CORRESPONDENCE: LETTERS TO THE EDITOR
The AFFIRM study: Approaches to control rate in atrial fibrillation
Rhidian J. Shelton, MBChB, MRCP (UK)
Academic Cardiology, University of Hull, Castle Hill Hospital, Cottingham, Kingston-upon-Hull, HU16 5JQ, United Kingdom
(Email: rhidianshelton{at}btopenworld.com).
The optimal heart rate for patients with atrial fibrillation (AF) remains unclear; current guidelines are primarily based on clinical experience (1). Recent randomized studies suggest combining beta-blockers or calcium channel blockers with digoxin to achieve better rate control at rest and during exercise (2–4). However, I believe clarification of the "approach to control rate in AF" by the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) investigators (4) is justified.
A total of 2,027 patients were randomized to the rate control arm of the AFFIRM trial between 1995 and 1999. Of these, 248 crossed over to the rhythm-control group due to "uncontrolled symptoms" and 108 underwent AV nodal ablation due to failure of pharmacologic therapy. Rate-control data at rest are available in only 740 (36.5%) patients, which deteriorates further to 361 (17.8%) if data regarding heart-rate control during exercise are desired.
This relative lack of data may be explained by the fact that 1,055 (52%) patients were in sinus rhythm at the time of randomization. The proportion of those in the rate-control group who maintained sinus rhythm during follow-up is unclear. Published data for the entire trial population suggest a similar number (49%) remaining in sinus rhythm at study end.
Therefore, the majority of data on rate control of AF comes from a minority of patients randomized to a rate-control strategy. Because of the nature of data collection (only patients with AF at the time of assessment were selected for analysis), care should be taken in interpreting these results. The data predominantly represent patients with persistent and permanent AF and significantly underrepresent those with paroxysmal AF.
It is difficult to make conclusions on the control of ventricular rate during paroxysms of AF from this study, the occurrence of which greatly depends on variations of the autonomic tone (5).
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1. Fuster V, Ryden LE, Asinger RW, et al. ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation: executive summaryA report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Committee to Develop Guidelines for the Management of Patients With Atrial Fibrillation) developed in collaboration with the North American Society of Pacing and Electrophysiology. Circulation 2001;104:2118-2150.[Free Full Text]
2. Farshi R, Kistner D, Sarma JS, Longmate JA, Singh BN. Ventricular rate control in chronic atrial fibrillation during daily activity and programmed exercise: a crossover open-label study of five drug regimens J Am Coll Cardiol 1999;33:304-310.[Abstract/Free Full Text]
3. Khand AU, Rankin AC, Martin W, Taylor J, Gemmell I, Cleland JG. Carvedilol alone or in combination with digoxin for the management of atrial fibrillation in patients with heart failure? J Am Coll Cardiol 2003;42:1944-1951.[Abstract/Free Full Text]
4. Olshansky B, Rosenfeld LE, Warner AL, et al. for the AFFIRM investigators The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study: approaches to control rate in atrial fibrillation J Am Coll Cardiol 2004;43:1201-1208.[Abstract/Free Full Text]
5. Bettoni M, Zimmermann M. Autonomic tone variations before the onset of paroxysmal atrial fibrillation Circulation 2002;105:2753-2759.[Abstract/Free Full Text]
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