While this analogy is perhaps somewhat harsh, it expresses the low opinion held by many physicians concerning the technique of metanalysis. Others view the metanalysis as a practitioner's “wild card”—if the results of the metanalysis support your position on some question, it was a “carefully done, well-conducted metanalysis.” If, on the other hand, its major conclusions are at odds with your position, the response is, “well, it was just a metanalysis.” The purpose of the metanalysis is to pool the data from several relatively small studies that may individually lack adequate subject numbers to show statistical significance, in order to discern if questions posed in the small studies can be more firmly answered, with greater statistical power.
The metanalysis regarding catheter ablation of atrial fibrillation (AF) by Nair et al. in this issue of the Journal 1 will likely share the fate of former metanalyses (extolled by some, derided by others). However, given the material with which they had to work, the authors did as good an analysis as the data would permit. The usual impediments to this type of review (differences in study design, patient cohorts, endpoints) are perhaps amplified in the AF population because of the different presentations of AF as well as the great variety of ablation procedures performed and lack of consistent outcome measures. The authors acknowledge these shortcomings in their article. One of the most striking features of the article is their finding that, after an exhaustive search of the literature, only six studies fulfilled their appropriately stringent inclusion criteria—encompassing all of 693 patients (despite the fact that thousands of patients undergo these procedures annually). Although their analysis revealed that ablation does confer benefit and the studies were consistent in this result, it is a sad commentary on our field that so little objective data are available to support such a frequently performed procedure. In addition, real-world results may not be as good as those found in Nair et al.'s analysis, since among the studies they surveyed, the ablation procedures were performed at relatively high-volume institutions by talented and seasoned practitioners.
The fact that a metanalysis concerning catheter ablation for atrial fibrillation (AF) is even relevant should be concerning to those of us who perform these procedures, since it indicates that there are no large-scale clinical trials showing that what we are doing offers better results than medical therapy. Seasoned practitioners all “know” that catheter ablation ameliorates symptoms in patients with AF (if not “curing” them), but how broadly does this apply, and how certain is the result? For years, based on small studies, we “knew” that serial drug testing was good treatment for ventricular tachycardia, that elimination of premature ventricular complexes in patients with structural heart disease was a worthy goal, and that dual-site atrial pacing prevented AF. While individual patients may have benefited from each of these supposed good therapies, all have gone by the wayside after larger trials showed their shortcomings when applied to larger groups of patients.
Even the best-intended therapies often have unanticipated adverse consequences—one need look no further for examples than AF ablation, with the potential for pulmonary vein stenosis, left atrial-esophageal fistula, phrenic and vagal nerve trunk damage. Thus, we urgently need large scale, well-controlled trials to start addressing just how valuable AF ablation is, especially in certain subsets such as patients with very large left atria and those with minimally symptomatic AF. Cost analysis between separate treatment approaches is another important issue, as raised by the authors. While such large trials cannot address every question about AF ablation, they may provide information that can serve to help generate new hypotheses and questions for further study. One of the most difficult aspects of treating patients with AF is their almost universal desire to discontinue anticoagulant therapy after what appears to be a successful ablation. Although there are some data in the literature that bear on this question,2 it is not definitive and, clearly, further study is needed.
Many physicians who perform AF ablation have longed for a good, solid, multicenter clinical trial that answers once and for all (at least, for the momentary present since the field is changing rapidly) the question of just how much benefit patients receive on their investment in this procedure. After all, it is the patient who assumes the procedural risks, misses work or family duties, and has some monetary exposure—shouldn't they have some assurance that the procedure yields superior results to medical therapy in their situation? For many physicians, the complexities of designing such a trial are just too daunting—what type of patients to enroll, what procedure to use to ablate AF, what procedural and follow-up endpoints (and duration) are needed to give a meaningful answer. Considerable variation in these parameters can often be seen between operators even within the same institution. Certainly these are thorny problems, but we should start somewhere. The Catheter Ablation versus Antiarrhythmic Drug Therapy for Atrial Fibrillation (CABANA) trial,3 comparing catheter ablation to medical therapy with a total mortality primary endpoint, is one such attempt at a large-scale trial in AF ablation and has completed its pilot enrollment; the full-scale trial will hopefully begin enrollment in 2009. We urgently need the results of this and similar long-overdue trials to practice data-driven medicine of the highest quality for the benefit of our patients. Let's not have to rely on metanalysis, no matter how well-done, to justify our current practices.
1. Nair GM, Nery PB, Diwakaramenon S, Healey JS, Connolly SJ, Morillo CA: A systematic review of randomized trials comparing radiofrequency ablation with antiarrhythmic medications in patients with atrial fibrillation. J. Cardiovasc Electrophysiol 2008; DOI: 10.1111/j.1540-8167.2008.01285.x. [Context Link]
2. Oral H, Chugh A, Ozaydin M, Good E, Fortino J, Sankaran S, Reich S, Igic P, Elmouchi D, Tschopp D, Wimmer A, Dey S, Crawford T, Pelosi F Jr, Jongnarangsin K, Bogun F, Morady F: Risk of thromboembolic events after percutaneous left atrial radiofrequency ablation of atrial fibrillation. Circulation 2006;114:759–765. Ovid Full Text Bibliographic Links [Context Link]
3. Calkins H, Brugada J, Packer DL, Cappato R, Chen SA, Crijns HJ, Damiano RJ, Davies DW, Haines DE, Haissaguerre M, Iesaka Y, Jackman W, Jais P, Kottkamp H, Kuck KH, Lindsay BD, Marchlinski FE, McCarthy PM, Mont JL, Morady F, Nademanee K, Natale A, Pappone C, Prystowsky E, Raviele A, Ruskin JN, Shemin RJ: HRS/EHRA/ECAS expert Consensus Statement on catheter and surgical ablation of atrial fibrillation: recommendations for personnel, policy, procedures and follow-up. A report of the Heart Rhythm Society (HRS) Task Force on catheter and surgical ablation of atrial fibrillation. Heart Rhythm 2007;4: 816–861. [Context Link]
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