ETOMIDATE ADVERSELY ALTERS DETERMINANTS OF LEFT-VENTRICULAR AFTERLOADIN DOGS WITH DILATED CARDIOMYOPATHY

We tested the hypothesis that etomidate produces similar alterations i n left ventricular (LV) afterload in dogs with normal LV function or d ilated cardiomyopathy. Dogs were instrumented for LV and aortic pressu res, and aortic blood flow. LV afterload was measured with aortic inpu t impedance and quantified with a three-element Windkessel model. Zn o ne group of experiments, dogs (n = 6) were paced at 240 bpm for 18 +/- 2 days (mean +/- SEM). Hemodynamic data were recorded in sinus rhythm in the conscious state and during etomidate anesthesia (5, 10, and 20 mg.kg(-1).h(-1)). Identical experiments were conducted in a separate group of chronically instrumented dogs not subjected to LV pacing (n = 6). No changes in heart rate and arterial and LV pressures were obser ved during etomidate anesthesia in cardiomyopathic dogs. There were de creases in arterial and LV systolic pressure during the administration of 20 mg.kg(-1).h(-1) etomidate to dogs with normal LV function. Etom idate significantly (P < 0.05) increased total arterial resistance (R; 3220 +/- 290 dynes.s.cm(-5) during control to 6110 +/- 790 dynes.s.cm (-5) during 10 mg.kg(-1).h(-1)) and characteristic aortic impedance (Z (c); 141 +/- 22 dynes.s.cm(-5) during control to 161 +/- 23 dynes.s.cm (-5) during 20 mg.kg(-1).h(-1)) and decreased total arterial complianc e (C; 0.70 +/- 0.15 mL/mm Hg during control to 0.45 +/- 0.07 mL/mm Hg during 10 mg.kg(-1).h(-1)) in cardiomyopathic but not healthy dogs. Et omidate markedly reduced mean aortic blood flow (2.26 +/- 0.17 L/min d uring control to 1.39 +/- 0.20 L/min during 10 mg.kg(-1).h(-1)) and in creased the time constant of LV relaxation (54 +/- 3 ms during control to 74 +/- 9 ms during 20 mg.kg(-1).h(-1)) in dogs with LV failure. Ar terial pressure is maintained during etomidate anesthesia in the prese nce of LV dysfunction as a result of increases in R and Z(c) and decre ases in C. These deleterious increases in LV afterload further comprom ise LV systolic and diastolic performance in dogs with dilated cardiom yopathy. Implications: The results of this investigation indicate arte rial pressure is maintained during etomidate anesthesia as a consequen ce of increases in left ventricular (LV) afterload that further dimini sh LV systolic and diastolic performance in the presence of impaired L V function.