A COMPARISON OF CARDIAC RESPONSES TO EXERCISE AND DOBUTAMINE STRESS AS EVALUATED BY ECHOCARDIOGRAPHY

Abstract

PURPOSE: The purpose of this study was to compare myocardial responses to two means of inducing stress, exercise and intravenous dobutamine METHODS: Eighteen healthy volunteers (11 male, 7 female, mean age = 31.8 y) completed exercise stress ergometer (ESE) and dobutamine stress echocardiography (DSE) tests on separate days. Exercise: Subjects lay on an imaging table with their feet on the pedals of a Monark 868 cycle ergometer modified for recumbent use. Resting echocardiographic (ECHO) images were digitally acquired in both the long and short axis. Exercise was performed until the subjects reached target heart rates (0.85 × 220 - age) or attained maximal heart rate response. ECHO images were reacquired at peak exercise. Dobutamine: On a separate day, after resting ECHO images were obtained, dobutamine was infused via intravenous (IV) catheter at 10mcg/kg/min and increased by 10mcg/kg every three minutes to a maximum of 50mcg/kg. ECHO images were reacquired at peak dobutamine. Digital ECHO images were evaluated on a computer workstation running NIH Image software. RESULTS: Heart rate (157 to 119 bpm), end diastolic volume (110 to 86.6 ml), end systolic volume (20.8 to 11.1 ml), and cardiac output (13,996 to 8,742 ml/min) were greater with exercise than with dobutamine (p < .01). Differences in ventricular volumes at peak stress were due to greater LV chamber length (8.6 cm to 8.12 cm) and one of two short axis LV diameters (2.44 cm to 1.85 cm) with exercise (p < .001). Ejection fraction (87.2 to 81.1%) was greater with dobutamine than with exercise stress (p < .001). Dobutamine also increased the fractional shortening velocity 14.8% compared to exercise (p < .001). CONCLUSIONS: Exercise induces higher heart rates and chamber volumes at both end diastole and end systole, resulting in similar stroke volumes but greater cardiac output. Dobutamine causes increases in contractility resulting in greater ejection fraction and fractional shortening velocity, and may induce a pattern of asymmetrical contraction compared to exercise.