Redistribution of myocardial blood flow distal to a dynamic coronary arterial stenosis by sympathomimetic amines: comparison of dopamine, dobutamine and isoproterenol.

The effects of dopamine, dobutamine and isoproterenol on coronary hemodynamics, severity of stenosis, distal bed resistance and transmural myocardial perfusion gradients with radioactive microspheres were studied in dogs with a mild obstruction of the left circumflex coronary artery anesthetized with morphine-chloralose. Changes in transmural blood flow were related to the ratio of the diastolic aortic pressure-time index to tension-time index (DPTI/TTI) and the ratio of the distal diastolic coronary pressure-time index to tension-time index (DDPTI/TTI). At doses of 5 microgram/kg per min, dopamine had no significant effect on DPTI/TTI, DDPTI/TTI or endocardial/epicardial flow ratio; however, dobutamine produced a slight decrease in this flow ratio and in DDPTI/TTI. At doses of 10 microgram/kg per min, both drugs produced a significant (p less than 0.05) reduction in diastolic coronary pressure distal to the stenosis. DDPTI/TTI and endocardial/epicardial flow ratio without change in DPTI/TTI. In comparison, isoproterenol (0.01 and 0.05 microgram/kg per min) produced dose-related decreases in endocardial/epicardial flow ratio, DDPTI/TTI and DPTI/TTI. During infusion of each sympathomimetic agent, there was a corresponding reduction in distal bed vascular resistance but a concomitant increase in stenosis resistance. The results also show that dopamine and dobutamine, as well as isoproterenol, area capable of producing a maldistribution of coronary blood flow distal to a mild coronary arterial stenosis and that such a redistribution of glow is dependent on dose, reduction of the distal diastolic coronary pressure-time index and decrease in DDPTI/TTI. It is further concluded that hemodynamic changes distal to a coronary arterial stenosis seriously jeopardize the usefulness of DPTI/TTI; however, DDPTI/TTI can be used to predict drug effects on the endocardial/epicardial flow ratio in an ischemic area. This study demonstrates that "fixed" stenoses can undergo dynamic processes and sympathomimetic amines increase the resistance to flow through a stenotic coronary artery in the nonfailing heart.