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.