Contemporary clinical risk stratification schemata for predicting stroke and thromboembolism
(TE) in patients with atrial fibrillation (AF) are largely derived from risk factors
identified from trial cohorts. Thus, many potential risk factors have not been included.
We refined the 2006 Birmingham/National Institute for Health and Clinical Excellence
(NICE) stroke risk stratification schema into a risk factor-based approach by reclassifying
and/or incorporating additional new risk factors where relevant. This schema was then
compared with existing stroke risk stratification schema in a real-world cohort of
patients with AF (n = 1,084) from the Euro Heart Survey for AF.
Risk categorization differed widely between the different schemes compared. Patients
classified as high risk ranged from 10.2% with the Framingham schema to 75.7% with
the Birmingham 2009 schema. The classic CHADS(2) (Congestive heart failure, Hypertension,
Age > 75, Diabetes, prior Stroke/transient ischemic attack) schema categorized the
largest proportion (61.9%) into the intermediate-risk strata, whereas the Birmingham
2009 schema classified 15.1% into this category. The Birmingham 2009 schema classified
only 9.2% as low risk, whereas the Framingham scheme categorized 48.3% as low risk.
Calculated C-statistics suggested modest predictive value of all schema for TE. The
Birmingham 2009 schema fared marginally better (C-statistic, 0.606) than CHADS(2).
However, those classified as low risk by the Birmingham 2009 and NICE schema were
truly low risk with no TE events recorded, whereas TE events occurred in 1.4% of low-risk
CHADS(2) subjects. When expressed as a scoring system, the Birmingham 2009 schema
(CHA(2)DS(2)-VASc acronym) showed an increase in TE rate with increasing scores (P
value for trend = .003).
Our novel, simple stroke risk stratification schema, based on a risk factor approach,
provides some improvement in predictive value for TE over the CHADS(2) schema, with
low event rates in low-risk subjects and the classification of only a small proportion
of subjects into the intermediate-risk category. This schema could improve our approach
to stroke risk stratification in patients with AF.