Abstract
There are limited data regarding defibrillation thresholds (DFTs) for the subcutaneous implantable cardioverter-defibrillator (S-ICD), and factors associated with elevated DFTs remain incompletely understood. The objective of this study was to determine the factors associated with elevated DFTs in patients undergoing S-ICD implantation. A retrospective cross-sectional analysis of all patients undergoing S-ICD implantation at our institution between 2013 and 2016 who underwent step-down DFT testing was performed. Factors associated with a higher DFT were analyzed. In total, 56 patients (mean age: 49.3 ± 13.1 years, mean left ventricular ejection rate: 31.1% ± 13.7%) underwent S-ICD implantation in the study period. Full DFT testing was performed in 31 of the 56 patients (55%), with an average DFT of 46.4 joules (J) ± 25.9 J found among this cohort. The DFT was > 65 J in five of the 31 patients (16%). A high DFT was associated with increased body mass index (BMI) (37.7 kg/m2 versus 29.4 kg/m2; p = 0.02) and either increased septal or posterior wall thickness (1.5 cm versus 1.0 cm; p = 0.0003 and 1.4 cm versus 1.1 cm; p= 0.003, respectively). Patients with high DFTs also had higher failed shock impedance values (138 Ω versus 71 Ω; p = 0.005). Renal failure did not appear to affect DFT (51.4 J versus 51.7 J; p = 0.99). BMI, body surface area (BSA), and septal and posterior left ventricular wall thickness predicted elevated DFT on univariate analysis, although findings were not significant with multivariate analysis due to the small sample size. Thus, elevated S-ICD DFT appears to be associated with increased BMI, BSA, and septal or posterior wall thickness. In contrast, dialysis-dependent renal failure is not associated with elevated DFT. Further investigation is necessary in order to better characterize and predict which patients are at-risk for high DFTs.
Highlights
Implantable cardioverter-defibrillators (ICDs) have been shown to improve survival in patients at high-risk for sudden arrhythmic death for more than 30 years.[1]The survival benefits from ICDs stem from their ability to acutely terminate ventricular arrhythmias (VAs) using high-energy shocks
The practice of routine defibrillation thresholds (DFTs) testing at the time of implant has decreased over the years, owing to advancements in ICD technology including improved lead design and higher shock capacity
All patients were considered candidates for the subcutaneous implantable cardioverter-defibrillator (S-ICD) based on a lack of primary pacing indications, concomitant epicardial or unipolar pacing systems, and documented VA that could be terminated with anti-tachycardia pacing (ATP)
Summary
Implantable cardioverter-defibrillators (ICDs) have been shown to improve survival in patients at high-risk for sudden arrhythmic death for more than 30 years.[1]. The survival benefits from ICDs stem from their ability to acutely terminate ventricular arrhythmias (VAs) using high-energy shocks. While shock efficacy remains probabilistic, increased confidence in an ICD’s ability to successfully terminate spontaneous VAs can be established with defibrillation threshold (DFT) testing.[2] The practice of routine DFT testing at the time of implant has decreased over the years, owing to advancements in ICD technology including improved lead design and higher shock capacity. Several recent randomized trials have shown equivalent clinical outcomes with or without DFT testing at the time of initial transvenous ICD implantation across multiple cardiac substrates.[3] These results have led to changes in
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