Hemodynamic effects of intravenous metoprolol in acute myocardial infarction: the role of anatomic subsets in predicting patient response.

The acute effects of intravenous metoprolol were evaluated in 30 patients with myocardial infarction by means of serial hemodynamic and radionuclide measurements of left ventricular function. Within 1 hour of completion of the metoprolol dosing, 90% of the patients underwent cardiac catheterization to define anatomy and to assess patients for interventional therapy; the remainder had catheterization by 72 hours. All patients tolerated intravenous metoprolol without significant side effects. Patient responses to therapy were divided into two groups based on the angiographic findings. At catheterization, all group 1 patients had visible collaterals to or a patent vessel supplying the vascular distribution of the infarction. All group 2 patients had occluded coronary arteries without evidence of collaterals to the infarct zone. Group 1 (n = 13) improved both systolic and diastolic left ventricular function (mean ejection fraction [EF] = 46% to 55%, peak filling rate [PFR] = 2.1 to 3.2 Edv/sec), while group 2 (n = 17) patients were unchanged (EF = 43% to 42%, PFR = 2.0 to 1.9). Patient characteristics and time to treatment were similar in both groups, as were the hemodynamic effects of metoprolol. Heart rate decreased 20% in group 1 and 22% in group 2 and cardiac output fell 22% in group 1 and 32% in group 2. Acute improvement in ventricular function in these patients appears to be closely related to the coronary anatomy, and in those with flow to the infarct zone, intravenous metoprolol may be effective in preserving left ventricular function.