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 less than 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-t/T) after intravenous metoprolol (T from 59 +/- 13 to 72 +/- 12 ms, p less than 0.001). Peak systolic circumferential LV wall stress decreased after beta-adrenergic blockade (330 +/- 93 to 268 +/- 89 g/cm2, p less than 0.05) and LV contractility decreased (dP/dtmax from 1,480 +/- 450 to 1,061 +/- 340 mm Hg/s, p less than 0.001). The ejection fraction decreased (48 +/- 7 to 43 +/- 7%, p less than 0.05) due to an increase in LV end-systolic volume (85 +/- 19 to 93 +/- 19 ml, p less than 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, (+)dP/dtmax, ejection fraction, isovolumic relaxation, LV end-diastolic pressure and end-diastolic volume remain unchanged.