Background Stroke risk in atrial fibrillation (AF) is often assessed at initial presentation, and risk stratification performed as a 'one off'. In validation studies of risk prediction, baseline values are often used to 'predict' events that occur many years later. Many clinical variables have 'dynamic' changes over time, as the patient is followed up. These dynamic changes in risk factors may increase the CHA 2 DS 2 -VASc score, stroke risk category and absolute ischaemic stroke rate. Objective This article evaluates the 'dynamic' changes of CHA 2 DS 2 -VASc variables and its effect on prediction of stroke risk. Patients and Methods From the Korea National Health Insurance Service database, a total of 167,262 oral anticoagulant-naive non-valvular AF patients aged ≥ 18 years old were enrolled between January 1, 2002, and December 31, 2005. These patients were followed up until December 31, 2015. Results At baseline, the proportions of subjects categorized as 'low', 'intermediate' or 'high risk' by CHA 2 DS 2 -VASc score were 15.4, 10.6 and 74.0%, respectively. Mean CHA 2 DS 2 -VASc score increased annually by 0.14, particularly due to age and hypertension. During follow-up of 10 years, 46.6% of 'low-risk' patients and 72.0% of 'intermediate risk' patients were re-classified to higher stroke risk categories. Among the original 'low-risk' patients, annual ischaemic stroke rates were significantly higher in the re-classified 'intermediate' (1.17 per 100 person-years, p < 0.001) or re-classified 'high-risk' groups (1.44 per 100 person-years, p = 0.048) than consistently 'low-risk' group (0.29 per 100 person-years). The most recent CHA 2 DS 2 -VASc score and the score change with the longest follow-up had the best prediction for ischaemic stroke. Conclusion In AF patients, stroke risk as assessed by the CHA 2 DS 2 -VASc score is dynamic and changes over time. Rates of ischaemic stroke increased when patients accumulated risk factors, and were re-classified into higher CHA 2 DS 2 -VASc score categories. Stroke risk assessment is needed at every patient contact, as accumulation of risk factors with increasing CHA 2 DS 2 -VASc score translates to greater stroke risks over time.
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