Real-world evaluation of the PRAETORIAN score in subcutaneous ICD recipients: a multicenter registry

Background Patients at high risk of ventricular arrhythmias require implantable cardioverter-defibrillator (ICD) therapy. Subcutaneous ICD (S-ICD) devices are a safe and effective alternative to transvenous systems. The PRAETORIAN Score (PS) is a recently developed X-ray-based tool to predict an elevated risk of ineffective defibrillation. Purpose The aim of this study was to evaluate the clinical performance of the PS as a marker of implantation quality in a real-world S-ICD cohort. Methods All S-ICD procedures at three European centers (2015 – 2024) were retrospectively analyzed. For each patient, the PS was calculated based on postero-anterior and lateral chest X-rays using the original four-step algorithm: (1) coil-to-sternum distance (2) generator position (3) generator-to-rib distance (4) adjustment for BMI 25 kg/m2. Procedural parameters and outcomes were analyzed. Results Of 516 patients undergoing S-ICD implantation, 418 with available chest X-rays were included (age: 46.2 ± 14.4 years; 287 (68.7%) male; BMI 27.4 ± 6.2 kg/m2). The PS was < 90 in 368 (88.0%), ≥ 90 and < 150 in 31 (7.4%) and ≥ 150 in 19 (4.6%) patients, respectively. Most patients received intermuscular generator implantation (n = 313, 98.4%), whereas only 1.2% (n = 5) had a subcutaneous generator position. A two-incision implantation technique was associated with a lower PS than three-incisions (n = 369; p < 0.001). A coil-to-sternum distance ≥ one coil width was observed in 33.0% of patients, whereas suboptimal generator position (3.1%) and relevant sub-generator fat (7.7%) were less frequent. The total PS correlated with shock impedance (n = 283; p < 0.001), but among its radiographic components (steps 1-3), only the coil-to-sternum distance correlated independently (p < 0.001). BMI was an independent predictor of a PS ≥ 90 (p < 0.001) and 98.3% of normal weight patients had a PS < 90. Moreover, higher BMI correlated with an increased shock impedance (p < 0.001). Of 310 patients undergoing defibrillation testing, 20 (6.5%) showed conversion failure. In 5 (25.0%) of these, generator and/or lead were repositioned. Among the remaining 15 patients with conversion failure, 4 (26.7%) had a Praetorian score of ≥ 90 compared to 36 (11.3%) patients with successful defibrillation testing. This corresponded to a positive predictive value of 3.7% (95% CI 2.1–6.6%) and a negative predictive value of 90.0% (95% CI 76.9–96.0%). Conclusion In this multicenter cohort, most patients had a low PS, reflecting a low predicted risk of conversion failure. The total score and coil-to-sternum distance correlated with shock impedance underscoring the value of the PS in assessing implantation quality. A two-incision technique may help achieve a lower PS.