CE-454611-1 ISOLATED HIGH SHOCK IMPEDANCE DUE TO CALCIFIED POCKET AND THE MANAGEMENT

Abstract

Impedance is the ratio of voltage to current in an electrical circuit. The most common causes of high shock impedance are lead conductor fracture and lead calcification often associated with lead malfunction. We present the first two cases of isolated high shock impedance from pocket calcification in which the lead function is normal. Case 1: A 73-year-old male with ICM, EF 10%, LBBB, sever COPD and Boston biventricular (BiV) ICD in 2013 that normalized EF. Shock impedance slowly rose from 70 Ω to 122 Ω in 2019 and 189 Ω in 2021. Lead extraction with a new system was considered at the time for generator exchange; however, the patient declined. The pocket was severely calcified, with normal defibrillator lead pacing parameters (pace impedance 796 Ω, pace threshold 0.8 V @ 0.4 msec). The calcium shell was removed (Figure 1A), and the shock impedance dropped to 146 Ω, and remained 137 Ω in one year follow up. Case 2: A 65-year-old female with NICM, EF 20%, LBBB, and Boston BiV ICD in 2013 that normalized QRS (Figure 1B). Shock impedance slowly rose from 65 Ω to 138 Ω (2019) and 165 Ω (2022). At the time of generator exchange, the pocket was heavily calcified. Defibrillator lead pacing parameters were normal (pace impedance 868 Ω, pace threshold 0.6 V @ 0.4 msec). After pocket decalcification, shock impedance reduced to 128 Ω. At one month follow up, shock impedance was stable at 130 Ω. N/A High shock impedance is a result of increased impedance in the circuit which includes the can. Lead fracture or calcification will alter lead function as well as shock impedance. This is managed by extraction. In contrast, pocket calcification, which only increases shock impedance, and can be easily managed by pocket decalcification. In both cases, patients benefited greatly from keeping their functional device and avoiding lead exchange. Lead fracture often results in abrupt increase in shock impedance. Calcification at the lead tip or at the pocket causes slow impedance rise. Unipolar and bipolar pacing impedance can also be used to localize the area of calcification. Normal bipolar pacing impedance and slow isolated high shock impedance should raise the suspicion of pocket calcification. Our cases highlight the importance of recognizing pocket calcification in the context of high shock impedance. Calcium removal at the pocket significantly reduces shock impedance. This management strategy can help to avoid lead extraction, a potentially high-risk operation.