Provocative Cases -> Teaching Case Reports D-AB16 - Conundrums for Device Implanters (ID 2) Abstract

D-AB16-03 - Undersensing Of Ventricular Fibrillation And Failure To Defibrillate In A Patient With A Subcutaneous Icd Due To Weight Gain - A Big Problem (ID 713)

 B.B. Holmes: Nothing relevant to disclose.


Background: Subcutaneous implantable defibrillators (S-ICDs) are commonly used for prevention of sudden cardiac death. Studies have shown that shock efficacy is associated with system position and an appropriate high-voltage impedance. Inadequate coil position > 3mm from the sternum is associated with a high impedance value and lower rate of defibrillation success.
Objective: We present a case of undersensing of ventricular fibrillation (VF) and failure to defibrillate an individual three years after successful defibrillation testing (DFT) at implantation of an S-ICD.
Results: A 30 year-old man was admitted for shocks from his S-ICD. The device interrogation revealed both undersensing of VF and failure of the device to defibrillate the patient (shock impedance 109 ohms). The device was placed three years prior for secondary prevention following an out-of-hospital cardiac arrest for idiopathic VF. DFT testing at implant was successful with a shock impedance of 50 ohms. The patient’s weight had increased from 194lbs at implant to 247lbs. Imaging demonstrated an increase in adiposity leading to anterior displacement of the coil from the chest wall. No other significant cause for the elevated shock impedance was identified including medications or progressive LV failure. His S-ICD was explanted and a trans-venous system placed.
Conclusion: Significant weight gain in patients with S-ICDs place them at risk for failure to defibrillate due to anterior displacement of the coil. More research is needed to determine if repeat defibrillation threshold testing is necessary in these patients.