Temporal decline in defibrillation thresholds with an active pectoral leadsystem

OBJECTIVES The objective of this study was to characterize temporal changes in defibrillation thresholds (DFT's) after implantation with an active pec toral, dual-coil transvenous lead system. BACKGROUND Ventricular DFTs rise over time when monophasic waveforms are us ed with nonthoracotomy lead systems. This effect is attenuated when biphasi c waveforms are used with transvencus lead systems; however, significant in creases in DFT still occur in a minority of patients. The long-term stabili ty of DFTs with contemporary active pectoral lead systems is unknown. METHODS This study was a prospective assessment of temporal changes in DFT using a uniform testing algorithm, shock polarity and dual-coil active pect oral lead system. Thresholds were measured at implantation, before discharg e and at long-term follow-up (70 +/- 40 weeks) in 50 patients. RESULTS The DFTs were 9.2 +/- 5.4 J at implantation, 8.3 +/- 5.8 J before d ischarge and 6.9 +/- 3.6 J at long term follow-up (p < 0.01 by analysis of- variance; p < 0.05 for long-term follow-up vs. at implantation or before di scharge). The effect was most marked in a prespecified subgroup with high i mplant DFTs (greater than or equal to 15 J). No patient developed an inadeq uate safety margin (<9 J) during follow-up. CONCLUSIONS The DFTs declined significantly after implantation with an acti ve pectoral, dual-coil transvenous lead system, and no clinically significa nt increases in DFT were observed. Therefore, routine defibrillation. testi ng may not be required during the first two, years after implantation with this lead system, in the absence of a change in the cardiac substrate or tr eatment with antiarrhythmic drugs. (C) 2001 by the American College of Card iology.