CHADS Score

Overview
CHADS score or CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with non-rheumatic atrial fibrillation (AF), 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, 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 blood 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 was validated by a study of nonrheumatic atrial fibrillation patients aged 65 to 95 who were not prescribed the anticoagulant warfarin.

Method
The CHADS2 scoring table is shown above:

Adding together the points that correspond to the conditions that a patient has will result in the CHADS2 score. This score is used in the next section to estimate stroke risk.

Risk of stroke
According to the findings of the validation study, the risk of stroke as a percentage per year is shown in the table titled Annual Stroke Risk:

While the CHADS2 score provides prognostic information regarding the natural history of non-valvular atrial fibrillation (NVAF) in the absence of warfarin therapy, it should be noted that warfarin therapy also has an associated stroke risk (particularly hemorrhagic stroke) and a risk of major bleeding, and these considerations were taken into account in the development of the recommendations in the next section.

The CHADS2 score has various limitations, which have been debated. Notably, many stroke risk factors have not been included, and whilst simple, the score has only modest predictive value for thromboembolism.

In order to improve upon the prognostic utility of the CHADS2 score and to incorporate additional stroke risk factors, the CHA2DS2-VASc score has been proposed. These additional 'clinically relevant non-major' stroke risk factors include 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 CHA2DS2-VASc score has been used in the new European Society of Cardiology guidelines for the management of atrial fibrillation.

The European Society of Cardiology (ESC) guidelines recommend that if the patient has a CHADS2 score of 2 and above, oral anticoagulation (OAC) therapy is recommended. OAC options include warfarin with an INR target of 2-3 or dabigatran.

If the CHADS2 score is 0-1, other stroke risk modifiers should be considered: (i) If there are 2 or more risk factors (essentially a CHA2DS2-VASc score score of 2 or more), OAC is recommended; and (ii) If there is 1 risk factor (essentially a CHA2DS2-VASc score score=1), then antithrombotic therapy with either OAC or aspirin (OAC preferred) is recommended.

If patients have a CHA2DS2-VASc score of 0, then such patients are ‘truly low risk’. The ESC guidelines recommend either aspirin or no antithrombotic therapy, but 'no antithrombotic therapy' is preferred.

Anticoagulation based on the CHADS2 score
The following treatment strategies are recommended in the table below entitled Anticoagulation based on the CHADS2 score:

For detailed recommendations on how the treatment recommendations based on the CHADS2 score are modified by considering additional 'stroke risk modifier' risk factors using the CHA2DS2-VASc score, see ESC guideline recommendations.

Use of the CHADS2 Score in Populations without Atrial Fibrillation
The CHADS2 score has been shown to also predict the risk of ischemic stroke among those patients who do not have atrial fibrillation It should be noted however, that the CHADS2 Score has not been used to guide the selection of anticoagulation therapy in patients without atrial fibrillation.

Limitations
The CHADS2 score may underestimate the risk of stroke in those patients over the age of 75 years. For this reason, some authors have advocated the use of anticoagulation among patients who are over the age of 75 years if there are no contraindications.