AJP - Heart and Circulatory Physiology, Vol 253, Issue 2 422-H431, Copyright © 1987 by American Physiological Society
Coronary vasodilator reserve persists despite tachycardia and myocardial ischemia
J. D. Bristow, E. O. McFalls, C. G. Anselone and G. A. Pantely
During myocardial ischemia, we tested whether coronary blood flow would
increase in response to tachycardia, thereby employing known coronary flow
reserve. We instrumented the left anterior descending (LAD) coronary
circulation in anesthetized pigs and performed three sets of experiments
while coronary pressure was controlled and several heart rate increases
were produced. Pacing-induced tachycardia at normal LAD pressure was
characterized by increased LAD flow and myocardial oxygen consumption,
without production of lactate. Tachycardia at a mean LAD pressure of 38
mmHg was associated with a lower, fixed coronary flow and oxygen
consumption. At average heart rates of 90 and 150 beats/min, LAD flow was
19.6 and 19.4 ml/min and corresponding myocardial blood flows were 0.59 and
0.54 ml X g-1 X min-1. Lactate was produced at all rates and local
myocardial function declined progressively. Coronary flow at low LAD
pressure doubled during tachycardia when intracoronary adenosine was added.
The increase to the subepicardium was greater than 100%, whereas
subendocardial flow changed little. There is persistent coronary flow
reserve during moderately severe myocardial ischemia, even when metabolic
demand is increased by tachycardia. This reserve, however, is predominantly
subepicardial.
