Inotropic Effects of Propofol, Thiopental, Midazolam, Etomidate, and Ketamine on Isolated Human Atrial Muscle

Background: Cardiovascular instability after intravenous induction of anesthesia may be explained partly by direct negative inotropic effects. The direct inotropic influence of etomidate, ketamine, midazolam, propofol, and thiopental on the contractility of isolated human atrial tissue was determined. Effective concentrations were compared with those reported clinically.

Methods: Atrial tissue was obtained from 16 patients undergoing coronary bypass surgery. Each fragment was divided into three strips, and one anesthetic was tested per strip in increasing concentrations (10 sup -6 to 10 sup -2 M). Strips were stimulated at 0.5 Hz, and maximum isometric force was measured. Induction agents were studied in two groups, group 1 (n = 7) containing thiopental, midazolam, and propofol, and group 2 (n = 9) consisting of etomidate, ketamine, and propofol.

Results: The tested anesthetics caused a concentration-dependent depression of contractility resulting in complete cessation of contractions at the highest concentrations. The IC50 S (mean +/-SEM; micro Meter) for inhibition of the contractility were: thiopental 43+/-7.6, propofol 235+/-48 (group 1), and 246+/-42 (group 2), midazolam 145+/-54, etomidate 133 +/-13, and ketamine 303+/-54.