Differential effects of dobutamine versus treadmill exercise on left ventricular volume and wall stress

Dobutamine and exercise echocardiography are well-validated modalities used for the evaluation of patients with suspected myocardial ischemia. Patients undergoing dobutamine stress echocardiography (DSE), however, experience less angina, ST-segment depressions, and wall motion abnormalities. Other than the effect on heart rate, the physiologic and volumetric differences between pharmacologic and exercise-induced stress that affect myocardial oxygen demand are not well defined. The aim of this study was to test the hypothesis that in the absence of ischemia, dobutamine reduces left ventricular (LV) volume, wall tension (WTN), and peak systolic stress (PSS) compared with exercise.

Seventy patients without ischemia were prospectively enrolled (35 underwent exercise echocardiography and 35 DSE), and various hemodynamic parameters were measured and LV volumes calculated (using the Simpson and Teichholz formulas). Systolic WTN and PSS were determined at rest and stress.

LV end-diastolic volume index fell significantly more with dobutamine than with exercise (-34% vs -9%, P < .0001), as did mean end-systolic volume index (-55% vs -37%, P = .07). Systolic blood pressure increased more with exercise (41 ± 22 vs 1 ± 33 mm Hg, P < .0001), as did cardiac index (2.5 ± 0.7 vs 1.0 ± 0.8 L/min/m(2), P < .0001). Systolic WTN increased with exercise by 24% (P < .0001) but decreased with dobutamine by 18% (P < .0001). PSS increased with exercise by 21% (P < .0001) but decreased with dobutamine by 23% (P < .0001).

The degree of stress achieved with DSE appears to be considerably different than with exercise. DSE produces greater reductions in LV end-diastolic and end-systolic volumes than exercise and decreases rather than increases in WTN and PSS. The lower WTN and PSS were related to both a decrease in LV volume and lower systolic blood pressure with dobutamine. These observations support recommendations favoring exercise stress testing in patients able to exercise and reinforce the notion that high-risk echocardiographic features of ischemia such as stress-induced LV dilatation may be less striking or absent with DSE.