Metoprolol medication and coronary artery bypass grafting operation

Twenty patients undergoing a coronary artery bypass grafting operation with high-dose fentanyl anaesthesia, all on long-term metoprolol medication, were randomly divided into a metoprolol group (last metoprolol dose given 1.5 h before the anaesthesia) and a control group (last metoprolol dose 12 h before the anaesthesia). Haemodynamics were measured and the ECG was recorded serially in order to compare the responses to the anaesthesia induction and skin incision in these two groups and to evaluate possible harmful effects of the maintained metoprolol medication. The ECG showed ischaemic signs in five control group patients during the anaesthesia induction; these patients also had a relatively high rate-pressure product. No metoprolol group patient developed ECG changes indicative of ischaemia at this stage, despite a low plasma metoprolol concentration in two patients. Surgical stimulation caused no signs of myocardial ischaemia in either group. There were no inter-group differences in the haemodynamics or oxygen transportation. No harmful effects of the maintained metoprolol on the post-bypass cardiac performance nor on the occurrence of rhythm or conduction disturbances could be seen, although a high plasma metoprolol concentration was maintained in several metoprolol group patients over the bypass time. It is concluded that continuation of long-term metoprolol medication up to 1.5 h before high-dose fentanyl anaesthesia for coronary artery bypass grafting has no harmful effects on the haemodynamics during the operation or the restoration of the cardiac function after the cardiopulmonary bypass, but it evidently does help to maintain the myocardial oxygen supply/demand balance during the anaesthesia induction.