WARFARIN FOR ATRIAL-FIBRILLATION - THE PATIENTS PERSPECTIVE

Objective: To determine the minimal clinically important difference (M CID) of warfarin therapy for the treatment of nonvalvular atrial fibri llation from the perspective of patients using 2 different elicitation methods. Design: All patients completed 2 face-to-face interviews, wh ich were 2 weeks apart. For each interview, they were randomized to re ceive 1 of 2 elicitation methods: ping-ponging or starting at the know n efficacy. Setting: The practices of 2 university-affiliated family m edicine centers (8 physicians each), 14 community-based family physici ans, and 2 cardiologists. Patients: Sixty-four patients with nonvalvul ar atrial fibrillation who were initiated with warfarin therapy at lea st 3 months before the study. Intervention: During each interview, the patients' MCIDs were determined by using (1) a pictorial flip chart t o describe atrial fibrillation; the consequences of a minor stroke, a major stroke, and a major bleeding episode; the chance of stroke if no t taking warfarin; the chance of a major bleeding episode if taking wa rfarin; examples of the inconvenience, minor side effects, and costs o f warfarin therapy; and then (2) 1 of the 2 elicitation methods to det ermine their MCIDs (the smallest reduction in stroke risk at which the patients were willing to take warfarin). Patients' knowledge of their stroke risk, acceptability of the interview process, and factors dete rmining their preferences were also assessed. Main Results: Given a ba seline risk of having a stroke in the next 2 years, if not taking warf arin, of 10 of 100, the mean MCID was 2.01 of 100 (95% confidence inte rval, 1.60-2.42). Fifty-two percent of the patients would take warfari n for an absolute decrease in stroke risk of 1% over 2 years. Before e liciting their MCIDs, patients showed poor knowledge of their stroke r isk, which improved afterward. The interview process was well accepted by the patients. The MCID using the ping-ponging elicitation method w as 1.015 of 100 smaller compared with use of the starting at the known efficacy method (P=.01). Conclusions: We were able to determine the M CID of warfarin therapy for the prevention of stroke from the perspect ive of patients with nonvalvular atrial fibrillation. Their MCIDs were much smaller than those that have been implied by some experts and cl inicians. The interview process, using the flip chart approach, appear ed to improve the patients' knowledge of their disease and its consequ ences and treatment. The method used to elicit the patients' MCIDs can have a clinically important effect on patient responses. The method u sed in our study can be generalized to other conditions and, thus, cou ld be helpful in 3 ways: (1) from a clinical decision-malting perspect ive, it could facilitate patient-physician communication; (2) it could clarify the patient perspective when interpreting the results of prev iously completed trials; and (3) it could be used to derive more clini cally relevant sample sizes for randomized treatment trials.