Anticoagulation in Patients with Atrial Fibrillation
Although anticoagulation decreases the risk of stroke by about two thirds in patients with nonvalvular atrial fibrillation, this therapy continues to be significantly underused. Current guidelines for clinical practice are complex and may appear confusing and inconsistent to physicians. Thomson and colleagues used a systematic literature review to develop a decision analysis model for the use of anticoagulants in patients with atrial fibrillation and applied the model to data on more than 200 patients.
Guidelines for Warfarin Treatment in Atrial Fibrillation 
NOTE: In addition to the steps given in the flow chart, it is important to review reversible risk factors (e.g., smoking or uncontrolled hypertension) and to consider whether addressing the risk factors might alter the need for anticoagulation. Patients should be reviewed annually to reassess advice. Because the tables (see sample table in Figure 2) are derived from average values, it is important to consider the individual patient's preferences. For example, the threshold for advising treatment will be lower if patients have little or no aversion to warfarin treatment but will be higher in patients who are particularly averse to treatment; in the latter situation, a trial of therapy may be justified.
FIGURE 1. Guidelines for warfarin treatment of patients who have atrial fibrillation. Adapted with permission from Thomson R, Parkin D, Eccles M, Sudlow M, Robinson A. Decision analysis and guidelines for anticoagulant therapy to prevent stroke in patients with atrial fibrillation. Lancet 2000;355:958.
Published studies were identified through MEDLINE and other databases, and were appraised using the criteria of the Evidence-Based Medicine Working Group. When possible, original data were reanalyzed to meet objective end points. Overall, the data indicated that anticoagulated patients had 42 percent of the stroke risk of placebo-treated patients. Large community-based studies were used to calculate risk of death, disability and subsequent stroke in patients with atrial fibrillation. Interviews with 57 patients with atrial fibrillation were used to provide data on quality of life associated with different health states. Finally, cost estimates were formulated for stroke (mild, severe and fatal) and for anticoagulant therapy and its complications.
Guidelines for Warfarin Treatment in Men 60 to 64 Years of Age FIGURE 2. Sample lookup table of guidelines for warfarin treatment in men who have atrial fibrillation. (DM = diabetes mellitus; HT = antihypertensive therapy; Cigs = current smoker; CVD = cardiovascular disease; LVH = left ventricular hypertrophy) The treatment decisions were modeled as a Markov process using a hypothetic cohort of patients followed over several time cycles. All assumptions were made to replicate, as closely as possible, a real practice situation. If necessary, a group consensus model was used to make or validate these assumptions.
The model indicated that warfarin should be used in all patients with atrial fibrillation who had three or more risk factors for stroke (Figure 1). In men with atrial fibrillation, warfarin should be used whenever left ventricular hypertrophy and at least one other risk factor are present. Aspirin therapy should be considered in patients with atrial fibrillation who have contraindications to warfarin or anticoagulation.
The authors also prepared a set of decision tables to help physicians determine the risks and likely benefits of warfarin therapy in individual patients based on age, sex, blood pressure and risk factors such as smoking or diabetes (Figure 2).
ANNE D. WALLING, M.D.
Thomson R, et al. Decision analysis and guidelines for anticoagulant therapy to prevent stroke in patients with atrial fibrillation. Lancet March 18, 2000;355:956-62.
Copyright © 2000 by the American Academy of Family Physicians.
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