PO-04-084 LOW SHOCK IMPEDANCE OF SUBCUTANEOUS IMPLANTABLE CARDIAC DEFIBRILLATOR (S-ICD) IN THE SETTING OF ACUTE DECOMPENSATED HEART FAILURE

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Shock impedance represents the resistance between the coil and generator of subcutaneous ICDs. It is an important metric to predict device defibrillation success. Several factors have been implicated in determining system impedance of S-ICDs such as generator-lead distance, body habitus as well as generator position (subcutaneous vs. intermuscular pocket). We present a case report highlighting the impact of volume status on shock impedance. N/A A 60-year-old female presents to the office. She has a past medical history of obesity, Heart Failure with Preserved Ejection Fraction (HFpEF), ventricular fibrillation followed by implantation of transvenous ICD. This was complicated by device infection requiring device extraction and implantation of S-ICD. She has been having progressive shortness of breath with minimal exertion weeks prior to presentation. She denied chest pain, palpitations or dizziness but endorsed generalized fatigue as well as significant weight gain. She usually weighs around 165-170 lbs, but was 220 lbs on presentation. Her physical exam was remarkable for elevated jugular venous pressure, anasarca with crackles in the lung bases as well as abdominal ascites and lower extremity edema. Interrogation of her device was performed which showed no significant arrythmias. However, device detected low system impedance of <30 ohms. Her previous interrogation about 3 months earlier showed impedance of 50 Ohms. She was admitted for inpatient intravenous diuresis. Chest radiograph demonstrated normal position of the generator in the posterolateral chest wall and normal lead position in the parasternal area. Serial device interrogations were performed during the hospitalization showing gradual improvement in system impedance up to 45 Ohms once euvolemia was achieved (Figure 1). Due to improvement in shock impedance with diuresis, defibrillation threshold testing (DFT) was deferred and patient was discharged home in stable condition. Her repeat interrogation at follow up showed an impedance of 60 ohms. In the setting of heart failure exacerbation, excess fluid accumulation in the chest and abdominal cavities may result in a decrease in S-ICD shock impedance. Interpretation of device impedance should factor in patient’s volume status. Further studies are needed to ascertain if low impedance caused by fluid overload can impact device defibrillation success rate.