Key result
Impedance falls short of the PRAETORIAN score as a surrogate for predicting DFT success.
Why the study?
There is a trend of replacing defibrillation testing with impedance after S-ICD implantation, but situations exist where impedance may give a false sense of security.
Does impedance accurately predict defibrillation testing success compared to the PRAETORIAN score in patients undergoing S-ICD implantation?
RCT (n=965)
Yes
Does impedance accurately predict defibrillation testing success compared to the PRAETORIAN score in patients undergoing S-ICD implantation?
Impedance is an insufficient surrogate for defibrillation testing success after S-ICD implantation because it misses 50% of DFT failures, highlighting the need for imaging confirmation.
Supports selective DFT omission for impedance <90 Ω; extends RCT evidence on impedance-guided testing decisions.
Background The subcutaneous implantable cardioverter-defibrillator (S-ICD) is a completely extra-vascular device, making implantation position crucial. This can be evaluated using the PRAETORIAN score, but defibrillation testing (DFT) is currently recommended. There is a trend in replacing DFT with impedance. However, there are situations in which impedance can give a false sense of security. Purpose To compare predictive values of impedance and the PRAETORIAN score for DFT success. Methods The multicenter PRAETORIAN-DFT trial randomized 965 patients between DFT and PRAETORIAN score calculation after S-ICD implantation. DFT was successful if the ventricular arrhythmia converted to sinus rhythm or atrial fibrillation within 5 seconds from 65J shock delivery within two inductions. Predictive values of impedance and PRAETORIAN score were calculated, using a cutoff of 90 for both values. Results Overall, 457 patients underwent DFT according to protocol. DFT was successful in 445 patients and unsuccessful in 12. The failed DFT group had significantly higher impedance (87(IQR 63-108) vs. 68(IQR 57-78), P=0.014). Impedance <90 ohm had a negative predictive value (NPV) of 98% for successful DFT, but only half of failed DFTs had an impedance ≥90 ohm (sensitivity 50%). A PRAETORIAN score <90 had a NPV of 99% with a sensitivity of 70%. Conclusion Impedance <90 ohm predicts DFT success with a NPV of 98% but misses 50% of DFT failures and is therefore an insufficient surrogate for DFT. Impedance might serve as an intra-operative tool to estimate correct implant position, but this should always be confirmed with imaging to assure effective shock delivery.Impedance and DFT success
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Veld et al. (2026) conducted an RCT in Subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation (n=965). Impedance <90 ohm vs. PRAETORIAN score <90 was evaluated on Defibrillation testing (DFT) success (ventricular arrhythmia converted to sinus rhythm or atrial fibrillation within 5 seconds from 65J shock delivery within two inductions). Impedance <90 ohm predicted DFT success with a negative predictive value of 98% and sensitivity of 50%, compared to 99% and 70% for a PRAETORIAN score <90, making it an insufficient surrogate.
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