The net clinical benefit of warfarin anticoagulation in atrial fibrillation.

Massachusetts General Hospital, Boston, Massachussetts 02114, USA.
Annals of internal medicine (Impact Factor: 16.1). 10/2009; 151(5):297-305.
Source: PubMed

ABSTRACT Guidelines recommend warfarin use in patients with atrial fibrillation solely on the basis of risk for ischemic stroke without antithrombotic therapy. These guidelines rely on ischemic stroke rates observed in older trials and do not explicitly account for increased risk for hemorrhage.
To quantify the net clinical benefit of warfarin therapy in a cohort of patients with atrial fibrillation.
Mixed retrospective and prospective cohort study of patients with atrial fibrillation between 1996 and 2003.
An integrated health care delivery system.
13 559 adults with nonvalvular atrial fibrillation.
Warfarin exposure, patient characteristics, CHADS(2) score (1 point for each of congestive heart failure, hypertension, age, and diabetes and 2 points for stroke), and outcome events were ascertained from health plan records and databases. Net clinical benefit was defined as the annual rate of ischemic strokes and systemic emboli prevented by warfarin minus intracranial hemorrhages attributable to warfarin, multiplied by an impact weight. The base-case impact weight was 1.5, reflecting the greater clinical impact of intracranial hemorrhage versus thromboembolism.
Patients accumulated more than 66 000 person-years of follow-up. The adjusted net clinical benefit of warfarin for the cohort overall was 0.68% per year (95% CI, 0.34% to 0.87%). Adjusted net clinical benefit was greatest for patients with a history of ischemic stroke (2.48% per year [CI, 0.75% to 4.22%]) and for those 85 years or older (2.34% per year [CI, 1.29% to 3.30%]). The net clinical benefit of warfarin increased from essentially zero in CHADS(2) stroke risk categories 0 and 1 to 2.22% per year (CI, 0.58% to 3.75%) in CHADS(2) categories 4 to 6. The patterns of results were preserved when weighting factors for intracranial hemorrhage of 1.0 and 2.0 were used.
Residual confounding is a possibility. Some outcome events were probably missed by the screening algorithm or when medical records were unavailable.
Expected net clinical benefit of warfarin therapy is highest among patients with the highest untreated risk for stroke, which includes the oldest age category. Risk assessment that incorporates both risk for thromboembolism and risk for intracranial hemorrhage provides a more quantitatively informed basis for the decision on antithrombotic therapy in patients with atrial fibrillation.
National Institute on Aging; National Heart, Lung, and Blood Institute; and Massachusetts General Hospital.

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    ABSTRACT: We aimed to study differences in the prescribing of warfarin, aspirin and statins to patients with atrial fibrillation (AF) in socio-economically diverse neighborhoods. We also aimed to explore the effects of neighborhood deprivation on the relationship between CHADS2 risk score and warfarin prescription. Data were obtained from primary health care records that contained individual clinical data that were linked to national data on neighborhood of residence and a deprivation index for different neighborhoods. Logistic regression was used to estimate the potential neighborhood differences in prescribed warfarin, aspirin and statins, and the association between the CHADS2 score and prescribed warfarin treatment, in neighborhoods with high, middle (referent) and low socio-economic (SES). After adjustment for age, socio-economic factors, co-morbidities and moves to neighborhoods with different SES during follow-up, adults with AF living in high SES neighborhoods were more often prescribed warfarin (men odds ratio (OR) (95% confidence interval (CI): 1.44 (1.27-1.62); and women OR (95% CI): 1.19 (1.05-1.36)) and statins (men OR (95% CI): 1.23 (1.07-1.41); women OR (95% CI): 1.23 (1.05-1.44)) compared to their counterparts residing in middle SES. Prescription of aspirin was lower in men from high SES neighborhoods (OR (95% CI): 0.75 (0.65-0.86)) than in those from middle SES neighborhoods. Higher CHADS2 risk scores were associated with higher warfarin prescription which remained after adjustment for neighborhood SES. The apparent inequalities in pharmacotherapy seen in the present study call for resource allocation to primary care in neighborhoods with low and middle socio-economic status. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
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