CHADS Score (2009)
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CHADS score or CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with nonrheumatic, or nonvalvular, atrial fibrillation (AF) a common and usually benign heart arrythmia. It is used to determine the degree of anticoagulation therapy required, 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 and cause a stroke. The higher a CHADS2 score, the greater the risk of stroke.
2 Risk of stroke
3 Recommendations for anticoagulation
The CHADS2 scoring table is shown below:
C Congestive heart failure 1
H Hypertension (or treated hypertension) 1
A Age >75 years 1
D Diabetes 1
S2 Prior Stroke or TIA 2
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
The CHADS2 method for estimating stroke risk was validated by a cohort study of 1,733 nonrheumatic atrial fibrillation patients aged 65 to 95 who were tracked through Medicare claims. The patients were not given antithrombotic therapy, such as the anticoagulant warfarin or aspirin. According to this study, the annual percentage risk of stroke without antithrombotic therapy is:
Annual Stroke Risk CHADS2 Score Stroke Risk % 95% CI
0 1.9 1.2 – 3.0
1 2.8 2.0 – 3.8
2 4.0 3.1 – 5.1
3 5.9 4.6 – 7.3
4 8.5 6.3 – 11.1
5 12.5 8.2 – 17.5
6 18.2 10.5 – 27.4
To understand what this table means, let’s consider a special type of casino that has a game of chance called Wheel of Misfortune. For example, suppose you have a CHADS2 score of 2 and you don’t take antithrombotic medication such as warfarin or aspirin. Then the table indicates that your annual risk of stroke is 4%. The corresponding Wheel of Misfortune would have 100 possible places to end up on with 4 of the places (i.e. 4 %) marked with the word “stroke” and the rest of the places marked with “safe”. Being a strange casino, a bet is placed for you once a year on some random day without your knowledge. When your Wheel of Misfortune is spun, ending up on any one of the 4 “stroke” places would cause you to have a stroke, while ending up on any of the other places would be safe. This is similar to what a 4% annual stroke risk means.
However, warfarin has its own stroke risk and other drawbacks, which were considered in developing the recommendations of the next section.