The reversal of amiodarone-induced perioperative reduction in cardiac systolic reserve in dogs

AbstractThere is controversy about the myocardial depressant effects of amiodarone in patients with decreased cardiac function undergoing surgery. Some surgeons believe that these effects complicate the discontinuation of cardiopulmonary bypass. Accordingly, the hemodynamic effects of amiodarone were evaluated in two groups of anesthetized mongrel dogs that had undergone a median sternotomy. A control group of 10 dogs and an amiodarone-treated group (15 mg/kg per day for 3 weeks) of 10 dogs were studied, and serum (0.26 to 1.09 μg/ml) and tissue (cardiac 2.97 to 11.60 μg/ml) levels of amiodarone were measured by liquid chromatography.Hemodynamic measurements were made at baseline and after administration of routine therapeutic intravenous doses of dobutamine (10 μg/kg per min), isoproterenol (0.06 μg/kg per min) and epinephrine (2 μg/min). The amiodarone-treated dogs had a smaller increase in cardiac output compared with baseline than did control dogs. For each drug when the amiodarone-treated group was compared with the control group, increases in cardiac output (liters/min) were: dobutamine, 1.32 ± 0.24 versus 1.73 ± 0.31; isoproterenol, 0.84 ± 0.26 versus 1.43 ± 0.28; epinephrine, 0.25 ± 0.15 versus 0.44 ± 0.53. Amiodarone-treated dogs were also given higher doses of drugs, dobutamine (50 μg/kg per min), isoproterenol (1.2 μg/kg per min) and epinephrine (20 μg/min). Increases in cardiac output were 1.24 ± 0.24, 1.62 ± 0.25 and 2.82 ± 0.64, respectively. All cardiac outputs were significantly increased from the baseline values (p < 0.05) except those measured in the amiodarone group receiving the lower dose of epinephrine.Thus, amiodarone-treated dogs bave a relative reduction of perioperative cardiac systolic reserve. Reversal of this myocardial depression may require the use of drugs in excess of standard doses. Epinephrine was the most effective drug in this study. It produced improvements in cardiac output by increasing stroke volume, whereas changes secondary to dobutamine or isoproterenol were more closely related to changes in heart rate. These findings have implications for amiodarone-treated patients during and after cardiopulmonary bypass