Value of defibrillation threshold testing in children with nontransvenous implantable cardioverter defibrillators: Are routine DFT tests indicated?

Background: Nontransvenous implanted cardioverter defibrillators (NT-ICD) are used in infants and small children with life-threatening ventricular tachyarrhythmias. With growth, shock vector shift may result in increase of defibrillation threshold (DFT) and fatal ICD failure.

Objectives: To date, the only way to verify ICD function in children with NT-ICD is repetitive DFT testing, which is potentially harmful and may even be life threatening. The aim of the study was to analyze data from NT-ICD DFT testing to prospectively predict individual DFT.

Patients And Methods: Data from all pediatric patients with NT-ICD implanted in our center from July 2004 to August 2019 were collected. Postoperative DFT testing was scheduled according to individual DFT but at least annually. Surgical revision of NT-ICD was performed if DFT was > 25 J. Selected noninvasive parameters from DFT testing were analyzed as predictors for DFT using a logistic regression model.

Results: A total of 46 children with NT-ICD underwent a total of 402 DFT tests. Mean age at implantation had been 5.4 ± 3.3 years, mean follow-up was 5.6 ± 3.7 years in 5 (1%) DFT testing, maximum device output failed, and external defibrillation was necessary. A retrospective multiple mixed logistic regression model was able to predict a DFT ≥25 J (area under the curve [AUC] = 0.836). However, when prospectively validated the model showed moderate performance only (AUC = 0.70).

Conclusion: A significant number of NT-ICD failures were detected by serial DFT testing. Serial DFT testing was safe in pediatric patients with an NT-ICD as all induced arrhythmia could be terminated. Prediction of DFT with noninvasive markers remains difficult and might help to schedule intervals for routine DFT tests to avoid unnecessary tests.