High-dose intravenous beta 1-blockade in patients early after cardiac operations. Negative inotropism versus myocardial oxygen economy.

A high adrenergic strain during reperfusion after ischemia impedes functional recovery. Conversely, adrenergic blockade may be beneficial during reperfusion. Negative inotropic effects may outweigh the expected benefit, however. Against this background hemodynamic and metabolic effects of early postoperative infusion with the beta 1-selective agent metoprolol were studied in 22 patients after coronary operations. During basal postoperative conditions, intravenous metoprolol reduced cardiac index and stroke volume index compared with control patients, while other variables were unaffected. During the higher adrenergic level of a dopamine infusion (7 micrograms/kg per minute), the heart rate, rate pressure product, and myocardial oxygen uptake were attenuated in proportion to the plasma level of metoprolol. Intravenous beta 1-blockade did not affect the cardiac output or stroke volume responses to dopamine (the cardiac output was still, however, 19% lower than in control patients). A release of myocardial creatinine kinase isoenzyme myocardial band was observed during dopamine infusion, suggesting that myocardial ischemia was induced. The release was not influenced by metoprolol, but it correlated with heart rate (r = 0.60; p < 0.01). It is concluded that infusion of metoprolol early after coronary operations depresses myocardial contractility with some 19%, which was without clinical significance in straightforward patients; the increased myocardial metabolic demand during a period of increased adrenergic stress was attenuated by metoprolol. This may be of importance for myocardial recovery.