Toolbox - the CHA2DS2VASc risk tool

The tool

The original CHADS₂ tool was developed to identify those patients with AF at high risk of having an AF-related stroke.¹ The new 2013-14 QOF uses CHADS₂ in an indicator requiring that all patients with AF should have an annual risk score where 1 point is given for each of the risk factors and 2 for a previous stroke.

When the score is 2 or more the patient is at high risk of stroke and an oral anticoagulant should be considered (QOF indicator AF004). When the score is 1 then the risk is moderate with an annual stroke rate of 2.8%, and patients should discuss the option of anticoagulation (AF003). A score of 0 does not necessarily infer a low risk, as the mean annual risk is 1.9%. There are other risk factors which have been identified which help to identify those people at lowest risk and they are included in the CHA₂DS₂VASc tool.²

CHADS₂ scoring system for non-valvular AF¹

	RISK FACTOR	YES	NO
C	Congestive heart failure	1 point	0
H	Hypertension (160/90)	1 point	0
A	Age >75	1 point	0
D	Diabetes	1 point	0
S₂	Stroke or TIA	2 points	0
	Consider warfarin	>=2

CHADS₂ score and stroke¹

CHADS₂ score	Adjusted annual stroke rate (%)	NNT 1 year warfarin
0	1.9	80
1	2.8	55
2	4	38
3	5.9	26
4	8.5	18
5	12.5	12
6	18.2	8

When to use the new tool

The CHADS₂ tool is easy to remember and if the patient scores 1 or more then they should be considered at moderate or high stroke risk.

In those who score less than 2 then the CHA₂DS₂VASc tool will help identify the truly low risk and enable all other patients with AF to be considered for anticoagulation.

This is important for women, those over 65 and people who have existing vascular disease other than stroke - all have an increased risk in addition to the factors included in the original CHADS₂ score.

A recent study³ followed up patients with a CHADS₂ score of 0 and found that at one year there was a thromboembolism rate of 1.67%, but when patients were scored using CHA₂DS₂VASc those with a score of 0 had an annual thromboembolism rate of 0.78%, highlighting the value of the tool.

CHA₂DS₂VASc to identify the truly low risk (score=0)

	RISK FACTOR	YES
C	Congestive heart failure	1 point
H	Hypertension (160/90)	1 point
A₂	Age >75	2 points
D	Diabetes	1 point
S₂	Stroke or TIA	2 points
V	Vascular disease, PAD, aortic plaque	1 point
A	Age 65-74	1 point
Sc	Sex category female (important over 65)	1 point
	Score 2 or more, high risk =>20% 10 year

This means that a lady of 72 who has had a previous MI will have an additional three risk factors and that her score will have been increased by 3 and her annual stroke risk increase from 1.9% to 3.2%, requiring a discussion about the benefits of oral anticoagulation for stroke prevention.

Comparison of the two scores

CHADS₂	Annual stroke risk (%)	CHA₂DS₂VASc	Annual stroke risk (%)
0	1.9	0	0
1	2.8	1	1.3
2	4	2	2.2
3	5.9	3	3.2
4	8.5	4	4.0
5	12.5	5	6.7
6	18.2	6	9.8
		7	9.6
		8	6.7
		9	15.2

Why has this become important?

GPs are much more aware of the high risk of thrombotic stroke associated with AF and the benefits of anticoagulation. There is a large evidence base for the benefits of well-controlled warfarin with patients at low bleeding risk when INR is within the pre-specified ranges. There is also the option to use other effective oral agents which may be considered more suitable for some patients, in particular for those in whom anticoagulation within the target ranges was difficult to achieve.

GPs are more confident at discussing the risks and benefits of anticoagulation in those at lower risk who are now clearly identified using the CHA₂DS₂VASc tool.

It is now clear that those at intermediate risk do not benefit from antiplatelet therapy and aspirin is not included in the updated ESC Guidelines from 2012.⁴ Where the choice is anticoagulation or no antithrombotic therapy it is extremely important to assess risk as accurately as possible and offer our patients the best treatment.

Dr Kathryn Griffith is GP and GPSI in cardiology in York

References