1026-88 Rise In Chronic Defibrillation Threshold Necessitating Defibrillator Lead System Revision

At least a 10J defibrillation safety margin is usually required for implantation of a defibrillator (ICD). While the defibrillation threshold (DFT) with a nonthoracotomy lead (NTL) system is known to rise during the initial 6 months following implantation, revision of the defibrillation system previously has not been reported. For epicardial lead systems, the DFT is thought to be stable.Six patients (pt) were identified with a rise in their chronic DFT resulting in a loss of a 10J DFT safety margin necessitating revision of the lead system. The mean age was 64±10 and 5 pts were men. Four pts had an ischemic and 2 had a nonischemic cardiomyopathy. Two pts had epicardial and 4 pts had NTL systems and each ICD generator delivered monophasic waveform shocks. The acute DFT was determined by a step-down protocol in 5 pts. For these pts, the mean acute DFT was 17.5±3.9J. Elevated DFT's were observed in 4 pts with NTL's during a 2 month post-ICD implantation evaluation of the DFT (2.8±1 month), and in 2 pts with epicardial leads at replacement of the ICD generator for end-of-life battery status (at 36 and 41 months). The chronic DFT was determined by a step-down protocol and was 31.4±3.8J. The integrity of the lead system was evaluated and was intact for each pt.A 10J defibrillation safety margin was achieved in each pt by either placing an additional defibrillating electrode (n=2). placing an ICD with biphasic shocks (n=2), or a combination of these two (n=1). In the 2 pts with epicardial leads, one was managed with placement of a biphasic ICD and the other required placement of a transvenous defibrillating electrode and a biphasic ICD. In the 4 pts with NTL's, 1 required a biphasic lCD, 2 required the addition of epicardial patches and 1 pt refused ICD revision. The mean DFT was 17.0±6.8J acutely after lead revision and, 2 months later, the mean DFT was 16.8±7.5J.This is the first report describing a rise in the chronic DFT-eliminating a 10J DFT safety margin necessitating ICD lead revision for both epicardial and NTL systems. This anecdotal report suggests that routine reevaluation of the chronic DFT is necessary. When loss of the 10J safety margin is demonstrated, management is directed at obtaining an adequate defibrillation safety margin by revising either the lead configuration or the defibrillation waveform