Thromboembolism and Atrial Fibrillation

Thromboembolism is a condition in which a thrombus detaches from its site of origin, circulates in the bloodstream as an embolus, and subsequently causes an embolism (occlusion or stenosis of a vessel) at another site in the body.

Atrial fibrillation (AF) is one of the major risk factors for thromboembolism, which in AF most commonly manifests as embolic ischemic stroke (IS).

The risk of ischemic stroke in AF (without anticoagulant therapy) can be calculated using the CHA₂DS₂-VA score.

When estimating thromboembolic risk, the diagnosis of “atrial fibrillation” is essential,

regardless of the AF type according to episodes (paroxysmal, persistent, permanent),
regardless of whether AF is symptomatic or asymptomatic.
Patients with silent AF are at the highest risk, because these patients are unaware that they have AF

and therefore do not receive any anticoagulant therapy, if indicated.

Risk of thromboembolism in AF without anticoagulant therapy

is 0.5–20%, depending on comorbidities and risk factors.
The following table shows the localization and clinical manifestations of thromboembolism in AF.

Illustration depicting a thrombus in the left atrial appendage in atrial fibrillation and its association with thromboembolic complications including ischemic stroke and peripheral embolism.

Thromboembolism and Atrial Fibrillation
Site of embolization	Prevalence	Clinical manifestation
Cerebral arteries	50 – 70 %	Ischemic stroke (IS) Transient ischemic attack (TIA)
Arteries of the lower extremities	15 – 25 %	Ischemia and gangrene of the lower extremities
Renal arteries	10 – 15 %	Lumbar pain Hematuria Arterial hypertension Acute kidney injury
Mesenteric artery	5 – 10 %	Abdominal pain Nausea Vomiting
Coronary arteries	< 5 %	Angina pectoris Myocardial infarction (STEMI, NSTEMI)

20% of all ischemic strokes are caused by thromboembolism in AF.

Mainly in silent AF. These patients are unaware that they have AF and therefore do not receive anticoagulant therapy.

For prevention of thromboembolism, anticoagulant therapy is recommended, not antiplatelet therapy.

Because in AF a fibrin thrombus develops due to blood stasis, most commonly in the left atrial appendage.

There are several scoring systems,

which are able to determine the risk of thromboembolism over one year based on comorbidities and risk factors.
The most common manifestation of thromboembolism in AF is ischemic stroke.
Therefore, scoring systems often assess the risk of ischemic stroke in AF.

Scoring systems use comorbidities and risk factors associated with AF, for example:

Arterial hypertension, diabetes mellitus, obesity, age, left ventricular hypertrophy, left atrial size, sex,
Previous stroke, transient ischemic attack (TIA), proteinuria, chronic kidney disease.

The best-known scoring systems include:

CHADS₂, ATRIA, ABC stroke, GARFIELD-AF, CHA₂DS₂-VASc, CHA₂DS₂-VA.
The most widely used is the CHA₂DS₂-VASc score:

in 2024 it was modified (female sex was removed as a risk factor)
and the CHA₂DS₂-VA score was created.

Each scoring system uses different parameters, but most agree:

that if the risk of thromboembolism is >1–2% per year,
then anticoagulant therapy is indicated for prevention of thromboembolism.

Thromboembolic risk and atrial fibrillation	Class
Atrial fibrillation is one of the major risk factors for thromboembolism, regardless of whether AF is paroxysmal, persistent, permanent, symptomatic, or asymptomatic.	I
Annual thromboembolic risk in % is estimated using the CHA₂DS₂-VASc score or the newer CHA₂DS₂-VA score (since 2024).	I
For prevention of thromboembolism in atrial fibrillation, anticoagulant therapy (not antiplatelet therapy) is recommended.	I
Antiplatelet therapy (Aspirin, Clopidogrel) is not recommended for prevention of thromboembolism in atrial fibrillation.	III

The following table shows the risk of thromboembolism according to the CHA₂DS₂-VASc score,

in patients without anticoagulant therapy.

CHA₂DS₂-VASc score and risk of thromboembolism (1 year)
CHA₂DS₂-VASc	Ischemic stroke	Ischemic stroke/TIA/systemic embolism
0	0,2 %	0,3 %
1	0,6 %	0,9 %
2	2,2 %	2,9 %
3	3,2 %	4,6 %
4	4,8 %	6,7 %
5	7,2 %	10,0 %
6	9,7 %	13,6 %
7	11,2 %	15,7 %
8	10,8 %	15,2 %
9	12,2 %	17,4 %

IS – Ischemic stroke. TIA – Transient ischemic attack.