ARE PATIENTS CHRONICALLY TREATED WITH BETA(1)-ADRENOCEPTOR ANTAGONISTS IN FACT BETA-BLOCKED

To determine cardiovascular beta-receptor function in patients with ischemic heart disease chronically treated with beta 1-adrenoceptor antagonists.Prospective, single-blind, nonrandomized clinical trial.University Department of Cardiothoracic Anesthesia.Forty middle-age men scheduled for primary elective coronary artery bypass surgery. Twenty patients were treated with beta 1-antagonists.After induction of anesthesia, increasing intravenous bolus doses of isoproterenol were administered in order to increase heart rate more than 25 BPM. From this dose-response curve, the isoproterenol dose needed to increase heart rate by exactly 25 BPM was calculated.Baseline cardiovascular variables and the pharmacodynamic responses to isoproterenol were monitored with catheters in the radial and the pulmonary artery (thermodilution catheter). Heart rate was continuously calculated from the electrocardiogram. The hemodynamic status after induction of a standardized fentanyl anesthesia and the chronotropic and inotropic responses to the isoproterenol titration procedure were identical in the 20 beta 1-blocked patients and in the 20 control patients. The median dose of isoproterenol needed to increase heart rate 25 BPM was 10.9 micrograms in the beta-blocked patients and 9.4 micrograms in the control group.Patients chronically treated with beta 1-antagonists compensate for the perturbation to such a degree that cardiovascular beta-receptor function is in fact normal.