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Wikipedia

CHADS score or CHADS₂ score is a clinical prediction rule for estimating the risk of stroke in patients with nonrheumatic 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. A high CHADS₂ score corresponds to a greater risk of stroke, and vice-versa. 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 below:

	Condition	Points
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

According to the findings of the validation study, the risk of stroke as a percentage per year 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 the anticoagulant warfarin. Then 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 marked with the word "stroke" and 96 of the places marked with "safe". Being a strange casino, a bet is placed for you once a year on any 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 and ending up on any of the other 96 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.

Recommendations for anticoagulation

The following treatment strategies were recommended:

Score	Risk	Anticoagulation Therapy	Considerations
0	Low	Aspirin	325 mg/day most likely to offer benefit, although lower doses may be similarly efficacious
1	Moderate	Aspirin or Warfarin	ASA daily or Raise INR to 2.0-3.0, depending on factors such as patient preference
2 or greater	Moderate or High	Warfarin	Raise INR to 2.0-3.0, unless contraindicated (e.g., history of falls, clinically significant GI bleeding, inability to obtain regular INR screening)