Atrial fibrillation (AF) patients and treating physicians have to remember that stroke represents a devastating complication from AF. There exists many situations where one can live reasonably well with partially damaged organs; the brain is often not one of these. Sight, memory, speech, cognition, ambulation, and continence are all brain-controlled functions that directly relate to quality living. Stroke is to be avoided.

Although bleeding is a risk of blood thinners, bleeds infrequently leave permanent damage as compared to strokes. Bleeds can be treated and often are impermanent–unlike stroke.

The CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with non-rheumatic atrial fibrillation, a common and serious heart arrhythmia associated with thromboembolic stroke. It is used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy. AF can cause stasis of blood in the upper heart chambers, leading to the formation of a clot that can dislodge into the blood flow, reach the brain, cut off supply to the brain, and cause a stroke. A high CHADS2 score corresponds to a greater risk of stroke, while a low CHADS2 score corresponds to a lower risk of stroke. The CHADS2 score is simple and has been validated by many studies.

The CHADS2 scoring table is shown below: adding together the points that correspond to the conditions that are present results in the CHADS2 score, that is used to estimate stroke risk.

CHADS2 Score

CHADS2 was designed as a scoring system to classify the risk of stroke in patients with atrial fibrillation. Prior to the study, there were conflicting data regarding independent risk factors and their importance in predicting the risk of stroke. CHADS2 was developed from an independent registry of Medicare-aged patients with non-rheumatic atrial fibrillation who were not given warfarin at hospital discharge. Due to the constraints of the database, the study only included patients aged 65 to 95 years and was retrospective in data collection and analysis, relying on Medicare claims to assist with study endpoints.

Condition Points
C Congestive Heart Failure 1
H Hypertension 1
A Age > 75 years 1
D Diabetes Mellitus 1
S2 Prior Stroke or TIA or Thromboembolism 2


CHADS2 Score and Stroke Risk

Each increase in CHADS2 was shown to predict ischemic stroke rate per year in a linear fashion:

CHASDS2 Score Stroke Rate (% per year)
0 1.9
1 2.8
2 4
3 5.9
4 8.5
5 12.5
6 18.2

Discrimination of Risk Factor Severity

At the expense of bedside simplicity, the CHADS2 system is unable to account for higher severity of illness with each risk factor considered. As an example, poorly controlled hypertension and diabetes have equal weight to that of a controlled patient. For this reason, it is important for clinicians to use the scoring system as a guide, not as an absolute answer.

Female Gender

Previous scoring systems used a combination of both age > 75 years AND female sex as a risk factor. In the CHADS2 system, age was preserved as a risk factor but female sex was discarded. However, there are strong studies that validate female sex as an independent risk factor for stroke in AF patients.

Prisco et al. reported on 780 AF patients on blood-thinners in the British blood journal, Thrombosis Haemostasis, reported three main findings:

  • Female gender did not increase the risk of bleeding.
  • Female gender—even when correcting for age–doubled the risk of stroke.
  • Females had more disabling strokes, including a three-fold greater risk of fatal stroke.

The British Medical Journal published the results of a Danish registry study of more than 70,000 patients which showed that female gender alone increased the risk of stroke. Additionally, adding female gender with other moderate risk factors (high blood pressure, age > 65 and vascular disease) greatly accentuated stroke risk. It was a strong study due to the huge number of subjects.

One of the strongest studies to date on gender-related differences in the risk of stroke in AF comes from the ATRIA study, published in 2005 in Circulation. Researchers from California and Boston looked back at more than 13,000 AF patients. They found that females had a 60% greater risk of stroke. The enhanced risk occurred at all ages and held up after correction for confounding diseases. Reassuringly, they also found that warfarin reduced stroke risk equally in females and males.

CHADS2-VASc Score and Stroke Risk

The CHA2DS2-VASc score is a refinement of CHADS2  score and extends the latter by including additional common stroke risk factors, as discussed below. Given the strong evidence regarding female sex and a higher risk of stroke, sex was added to the more contemporary CHA2DS2-VASC classification system.

The maximum CHADS2 score is 6, whilst the maximum CHA2DS2-VASc score is 9 (for age, either the patient is ≥75 years and gets two points, is between 65-74 and gets one point, or is under 65 and does not get points). Note that female gender only scores one point if the patient has at least one other risk factor, and does not score any points in isolation.

Unlike the original CHADS2 score, which was based on a retrospective Medicare registry, CHA2DS2-VASc prospectively included patients from multiple countries who were aged 18 years and older. Patients were both ambulatory and hospitalized, and were followed for a total of 12 months.

Condition Points
C Congestive Heart Failure 1
H Hypertension 1
A2 Age > 75 years 2
D Diabetes Mellitus 1
S2 Prior Stroke or TIA or Thromboembolism 2
V Vascular disease (e.g. peripheral artery disease, myocardial infarction, aortic plaqu) 1
A Age 65-74 years 1
Sc Sex category (i.e. female sex) 1

Each increase in CHADS2-VASc was shown to predict ischemic stroke rate per year in a linear fashion:

CHADS2-VASc Stroke (% per Year)
1 1.3
2 2.2
3 3.2
4 4
5 6.7
6 9.8
7 9.6
8 6.7
9 15.2


Accuracy of CHADS2 vs. CHADS2-VASc

In a comparison study of multiple risk assessment tools for atrial fibrillation, CHA2DS2-VASc did not seem to outperform CHADS2. To classify the predictive ability of a scoring system, a C statistic is sometimes used. The C statistic is a number between 0.5 (no better than chance) and 1.0 (perfect prediction) indicating predictive ability. In this case, CHADS2 was 0.637 compared to CHADS2-VASc at 0.647. A “good” C statistic is usually at least 0.7 or better, indicating than neither system is particularly accurate in predicting stroke risk.

Classification of CHADS2 vs CHADS2-VASc

In both scoring systems, a score of 0 is “low” risk of stroke, 1 is “moderate”, and any score above 1 is a “high” risk. The CHADS2-VASc system, with having three more potential variables, inevitably classifies more patients into a high-risk group. As shown in the diagram below, CHADS2-VASc classifies the same patient group into a higher risk category compared to CHADS2.

Gender and the Caveat to CHA2DS2-VASc

In general, a CHA2DS2-VASc score of 1 should warrant strong consideration for full oral anticoagulation. The one exception, however, is in patients who have a score of 1 due to gender alone. In these patients (female < 65 years old without other risk factors), antithrombotic therapy should not be given. This special situation may not be intuitive with the CHA2DS2-VASc scoring system.


Treatment strategies recommended based on the CHADS2 or CHADS-VASC score are shown below in the table.




Anticoagulation Therapy



None or Aspirin



Aspirin, Warfarin, or other oral anticoagulant

2 or greater

Moderate or High

Warfarin or other oral anticoagulant


Proper risk stratification of patients with atrial fibrillation is imperative in order to prevent possible stroke.  With the use of relatively simple risk scoring algorithms one can accurately assess and treat patients’ atrial fibrillation and prevent a possibly devastating stroke.


References and Additional Reading

    1. Lip GY, Frison L, Halperin JL, Lane DA. Identifying patients at high risk for stroke despite anticoagulation: a comparison of contemporary stroke risk stratification schemes in an anticoagulated atrial fibrillation cohort. Stroke. 2010;41(12):2731-8. PMID 20966417.
    2. Camm AJ, Lip GY, De Caterina R, et al. 2012 focused update of the ESC Guidelines for the management of atrial fibrillation: an update of the 2010 ESC Guidelines for the management of atrial fibrillation. Eur Heart J. 2012;33(21):2719-47. PMID 22922413.
    3. Guyatt GH, Akl EA, Crowther M, et al. Executive summary: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):7S-47S. PMID 22315257.
    4. Lip GY, Nieuwlaat R, Pisters R, et al. Refining clinical risk stratification for predicting stroke and thromboembolism in atrial fibrillation using a novel risk factor-based approach: the euro heart survey on atrial fibrillation. Chest. 2010;137(2):263-72. PMID 19762550
    5. Poli D, Antonucci E, Grifoni E, Abbate R, Gensini GF, Prisco D. Gender differences in stroke risk of atrial fibrillation patients on oral anticoagulant treatment. Thromb Haemost. 2009 May; 101 (5):938-42.
    6. Validation of risk stratification schemes for predicting stroke and thromboembolism in patients with atrial fibrillation: nationwide cohort study. BMJ 2011;342:d124
    7. Gender Differences in the Risk of Ischemic Stroke and Peripheral Embolism in Atrial Fibrillation. The AnTicoagulation and Risk factors In Atrial fibrillation (ATRIA) Study. Circulation. 2005; 112: 1687-1691
    8. Gage BF, Waterman AD, Shannon W, et al. Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA. 2001;285(22):2864-70. PMID 11401607.



About the Author:

Rishi G Anand, MD is board certified, and well published cardiovascular disease specialist and cardiac electrophysiologist. He serves as the Director of an Electrophysiology laboratory in Fort Lauderdale, Florida. He also serves as an author and Editorial board member for EP Lab Digest which is a nationwide publication. He serves an advisor to Medicare at the state level on health coverage policy matters. He has been nominated to serve as an expert advisor to the center for Medicare/Medicaid services (CMMS) Medicare Evidence Development and Coverage Advisory Committee (MEDCAC). MEDCAC is utilized by CMMS to supplement its own research and allow for additional expert and public input on coverage topics, including those that are highly complex or have a major potential impact on the health of beneficiaries and/or the Medicare program itself.