In Reply We thank Wase et al for their interest in our article¹ and comments regarding chronic kidney disease and the use of defibrillation threshold (DFT) testing among subcutaneous implantable cardioverter defibrillator (S-ICD) recipients. Wase et al raised concerns about our finding of underuse of DFT testing among all patients with S-ICDs and emphasized that the class I recommendation for DFT testing after S-ICD implantation should be strictly followed, citing increased DFTs^2,3 and arrhythmic death³ among patients with chronic kidney disease receiving transvenous ICDs.

The class I recommendation for the use of DFT testing in all patients with S-ICD is notable for being based solely on the absence of data demonstrating it is safe to forgo DFT testing.⁴ This is in contrast to transvenous ICD testing,⁴ where there is strong evidence that compulsory DFT testing is not necessary for all patients.⁵ Based on our findings that 92.7% of S-ICD recipients had a sufficient safety margin (≤65 J) and 99.7% of S-ICD recipients could be defibrillated at the maximum device output (≤80 J) during DFT testing, it is likely that the field and guidelines will move toward a more targeted approach to DFT testing with time and additional data. Given the differences in electrode position and electrical field during defibrillation with the S-ICD compared with the transvenous ICD, it is unclear if risk factors for increased DFTs in patients with transvenous ICDs (eg, those with chronic kidney disease^2,3) are similar to those for patients with S-ICDs. Finally, it is not clear if, as the authors suggest, DFT testing may meaningfully reduce the risk of sudden death among dialysis-dependent ICD recipients, who may be at a substantial risk for sudden death due to asystole and pulseless electrical activity.