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

Abstract 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/m2, 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/m2 (range 23.8‐29.1 kg/m2). 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.