Integration of PRAETORIAN Score, defibrillation testing and follow-up outcomes for the assessment of conversion failure in patients with subcutaneous implantable cardioverter defibrillator: Results from the iSUSI registry

Although reports of good clinical outcomes after avoiding defibrillation testing (DFT) during subcutaneous implantable cardioverter defibrillator (S-ICD) implantation have increased over recent years, current guidelines still recommend performing DFT at the time of implant.

We aimed to identify predictors of conversion failure in a real-world S-ICD population and assess whether PRAETORIAN score performance is improved by additional clinical variables.

We analyzed 1063 patients from the international subcutaneous implantable cardioverter defibrillator (iSUSI) registry with available imaging and complete follow-up. The primary endpoint was a composite of DFT failure and ineffective appropriate shocks during follow-up. PRAETORIAN score and individual components were assessed, and receiver operating characteristic curve analysis with DeLong's test was used to evaluate model performance.

Patients were classified into low (76.6%), intermediate (16.3%), and high-risk (7.2%) PRAETORIAN score categories. Among 748 patients who underwent DFT, 64 (8.6%) experienced DFT failure; 17 ineffective shocks occurred during follow-up. Primary outcome occurred in 4.5% of low, 6.7% of intermediate-, and 16.8% of high-risk patients. PRAETORIAN score step 1, anterior generator position at PRAETORIAN score step 2 (odds ratio 2.3 [1.2-4.2], P = .006), high body mass index (BMI) and post-shock impedance, independently predicted conversion failure. Overall PRAETORIAN score (area under the curve [AUC] 0.71) outperformed individual steps (step 1-3 AUCs: 0.68-0.70; P > .05 for all comparisons). A multivariable model combining PRAETORIAN score, BMI, and impedance significantly improved predictive accuracy (AUC 0.78 vs 0.71; P = .0078).

PRAETORIAN score, BMI, and impedance are independent predictors of defibrillation failure. Their combined use may improve risk stratification and may help guide clinical decision-making, especially when DFT is omitted.