Published Online
on April 15, 2002

A more recent version of this article appeared on April 30, 2002

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Submitted on November 12, 2001
Revised on February 22, 2002
Accepted on February 22, 2002

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, and 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. Hessen); 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).

^* To whom correspondence should be addressed. 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 in all 392 patients, as was randomization to chronic programming at either 2 steps above DFT++ or maximal output in all patients. 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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