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(Circulation. 2002;106:233.)
© 2002 American Heart Association, Inc.

Clinical Investigation and Reports

Effect of Implantable Defibrillators on Arrhythmic Events and Mortality in the Multicenter Unsustained Tachycardia Trial

Kerry L. Lee, PhD; Gail Hafley, MS; John D. Fisher, MD; Michael R. Gold, MD; Eric N. Prystowsky, MD; Mario Talajic, MD; Mark E. Josephson, MD; Douglas L. Packer, MD; Alfred E. Buxton, MD, for the Multicenter Unsustained Tachycardia Trial Investigators

From Duke Clinical Research Institute and Duke University School of Medicine, Durham, NC (K.L.L., G.H.); Montefiore Medical Center and Albert Einstein School of Medicine, Bronx, NY (J.D.F.); University of Maryland School of Medicine, Baltimore, Md (M.R.G.); Northside Cardiology, Indianapolis, Ind (E.N.P.); Montreal Heart Institute, Montreal, Quebec, Canada (M.T.); Beth Israel Deaconess Medical Center, Boston, Mass (M.E.J.); Mayo Clinic, Rochester, Minn (D.L.P.); and Brown Medical School and Rhode Island Hospital, Providence, RI (A.E.B.).

Correspondence and reprint requests to Kerry L. Lee, PhD, Department of Biostatistics and Bioinformatics, Duke University Medical Center, Duke Clinical Research Institute, 2400 Pratt St, Durham, NC 27705. E-mail Kerry.Lee{at}duke.edu

Background— The Multicenter Unsustained Tachycardia Trial (MUSTT) was designed to evaluate an antiarrhythmic treatment strategy, including drugs and implantable defibrillators (ICDs), guided by electrophysiological (EP) testing. We performed several statistical analyses to assess the contribution of defibrillators to the observed treatment benefit.

Methods and Results— First, the effects of defibrillators were indirectly examined by comparing the randomized treatment arms (EP-guided therapy versus no antiarrhythmic therapy) within subgroups that varied according to ICD usage. Use of ICDs increased during the trial; hence, the randomized treatments were compared according to date of enrollment. There were also site-specific differences in ICD use; hence, the randomized arms were compared within groups of sites defined by level of ICD use. There was a distinct "dose response" in relation to ICD use. Where ICD use was high, EP-guided therapy produced significant reductions in arrhythmic death or cardiac arrest (P<0.004). Where ICD use was low, there was no benefit of EP-guided therapy. Finally, outcomes of EP-guided therapy patients who received an ICD were directly compared with outcomes of other patients using the Cox proportional hazards model with receipt of an ICD as a time-dependent covariate. Adjusted for other prognostic factors, patients who received an ICD had risk reductions of >70% in arrhythmic death or cardiac arrest and >50% in total mortality (P<0.001 for both end points).

Conclusions— The benefit of EP-guided antiarrhythmic therapy observed in MUSTT was due to improved outcomes among patients who received an ICD but not among patients who received antiarrhythmic drugs.

Key Words: statistics • defibrillation • electrophysiology • antiarrhythmia agents • tachyarrhythmias

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