Cardiac safety of acute beta blockade: Intrinsic sympathomimetic activity is superior to beta-1 selectivity

Abstract

Regional myocardial function was assessed by multidirectional echocardiography from eight standardized segments around the left ventricle. Thirty-six subjects (healthy, severe angina pectoris, or acute myocardial infarction) were studied 15 minutes either after the beta-1-selective beta-blocking drug metoprolol had been administered in total doses of 2 and 10 mg intravenously or after pindolol, a beta blocker with intrinsic sympathomimetic activity (ISA), in total doses of 0.2 and 1.0 mg intravenously had been given. Metoprolol and pindolol reduced rate-pressure product ( p < 0.001 each), heart rate ( p < 0.001), and systolic blood pressure ( p < 0.05 to 0.001) in almost the same way. In patients with acute myocardial infarction, 0.2 mg pindolol improved ST segments by 33% and 2 mg metoprolol by 18%. Left ventricular diameter increased ( p < 0.001) and ejection fraction decreased ( p < 0.05) after metoprolol but not after pindolol. Pindolol did not reduce wall motion amplitudes of healthy myocardial segments, while metoprolol did ( p < 0.01). The overall contractile function of the left ventricle is characterized by composite segmental amplitudes from both ischemic and healthy ventricular regions. In ischemic hearts this function remained unchanged after metoprolol but improved markedly after pindolol ( p < 0.005). Thus, while intravenous pindolol and metoprolol produced equal reductions in rate-pressure product, pindolol, a beta-adrenergic-blocking drug with intrinsic sympathomimetic activity, evoked less cardiac depression and thus provided a cardiac safety factor not afforded by the beta-1-selective metoprolol.