title: Efficacy and temporal stability of reduced safety margins for ventricular defibrillation: primary results from the Low Energy Safety Study (LESS).
abstract: BACKGROUND
  Traditionally, a safety margin of at least 10 J between the maximum output of the pulse generator and the energy needed for ventricular defibrillation has been used because lower safety margins were associated with unacceptably high rates of failed defibrillation and sudden cardiac death. The Low Energy Safety Study (LESS) was a prospective, randomized assessment of the safety margin requirements for modern implantable cardioverter-defibrillator (ICD) systems.
  
  
  RESULTS
  A total of 636 patients undergoing initial ICD implantation with a dual-coil lead and active pulse generator were evaluated. The defibrillation threshold (DFT) and enhanced DFT (DFT+ and DFT++) were measured using a modified step-down protocol. Conversion testing of induced ventricular fibrillation before discharge, at 3 months, and at 12 months was performed, as was randomization to chronic programming at either 2 steps above DFT++ or maximal output. The induced ventricular fibrillation data had conversion success rates of 91.4%, 97.9%, 99.1%, 99.6%, and 99.8% for safety margins of 0, 1, 2, 3, and 4 steps above the DFT++, respectively. A margin of 4 to 6 J was adequate to maintain high conversion success over time (98.9% before discharge versus 99.2% at 12 months; P=NS). Over a mean follow-up of 24+/-13 months, conversion of spontaneously occurring ventricular tachyarrhythmias >200 bpm was identical (97.3%), despite a safety margin difference of 5.2+/-1.1 J for the 2-step group versus 20.8+/-4.2 J for maximal output.
  
  
  CONCLUSIONS
  With a rigorous implantation algorithm, a safety margin of about 5 J is adequate for safe implantation of modern ICD systems.
authors: Medical University of South Carolina, Division of Cardiology, Charleston 29425, USA. Goldmr@musc.edu
authors: Michael R
authors: MR
authors: Gold
authors: Steven
authors: S
authors: Higgins
authors: Richard
authors: R
authors: Klein
authors: F Roosevelt
authors: FR
authors: Gilliam
authors: Harry
authors: H
authors: Kopelman
authors: Scott
authors: S
authors: Hessen
authors: John
authors: J
authors: Payne
authors: S Adam
authors: SA
authors: Strickberger
authors: David
authors: D
authors: Breiter
authors: Stephen
authors: S
authors: Hahn
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007700:Kinetics; D008297:Male; D017180:Tachycardia, Ventricular / Q000628:therapy*; D014693:Ventricular Fibrillation / Q000628:therapy*