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Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial
B F Gage1, A D Waterman, W Shannon
1Division of General Medical Sciences, Washington University School of Medicine Campus, Box 8005, 660 S Euclid Ave, St Louis, MO 63110, USA. bgage@im.wustl.edu
Insights
The CHADS(2) index accurately predicts stroke risk in atrial fibrillation (AF) patients, outperforming existing schemes. This tool can help guide antithrombotic therapy decisions for individuals with AF.
Area of Science:
- Cardiovascular Medicine
- Clinical Epidemiology
- Geriatric Medicine
Background:
- Patients with atrial fibrillation (AF) face an elevated stroke risk.
- Stroke risk in AF is influenced by patient age and coexisting medical conditions.
Purpose of the Study:
- To evaluate the predictive capability of current stroke risk classification systems in AF patients.
- To validate the newly developed CHADS(2) index against existing schemes.
Main Methods:
- A new stroke risk scheme, the CHADS(2) index, was created by combining two existing systems.
- The CHADS(2) index assigns points for congestive heart failure, hypertension, age ≥75, diabetes, and prior stroke/TIA.
- Validation involved a National Registry of AF (NRAF) comprising 1733 Medicare beneficiaries aged 65-95.
Main Results:
- The CHADS(2) index demonstrated superior accuracy in predicting stroke risk (c-statistic 0.82) compared to AFI (0.68) and SPAF III (0.74) schemes.
- A significant increase in stroke rate was observed with each incremental point in the CHADS(2) score.
- The stroke rate per 100 patient-years increased substantially for higher CHADS(2) scores, particularly without antithrombotic therapy.
Conclusions:
- The CHADS(2) index is a highly accurate tool for quantifying stroke risk in patients with atrial fibrillation.
- This validated index can assist clinicians in selecting appropriate antithrombotic therapies for AF patients.
Context:
Patients who have atrial fibrillation (AF) have an increased risk of stroke, but their absolute rate of stroke depends on age and comorbid conditions.
Objective:
To assess the predictive value of classification schemes that estimate stroke risk in patients with AF.
Design, Setting, And Patients:
Two existing classification schemes were combined into a new stroke-risk scheme, the CHADS( 2) index, and all 3 classification schemes were validated. The CHADS( 2) was formed by assigning 1 point each for the presence of congestive heart failure, hypertension, age 75 years or older, and diabetes mellitus and by assigning 2 points for history of stroke or transient ischemic attack. Data from peer review organizations representing 7 states were used to assemble a National Registry of AF (NRAF) consisting of 1733 Medicare beneficiaries aged 65 to 95 years who had nonrheumatic AF and were not prescribed warfarin at hospital discharge.
Main Outcome Measure:
Hospitalization for ischemic stroke, determined by Medicare claims data.
Results:
During 2121 patient-years of follow-up, 94 patients were readmitted to the hospital for ischemic stroke (stroke rate, 4.4 per 100 patient-years). As indicated by a c statistic greater than 0.5, the 2 existing classification schemes predicted stroke better than chance: c of 0.68 (95% confidence interval [CI], 0.65-0.71) for the scheme developed by the Atrial Fibrillation Investigators (AFI) and c of 0.74 (95% CI, 0.71-0.76) for the Stroke Prevention in Atrial Fibrillation (SPAF) III scheme. However, with a c statistic of 0.82 (95% CI, 0.80-0.84), the CHADS( 2) index was the most accurate predictor of stroke. The stroke rate per 100 patient-years without antithrombotic therapy increased by a factor of 1.5 (95% CI, 1.3-1.7) for each 1-point increase in the CHADS( 2) score: 1.9 (95% CI, 1.2-3.0) for a score of 0; 2.8 (95% CI, 2.0-3.8) for 1; 4.0 (95% CI, 3.1-5.1) for 2; 5.9 (95% CI, 4.6-7.3) for 3; 8.5 (95% CI, 6.3-11.1) for 4; 12.5 (95% CI, 8.2-17.5) for 5; and 18.2 (95% CI, 10.5-27.4) for 6.
Conclusion:
The 2 existing classification schemes and especially a new stroke risk index, CHADS( 2), can quantify risk of stroke for patients who have AF and may aid in selection of antithrombotic therapy.
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