To the Editor - Response

Abstract

We appreciate Dr. Wase’s thoughtful comments on our article in the September 2006 issue of Heart Rhythm.1 Mainigi S.K. Cooper J.M. Russo A.M. Nayak H.M. Lin D. Dixit S. Gerstenfeld E.P. Hsia H.H. Callans D.J. Marchlinski F.E. Verdino R.J. Elevated defibrillation thresholds in patients undergoing biventricular defibrillator implantation: incidence and predictors. Heart Rhythm. 2006; 3: 1010-1016 Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar As reported in our article, implanters in our retrospective investigation used a defibrillation efficacy strategy in which patients who did not respond to defibrillation ≥10 J below the maximum output of the device were defined as having an elevated defibrillation threshold (DFT). This technique has been shown to predict implantable cardioverter-defibrillator (ICD) success to a high degree 2 DeGroot P. DeSouza C.M. Wang W.X. Is testing defibrillation efficacy during defibrillation implant worth it?. Pacing Clin Electrophysiol. 1999; 22: 723 Google Scholar and is a clinically more efficient testing method, albeit one that does not define the precise DFT. We disagree with the criticism that this strategy would lead to erroneously high DFTs among patients. A patient with a 35-J device who had two successful shocks at 25 J was categorized in our study as not having an elevated DFT. However, a similar patient who failed at 25 J but subsequently was successful between 26 and 35 J would have been included in the elevated DFT group. Although it is true that the actual DFT might well be lower than 25 J, we did not assess DFT as a continuous variable but rather one with a binary value—elevated or not elevated. Thus, only patients with a safety margin <10 J were categorized as having high DFT, and such patients would be equally identified with either a DFT or a defibrillation efficacy strategy. This 10-J safety margin was chosen because of its common acceptance in clinical practice and its support from early evaluation. 3 Marchlinski F.E. Flores B. Miller J.M. Gottlieb C.D. Hargrove 3rd, W.C. Relation of the intraoperative defibrillation threshold to successful postoperative defibrillation with an automatic implantable cardioverter defibrillator. Am J Cardiol. 1988; 62: 393-398 Abstract Full Text PDF PubMed Scopus (112) Google Scholar A significantly more rigorous DFT testing strategy would not have more accurately defined patients with DFT <10 J below the maximum output of the device. Elevated Defibrillation Thresholds With Biventricular PacingHeart RhythmVol. 4Issue 2PreviewIn an article published in the September 2006 issue of Heart Rhythm, Mainigi et al1 address an important issue of elevated defibrillation thresholds (DFTs) among recipients of a biventricular implantable cardioverter-defibrillator (ICD). However, the study design had some serious flaws, as acknowledged by the authors. Full-Text PDF