Effects of metoprolol on systemic haemodynamics, myocardial performance and the coronary circulation during halothane anaesthesia.

The effects of metoprolol 1 mg kg-1 i.v. on the systemic and coronary circulations and on myocardial performance were studied in nine open-chested dogs ventilated with halothane 0.8% in oxygen at normocarbia. In terms of the chronotropic effect, this dose of metoprolol produced a substantial shift to the right of the dose-response curve to isoprenaline; substantial reductions of arterial pressure (10%), cardiac output (21%), aortic blood acceleration (13%), left ventricular dP/dt max (13%) and left ventricular power (25%) were observed. Both preload, represented by left ventricular end diastolic pressure, and afterload, represented by systemic vascular resistance, increased. Left circumflex coronary blood flow and myocardial oxygen consumption decreased by approximately the same amount as peak ventricular power.