Abstract 14961: Predictors of an Insufficient Defibrillation Testing Safety Margin Among Patients Implanted With a Subcutaneous Implantable Cardioverter Defibrillator: A Report From the National Cardiovascular Data Registry

Introduction: Compared to tranvenous (TV) implantable cardioverter defibrillators (ICD), subcutaneous (S) ICDs require a higher energy for effective defibrillation due to an entirely subcutaneous defibrillation coil and a different shock vector. A defibrillation safety margin is the difference between the defibrillation threshold (DFT) and the maximum ICD output. Although predictors of insufficient safety margin (ISM) at the time of DFT testing have been established for TV-ICDs, little is known about predictors of ISM among SICDs. Hypothesis: We hypothesized that patient characteristics could predict ISM among SICD patients. Methods: We studied first time SICD recipients (September 28, 2012 through April 1, 2016) who underwent DFT testing and were reported to the National Cardiovascular Database Registry ICD Registry. Multivariable logistic regression was used to examine the association between baseline characteristics and an ISM (DFT>65J); a risk score was created by weighting β-coefficients. Results: Of the 4,864 patients who met study criteria, 336 (6.9%) were found to have an ISM; 2 patients required a separate procedure to address the ISM. The adjusted model (AUC = 0.679) demonstrated ISM was more common among patients with: white race, ventricular pacing on the preimplant ECG, increased blood pressure, increased body surface area, increased body mass index, and decreased ejection fraction. Prior coronary artery bypass grafting was associated with a lower likelihood of ISM. There was no association between ISM and age, sex, NYHA class, primary vs. secondary prevention indication, hypertrophic cardiomyopathy, or dialysis status. A risk score was able to identify patients at low ( 10% for scores ≥17) for ISM ( Figure ). Conclusions: Baseline characteristics can predict ISM among SICD patients and could be considered when selecting an ICD system or applying a targeted approach to DFT testing.