Comparison of selective (beta 1) and nonselective (beta 1 and beta 2) beta-adrenergic blockade on systemic and coronary hemodynamic findings in angina pectoris

Abstract

To investigate the influence of selective β 1-adrenergic blockade, in contrast to β 1- and β 2-adrenergic blockade, systemic and coronary hemodynamics were studied. Measurements were made at rest and during exercise in 23 patients with suspected coronary artery disease (CAD) before and after either metoprolol or propranolol, given in doses to provide comparable β 1-receptor blockade. Quantitative coronary angiography was performed at rest. Using a randomized, double-blind protocol, either β 1 and β 2 blockade was produced by propranolol (0.1 mg/kg intravenously), or selective β 1 blockade was produced by metoprolol (0.15 mg/kg intravenously). As expected, at these doses both drugs produced a comparable decrease in heart rate at rest and during exercise, averaging 9% and 14% after propranolol and 10% and 16% after metoprolol. Exercise duration to ischemia was prolonged in most patients with severe CAD after either propranolol (5 of 7) or metoprolol (6 of 10) treatment. The effects of these 2 β-blocking drugs on systemic hemodynamic values at rest and during exercise were similar. Additionally, coronary sinus flow was usually unchanged by both drugs at rest (−5% after propranolol and −4% after metoprolol, differences not significant) and decreased a similar amount during exercise (−15% after propranolol and −9% after metoprolol, both p <0.05). Coronary resistance did not change significantly with either drug (0% after propranolol and 3% after metoprolol), and during exercise (11% after propranolol and 3% after metoprolol), suggesting that decreases in flow were secondary to reduced demand. Furthermore, neither drug produced detectable changes in coronary artery size. For example, the average change in the minimal diameter of 29 coronary stenoses was −2% after propranolol and 0% after metoprolol (difference not significant).