Defibrillation Energy Requirements Differ Between Anesthetic Agents

We examined the effect of anesthesia on the energy requirements for internal defibrillation (DF) in dogs anesthetized with pentobarbital (30 mg/kg IV followed by 2–3 mg/kg/hr constant infusion) (n = 20), fentanyl (25 μg/kg/hour) (n = 25), and enflurane (0.5%–1.5%) (n = 8). Multiple shocks of varying energies were applied through left and right ventricular epicardial patch electrodes to relate delivered energy to percent success in DF. The energies required for 50% success (E₅₀) and 80% success (E₈₀) in DF were estimated using logistic regression. E₅₀ in fentanyl anesthetized animals (3.8 ± 2.3 J) was significantly lower than in those given pentobarbital (6.9 ± 3.0 J) (P < 0.01), and lawer than those given enflurane (5.7 ± 2.8 J) (NS). E₈₀ with fentanyl (6.5 ± 4.0 J) was also lower than that of pentobarbital (10.4 ± 4.9 J) (P < 0.01) and enflurane (7.6 ± 4.3 J) (NS) animals. lawer defibrillation energy requirements (DER) with fentanyl anesthesia, when compared with pentobarbital, were associated with significantly longer ventricular effective refractory periods (VERP) (171 ± 20 versus 142 ± 15 msec: P < 0.01), lower mean arterial pressures (114 ± 20 vs 136 ± 25 mmHg: P < 0.01), and Iower heart rates (90 ± 37 versus 164 ± 19 b/m; P < 0.01).
Anesthetic agents may modify DER; their effects need to be taken into account in the assessment of DER in patients receiving implanted defibrillators and in the evaluation of the results of defibrillation research in anesthetized animals.