Isoproterenol-induced myocardial dysfunction in dogs with coronary stenosis.

Stress-induced regional myocardial ischemia in the presence of mild coronary stenosis was studied in five dogs 2-4 wk after implantation of pairs of ultrasonic crystals to measure left ventricular wall thickening (% delta WT) and subendocardial segmental shortening (% delta L). Isoproterenol (0.2 micrograms.kg-1.min-1) was infused before and after production of coronary stenosis, which produced no resting dysfunction. During isoproterenol infusion with coronary stenosis % delta WT and subendocardial % delta L were significantly decreased although blood flow was comparable to conditions at rest, indicating that the demand for blood flow exceeded supply. Linear regression analysis of mean transmural blood flow versus % delta WT during isoproterenol demonstrated that wall thickening was significantly related to changes in mean blood flow: y (percentage wall thickening) = 27.5 X (transmural blood flow) -8.2 (r = 0.83); likewise % delta L was significantly related to subendocardial blood flow during isoproterenol infusion: y (percentage shortening) = 17.1 X (subendocardial blood flow) -0.4 (r = 0.85). These results indicate that both regional % delta WT and % delta L sensitively reflect the adequacy of myocardial perfusion even during stress-induced changes in myocardial O2 demands and blood flow.