The predictive value of impedance for defibrillation success after subcutaneous implantable cardioverter-defibrillator implantation: a reliable indicator?
J De Veld, M F El-Chami, C Marquie, P D Lambiase, L V A Boersma, M C Burke, A De Weger, T R Betts, M A Miller, J Kuschyck, H Bonnemeier, L R A Olde Nordkamp, S Boveda, L Smeding, R E KnopsAbstract
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