ISOFLURANE, BUT NOT HALOTHANE, IMPROVES INDEXES OF DIASTOLIC PERFORMANCE IN DOGS WITH RAPID VENTRICULAR, PACING-INDUCED CARDIOMYOPATHY

Background: The left ventricular (LV) mechanical effects of isoflurane and halothane were examined in dogs with rapid LV pacing-induced card iomyopathy, These experiments tested the hypothesis that isoflurane an d halothane differentially enhance indices of diastolic performance in dogs with moderate LV dysfunction. Methods: Eight dogs were chronical ly instrumented for measurement of LV and aortic pressures, subendocar dial segment length, and cardiac output, Contractility was quantified by preload recruitable stroke work (M(W)). Diastolic function was eval uated with a time constant of isovolumic relaxation (tau), segment len gthening velocities and time-velocity integrals during early filling ( dL/dt(E) and TVI-E) and atrial systole (dL/dt(A) and TVI-A), and a reg ional chamber stiffness constant (K-p). Hemodynamics and LV function w ere recorded in the conscious state before pacing. The left ventricles of the dogs were then continuously paced at ventricular rates between 220 and 240 beats . min(-1) for 10 +/- 1 days and monitored on a dail y basis, After the development of moderate LV dysfunction, pacing was temporarily discontinued, and dogs were studied in sinus rhythm in the conscious state and after 20 min equilibration at 1.1, 1.4, and 1.7 m inimum alveolar concentration isoflurane and halothane on separate day s, Results: Chronic rapid pacing increased baseline (sinus rhythm) hea rt rate, LV end-diastolic pressure, and end-diastolic segment length a nd decreased mean arterial pressure, LV systolic pressure, and cardiac output, M(W) decreased and tau and K-p increased, consistent with LV systolic and diastolic dysfunction, Reductions in dL/dt(E)/dL/dt(A) an d TVI-E/A occurred, which indicated that LV filling was more dependent on atrial systole, Zn dogs with cardiomyopathy, isoflurane and haloth ane increased heart rate and decreased mean arterial pressure, LV syst olic pressure, LV end-diastolic pressure, cardiac output, M(W), and K- p. Decreases in LV end-diastolic pressure were more pronounced in dogs anesthetized with 1.1 minimum alveolar concentration Isoflurane compa red with halothane. Halothane-induced decreases M(W) were greater than those observed with equi-minimum alveolar concentration isoflurane. A reduction in tau and increases in TVI-E/TVI-A and the ratio of early to total LV filling were observed with isoflurane, In contrast, haloth ane caused dose-related reductions in dL/dt(E), dL/dt(A), TVI-E, and T VI-A, and did not improve the ratios of these variables. Conclusions: Isoflurane, but not halothane, improved several indices of diastolic p erformance in dogs with pacing-induced LV dysfunction, despite produci ng simultaneous negative inotropic effects, These findings can probabl y be attributed to favorable reductions in LV preload and not to direc t lusitropic effects, Improvement of filling dynamics may partially of fset the decrement in LV systolic function by isoflurane in the settin g of LV dysfunction.