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Background Device impedance for subcutaneous ICDs (S-ICDs) may rise over time reflecting changes in tissue electrical conduction due to fibrosis from the natural foreign body response, increasing the risk of defibrillation failure. A biologic envelope optimized for S-ICDs may mitigate fibrosis and encourages angiogenesis around the device possibly decreasing impedance rise over time. The S-ICD system performs routine low-voltage Z-lead (LVZ) impedance testing (impedance between shocking coil and can) that may provide insight into the impedance changes on device functionality and efficacy over time. Purpose Explore early and late impedance changes over time in S-ICDs implanted with and without envelopes using periodic LVZ measurements. Methods 30 patients received S-ICDs (15 with envelope) between 1/2017 and 3/2021, after excluding those with device complications, uncontrolled comorbidities, or recent cardiac surgery. Impedance data was recorded at initial implantation. LVZ impedance data was extracted from the wireless remote monitoring system, trended over 0–4 years post implant, and analyzed blinded to patient information. Results 24 patients (12 envelope) had evaluable implant and chronic data sets. Baseline clinical characteristics were similar between groups. Impedance in general was higher in the envelope group at initial implantation (LVZ mean 89 Ω vs 74 Ω) and throughout the first year. Comparing envelope to no envelope, the initial average shock impedance was 87.3±30.50 vs 66.7±10.40, followed by an average low-V impedance drop of 29 Ω vs 17 Ω during the first month, with a recovery to 109 Ω vs 91 Ω at 30 months post implant. After 30 months, impedance trends demonstrated a modest linear increase up to 48 months in the no envelope group in comparison with a modest decrease in the envelope group (sample sizes too small to determine significance) (Figure 1). Conclusion The results demonstrate periodic LVZ testing in the S-ICD monitoring system can reliably trend changes in system impedance over time. Impedance measurements within the first 6–7 months (and most markedly within the first 3 months) appear to be transiently lower than the values seen after this timepoint suggesting that early impedance measurements may not predict steady-state impedance. Further studies are needed to explore the impact of envelope use and the S-ICD impedance changes beyond 30 months. Funding Acknowledgement Type of funding sources: None.

Background Microfidelity Cateter Technology has proven efficacy in ablating atrial arrhythmias in multiple pilot studies. Closely spaced radial microelectrodes render a focused near-field electrogram. Case series suggest that this catheter design facilitates accurate ablations with fewer radiofrequency (RF) lesions. Atrioventricular junction (AVJ) ablation is regarded as a straightforward procedure, but case records show wide variance in procedure times and number of RF lesions required. Methods Twenty-four patients scheduled for AVJ ablation were randomized to treatment with either the Microfidelity technology or standard 8mm/8 French ablation catheter. Both groups located the AVJ by fluoroscopic landmarks and His electrograms, and the MiFi group used electroanatomical mapping to create the location of his electrograms. The primary endpoints were development of Junctional Rhythm (JR) or Complete Heart Block (CHB), and time from first RF lesion until rhythm change. Secondary endpoints included number of RF applications. Results Patients were randomized one-to-one to the MiFi arm or standard ablation arm. JR or CHB was achieved in all patients. Time from first RF lesion until JR/CHB was: (Median/IQR) 325 sec/250–1270 sec. vs 287 sec/101–406 sec. Number of RF applications was 5/3–15 applications vs 4.5/1–5 applications. Total procedure time in the lab was 134 min/73.5–172.5 min vs 58 min/52–146 min. Microfidelity Technology vs Standard Conclusion Analysis suggests that the MiFi catheter is efficacious in ablating the AVJ, but requires greater RF duration and number of lesions, with wider case-by-case variability to achieve JR or CHB. Microfidelity technology and electroanatomical mapping did not result in faster time to completion than using fluoroscopic landmarks and His electrograms alone. Preoperative choice of sheath for catheter stability and contact may also play a role in a more efficient timely successful ablation of the AV node. Acknowledgement/Funding Boston Scientific