Effects of low and high plasma concentrations of dexmedetomidine on myocardial perfusion and cardiac function in healthy male subjects

Background: Dexmedetomidine, a selective alpha(2)-adrenoceptor agonist, has counteracting effects on the cardiovascular system. It mediates sympatholysis by activating alpha(2) adrenoceptors in the central and peripheral nervous system, and vasoconstriction and vasorelaxation by activating postsynaptic a2 adrenoceptors in blood vessels. The goal of this study was to determine the effects of therapeutic and high concentrations of dexmedetomidine on myocardial perfusion and cardiac function in healthy subjects. Methods: The authors studied 12 healthy young men. Myocardial blood flow (assessed with positron emission tomography), myocardial function (by echocardiography), and hemodynamic data were collected before and during low (measured mean plasma concentration, 0.5 ng/ml) and high (5 ng/ml) plasma concentrations of dexmedetomidine. Results: The low concentration of dexmedetomidine reduced myocardial perfusion (mean difference, -27% from baseline [95% confidence interval, -31 to -23%], P < 0.001) in parallel with a reduction in myocardial oxygen demand (estimated by the rate-pressure product (-23% [-28 to -18%], P < 0.001). The high dexmedetomidine plasma concentration did not further attenuate myocardial perfusion (-3% [-12 to +6% from low dexmedetomidine, P > 0.05; -29% [-39 to -18%] from baseline, P < 0.001) or statistically significantly affect the rate-pressure product (+5% [0 to +10%], P > 0.05). Systolic myocardial function was attenuated by sympatholysis during the low infusion rate and was further attenuated by a combination of the sustained sympatholysis and increased afterload during the high infusion rate. Conclusions: In healthy subjects, plasma concentrations of dexmedetomidine that significantly exceed the recommended therapeutic level do not seriously attenuate myocardial perfusion below the level that is observed with usual therapeutic concentrations and do not induce evident myocardial ischemia.