CHADS2 Calculator for Atrial Fibrillation
Evaluates ischemic stroke risk in patients with atrial fibrillation
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4% (95% CI, 3.1% to 5.1%)
Based on the 2012 CHEST Guidelines,consider oral anticoagulation over aspirin (grade 1B).1
Note that this recommendation is a generalization based on stroke risk. Patient-specific considerations, such as other uncontrolled risk factors for stroke and bleeding risk, should be considered on a case-by-case basis.
About This Calculator
CHADS2 was designed as a scoring system to classify the risk of stroke in patients with atrial fibrillation. Prior to the study,2 there were conflicting data regarding independent risk factors and their importance in predicting the risk of stroke.
CHADS2 was developed from an independent registry of Medicare-aged patients with non-rheumatic atrial fibrillation who were not given warfarin at hospital discharge. Due to the constraints of the database, the study only included patients aged 65 to 95 years and was retrospective in data collection and analysis, relying on Medicare claims to assist with study endpoints.
CHADS2 Score and Stroke Risk
Each increase in CHADS2 was shown to predict ischemic stroke rate per year in a linear fashion:
Discrimination of Risk Factor Severity
At the expense of bedside simplicity, the CHADS2 system is unable to account for higher severity of illness with each risk factor considered. As an example, poorly controlled hypertension and diabetes have equal weight to that of a controlled patient. For this reason, it is important for clinicians to use the scoring system as a guide, not as an absolute answer.
Previous scoring systems used a combination of both age > 75 years AND female sex as a risk factor. In the CHADS2 system, age was preserved as a risk factor but female sex was discarded. Given the strong evidence regarding female sex and a higher risk of stroke, sex was added to the more contemporary CHA2DS2-VASC classification system.
References and Additional Reading
- 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(2 Suppl):7S-47S. PMID 22315257.
- Gage BF, Waterman AD, Shannon W, et al. Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA. 2001;285(22):2864-70. PMID 11401607.