was similar in the two groups of dogs at a heart rate of
100 beats/min and increased regularly during pacing in both groups of
animals. Increasing heart rates did not change the transmural pattern of
myocardial blood flow in the normal dogs, but in the animals with left
ventricular hypertrophy pacing at 250 beats/min resulted in a significant
redistribution of perfusion away from the subendocardium, with the ratio of
subendocardial/subepicardial blood flow falling from 1.03 +/- 0.08 at 100
beats/min to 0.83 +/0 0.06 at 250 beats/min (P < 0.01). This
redistribution of blood flow away from the subendocardium was especially
marked in the regions encompassing the papillary muscles and the
intervening left ventricular lateral wall.
