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.

Clinical impact of defibrillation testing in a real‐world S‐ICD population: Data from the ELISIR registry

“…S‐ICDs have emerged as a novel valid alternative to TV‐ICDs for the prevention of sudden cardiac death 1,9,10,14 . As suggested by the 2017 AHA/ACC/HRS guidelines, this technology might be particularly beneficial in patients with inadequate vascular access or with a high infective risk, due to the relevant complications associated with the extraction of infected transvenous leads 15 .…”

“…In TV‐ICD recipients instead, a 5‐J safety margin was demonstrated as effective as a larger one when a true defibrillation threshold is attained by a strict testing protocol, 19,20 while testing VF termination resulted hardly meaningful in the setting of a large safety margin 5,6,8 . Indeed, there is convincing evidence that S‐ICD safety margin is larger than expected, conversion rate at ≤40 J approaching 90% in three recent studies collecting about 400 patients 13,14,21 . Owing to its probabilistic nature, DT by a single VF induction should be questioned due to limited reproducibility, while multiple VF inductions are required to establish the true defibrillation threshold 22 .…”

Defibrillation testing during implantation of the subcutaneous implantable cardioverter-defibrillator: a necessary standard or becoming redundant?

“… Implant position Recently, a computer model study identified three factors that alter the defibrillation threshold in S‑ICD patients: 1) fat tissue underneath the coil, 2) fat tissue underneath the generator and 3) an anterior placement of the generator on the thoracic wall [ 17 ]. When implanting physicians alter their implanting technique with these aspects in mind, step-down testing showed a lower average defibrillation threshold [ 18 ]. When implanted intermuscularly with subsequently no fat tissue underneath the generator, another study demonstrated a successful DFT at ≤40J in 94% of the patients [ 19 ].…”

The relationship between the incision line and position of the latissimus dorsi muscle for subcutaneous implantable cardioverter‐defibrillator intermuscular implantations

“…To reduce the defibrillation threshold of S‐ICDs, computer simulations suggest that the generator should be implanted closer to the chest wall and dorsally 6 . There is a PRAETORIAN score that predicts whether the defibrillation threshold will be higher based on the implantation position, 7 and if the PRAETORIAN score is low, defibrillation could be achieved at a lower energy output than in the past 8–10 …”