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

OBJECTIVE: To examine whether warfarin use and outcomes differ across CHADS(2) and CHA(2)DS(2)-VASc risk strata for non-valvular atrial fibrillation (NVAF).
DESIGN: Population-based cohort study using linked administrative databases in Alberta, Canada.
SETTING: Inpatient and outpatient. PATIENTS: 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.
RESULTS: Of 42,834 NVAF patients, 22.7% were low risk on the CHADS(2) risk score (0), 27.5% were intermediate risk (1), and 49.8% were high risk (≥ 2). The CHA(2)DS(2)-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 CHADS(2) (p for trend = 0.85) or CHA(2)DS(2)-VASC (p = 0.35). In multivariable adjusted analyses, warfarin use was associated with substantially lower rates of death or cerebrovascular events for patients with CHADS(2) 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 CHA(2)DS(2)-VASc scores of ≥ 2 (OR 0.60, 95% CI 0.53 to 0.68).
CONCLUSIONS: In elderly patients with NVAF and elevated CHADS(2) or CHA(2)DS(2)-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.