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

Abstract

Aims: 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. This study evaluated the correlation between the PRAETORIAN score and clinical characteristics, as well as implantation variables.

Methods and results: We retrospectively analysed data from 1253 patients who had undergone implantation of an S-ICD across 33 centres. The intermuscular positioning of the pulse generator was adopted in all patients. Post-implantation posterior-anterior and lateral chest radiographs were analysed to calculate the PRAETORIAN score. A total of 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 < 25 kg/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 > 88 Ohm enabled to detect a PRAETORIAN score ≥ 90 with 98% (95% CI 97-99%) negative predictive value.

Conclusion: 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 favourable PRAETORIAN score is assured, making the score evaluation potentially unnecessary.

Clinical trial registration: URL: http://clinicaltrials.gov/ Identifier: NCT02275637.

Keywords: Conversion; Defibrillation test; Implantable defibrillator; Subcutaneous.

graphical abstract

Figure 1

Chest radiograph analysis according to the PRAETORIAN score. In A, the thickness of the adipose tissue is ≤1 coil width. This corresponds to 30 points in the score system (Step 1 of the PRAETORIAN score) and low predicted risk of shock failure. The lateral view also allows to evaluate the generator placement in relation to the midline (Step 2 of the PRAETORIAN score). The S-ICD generator is in an optimal position, posterior to the midline; the score is, therefore, multiplied by 1. In B, the postero-anterior chest radiograph view allows to determine the amount of sub-generator fat (Step 3 of the PRATEORIAN score). As a reference, the generator width is used. In the example, <1 generator width of fat tissue is observed between the nearest point of the generator and the thoracic wall. The score is multiplied by 1.

Figure 2

Distribution of the overall PRAETORIAN score and the three steps: (Step 1) thickness of the adipose tissue between the coil and the sternum, measured by using the coil width as a reference; (Step 2) position of the generator in relation to the midline; (Step 3) amount of fat tissue between the nearest point of the generator and the thoracic wall, measured by using the generator width as a reference.

Figure 3

(A) Stepwise increase of shock impedance according to the thickness of the adipose tissue between the coil and the sternum. (B) Receiver operating characteristic curve analysis of the shock impedance for the prediction of thickness of the adipose tissue between the coil and the sternum > 1 coil width (PRAETORIAN score Step 1: ≥60 points). Sensitivity and specificity were 51% (95% confidence interval 42–60%) and 100% (95% confidence interval 99–100%), respectively, at shock impedance > 88 Ohm.