Abstract 12826: Importance of Flexibility in Shock Polarity With Subcutaneous Only Implantable Cardioverter-Defibrillators
Introduction: An entirely subcutaneous ICD (S-ICD) has recently been shown to be effective in treating patients with ventricular tachyarrhythmias. This study explored the clinical utility of incorporating the option of reversing polarity in the programming algorithm.
Methods: From July 2005 to June 2007, 15 patients with a class I indication for a transvenous ICD underwent temporary placement of a subcutaneous defibrillating system to compare defibrillation thresholds using standard and reverse polarity of the S-ICD. After placement of a transvenous device, a temporary pocket was made with an incision down to deep fascia over the 6th L rib in the anterior axillary line. From this incision, a 3mm tripolar electrode with an 8 cm shocking coil was introduced to the base of the sternum and then aligned perpendicularly 1–2cm to the left of the sternal midline. The electrode was connected to an emulator metal can placed in the lateral pocket and the incision closed. A step-up/step-down DFT protocol using a 50% tilt biphasic waveform was used beginning at 40 J. All shocks were delivered following 10 seconds of ventricular fibrillation (VF). Maximum and minimum energies tested were 80J and 10J respectively and at least 5 minutes allowed between shocks. The polarity tested first was selected randomly. Seven patients had standard polarity tested first. The temporary system was explanted after completion of the study.
Results: There were 14 men and 1 woman, mean age 58 (44–74) yrs, mean weight 85 (66–104.5) Kg, normal EF 7 pts, 20–49% 7 pts. Eight pts had ICM, 1 DCM, 3 HCM, 1 each ARVC, Brugada syndrome and no known heart disease. The mean DFT was 35.5J (12.4J-71.6J) delivered energy with standard polarity and 33.1J (8.8–54.8J) with reverse polarity 2p < .003. Efficacy was greater with standard polarity in 8 pts, reverse polarity 6 pts and equal in 1 pt. In 7 pts, one polarity improved DFT > 10J (12 to 59.5J) with DFT improvements of >20 J and >50 J noted in 3 pts and 1 pt, respectively. All patients were successfully defibrillated with a stored energy of ≤ 80J.
Conclusions: Defibrillation at an acceptable energy level was effective with both polarities but there is sufficient individual variation to warrant a polarity switch if the initial shock is unsuccessful for the S-ICD.
- © 2010 by American Heart Association, Inc.