The comparative effects of dopamine and dobutamine on ventricular mechanics after coronary artery bypass grafting: A pressure-dimension analysis

To compare the contractile response to dopamine and dobutamine after coronary artery bypass grafting, 20 patients were instrumented with ultrasonic dimension transducers to measure left ventricular anterior/posterior minor-axis diameter and equatorial wall thickness. Micromanometers were placed to measure left ventricular transmural pressure. Pressure-dimension data were recorded and computer analyzed during dopamine and dobutamine infusions in each patient at 0, 2.5, 5.0, and 10.0 μg/kg/min 16 to 20 hr after surgery. Contractility was measured by determination of maximal velocity of shortening of the ventricular diameter (mm/sec) and wall excursion (mm). Preload was assessed with end-diastolic diameter and peak left ventricular wall stress (dynes-cm²) was calculated at each dose. End-diastolic diameter was unchanged at equal doses of dopamine and dobutamine. However, ejection phase indexes of contractility were significantly higher with dobutamine than dopamine, and were associated with lower levels of peak wall stress and peripheral vascular resistance. These data indicate that use of dobutamine results in greater enhancement of left ventricular contractility without the disadvantage of excess demand on myocardial oxygen reserve produced by higher levels of myocardial wall tension. Furthermore, the decreased peripheral vascular resistance induced by dobutamine accounts for some of the differences in drug response, and is beneficial in optimizing myocardial oxygen balance during pharmacologic inotropic support of the bypass graft patient or other patients in whom there is a potential for development of myocardial ischemia.