Stroke Rate in Atrial Fibrillation by CHA₂DS₂-VASc Score
The annual stroke rate in atrial fibrillation increases progressively with CHA₂DS₂-VASc score, ranging from 0% for a score of 0 to over 15% for a score of 9, with the most clinically relevant threshold being a score of 2 or higher (≥2.2% annual stroke rate) where oral anticoagulation is definitively indicated. 1
Annual Stroke Rates by CHA₂DS₂-VASc Score
The European Society of Cardiology provides the following validated annual thromboembolic event rates for each score category: 1
- Score 0: 0% per year 1
- Score 1: 0.6-1.3% per year 1
- Score 2: 1.6-2.2% per year 1
- Score 3: 3.2-3.9% per year 1
- Score 4: 1.9-4.0% per year 1
- Score 5: 3.2-6.7% per year 1
- Score 6: 3.6-9.8% per year 1
- Score 7: 8.0-9.6% per year 1
- Score 8: 6.7-11.1% per year 1
- Score 9: >15.2% per year 1
Critical Clinical Thresholds
The 1% annual stroke rate threshold traditionally justifies oral anticoagulation initiation. 1 However, the data show substantial variability depending on the validation cohort used, with some studies reporting rates as low as 0.5-0.9% for a score of 1. 1
Score of 1: The Gray Zone
For patients with a CHA₂DS₂-VASc score of 1, the evidence reveals considerable heterogeneity: 1
- Without anticoagulation: 1.4% (range 0.5-2.9%) per 100 patient-years 1
- With anticoagulation: 0.7% (range 0.1-1.3%) per 100 patient-years 1
- Euro-Heart Survey data: 0.6% adjusted annual stroke risk 1
- Swedish registry data: 0.5-0.9% adjusted event rate 1
A large Asian cohort study demonstrated that among males with a CHA₂DS₂-VASc score of 1, the annual stroke rate was 2.75%, with variation by specific risk factor from 1.96%/year (vascular disease) to 3.50%/year (age 65-74). 2
Sex-Specific Considerations
Women with a CHA₂DS₂-VASc score of 2 (female sex plus one additional risk factor) have an annual stroke rate of 2.55%, ranging from 1.91%/year (hypertension) to 3.34%/year (age 65-74). 2 The American College of Cardiology recognizes that women without other risk factors (score = 1 for sex alone) have truly low risk similar to men with a score of 0. 3
Risk Stratification Algorithm
For clinical decision-making, apply this framework: 3, 4
Score 0 (men) or 1 (women with sex as only factor): Truly low risk—no anticoagulation recommended 3, 4
Score 1 (men) or 2 (women): Intermediate risk—assess HAS-BLED score: 1
Score ≥2 (men) or ≥3 (women): High risk—oral anticoagulation definitively recommended 3, 4
Important Clinical Pitfalls
The CHA₂DS₂-VASc score is dynamic and changes over time. 5 A Korean nationwide study demonstrated that mean CHA₂DS₂-VASc score increased annually by 0.14 points, primarily due to aging and development of hypertension. 5 During 10-year follow-up, 46.6% of initially "low-risk" patients and 72.0% of "intermediate-risk" patients were reclassified to higher risk categories. 5
Not all risk factors carry equal weight despite equal point values. 2 Age 65-74 years confers the highest stroke rate (3.50%/year in men, 3.34%/year in women), while vascular disease confers the lowest (1.96%/year in men, 1.91%/year for hypertension in women). 2
Patients with CHADS₂ score of 0 are not necessarily low risk. 6 Among patients with CHADS₂ score of 0, one-year stroke rates ranged from 0.84% (CHA₂DS₂-VASc score 0) to 3.2% (CHA₂DS₂-VASc score 3), demonstrating the superior discriminatory ability of CHA₂DS₂-VASc. 6
Validation and Performance
The CHA₂DS₂-VASc score demonstrates superior predictive accuracy compared to CHADS₂ score, with c-statistics of 0.698 versus 0.561, and improves net reclassification by 11.7%. 7 Among Asian patients, those with CHA₂DS₂-VASc score of 0 had truly low risk with approximately 1% annual stroke rate, while those categorized as "low-risk" by other schemes had rates as high as 2.95%. 7