The CHADS2 score and its updated version, the CHA2DS2-VASc score, are clinical prediction rules for estimating the risk of stroke in patients with non-rheumatic atrial fibrillation (AF), a common and serious heart arrhythmia associated with thromboembolic stroke. Such a score is used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy, since AF can cause stasis of blood in the upper heart chambers, leading to the formation of a mural thrombus that can dislodge into the blood flow, reach the brain, cut off supply to the brain, and cause a stroke.
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A high score corresponds to a greater risk of stroke, while a low score corresponds to a lower risk of stroke. The CHADS2 score is simple and has been validated by many studies. In clinical use, the CHADS2 score (pronounced "chads two") has been superseded by the CHA2DS2-VASc score ("chads two vasc"), which gives a better stratification of low-risk patients.
The CHADS2 score does not include some common stroke risk factors, and its various pros/cons have been carefully discussed. 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.
CHA2DS2-VASc
To complement the CHADS2 score, by the inclusion of additional 'stroke risk modifier' risk factors, the CHA2DS2-VASc-score has been proposed.
In clinical use, the CHADS2 score has been superseded by the CHA2DS2-VASc score, which gives a better stratification of low-risk patients. The CHADS2 score has been outperformed by the CHA2DS2-VASc in multiple patient groups including patients with AF who are receiving outpatient elective electrical cardioversion.
Thus, the CHA2DS2-VASc score is a refinement of CHADS2 score and extends the latter by including additional common stroke risk factors, that is, age 65-74, female gender and vascular disease. In the CHA2DS2-VASc score, 'age 75 and above' also has extra weight, with 2 points.
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).
Treatment Guidelines
The CHA2DS2-VASc score has been used in the 2012 European Society of Cardiology guidelines for the management of atrial fibrillation. The 2014 American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society guidelines also recommend use of the CHA2DS2-VASc score.
The European Society of Cardiology (ESC), and National Institute for Health and Care Excellence (NICE) guidelines recommend that if the patient has a CHA2DS2-VASc score of 2 and above, oral anticoagulation therapy (OAC) with a Vitamin K Antagonist (VKA, e.g. warfarin with target INR of 2-3) or one of the non-VKA oral anticoagulant drugs (NOACs, e.g. dabigatran, rivaroxaban, edoxaban, or apixaban) is recommended.
If the patient is 'low risk' using the CHA2DS2-VASc score (that is, 0 in males or 1 in females), no anticoagulant therapy is recommended.
In males with 1 stroke risk factor (that is, a CHA2DS2-VASc score=1), antithrombotic therapy with OAC may be considered, and people values and preferences should be considered. Even a single stroke risk factor confers excess risk of stroke and mortality, with a positive net clinical benefit for stroke prevention with oral anticoagulation, when compared to no treatment or aspirin. Thromboembolic event rates differ according to various guideline treatment thresholds and methodological approaches.
Anticoagulation
Treatment recommendations based on the CHA2DS2–VASc score are shown in the following table:
Based on the ESC guidelines on Atrial Fibrillation, oral anticoagulation is recommended or preferred for patients with one or more stroke risk factors (i.e. a CHA2DS2-VASc score of ≥1 in males, or ≥2 in females). This is consistent with a recent decision analysis model showing how the 'tipping point' on the decision to anticoagulate has changed with the availability of the 'safer' NOAC drugs, where the threshold for offering stroke prevention (i.e. oral anticoagulation) is a stroke rate of approximately 1%/year.
Those patients recommended for stroke prevention treatment via oral anticoagulation, choice of drug (i.e. between a Vitamin K Antagonist and Non-Vitamin K Antagonist Oral Anticoagulant (NOAC)) can be evaluated using the SAMe-TT2R2 score to help decision-making on the most appropriate oral anticoagulant.
Bleeding risk
Stroke risk assessment should always include an assessment of bleeding risk. This can be done using validated bleeding risk scores, such as the HEMORR2HAGES or HAS-BLED scores. The HAS-BLED score is recommended in guidelines, to identify the high risk patient for regular review and followup and to address the reversible risk factors for bleeding (e.g. uncontrolled hypertension, labile INRS, excess alcohol use or concomitant aspirin/NSAID use). If the patient is taking warfarin, then knowledge of INR control is needed to assess the 'labile INR' criterion in HAS-BLED; otherwise for a non-warfarin patient, this criterion scores zero. A high HAS-BLED score is not a reason to withhold anticoagulation. Also, when compared to HAS-BLED, other bleeding risk scores that did not consider 'labile INR' would significantly underperform in predicting bleeding on warfarin, and would often inappropriately categorise many patients who sustained bleeds as 'low risk'.