Predictors of Elevated Defibrillation Threshold with the Subcutaneous Implantable Cardioverter-defibrillator

Abstract

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 4 65 J in five of the 31 patients (16%). A high DFT was associated with increased body mass index (BMI) (37.7 kg/m 2 versus 29.4 kg/m 2 ; p ¼ 0.02) and either increased septal or posterior wall thickness (1.5 cm versus 1.0 cm; p ¼ 0.0003 and 1.4 cm versus 1.1 cm; p ¼ 0.003, respectively). Patients with high DFTs also had higher failed shock impedance values (138 O versus 71 O; p ¼ 0.005). Renal failure did not appear to affect DFT (51.4 J versus 51.7 J; p ¼ 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.

Successful defibrillation verification in subcutaneous implantable cardioverter‐defibrillator recipients by low‐energy shocks

“…Moreover, we did not confirm the previously reported association between left ventricle wall thickness and defibrillation success 12 : our study is indeed more powered to assess the role of hypertrophy, because 33% of our patients had hypertrophic cardiomyopathy (the six with wall thickness in the 30-41 mm range had successful VF termination with ≤30 J), and the mean wall thickness of the whole population was 16 ± 8 mm, well above other literature reports. [3][4][5][6][7][8]12,13 As described by Friedman et al, 13 severely decreased ejection fraction was associated to a lower defibrillation safety margin also in our experience. However, defibrillation was successful at low shock energies even in patients with ejection fraction ≤35% in intermuscular implants, failure at ≤40 J being more common in the setting of a subcutaneous device placement.…”

“…A thinner body habit enables to place both the subcutaneous coil and the generator directly over the fascia without underlying fat tissue, thus resulting in lowered energy requirement to terminate VF. Moreover, we did not confirm the previously reported association between left ventricle wall thickness and defibrillation success: our study is indeed more powered to assess the role of hypertrophy, because 33% of our patients had hypertrophic cardiomyopathy (the six with wall thickness in the 30‐41 mm range had successful VF termination with ≤30 J), and the mean wall thickness of the whole population was 16 ± 8 mm, well above other literature reports . As described by Friedman et al, severely decreased ejection fraction was associated to a lower defibrillation safety margin also in our experience.…”

“…Similarly, Friedman et al found an association between increased body mass and lower defibrillation safety margin among S‐ICD recipients. In our study, the average BMI was 26 ± 5Kg/m 2 , quite different from the value of 31 ± 7 kg/m 2 in the population described by Do et al and from the 29 ± 7 kg/m 2 reported by Friedman et al . Nonetheless, we confirmed the association between high BMI and defibrillation test failure (Table ).…”

Single incision technique for implantation of subcutaneous implantable cardioverter defibrillators

“…This patient had several features characteristic of patients known to have high DFT, including young age, male gender, severely dilated left ventricle, and nonischemic cardiomyopathy . Furthermore, high BMI has been shown to be a predictor of failed DFT testing in patients implanted with S‐ICD . His device was subsequently extracted without incident and a conventional left prepectoral transvenous ICD was implanted.…”

“…Although the procedural duration was longer compared to the conventional technique, this is still a very early experience with the procedure. As with any newly introduced technique, there is a learning curve that needs to be overcome after which the procedure duration is expected to decrease to that like other implantation techniques of S‐ICD …”