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 tachyarrhythmias, the use of isoflurane appeared to significantly lower defibrillation thresholds (DFT) at implantation. In the first, at initial implantation and subsequent revision using isoflurane, adequate DFTs were verified by multiple tests. Post-implantation testing using midazolam and fentanyl revealed significantly higher DFTs, necessitating a third operation without isoflurane to obtain an adequate and subsequently verifiable DFT. During the second case, discontinuation of isoflurane intraoperatively resulted in a DFT rise within 25 minutes. In patients receiving general anesthesia for ICD implantation, this possible DFT effect of isoflurane should be recognized.