Xenon Does Not Impair the Responsiveness of Cardiac Muscle Bundles to Positive Inotropic and Chronotropic Stimulation

Abstract

Background Most volatile anesthetics exhibit a direct myocardial depressant effect. This side effect often limits their applicability in patients with impaired cardiac function. Xenon is a new gaseous anesthetic that did not show any adverse cardiovascular effects in clinical and experimental studies. The authors tested the hypothesis that xenon does not affect myocardial contractility or the positive inotropic effect of isoproterenol, calcium, and increase in pacing rate in isolated guinea pig ventricular muscle bundles. Methods Thin ventricular muscle bundles from guinea pig hearts with a mean diameter of 0.4-0.45 mm were prepared under stereomicroscopic control. Force of contraction and contraction times were studied in muscles superfused with medium equilibrated with either 65% xenon and 35% oxygen (xenon group), 1.2% isoflurane in oxygen (isoflurane group), or 65% nitrogen and 35% oxygen (control group). In addition, the positive inotropic effects of calcium, isoproterenol (10(-10)-3 x 10(-8) M) and increasing frequency (0.5-2 Hz) were studied during xenon and isoflurane exposure. Results In contrast to isoflurane, xenon did not alter myocardial force of contraction or contraction times. The positive inotropic effect of isoproterenol, calcium, and increasing pacing frequencies did not differ between the muscles exposed to xenon and the control group. Isoflurane elicited the expected negative inotropic effect (30% reduction of force of contraction) but did not impair the response to inotropic stimuli. Conclusions Xenon does not alter myocardial contractility and the response to inotropic stimuli such as calcium, isoproterenol, or increase in pacing frequency in isolated guinea pig ventricular muscle bundles.