1026-87 Long-term Changes in Defibrillation Thresholds Using Two Nonthoracotomy Lead Systems and a Biphasic Waveform

We implanted nonthoracotomy defibrillators in consecutive pts with sustained ventricular arrhythmias. A Ventritex Cadence (V-l00C) device using a bipbasic waveform was implanted in all pts. The first 21 systems (Grp l) consisted of a CPI (BT-1 0) endocardial lead at the RV apex for sensing and pacing, with a CPI(C-l0) spring electrode at the SVC/HRA junction and a large CPI patch (L67) implanted subcutaneously in the left axillary region for defibrillation. A single lead defibrillation system (CPI Endotak C, Model #0064) was implanted in 27 pts (Grp II). Mean age was 61±12 years and LVEF was 37±16%, Three successful shocks for sustained VF were required to define the defibrillation threshold (DFT). Implantation occurred if thresholds were≤650 V Adequate DFTs were initially obtained in all pts. DFTs (Volts) at implantation (IMPL), predischarge (PREDC), 1 month (MO), 6 MO, and 1 year (YR) were:IMPLPREDC1 MO8 MO1 YRN=484842224Group I562±63576±68580±54571±58538±48Group II471±84494±101511±74525±79-There was no significant change in DFT for Grp I, comparing IMPL to PREDC, PREDC to 1 MO, 1 MO to 6 MO, or 6 MO to 1 YR (p=NS). In contrast, there was a significant increase in DFT in Grp II comparing 1M PL to PREDC (p=0.01) and PREDC to 1 MO (p=0.01). There was no significant increase between 1 MO and 6 MO, but the number of pts was small. DFTs at IMPL were significantly lower in Grp II than in Grp I (p=<0.01). DFTs in Grp II increased by 50 V in 7 pts, 100 V in 3 pts, 200 V in 1 pt and 250 V in 1 pt. Two pts in Grp I and 1 pt in Grp II required lead revision before discharge, due to the increase in DFT.ConclusionUnlike a nonthoracotomy patch/lead system, an increase in DFT was noted on follow-up using a single lead Endotak system and device which delivers a biphasic waveform. However, DFTs at IMPL were relatively low using this single lead system and lead revision was rarely required. Because significant increases in DFTs may continue to occur after discharge, close follow-up is recommended