Essence of this Article
The incidence of stroke in patients with atrial fibrillation (AF) is 2–17 times greater than in the general population, depending on the cause of AF. In addition, cardioembolic stroke is one of the most common complications of AF. The risk of stroke in patients with AF is also dependent on several risk factors, including age, with older patients being at higher risk. Several risk assessment tools are available to clinicians to help estimate the risk of stroke. One well-validated and widely-used tool is the CHA2DS2-VASc score, which identifies both major risk factors and clinically relevant non-major risk factors.
Atrial fibrillation is a major risk factor for stroke
The incidence of stroke in patients with non-valvular AF (i.e. AF not caused by damage to the heart valves) is between two- and sevenfold greater than that in the general population. For patients with AF caused by valvular disease, the risk of stroke is increased 17-fold.183
Cardioembolic stroke is one of the main complications of AF, it occurs when stagnant blood in the fibrillating atrium forms a thrombus that embolizes to the circulation, blocking arterial blood flow and causing ischaemic injury. These characteristics are consistent with the three factors first identified by Virchow as contributing to the formation of deep vein thrombosis.
In AF, Virchow’s triad184 consists of:
- Stagnant blood flow in the left atrium, visible on an echocardiogram as spontaneous echo contrast
- Anatomical cardiac wall defects, such as progressive atrial dilatation
- Hyperactive platelets and activation of coagulation factors, contributing to an increased propensity for thrombus formation
The risk of stroke in patients with AF is dependent on the presence of additional risk factors. These include advancing age – in the Framingham study, the annual risk was 1.5% in those aged 50–59 years and 23.5% in those aged 80–89 years.179 Several risk assessment scoring systems are available to help clinicians estimate the risk of stroke in patients with AF, and to guide recommendations for antithrombotic therapy.
One simple, well-validated points-based risk assessment tool widely used to assess individual patient risk for stroke is known by the acronym ‘CHADS2’.185
Stroke risk assessment: CHADS2 score
|C||Congestive heart failure||1|
|A||Age ≥75 years||1|
|S2||Prior stroke/transient ischaemic attack/thromboembolism||2|
|Source: Adapted from Gage et al. (2001).185|
Link to online CHADS2 score calculator:
The CHADS2 risk assessment score does not incorporate a number of documented risk factors for stroke. Therefore, in an effort to improve its predictive value, especially for low-risk patients, the CHA2DS2-VASc score has been developed.186 This is now preferred over CHADS2 in the latest European 2012 and American 2014 guidelines.537, 187 CHA2DS2-VASc identifies ‘major’ risk factors, comprising stroke/transient ischaemic attack/thromboembolism and age ≥75 years, and ‘clinically relevant non-major’ risk factors, comprising congestive heart failure, hypertension, diabetes mellitus, age 65–74 years, female gender and vascular disease.188
Stroke risk assessment: CHA2DS2-VASc score
|C||Congestive heart failure/left ventricular dysfunction||1|
|A2||Age ≥75 years||2|
|S2||Stroke/transient ischaemic attack/thromboembolism||2|
|V||Vascular disease (prior myocardial infarction, peripheral artery disease, aortic plaque)||1|
|A||Age 65–74 years||1|
|Sc||Sex category (i.e. female gender)||1|
|Source: Adapted from Lip et al. (2010).186|
Link to online CHA2DS2-VASc score calculator:
In both schemes, patients with a score of ≥2 are considered to be at high risk of stroke and oral anticoagulation therapy is recommended by all guidelines. Those with a score of 1 are at moderate risk of stroke, unless they are female patients with a CHA2DS2-VASc-score of 1 by virtue of gender alone, in which case they should be classified as low risk.187 Guidelines vary in their recommendations for antithrombotic therapy for patients with moderate stroke risk.
Patients with a CHA2DS2-VASc score of 0 are at low risk of stroke and do not require antithrombotic therapy.186 Traditionally, patients with a CHADS2 score of 0 have also been considered to be at low risk of stroke. However, these patients may have a CHA2DS2-VASc score of between 0 and 3 (if they are female, aged 65–75 and have vascular disease) and registry data has demonstrated that the non-anticoagulated stroke rate in patients with a CHADS2 score of 0 can range from 0.8%/year (CHA2DS2-VASc score=0) to 3.2%/year (CHA2DS2-VASc score=3) after 1 year of follow-up.189 Thus patients with a CHADS2 score of 0 are not necessarily at low risk of stroke, and anticoagulation decisions simply based on a CHADS2 score of ≥1 may leave many patients at an unacceptable risk of stroke.