Dexmedetomidine produces similar alterations in the determinants of left ventricular afterload in conscious dogs before and after the development of pacing-induced cardiomyopathy.
BACKGROUND
The authors tested the hypothesis that intravenous dexmedetomidine produces alterations in left ventricular (LV) afterload that are deleterious to cardiac performance in conscious dogs with pacing-induced cardiomyopathy.


METHODS
Dogs (n = 8) were fitted with instruments for long-term measurement of LV and aortic blood pressure, aortic blood flow, and subendocardial segment length and received dexmedetomidine (1.25, 2.5, and 5 microg/kg) in a cumulative manner before and after 19+/-3 (mean +/- SEM) days of rapid LV pacing. LV afterload was measured with aortic input impedance [Zin(omega)] and quantified with a three-element Windkessel model. Hemodynamics and Zin(omega)) were assessed under control conditions and 5 and 60 min after administration of each dose.


RESULTS
Dexmedetomidine caused early and late decreases in heart rate, the maximum rate of increase of LV pressure, mean aortic blood flow, and stroke volume in dogs before and after pacing. Dexmedetomidine caused similar early increases in total arterial resistance and decreases in total arterial compliance in dogs before and after pacing. Early dexmedetomidine-induced increases in resistance and decreases in compliance caused similar reductions in mean aortic blood flow in cardiomyopathic compared with healthy dogs. Resistance and compliance returned to control values, and characteristic aortic impedance decreased late after dexmedetomidine in healthy dogs. In contrast, resistance remained elevated late after dexmedetomidine in dogs with dilated cardiomyopathy.


CONCLUSIONS
Dexmedetomidine causes similar alterations in hemodynamics and LV afterload in conscious dogs with and without pacing-induced cardiomyopathy.
Pagel
P S
PS
Department of Anesthesiology, Medical College of Wisconsin, Clement J. Zablocki Veterans Affairs Medical Center, Milwaukee 53226, USA. ambarnes@mcw.edu
Hettrick
D A
DA
Kersten
J R
JR
Warltier
D C
DC
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002304:Cardiac Pacing, Artificial; D002311:Cardiomyopathy, Dilated / Q000503:physiopathology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006439:Hemodynamics / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology*; D020926:Medetomidine; D016277:Ventricular Function, Left / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D020926:Medetomidine