CHADS2 Score Calculator

Atrial fibrillation removes coordinated atrial contraction, and blood stagnates in the left atrial appendage where thrombus forms and can embolise to the cerebral circulation. This mechanism raises stroke risk roughly fivefold, and the resulting strokes tend to be larger and more disabling than atherothrombotic ones. CHADS2 converts that risk into a single integer by awarding one point each for congestive heart failure or reduced ejection fraction, hypertension, age 75 or older, and diabetes, and two points for prior stroke or transient ischemic attack. The double weighting is not arbitrary: across the derivation cohorts a previous cerebrovascular event was by a wide margin the strongest single predictor of recurrence. Scores run 0 to 6, with observed annual stroke rates rising from about 1.9 percent at zero to roughly 18 percent at six. Most guidelines treat a score of 2 or more as the threshold for oral anticoagulation, using warfarin at an INR of 2.0 to 3.0 or a direct oral anticoagulant. The main weaknesses are what the score leaves out. It ignores vascular disease, age 65 to 74 and female sex, it lumps a large and heterogeneous group at a score of 1 where the treatment decision is genuinely uncertain, and it says nothing about bleeding, which must be assessed separately with a tool such as HAS-BLED. It was validated in non-valvular atrial fibrillation and does not apply to mechanical valves or moderate to severe mitral stenosis.

By the late 1990s two competing stroke risk classifications were in circulation: one from the Atrial Fibrillation Investigators, a pooled analysis of early anticoagulation trials, and one from the Stroke Prevention in Atrial Fibrillation trials. They disagreed about which patients were low risk, which left clinicians without a single defensible rule. Brian F. Gage and colleagues at Washington University in St Louis set out to reconcile them, combining the risk factors common to both schemes into one additive point system and testing all three against the same data. Their validation, published in JAMA in 2001, used 1,733 Medicare beneficiaries aged 65 to 95 with non-valvular atrial fibrillation drawn from the National Registry of Atrial Fibrillation, and showed the merged CHADS2 scheme predicted stroke better than either parent classification. Its arithmetic simplicity is what carried it into routine use. A decade later Gregory Lip and coworkers in Birmingham argued that CHADS2 was too blunt at the low end, and using the Euro Heart Survey cohort published the expanded CHA2DS2-VASc score in Chest in 2010, adding vascular disease, the 65 to 74 age band and female sex. European Society of Cardiology guidelines have preferred CHA2DS2-VASc since 2010, and it identifies truly low-risk patients more reliably, but CHADS2 survives in teaching and rapid bedside triage because it can be recalled and applied in seconds.