Risk stratification schemes, anticoagulation use and outcomes: the risk–treatment paradox in patients with newly diagnosed non-valvular atrial fibrillation

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To examine whether warfarin use and outcomes differ across CHADS2 and CHA2DS2-VASc risk strata for non-valvular atrial fibrillation (NVAF).


Population-based cohort study using linked administrative databases in Alberta, Canada.


Inpatient and outpatient.


42 834 consecutive patients ≥20 years of age with newly diagnosed NVAF.

Main outcome measures

Cerebrovascular events and/or mortality in the first year after diagnosis.


Of 42 834 NVAF patients, 22.7% were low risk on the CHADS2 risk score (0), 27.5% were intermediate risk (1), and 49.8% were high risk (≥2). The CHA2DS2-VASc risk score reclassified 16 722 patients such that 7.8% were defined low risk, 13.8% intermediate risk and 78.4% high risk. Of the elderly cohort (≥65 years) with definite NVAF visits (at least two encounters 30 days apart, n=8780), 49% were taking warfarin within 90 days of diagnosis. Warfarin use did not differ across risk strata using either the CHADS2 (p for trend=0.85) or CHA2DS2-VASC (p=0.35). In multivariable adjusted analyses, warfarin use was associated with substantially lower rates of death or cerebrovascular events for patients with CHADS2 scores of 1 (OR 0.52, 95% CI 0.41 to 0.67) or ≥2 (OR 0.61, 95% CI 0.53 to 0.71), or CHA2DS2-VASc scores of ≥2 (OR 0.60, 95% CI 0.53 to 0.68).


In elderly patients with NVAF and elevated CHADS2 or CHA2DS2-VASC scores, warfarin users exhibited lower rates of cerebrovascular events and mortality. However, warfarin use did not differ across risk strata, another example of the risk–treatment paradox in cardiovascular disease.

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