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Best Anesthetics for Assessing Left Ventricular Systolic Function by Echocardiography in Mice

Reviewing the literature of the major cardiovascular journals for the past three years, revealed that of all the studies using anesthesia for mouse echocardiography, the predominant anesthetic was isoflurane, which was used in 76% of the articles. The goal of this investigation was to determine if isoflurane is indeed the best anesthetic. Accordingly, we compared this anesthetic with tribromoethanol, ketamine/xylazine, and ketamine on different days in the same mice also studied in the conscious state. A randomized crossover study design was employed to compare the effects on left ventricular (LV) systolic function and heart rate of the 4 different anesthetic agents assessed by echocardiography and compared with values obtained in the conscious state. Fourteen mice (C57BL/6J, 129SVJ, FVB/N) underwent high resolution echocardiography. As expected each anesthetic depressed LV ejection fraction and heart rate compared with values in conscious mice. Surprisingly, isoflurane was not the best, but actually second to last in maintaining normal LV function and heart rate. The anesthetic with the least effect was ketamine alone at a dose of 150 mg/kg, which induced a surgical level of anesthesia, followed by tribromoethanol, 290 mg/kg, isoflurane, 3% induction and 1‐2% maintenance, and lastly ketamine/xylazine, 100/10 mg/kg.In summary, these results indicate that ketamine alone exerts the least depressant effects on LV function and heart rate, with avertin second; suggesting that these anesthetics should be used, when it is not feasible to study the animals in the conscious state, as opposed to the most commonly used anesthetic, isoflurane.