The risk of failure of subcutaneous implantable cardioverter defibrillator therapy: from PRAETORIAN score to clinical practice

Background: The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an alternative to traditional ICDs. The PRAETORIAN score, based on chest radiographs, has been validated to predict the probability of successful S-ICD defibrillation testing by assessing factors like fat thickness between the coil and sternum and generator placement. Objective: This study evaluated the correlation between the PRAETORIAN score and clinical characteristics, as well as implantation variables. Methods: We retrospectively analyzed data from 1253 patients who had undergone implantation of an S-ICD across 33 centers. The intermuscular positioning of the pulse generator was adopted in all patients. Post-implantation posterior-anterior and lateral chest radiographs were analyzed to calculate the PRAETORIAN score. Results: 95.7% of patients had a PRAETORIAN score <90, indicative of a low risk of conversion failure. Body mass index (BMI) was the only independent predictor of a score ≥90, and all patients with BMI <25kg/m2 (normal weight or underweight) had a score <90. The intermuscular positioning technique resulted in optimal posterior placement of the device in all patients and significant sub-generator fat in only 3% of cases. A shock impedance value >88Ohm enabled to detect a PRAETORIAN score ≥90 with 98% (95% CI 97%-99%) negative predictive value. Conclusions: In contemporary practice, the PRAETORIAN score can be simplified. By adopting an intermuscular approach, two of the three steps of the score-evaluating the adequate posterior positioning of the generator and measuring the sub-generator fat-become superfluous, and impedance may serve as a reliable surrogate of sub-coil fat thickness. Furthermore, our data suggest that for non-obese patients, a favorable PRAETORIAN score is assured, making the score evaluation potentially unnecessary.