AJP - Heart and Circulatory Physiology, Vol 259, Issue 3 872-H878, Copyright © 1990 by American Physiological Society
Pacing during reperfusion elevates regional myocardial oxygen consumption
J. Kedem, B. A. Acad and H. R. Weiss
Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854-5565.
Reperfusion after 2 h of coronary artery occlusion has been shown to result
in depressed coronary blood flow to the reperfused region and elevated
regional myocardial extraction. This suggests that reperfused myocardium,
even after 4 h of reperfusion, possesses limited flow and O2 consumption
reserves. We studied the capacity of reperfused myocardium to elevate
regional blood flow and regional O2 consumption in response to sustained
increased O2 demand, produced by atrial pacing. Two groups of anesthetized
open-chest dogs were subjected to 2 h of left anterior descending coronary
artery occlusion followed by 4 h of reperfusion. One group was subjected to
atrial pacing (40% increase in heart rate) during the entire 4-h
reperfusion period. Regional O2 saturation was measured by
microspectrophotometry in samples of reperfused and nonoccluded
subepicardium and subendocardium, which were taken at the end of the
reperfusion period. In the paced group, regional blood flow (radiolabeled
microspheres) to reperfused myocardium was significantly higher than to
corresponding regions of unpaced hearts (110 +/- 22 vs. 40 +/- 9 ml.min-1 x
100 g-1 in the subendocardium). In the control group, O2 extraction of
reperfused subendocardium was significantly higher than that measured in
the corresponding nonoccluded region (11.0 +/- 0.9 vs. 8.0 +/- 0.6 ml
O2/100 ml). Pacing did not elevate O2 extraction of reperfused myocardium
(8.7 +/- 0.6 vs. 8.3 +/- 0.7 ml O2/100 ml). Myocardial O2 consumption was
significantly elevated in all regions of the paced heart. It is concluded
that reperfused myocardium possesses significant unutilized O2 supply and
consumption reserves.
