Effect of isoflurane on defibrillation threshold in biphasic active-can defibrillation systems

In two patients receiving implantable cardioverter-defibrillators (ICD) for spontaneous and inducible ventricular tarhyarrhythmias, the use of isoflur ane appeared to significantly lower defibrillation thresholds (DFT) at impl antation. In the first, at initial implantation and subsequent revision usi ng isoflurane, adequate DFTs mere verified by multiple tests, Post-implanta tion testing using midazolam and fentanyl revealed significantly higher DFT s, necessitating a third operation without isoflurane to obtain an adequate and subsequently verifiable DFT, During the second case, discontinuation o f isoflurane intraoperatively resulted in a DFT rise within 25 minutes. In patients receiving general anesthesia for ICD implantation, this possible D FT effect of isoflurane should be recognized.