AJP - Heart and Circulatory Physiology, Vol 239, Issue 5 594-H600, Copyright © 1980 by American Physiological Society
Left ventricular asynergy during intracoronary isoproterenol infusion in dogs
A. Ilebekk, J. Lekven and F. Kiil
Myocardial contractions were examined in the left ventricle of
anesthetized, open-chest dogs during infusion of a beta-adrenergic agent,
isoproterenol (0.1-0.5 micrograms/min) into a shunt line to the left
anterior descending coronary artery. Myocardial chord lengths were
continuously monitored by pairs of ultrasonic elements inserted into the
isoproterenol-infused and control regions. Heart rate remained constant,
but isoproterenol altered contraction patterns in both control and infused
regions. Contraction in the infused region started before ejection and
stretched the control myocardium in early systole. Because of early
relaxation, however, the infusion region was stretched at the end of
ejection and in early diastole, while the control myocardium continued to
shorten. Thus, isoproterenol infusion to a part of the left ventricle
induces asynergic muscle contractions and despite localized inotropic
stimulation stroke volume may not be significantly increased.
