Defibrillation threshold in elective subcutaneous implantable defibrillator generator replacements: Time to reduce the size of the pulse generator?

INTRODUCTION: The first step-down defibrillation studies in the subcutaneous implantable cardioverter-defibrillator (S-ICD) described a defibrillation threshold (DFT) of 32.5 ± 17.0 J and 36.6 ± 19.8 J. Therefore, the default shock output of the S-ICD was set at 80 J. In de novo implants, the DFT is lower in optimally positioned S-ICDs. However, a retrospective analysis raised concerns about a high DFT in S-ICD replacements, possibly related to fibrosis. OBJECTIVE: We aimed to find the DFT in patients undergoing S-ICD generator replacement. METHODS: This prospective study enrolled patients who underwent S-ICD generator replacement with subsequent defibrillation testing. A pre-specified defibrillation testing protocol was used to determine the DFT, defined as the lowest shock output that effectively terminated the induced ventricular arrhythmia. RESULTS: A total of 45 patients were enrolled, 6.0 ± 2.1 years after initial implant. Mean DFT during replacement in the total cohort was 27.4 ± 14.3 J. In patients with a body mass index (BMI) 18.5-25 kg/m2 (N = 22, BMI 22.5 ± 1.6), median DFT was 20 J (IQR 17.5-30). In 18/22 patients, the DFT was ≤30 J and 5/22 patients were successfully defibrillated at 10 J. One patient with hypertrophic cardiomyopathy had a DFT of 65 J. In patients with a BMI >25 kg/m2 (N = 23, BMI 29.5 ± 4.2), median DFT was 30 J (IQR 20-40). In 15/23 patients, the DFT was ≤30 J and 4/23 patients had a successful defibrillation test at 10 J. CONCLUSIONS: This study eases concerns about a high DFT after S-ICD generator replacement. The majority of patients had a DFT ≤30 J, regardless of BMI, suggesting that the shock output of the S-ICD could be safely reduced.

Left cardiac sympathetic denervation in the Netherlands for the treatment of inherited arrhythmia syndromes.

INTRODUCTION: Treating therapy-resistant patients with inherited arrhythmia syndromes can be difficult and left cardiac sympathetic denervation (LCSD) might be a viable alternative treatment option. We provide an overview of the indications and outcomes of LCSD in patients with inherited arrhythmia syndromes in the only tertiary referral centre in the Netherlands where LCSD is conducted in these patients. METHODS: This was a retrospective study, including all patients with inherited arrhythmia syndromes who underwent LCSD in our institution between 2005 and 2013. LCSD involved ablation of the lower part of the left stellate ganglion and the first four thoracic ganglia. RESULTS: Seventeen patients, 12 long-QT syndrome (LQTS) patients (71 %) and 5 catecholaminergic polymorphic ventricular tachycardia (CPVT) patients (29 %), underwent LCSD. Most patients (94 %) were referred because of therapy-refractory cardiac events. In 87 % the annual cardiac event rate decreased. However, after 2 years the probability of complete cardiac event-free survival was 59 % in LQTS and 60 % in CPVT patients. Two patients (12 %) had major non-reversible LCSD-related complications: one patient suffered from a Harlequin face post-procedure and one severely affected LQT8 patient died the day after LCSD due to complications secondary to an arrhythmic storm during the procedure. CONCLUSION: LSCD for inherited arrhythmia syndromes, which is applied on a relatively small scale in the Netherlands, reduced the cardiac event rate in 87 % of the high-risk patients who had therapy-refractory cardiac events, while the rate of major complications was low. Therefore, LSCD seems a viable treatment for patients with inherited arrhythmia syndromes without other options for therapy.