Comparison of hemodynamic responses to isoproterenol infusion and surgical stress in patients given cardioselective and noncardioselective beta-adrenergic antagonists.

Recent studies have demonstrated the presence of physiologically active beta 2 receptors in the myocardium. We hypothesized that activation of cardiac beta 2 receptors by endogenously released epinephrine and norepinephrine during surgical stress would add to the positive chronotropic response mediated by beta 1 stimulation. Twenty patients scheduled for coronary artery bypass grafting were studied. Ten patients received a beta 1-selective antagonist (atenolol, 6; metoprolol, 4) and ten patients received a nonselective beta 1 and beta 2 antagonist (propranolol) preoperatively. An isoproterenol dose-heart rate response test was performed. After stabilization, general anesthesia was induced followed by tracheal intubation and surgery. Hemodynamic data were recorded before induction, 1 min after induction, 5 min after intubation, 1 min before and after skin incision, 1 min before and after sternotomy. The ten patients on cardioselective beta-blocker drugs had significantly greater increases in heart rate during isoproterenol administration than did the non-cardioselectively blocked group of patients. Heart rate responses to tracheal intubation and surgical stress were not significantly different between the two groups at any point. We conclude that changes in heart rate during perioperative stress are primarily mediated through activation of beta 1 receptors in the myocardium and that patients on either cardioselective or noncardioselective beta-blockers have similar protection to adrenergic-mediated stressful hemodynamic events.