Comparison of risk stratification schemes to predict thromboembolism in people with nonvalvular atrial fibrillation

Abstract

Objectives: We assessed 5 risk stratification schemes for their ability to predict atrial fibrillation (AF)-related thromboembolism in a large community-based cohort.

Background: Risk schemes can help target anticoagulant therapy for patients at highest risk for AF-related thromboembolism. We tested the predictive ability of 5 risk schemes: the Atrial Fibrillation Investigators, Stroke Prevention in Atrial Fibrillation, CHADS(2) (Congestive heart failure, Hypertension, Age >or= 75 years, Diabetes mellitus, and prior Stroke or transient ischemic attack) index, Framingham score, and the 7th American College of Chest Physicians Guidelines.

Methods: We followed a cohort of 13,559 adults with AF for a median of 6.0 years. Among non-warfarin users, we identified incident thromboembolism (ischemic stroke or peripheral embolism) and risk factors from clinical databases. Each scheme was divided into low, intermediate, and high predicted risk categories and applied to the cohort. Annualized thromboembolism rates and c-statistics (to assess discrimination) were calculated for each risk scheme.

Results: We identified 685 validated thromboembolic events that occurred during 32,721 person-years off warfarin therapy. The risk schemes had only fair discriminating ability, with c-statistics ranging from 0.56 to 0.62. The proportion of patients assigned to individual risk categories varied widely across the schemes. The proportion categorized as low risk ranged from 11.7% to 37.1% across schemes, and the proportion considered high risk ranged from 16.4% to 80.4%.

Conclusions: Current risk schemes have comparable, but only limited, overall ability to predict thromboembolism in persons with AF. Recommendations for antithrombotic therapy may vary widely depending on which scheme is applied for individual patients. Better risk stratification is crucially needed to improve selection of AF patients for anticoagulant therapy.

Figure 1. Annual TE Rates Across Risk Groups Using 5 Risk Stratification Schemes Used to Predict AF-Related TE

The double-barred lines represent 95% confidence intervals. ACCP = American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy; AF = atrial fibrillation; AFI = Atrial Fibrillation Investigators; CHADS₂ = congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, and prior stroke or transient ischemic attack; SPAF = stroke prevention in atrial fibrillation; TE = thromboembolism.

Figure 2. Proportion of ATRIA Cohort Off Warfarin and Categorized by CHADS₂ Scores, Stratified by Development of TE

The distribution of person-years contributed by patients not sustaining a TE is in blue and the distribution of person-years contributed by patients sustaining a TE is in yellow. Abbreviations as in Figure 1.

Figure 3. ROC Curves for 5 Risk Stratification Schemes Used to Predict AF-Related Thromboembolism

The 45° dotted line represents the line of no information. ROC = receiver-operating characteristic; other abbreviations as in Figure 1.