Antiremodeling effects on the left ventricle during beta-blockade with metoprolol in the treatment of chronic heart failure

OBJECTIVES The purpose of the study was to investigate the effects of beta1-blockade on left ventricular (LV) size and function for patients with chronic heart failure. BACKGROUND Large-scale trials have shown that a marked decrease in mortality can be obtained by treatment of chronic heart failure with beta-adrenergic blocking agents. Possible mechanisms behind this effect remain yet to be fully elucidated, and previous studies have presented insignificant results regarding suspected LV antiremodeling effects. METHODS In this randomized, placebo-controlled and double-blind substudy to the Metoprolol CR/XL Randomized Intervention Trial in Heart Failure (MERIT-HF), 41 patients were examined with magnetic resonance imaging three times in a six-month period, assessing LV dimensions and function. RESULTS Decreases in both LV end-diastolic volume index (150 ml/m2 at baseline to 126 ml/m2 after six months, P = 0.007) and LV end-systolic volume index (107 ml/m2 to 81 ml/m2, P = 0.001) were found, whereas LV ejection fraction increased in the metoprolol CR/XL group (29% to 37%, P = 0.005). No significant changes were seen in the placebo group regarding these variables. Left ventricular stroke volume index remained unchanged, whereas LV mass index decreased in both groups (175 g/m2 to 160 g/m2 in the placebo group [p = 0.005] and 179 g/m2 to 164 g/m2 in the metoprolol CR/XL group [p = 0.01]). CONCLUSIONS This study is the first randomized study to demonstrate that the beta1-blocker metoprolol CR/XL has antiremodeling effects on the LV in patients with chronic heart failure and consequently provides an explanation for the highly significant decrease in mortality from worsening heart failure found in the MERIT-HF trial.