AJP - Heart and Circulatory Physiology, Vol 247, Issue 1 52-H60, Copyright © 1984 by American Physiological Society
Effects of beta-blockade on regional myocardial flow and function during exercise
M. Matsuzaki, J. Patritti, T. Tajimi, M. Miller, W. S. Kemper and J. Ross Jr
We examined the effects of a cardioselective beta-blocking drug on
exercise-induced regional myocardial ischemia in 10 conscious dogs with
chronic coronary artery stenosis. An ameroid constrictor, Doppler
flowprobe, and hydraulic cuff were placed around the left circumflex
coronary artery, and left ventricular pressure (LVP), systolic wall
thickening (% delta WT; by sonomicrometry), and myocardial blood flow (MBF;
microspheres) were measured during control standing, control treadmill
exercise, and identical exercise after atenolol (1 mg/kg po). Prior to
study, in every dog % delta WT and MBF in the ischemic area were normal at
rest, indicating collateral development. During control exercise, % delta
WT in the ischemic region markedly decreased from 27 to 4%, and transmural
ischemia was evident in that region. Heart rate, systolic LVP, and LV
(+)dP/dt were significantly lower during exercise after atenolol than
during control exercise. % delta WT in the normal area was only 81% of that
during control exercise, but dysfunction in the ischemic area was improved
(77% increase compared with control exercise). Accompanying the improved
function was a significant increase of MBF/beat and relative MBF in the
ischemic zone; the endocardial-to-epicardial ratio increased from 0.27 to
0.47. Thus atenolol improved regional MBF distribution, thereby diminishing
exercise-induced regional myocardial dysfunction and accelerating its
recovery.
