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Background: The Subcutaneous Implantable Cardioverter Defibrillator (S-ICD) is indicated for patients who have a standard indication for a transvenous implantable cardioverter defibrillator (T-ICD) without the need for cardiac pacing. While recent literature questions the utility of defibrillation threshold testing (DFT) in T-ICDs, there are no evidence-based guidelines for DFT testing at the time of S-ICD implant. Additionally, management of DFT failure in S-ICD patients is not described.
Methods: We reviewed our database of S-ICD implants at our center from November 2012 through October 2016. Additional demographics were obtained from inpatient records.
Results: Our center had 124 S-ICD implants. Of those, 104 standard-polarity 65 Joule (J) DFT tests were performed. 93 DFT tests were successful in converting ventricular fibrillation during the first attempt and 11 were not. The shock impedance for successful DFTs was 74.6 Ohms (+/-25.5) compared to unsuccessful DFT shock impedance of 103.6 Ohms (+/-11.8) (P=0.001). Patients with unsuccessful DFTs had increased body weight compared to patients with successful DFTs (106 kg +/- 18 vs 87.3 kg +/- 21.5, p= 0.02) Patients who failed the initial 65J DFT had successful DFTs with reversing shock polarity (2), increasing Joules for the subsequent test with standard (2) and reversed polarity (1), repositioning the pulse generator (PG) (2), or repositioning the lead more directly over the sternum (1). 1 patient was unable to convert with PG repositioning and an 80 J test but on a subsequent day had a successful DFT at 80J.
Conclusions: Higher shock impedance and higher patient body weight are associated with failure of standard 65J DFT testing. We believe this is related to the lead being positioned in the adipose tissue above the sternum and not directly overlying the sternum or the pulse generator being positioned in the adipose and not adjacent to latissimus dorsi fascia. Elevated DFTs can almost always be managed by PG or lead repositioning. Additional approaches of shock polarity reversal can also be considered.
Poster Hall, Hall C
Friday, March 17, 2017, 10:00 a.m.-10:45 a.m.
Session Title: Arrhythmias and Clinical EP: Devices 1
Abstract Category: 5. Arrhythmias and Clinical EP: Devices
Presentation Number: 1109-083
- 2017 American College of Cardiology Foundation