Minimal defibrillation thresholds and the correlation with implant position in subcutaneous implantable-defibrillator patients

Background Since the introduction of the subcutaneous implantable-defibrillator (S-ICD) knowledge of factors elevating the defibrillation threshold (DFT), have increased. Optimal device positioning most likely results in a decrease in DFT. The PRAETORIAN score is a tool to systematically evaluate S-ICD implant position and predict conversion success by estimating the DFT on a chest X-ray. The objective of this study is to determine DFT in de novo S-ICD patients. Methods De novo S-ICD patients were enrolled with DFT testing using a single 30 J shock or a prespecified step-down protocol. Chest X-rays were obtained and implant position was evaluated using the PRAETORIAN score. Results Fifteen patients, age 47 (+/- 18) years and body mass index (BMI) 25(+/- 3) kg/m(2), underwent conversion testing with a single 30 J shock. Fourteen patients (93%) converted successfully. Implant position was optimal in all patients, PRAETORIAN score of 30 (100%). Twelve patients were available for analysis in the step-down DFT cohort, age 46 years (+/- 15), left ventricular ejection fraction 50% (+/- 15%) and a median BMI of 25.7 kg/m(2) (range 23.8-29.1 kg/m(2)). No complications occurred during DFT testing. Mean DFT was 29 J (+/- 12 J). Time to shock was 11 seconds (+/- 2 seconds) for a 20 J shock compared with 17 seconds in case of a 70 J shock output. Nearly all patients were implanted with optimal device positioning with the lowest possible PRAETORIAN score of 30 (92%). Conclusion DFT in S-ICD patients with optimal device positioning is lower than previously reported. Conversion testing using a low shock output reduced time to therapy by 6 seconds on average.