Haemodynamic effects of metroprotolol and intravenous nitroglycerin versus metroprolol alone in patients with acute myocardial infaction

Among the various treatments adopted to protect the acutely ischaemic myocardium, favourable results have been reported for beta-blockers. Nitrates can also reasonably be expected to exert favourable effects in acute myocardial infarction considering their haemodynamic action. In this study we compared the haemodynamic effect of metoprolol alone with the effect of metoprolol plus nitroglycerin. Fourteen patients, admitted within 12 hours from the clinical onset of acute myocardial infarction, were initially given intravenous metoprolol (5 + 5 + 5 mg) followed 15 minutes later by an additional 50 mg oral dose. Thereafter, they were randomly allocated to a treatment with metoprolol alone (Group 1) or metoprolol plus intravenous nitroglycerin (Group 2). The two groups were comparable with regard to age, sex, time to admission, time to therapy, site of necrosis, Killip class, and infarct size. Acute beta-blockade induced a marked decrease of cardiac output, systolic blood pressure and heart rate along with a small increase of pulmonary wedge pressure and a marked systemic vasoconstriction. In Group 1 patients these haemodynamic changes persisted up to twelve hours after randomization; in Group 2 patients the addition of nitroglycerin induced a prompt decrease of pulmonary wedge pressure and peripheral vascular resistance whereas the double product was unchanged. In conclusion, intravenous nitroglycerin induces a beneficial haemodynamic effect after early beta-blockade with metoprolol.