Primary Causes of Embolic Stroke
Cardiogenic embolism (20% of ischemic strokes), large-artery atherosclerosis (20%), and small-vessel disease (25%) are the main causes of embolic stroke, with approximately 30% remaining cryptogenic despite thorough evaluation. 1
Cardiac Sources of Embolism
Atrial Fibrillation
- Most common cardiac cause of embolic stroke
- Risk increases with additional factors such as:
- Prior stroke/TIA
- Hypertension
- Heart failure
- Diabetes mellitus
- Age ≥75 years
Valvular Heart Disease
- Rheumatic mitral valve disease significantly increases embolic risk even without AF 1
- Mitral stenosis with prior embolic event or left atrial thrombus requires anticoagulation 1
- Mitral valve prolapse increases stroke risk (RR 2.2), especially with:
- Mitral valve thickening
- Development of AF
- Older age 1
- Mitral annular calcification increases stroke risk (RR 2.1-3.1) 1
- Prosthetic heart valves, especially mechanical valves, pose significant embolic risk 1
Other Cardiac Conditions
- Myocardial infarction with left ventricular thrombi
- Cardiomyopathy with reduced ejection fraction
- Endocarditis (infective and non-bacterial thrombotic)
- 20-40% of endocarditis patients suffer embolic events 1
- Risk factors include vegetation size, mitral valve involvement, and S. aureus infection
- Cardiac tumors
- Myxomas (most common cardiac tumor, 30-40% embolize)
- Papillary fibroelastomas (stroke/TIA is presenting symptom in 50%) 1
Patent Foramen Ovale (PFO) and Atrial Septal Aneurysm (ASA)
- Can allow paradoxical embolism from venous sources
- Particularly significant when both PFO and ASA are present 1
Non-Cardiac Sources
Large-Artery Atherosclerosis (20% of ischemic strokes)
- Extracranial or intracranial segments of carotid or vertebrobasilar arteries 1
- Mechanism: artery-to-artery embolism or hemodynamic insufficiency 1
- Even "non-stenotic" carotid plaques may constitute important sources of cerebral embolism 1
- Aortic arch atherosclerosis
Small-Vessel Disease (25% of ischemic strokes)
- Causes lacunar or subcortical strokes
- Associated with diabetes or hypertension
- Not usually caused by atherosclerosis 1
Other Uncommon Causes
- Fat embolism after trauma
- Tumor embolism
- Gas embolism
- Nonatherosclerotic vasculopathies
- Hypercoagulable states
- Hematologic disorders 1, 2
Cryptogenic Stroke (30% of ischemic strokes)
- Embolic strokes of undetermined source (ESUS)
- Likely thromboembolic in nature
- Potential sources include:
- Minor-risk or covert cardiac sources
- Paradoxical embolism via PFO
- Non-occlusive atherosclerotic plaques 3
Clinical Implications and Pitfalls
Important Diagnostic Considerations
- Timing of symptom onset is crucial for treatment decisions 1
- Multiple small cortical infarcts in middle cerebral artery territory suggest embolic source 1
- Silent cerebral infarctions on imaging may indicate increased stroke risk 1
Treatment Considerations
- Anticoagulation is indicated for:
- Antiplatelet therapy for:
- Non-cardioembolic stroke sources
- Mitral valve prolapse with TIA 1
Common Pitfalls
- Failing to identify the embolic source may lead to inappropriate secondary prevention
- Anticoagulants are contraindicated in infective endocarditis unless indicated for other cardiovascular conditions 1
- Novel oral anticoagulants (factor Xa inhibitors and direct thrombin inhibitors) are not indicated for mechanical heart valves 1
- Assuming emboli from carotid sources only travel ipsilaterally - they can reach contralateral hemispheres through collateral circulation 6
Understanding the specific cause of embolic stroke is essential for implementing appropriate secondary prevention strategies to reduce morbidity and mortality.