Beneficial effects of metoprolol on myocardial sympathetic function: Evidence from a randomized, placebo-controlled study in patients with congestive heart failure

Background We sought to investigate whether β-blockers exert a presynaptic effect in the myocardium as measured by 123I-metaiodobenzylguanidine. Methods The study comprised 59 patients with congestive heart failure, New York Heart Association class II or III, and left ventricular ejection fraction <35%. After an open label titration phase, patients were randomized to their maximal tolerable dose of metoprolol or placebo. Myocardial MIBG uptake was measured before the titration phase and after 6 months of treatment. Other parameters were maximal oxygen consumption, 6-minute walking test, plasma neurohormones, and echocardiographic parameters. Results We found a 21.9% increase in mean myocardial MIBG uptake after 6 months of treatment with metoprolol. In contrast, MIBG uptake decreased by 7.8% in the placebo group (P = 0.03 compared with metoprolol). Left ventricular end-diastolic diameter decreased from 74 ± 11 mm to 67 ± 10 mm (P < .05, within-group comparison) and LVEF increased from 25.3% ± 7.4% to 32.6% ± 9.6% (P < .05, within-group comparison) in the metoprolol group. Placebo-treated patients showed no significant changes. Comparison of changes in left ventricular end-diastolic diameter and LVEF between metoprolol and placebo did not reach statistical significance (P = 0.2). Conclusions This randomized, placebo-controlled study demonstrates that metoprolol has a presynaptic effect as measured by myocardial MIBG scintigraphy in both ischemic and nonischemic cardiomyopathy. (Am Heart J 2002;144:e3.)