Condition	Points
C	Congestive heart failure Congestive heart failure Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...	1
H	Hypertension Hypertension Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and... : blood pressure consistently above 140/90 mmHg (or treated hypertension on medication)	1
A	Age ≥75 years	1
D	Diabetes mellitus Diabetes mellitus Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...	1
S2	Prior Stroke Stroke A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...  or TIA Transient ischemic attack A transient ischemic attack is a transient episode of neurologic dysfunction caused by ischemia – either focal brain, spinal cord or retinal – without acute infarction...	2

The CHADS₂ score is a clinical prediction rule

Clinical prediction rule

A clinical prediction rule is type of medical research study in which researchers try to identify the best combination of medical sign, symptoms, and other findings in predicting the probability of a specific disease or outcome....

 for estimating the risk of stroke

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

 in patients with non-rheumatic

Rheumatic fever

Rheumatic fever is an inflammatory disease that occurs following a Streptococcus pyogenes infection, such as strep throat or scarlet fever. Believed to be caused by antibody cross-reactivity that can involve the heart, joints, skin, and brain, the illness typically develops two to three weeks after...

 atrial fibrillation

Atrial fibrillation

Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...

 (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 chamber

Heart chamber

aHeart chamber is a general term used to refer to any chambers of the mammalian heart. The heart consists of four chambers: the right and left atrium and the right and left ventricle. The top chambers are connected to the bottom chambers by valves and are separated by the coronary sulcus...

s, 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. 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 above: adding together the points that correspond to the conditions that are present results in the CHADS₂ score, that is used to estimate stroke risk.

Stroke risk assessment, and antithrombotic therapy

Annual Stroke Risk

CHADS2 Score	Stroke Risk %	95% CI Confidence interval In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
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

According to the findings of the initial validation study, the risk of stroke as a percentage per year for the CHADS₂ score is shown in the Table.

The CHADS₂ score does not include some common stroke risk factors and its various pros/cons have been carefully discussed. Nonetheless, this score is simple and thus it has become widely used.

To complement the CHADS₂ score, by the inclusion of additional 'stroke risk modifier' risk factors, the CHA2DS2-VASc score has been proposed. These additional non-major stroke risk factors include age 65-74, female gender and vascular disease. In the CHA2DS2-VASc score 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 therapy (OAC) such as warfarin (target INR

Prothrombin time

The prothrombin time and its derived measures of prothrombin ratio and international normalized ratio are measures of the extrinsic pathway of coagulation. This test is also called "ProTime INR" and "INR PT". They are used to determine the clotting tendency of blood, in the measure of warfarin...

 of 2-3) or one of the new OAC drugs, such as dabigatran) should be prescribed.

If the CHADS₂ score is 0-1, other stroke risk modifiers could 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), antithrombotic therapy with OAC or aspirin (OAC preferred) is recommended, and patient values and preferences should be considered.

A CHA2DS2-VASc score score=0 corresponds to a 'truly low risk,’ and thus the recommendation is to prescribe either aspirin or no antithrombotic therapy, but 'no antithrombotic therapy' is preferred.

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 latter is recommended in the ESC and Canadian guidelines. 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 scores zero.

Anticoagulation

Score	Risk	Anticoagulation Therapy	Considerations
0	Low	None or Aspirin Aspirin Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...	Aspirin daily
1	Moderate	Aspirin or Warfarin	Aspirin daily or raise INR to 2.0-3.0, depending on patient preference
2 or greater	Moderate or High	Warfarin Warfarin Warfarin is an anticoagulant. It is most likely to be the drug popularly referred to as a "blood thinner," yet this is a misnomer, since it does not affect the thickness or viscosity of blood...	Raise INR to 2.0-3.0, unless contraindicated

Treatment strategies recommended based on the CHADS₂ score are shown in the table.

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, which recommend the management as shown in the following table:

CHA₂DS₂-VASc

	Condition	Points
C	Congestive heart failure (or Left ventricular systolic dysfunction)	1
H	Hypertension Hypertension Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and... : blood pressure consistently above 140/90 mmHg (or treated hypertension on medication)	1
A2	Age ≥75 years	2
D	Diabetes Mellitus	1
S2	Prior Stroke Stroke A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...  or TIA Transient ischemic attack A transient ischemic attack is a transient episode of neurologic dysfunction caused by ischemia – either focal brain, spinal cord or retinal – without acute infarction...  or thromboembolism	2
V	Vascular disease (eg. peripheral artery disease, myocardial infarction, aortic plaque)	1
A	Age 65-74 years	1
Sc	Sex category (i.e. female gender)	1

The CHA₂DS₂-VASc score is a refinement of CHADS₂ score and extends the latter by including additional common stroke risk factors, as discussed below.

The maximum CHADS₂ score is 6, whilst the maximum CHA₂DS₂-VASc score is 9.

Anticoagulation

Score	Risk	Anticoagulation Therapy	Considerations
0	Low	No antithrombotic therapy (or Aspirin Aspirin Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer... )	No antithrombotic therapy (or Aspirin 75-325mg daily)
1	Moderate	Oral anticoagulant (or Aspirin)	Oral anticoagulant, either new oral anticoagulant drug eg dabigatran or well controlled warfarin at INR 2.0-3.0 (or Aspirin 75-325mg daily, depending on factors such as patient preference)
2 or greater	High	Oral anticoagulant	Oral anticoagulant, using either a new oral anticoagulant drug (eg rivaroxaban or dabigatran) or well controlled warfarin at INR 2.0-3.0

Based on the ESC guidelines on Atrial Fibrillation, oral anticoagulation is recommended or preferred for patients with one or more stroke risk factors (ie. a CHA₂DS₂-VASc score of 1 and above). 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 new 'safer' OAC drugs.