Isoflurane and halothane do not alter the enhanced afterload sensitivity of left ventricular relaxation in dogs with pacing-induced cardiomyopathy

Abstract

Background: The afterload dependence of left ventricular (LV) relaxation is accentuated in the failing heart. The authors tested the hypothesis that isoflurane and halothane alter the afterload sensitivity of LV relaxation in dogs with pacing-induced cardiomyopathy. Methods: Dogs (n = 6) were chronically instrumented for measurement of LV and aortic pressures and subendocardial segment length. Hemodynamics were recorded, and LV relaxation was evaluated with a time constant of isovolumic relaxation (τ) under control conditions and during decreases and increases in LV load produced by abrupt inferior vena caval (IVC) occlusion and phenylephrine (intravenous infusion), respectively, in the conscious state and during isoflurane and halothane anesthesia (1.5 MAC) on separate days before and after the development of pacing-induced cardiomyopathy. The slope (R) of the τ versus LV end-systolic pressure (P(cs)) relation was also used to determine the afterload sensitivity of LV relaxation. Results: IVC occlusion and phenylephrine produced similar or less profound changes in P(cs), regional end-systolic force (an index of LV afterload), and end-systolic segment length in cardiomyopathic compared with healthy dogs. However, IVC occlusion and phenylephrine caused more pronounced alterations in τ in conscious and isoflurane- and halothane-anesthetized dogs after the development of cardiomyopathy. R was also greater in cardiomyopathic compared with healthy dogs (e.g., 0.32 ± 0.03 before pacing to 1.00 ± 0.13 ms/mmHg in conscious dogs). No differences in the load dependence of LV relaxation were observed between the conscious and anesthetized states before and after production of LV dysfunction. Conclusions: The results indicate that isoflurane and halothane do not alter the afterload dependence of LV relaxation in the normal and cardiomyopathic heart. The lack of effect of the volatile anesthetics is probably related to anesthetic-induced reductions in the resistance to LV ejection concomitant with simultaneous negative inotropic effects.