High defibrillation threshold in patients with implantable defibrillator: how effective is the subcutaneous finger lead?

OBJECTIVE Even in the era of high output implantable cardioverter defibrillator (ICD) devices, a certain proportion of patients cannot be successfully defibrillated with 10 J safety margin. In practice, either the use of a single- or double-coil lead does not guarantee successful termination of induced ventricular fibrillation. Therefore, we investigated the effectiveness of the subcutaneous finger lead placed at the subcutaneous tissue dorsal to the left ventricle in terms of defibrillation threshold (DFT) lowering. METHODS Two thousand, eight hundred and three consecutive, unselected patients underwent first-time ICD implantation or ICD device exchange from 6/1999 through 3/2007. The mean age of the patients was 65.4 years. A total of 79.3% of the patients were male. The only implanted subcutaneous lead was the 6996 model by Medtronic Inc. RESULTS One hundred and seventy-seven patients (6.3%) received a subcutaneous finger lead implantation. According to the current institutional DFT testing protocol, any failure of the two standard DFT tests in first-time ICD implantation or a failure at the single test in ICD exchange operations was the trigger for subcutaneous finger lead implantation. The proportion of subcutaneous finger lead implantations increased parallel to a markedly larger amount of implantations. Since high output devices became standard, the implantation number of subcutaneous finger leads decreases. The mean of unsuccessful DFTs prior to subcutaneous finger lead implantation was 27.2+/-5.3 J. After subcutaneous finger lead implantation, the mean successful DFT was 17.9+/-3.3 J. No complication due to subcutaneous finger lead implantation occurred. CONCLUSION The subcutaneous finger lead is a quick, safe and effective method for DFT lowering.