Dobutamine is a new inotropic agent that may induce prolonged clinical improvement in patients with
congestive cardiomyopathy. Sixteen patients with severe
heart failure but without obstructive
coronary disease were studied by serial functional class determinations and by noninvasive measurements of left ventricular function before and after
bedrest control period and then after a 3-day infusion of
dobutamine. An endomyocardial biopsy procedure was performed on 11 patients before and after the
bedrest and on all 16 patients before and after
dobutamine. Quantitative ultrastructural analysis of the biopsies was performed on electron micrographs (31,200 X) by a grid technique. The number of electron dense particles per 100 mitochondria did not change after
bedrest but there was a significant decrease from 84 +/- 14 to 65 +/- 12 (P < .005) in the pre- to postdobutamine biopsies. The cristae to matrix ratio of the mitochondria did not change with
bedrest but improved from 0.37 +/- 0.04 to 0.47 +/- 0.05 (P < .02) after
dobutamine. The average mitochondrial size did not change significantly in the
bedrest control nor in the
dobutamine biopsy samples. However, when the 16 patients were divided into those who had a good clinical response (by functional class and noninvasive measurements of left ventricular function) and those who had no or little response, the 10 responders did decrease their average mitochondria size from 0.26 +/- 0.03 mu 2 to 0.23 +/- 0.02 mu 2 (P < .02). The mechanism by which a 3-day infusion of
dobutamine induces a prolonged clinical improvement is not well understood. The use of quantitative ultrastructural technique in this study has demonstrated that there is a morphologic basis to the improvement.