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(Circulation. 2002;105:2043.)
© 2002 American Heart Association, Inc.

Clinical Investigation and Reports

Efficacy and Temporal Stability of Reduced Safety Margins for Ventricular Defibrillation

Primary Results From the Low Energy Safety Study (LESS)

Michael R. Gold, MD, PhD; Steven Higgins, MD; Richard Klein, MD; F. Roosevelt Gilliam, MD; Harry Kopelman, MD; Scott Hessen, MD; John Payne, MD; S. Adam Strickberger, MD; David Breiter, MS; Stephen Hahn, PhD

From the Medical University of South Carolina, Charleston (M.R.G.); Scripps Memorial Hospital, La Jolla, Calif (S. Higgins); University of Utah, Salt Lake City (R.K.); Chippenham Medical Center, Richmond, Va (F.R.G.); Saint Joseph’s Hospital of Atlanta, Atlanta, Ga (H.K.); Hahnemann University, Philadelphia, Pa (S. Hennen); Baylor College of Medicine, Houston, Tex (J.P.); University of Michigan, Ann Arbor (S.A.S.); and Guidant Corporation, St Paul, Minn (D.B., S. Hahn).

Correspondence to Michael R. Gold, MD, PhD, Medical University of South Carolina, Division of Cardiology, 96 Jonathan Lucas Street, PO Box 250623, Charleston, SC 29425. E-mail Goldmr{at}musc.edu

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.

Methods and 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.

Key Words: defibrillation • tachyarrhythmias • defibrillators, implantable • safety

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