PATHOPHYSIOLOGIC MECHANISMS UNDERLYING DOBUTAMINE-INDUCED AND EXERCISE-INDUCED WALL-MOTION ABNORMALITIES

Background Dobutamine and exercise echocardiography are accepted as te sts of comparable efficacy for the diagnosis of coronary artery diseas e. Although dobutamine has been classified as ''exercise simulating,'' the mechanisms of ischemia with dobutamine and exercise have nor been well studied. This study sought to compare the determinants of myocar dial oxygen consumption. Methods and Results We studied 54 patients wi th coronary artery disease undergoing dobutamine and exercise stress. A subgroup of 13 patients with comparable degrees of wall motion abnor malities and ST-segment changes during both stresses were selected to compare the determinants of ischemia in comparable circumstances. Dobu tamine was infused to a mean maximal dose of 32 +/- 8 mu g/kg/min, and exercise was stopped at an average of 135 +/- 25 W. The mean regional wall motion score was not statistically different between the two pro tocols (p = 0.27). At the onset of wall motion abnormalities and peak stress, the heart rate increased significantly less during dobutamine than during exercise (106 +/- 23 vs 126 +/- 19 beats/min, p < 0.001). The same was true of systolic blood pressure (155 +/- 21 vs 205 +/- 24 mm Hg, p < 0.001) and the rate-pressure product (16.5 +/- 4.6 vs 25.9 +/- 5, p < 0.001). Cardiac volumes were similar during both tests. Co nclusions Ischemia occurs at a lower level of external cardiac work du ring dobutamine than during exercise stress. We suspect that additiona l mechanisms, such as the oxygen wasting effect of dobutamine, may be responsible for this observation.