About 2.3 million Americans are affected by atrial fibrillation and atrial flutter (AF), a condition that causes 15% of the 700,000 strokes that occur annually in the United States. Anticoagulants like warfarin can help prevent stroke in AF patients, but these therapies can also cause bleeding in some cases. “Prediction tools, such as the CHADS2 score, have been developed to estimate stroke risk and are now recommended by clinical guideline statements,” says Mintu P. Turakhia, MD, MAS. “These guidelines, however, vary considerably in describing how stroke and bleeding risk should be evaluated and integrated into clinical decision making.”

Assessing Potential Variations in Warfarin Use

It has been suspected that use of warfarin in AF may vary by specialty and over time. In the American Heart Journal, Dr. Turakhia and colleagues had a study published that evaluated differences and trends in warfarin prescription by treating specialty for new AF cases. Using VA data from the TREAT-AF study, the investigators reviewed more than 141,000 participants with newly diagnosed AF in which patients had at least one internal medicine, primary care, or cardiology encounter within 90 days of their diagnosis. The primary outcome was prescription of warfarin.

According to results, care of patients with new AF from cardiologists appeared to be associated with a greater likelihood of warfarin prescription when compared with care only from primary care physicians (Table 1), even after adjusting for covariates and a propensity for cardiology care. The observation was also consistent across subgroups of patients, including those who were at lowest risk for bleeding. Furthermore, warfarin prescriptions were more frequently provided to those at highest risk for stroke, those who were prescribed other drugs for AF, and those with the highest service eligibility of medical coverage (Table 2). There was also a divergent trend in risk-adjusted warfarin use over time.

Managing-AF-Callout

“Treating specialty appears to influence stroke prevention care and may impact clinical outcomes,” says Dr. Turakhia. “The overall warfarin prescription rate observed in our study is consistent with that of previous studies of newly detected AF among patients in the U.S.”

Warfarin Prescription & CHADS2 Scores

Dr. Turakhia and colleagues also found that the unadjusted prevalence of warfarin use, when stratified by CHADS2 score, increased among primary-care-only patients but slightly decreased among cardiology patients. Among patients with a CHADS2 score of 0, 68.4% of cardiology patients had warfarin prescribed, compared with a 50.8% rate seen among primary-care-only patients. “This finding is noteworthy because it could reflect the convergence of opinion on the suitability of anticoagulation among both physician specialty groups,” Dr. Turakhia says. “It raises the possibility that low-risk patients may be receiving anticoagulation from specialists in situations where the risks of anticoagulation may outweigh its benefits.”

“Treating specialty appears to influence stroke prevention care and may impact clinical outcomes.”

There are several potential explanations for the findings on warfarin prescription based on CHADS2 scores, including differences in the perception and estimation of thromboembolic risk, bleeding risk, contraindications, compliance, and net clinical benefit. “The awareness or adoption of guidelines among cardiologists could also influence primary care and specialty physician behavior differently,” adds Dr. Turakhia. “It’s also possible that primary care physicians have a higher threshold to anticoagulate after considering potential harms.”

Improving Treatment Variation Among Cards & PCPs

Further study of how bleeding risk is estimated in practice and affects decision making is crucial, according to Dr. Turakhia. “New oral anticoagulants and device-based therapies may have comparable or superior stroke prevention to warfarin, but they also appear to have lower bleeding risk.” He adds that clinicians should keep AF in mind during clinical encounters if predisposing risk factors are present. It is also possible that providers in different specialties have different thresholds for treating AF. For example, non-cardiac physicians may wait longer to prescribe AF therapy. “The best time to think about stroke prevention is when you first make the diagnosis of AF, not months or years later,” says Dr. Turakhia.

A major obstacle to decreasing variation in warfarin use is the fact that current recommendations are not consistent across guidelines. “Greater efforts are needed to reconcile or consolidate guidelines and performance measures across primary care, internal medicine, pulmonary medicine, neurology, surgery, and cardiology so that we can improve upon treatment variation,” Dr. Turakhia says. “In addition, future investigations should aim to explore reasons for not prescribing or considering anticoagulation. Approaches to testing and treating AF continue to improve. By overcoming barriers to care, it’s hoped that more patients can be treated appropriately and in a timely manner to reduce the burden of AF in the future.”

References

Turakhia MP, Hoang DD, Xu X, et al. Differences and trends in stroke prevention anticoagulation in primary care vs cardiology specialty management of new atrial fibrillation: the retrospective evaluation and assessment of therapies in AF (TREAT-AF) study. Am Heart J. 2013;165:93-101. Available at: http://www.ahjonline.com/article/S0002-8703(12)00673-4/fulltext.

Fonarow GC, Albert NM, Curtis AB, et al. Improving evidence-based care for heart failure in outpatient cardiology practices: primary results of the Registry to Improve the Use of Evidence-Based Heart Failure Therapies in the Outpatient Setting (IMPROVE HF). Circulation. 2010;122:585-596.

Guyatt GH, Akl EA, Crowther M, et al. Executive summary: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians evidence-based clinical practice guidelines. Chest. 2012;141(suppl):7S-47S.

Reynolds MR, Shah J, Essebag V, et al. Patterns and predictors of warfarin use in patients with new-onset atrial fibrillation from the FRACTAL Registry. Am J Cardiol. 2006;97:538-543.

Fang MC, Go AS, Chang Y, et al. A new risk scheme to predict warfarin-associated hemorrhage the ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) study. J Am Coll Cardiol. 2011;58:395-401.

Singer D, Albers G, Dalen J, et al. Antithrombotic therapy in atrial fibrillation: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest. 2004;126(Suppl):429S-456S.