CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Roderick Tung, MD*
* UCLA Medical Center, Arrhythmia Center, 10833 Le Conte Avenue, BH 307 CHS, Los Angeles, California 90095 (Email: rtung{at}mednet.ucla.edu).
We thank Dr. Stamato for his interest in our paper (1) and we echo his sentiments. We also appreciate the accompanying editorial by Epstein (2), which provided counterbalancing insights into this important issue. As electrophysiologists, we all share the common goal of optimizing and refining our current method of selecting at-risk patients who are most likely to benefit and least likely to suffer harm from implantable cardioverter-defibrillator (ICD) therapy. At present, our updated guidelines are indeed based on the best available evidence, although it is imperative that we keep these data in perspective. Our assertion regarding disparate low rates of beta blockade in the landmark trials was merely to illustrate that the net clinical benefit may have been amplified, but not to suggest that the entire benefit of ICD can be accounted for by beta-blocker inequity.
There are at least 2 degrees of separation that contribute to the difficulty in generalizing and applying ICD clinical trial data into the real world. First, there is the discordance between the inclusion criteria of a study and the actual population that is enrolled. As an example, the average enrolled ejection fraction is almost 10% less than the enrollment cutoff, although published guidelines are strictly based on inclusion criteria. This point is nicely reiterated by Myerburg (3) in his recent review on defibrillator usage after myocardial infarction.
Second, there comes the discrepancy between the actual enrolled population and the patient characteristics seen in the real world, thereby amplifying this generalizability gap. As Dr. Stamato points out, patients with noncardiac comorbidities, including advanced age, diabetes mellitus, peripheral vascular disease, renal disease, and pulmonary disease, tend to be under-represented in clinical trials. The potential futility of ICD efficacy in patients with chronic and end-stage renal disease has been suggested by multiple retrospective cohort analyses (4–8). Indeed, there exists a discrepancy in the real world between eligibility and implantation rates (9). Dr. Stamato may be correct in asserting that practicing physicians do factor in this generalizability gap by favoring sound clinical judgment over the implementation of broad guidelines.
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References
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1. Tung R, Zimetbaum P, Josephson ME. A critical appraisal of implantable cardioverter-defibrillator therapy for the prevention of sudden cardiac death J Am Coll Cardiol 2008;52:1111-1121.[Abstract/Free Full Text]2. Epstein AE. Benefits of the implantable-cardioverter defibrillator J Am Coll Cardiol 2008;52:1122-1127.[Abstract/Free Full Text] 3. Myerburg RJ. Implantable cardioverter-defibrillators after myocardial infarction N Engl J Med 2008;359:2245-2253.[Free Full Text] 4. Bruch C, Bruch C, Sindermann J, Breithardt G, Gradaus R. Prevalence and prognostic impact of comorbidities in heart failure patients with implantable cardioverter defibrillator Europace 2007;9:681-686.[Abstract/Free Full Text] 5. Lee DS, Tu JV, Austin PC, et al. Effect of cardiac and noncardiac conditions on survival after defibrillator implantation J Am Coll Cardiol 2007;49:2408-2415.[Abstract/Free Full Text] 6. Dasgupta A, Montalvo J, Medendorp S, et al. Increased complication rates of cardiac rhythm management devices in ESRD patients Am J Kidney Dis 2007;49:656-663.[CrossRef][Web of Science][Medline] 7. Hreybe H, Razak E, Saba S. Effect of end-stage renal failure and hemodialysis on mortality rates in implantable cardioverter-defibrillator recipients Pacing Clin Electrophysiol 2007;30:1091-1095.[CrossRef][Medline] 8. Cuculich PS, Sanchez JM, Kerzner R, et al. Poor prognosis for patients with chronic kidney disease despite ICD therapy for the primary prevention of sudden death Pacing Clin Electrophysiol 2007;30:207-213.[CrossRef][Medline] 9. Hernandez AF, Fonarow GC, Liang L, et al. Sex and racial differences in the use of implantable cardioverter-defibrillators among patients hospitalized with heart failure JAMA 2007;298:1525-1532.[Abstract/Free Full Text]
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