Effect of intravenous metoprolol on left ventricular performance in Q-wave acute myocardial infarction.

To determine the effects of intravenous metoprolol on left ventricular (LV) function in acute myocardial infarction (AMI), 16 patients were studied within 48 hours of Q-wave AMI (mean ejection fraction 47 ± 6%, mean pulmonary artery wedge pressure 22 ± 6 mm Hg) with high fidelity pressure and biplane cineventriculography before and after intravenous metoprolol (dose 12 ± 4 mg). Heart rate decreased from 90 ± 13 to 74 ± 11 beats/min (p < 0.001), pulmonary arterial wedge pressure and LV end-diastolic pressure were unchanged (22 ± 6 to 21 ± 6 and 27 ± 8 to 26 ± 8 mm Hg, respectively), despite impaired LV relaxation (P = Poe−tT) after intravenous metoprolol (T from 59 ± 13 to 72 ± 12 ms, p < 0.001). Peak systolic circumferential LV wall stress decreased after β-adrenergic blockade (330 ± 93 to 268 ± 89 g/cm2, p < 0.05) and LV contractility decreased (dPdtmax from 1,480 ± 450 to 1,061 ± 340 mm Hg/s, p < 0.001). The ejection fraction decreased (48 ± 7 to 43 ± 7%, p < 0.05) due to an increase in LV end-systolic volume (85 ± 19 to 93 ± 19 ml, p < 0.05) since LV end-diastolic volume was unchanged (161 ± 30 to 163 ± 30 ml, difference not significant). In patients with Q-wave AMI, intravenous metoprolol reduces the major determinants of myocardial oxygen demand including heart rate, contractility and peak systolic wall stress. Further, despite decreased heart rate, (+)dPdtmax, ejection fraction, isovolumic relaxation, LV end-diastolic pressure and end-diastolic volume remain unchanged.