Background: Compared to the transvenous implantable cardioverter defibrillator (ICD), the subcutaneous (S) ICD has a unique shock vector and higher defibrillation energy requirement. In the absence of data suggesting it is safe to forgo defibrillation threshold (DT) testing after S-ICD implant, performing DT testing at the time of S-ICD implant was made a Class I (level of evidence C) recommendation. Recent data have demonstrated declining performance of DT testing during S-ICD implant.
Methods: We studied first time S-ICD implants (between September 28, 2012 and April 1, 2016) reported to the National Cardiovascular Database Registry ICD Registry to assess the relative association between patient and facility level factors and performance of DT testing. We employed multivariable logistic regression for patient level modeling. Generalized linear mixed models (GLMM) and hospital specific median odds ratios (HSMOR) were used to understand facility effects.
Results: Of the 6,956 S-ICD patients who met study criteria, 4,913 (70.6%) underwent DT testing. Deferral of DT testing was associated with several patient characteristics (Table), including increased body mass index, increased body surface area, severely reduced ejection fraction, dialysis dependence, warfarin use, and anemia. DT testing was more common in patients with prior coronary artery bypass grafting, hypertrophic cardiomyopathy, and implant at a public hospital. The AUC for the GLMM was substantially greater than the patient level model (0.877 vs. 0.619) and the HSMOR was 5.16, demonstrating facility preference is a major determinant of DT testing.
Conclusions: Although deferral of DT testing after S-ICD implant is associated with several patient characteristics suggesting the patterns of performing this test are influenced by clinical factors, non-patient factors (e.g. hospital characteristics and preferences) are strongly associated with performance of DT testing.