RISE IN CHRONIC DEFIBRILLATION THRESHOLDS IN NONTHORACOTOMY IMPLANTABLE DEFIBRILLATOR

Background To establish the chronic stability of defibrillation thresh olds (DFTs) in a transvenous cardioverter/defibrillator (TCD) system, we studied 37 consecutive patients with TCD systems implanted for >6 m onths. Methods and Results DFT was measured by a step-down method at i mplant and 2 and 6 months later. The mean ejection fraction was 34.5+/ -14.3%. Coronary artery disease with previous myocardial infarction wa s present in 31 patients. The mean DFT rose from 13.3+/-4.3 J at impla nt to 16.5+/-4.7 J at 2 months (P<.001) and 17.6+/-5.4 J at 6 months ( P<.0001). ANOVA revealed a statistically significant rise in DFT over time (P<.0005). At 2 months, 25 patients had a rise in DFT, and 14 had a rise greater than or equal to 5 J. The observed rise at 2 months pe rsisted in 19 patients. A chronic rise, defined as greater than or equ al to 5 J rise at 6 months, occurred in 17 patients. Univariate analys is of clinical as well as implant variables revealed no predictors of a rise in DFT in this group, Conclusions We conclude that there is a s ignificant rise in DFT at 2 and 6 months in this TCD system. Although the chronic threshold remained well within the available energy range of the pulse generator, this observation has important implications fo r implantation guidelines, programming, and future pulse generator dev elopment for TCD patients.