Small, oral dose of clonidine reduces the incidence of intraoperative myocardial ischemia in patients having vascular surgery

Most new perioperative myocardial ischemic episodes occur in the absence of hypertension or tachycardia. The ability of alpha 2-adrenoceptor agonists to inhibit central sympathetic outflow may benefit patients with coronary artery disease by increasing the myocardial oxygen supply and -demand ratio. A randomized double-blind study design was used in 297 patients scheduled to have elective vascular surgical procedures to evaluate the effects of 2 micrograms/kg-1 oral clonidine (n = 145) or placebo (n = 152) on the incidence of perioperative myocardial ischemic episodes, myocardial infarction, and cardiac death. Continuous real-time S-T segment trend analysis (lead II and V5) was performed during anesthesia and surgery and correlated with arterial blood pressure and heart rate before and during ischemic events. Dose requirements for vasoactive and antiischemic drugs to control blood pressure and heart rate as well as episodes of myocardial ischemia (i.e., catecholamines, beta-adrenoceptor antagonists, nitrates, and systemic vasodilators) and fluid volume load were recorded. Administration of clonidine reduced the incidence of perioperative myocardial ischemic episodes from 39% (59 of 152) to 24% (35 of 145) (P < 0.01). Hemodynamic patterns, percentage of ischemic time, and the number of ischemic episodes per patient did not differ. Nonfatal myocardial infarction developed after operation in four patients receiving placebo compared with none receiving clonidine (day 2 to 21; P = 0.07). The incidence of fatal cardiac events (1 vs. 2) was not different. Dose requirements for vasoactive and antiischemic drugs did not differ between the groups, but the amount of presurgical fluid volume was slightly greater in patients receiving clonidine (951 +/- 388 vs. 867 +/- 381 ml; P < 0.03). A small oral dose of clonidine, given prophylactically, can reduce the incidence of perioperative myocardial ischemic episodes without affecting hemodynamic stability in patients with suspected or documented coronary artery disease.