Effects of beta receptor antagonists on left ventricular function in patients with clinical evidence of heart failure after myocardial infarction. A double-blind comparison of metoprolol and xamoterol. Echocardiographic results from the Metoprolol and Xamoterol Infarction Study (MEXIS)

Abstract

Two hundred and ten patients with clinical evidence of heart failure, developing after an acute myocardial infarction, were randomized to treatment with the beta 1-receptor antagonist metoprolol 50-100 mg b.i.d. (n = 106) or the beta 1-receptor partial agonist xamoterol 100-200 mg b.i.d. (n = 104). Left ventricular systolic and diastolic function were assessed with echocardiography and transmitral Doppler cardiography before and after 3 and 12 months of double-blind treatment. E-point septal separation and percent left ventricular fractional shortening were used as indices of systolic function. The ratio between peak early and late mitral diastolic flow (E/A ratio) and isovolumic relaxation time were used as indices of diastolic function. In the xamoterol group, there was a deterioration in E-point septal separation (P < 0.05). A difference between the treatment groups was present both at 3 months (E-point septal separation 11.4 vs 13.0 mm, P < 0.01, fractional shortening 27.1 vs 25.2%, P < 0.05) and 12 months (E-point septal separation 11.1 vs 13.2 mm. P < 0.005, fractional shortening 26.9 vs 25.0%, P < 0.05). E/A ratio increased in the metoprolol group (P < 0.05) but not in the xamoterol group. At 3 months there was a significant difference (0.85 vs 0.67, P < 0.005) between the groups but not at 12 months. In comparison with the beta 1-receptor antagonist metoprolol, the beta 1-receptor partial agonist xamoterol impaired left ventricular systolic function in patients with clinical evidence of heart failure after an acute myocardial infarction.