Left atrial thrombus is a clinically significant finding, most commonly associated with atrial fibrillation, rheumatic mitral valve disease, and severe left ventricular dysfunction. Proper classification helps guide anticoagulation, cardioversion planning, and interventional strategy.
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1. Classification Based on Location
A. Left Atrial Appendage (LAA) Thrombus
Most common site (>90% in non-valvular AF)
Best visualized on TEE
Often associated with:
Atrial fibrillation
Low LAA emptying velocity (<20 cm/s)
Spontaneous echo contrast (“smoke”)
Clinical significance: Contraindication to cardioversion and catheter ablation until resolved.
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B. Left Atrial Body Thrombus
Seen in:
Rheumatic mitral stenosis
Severely dilated LA
May be mural or mobile
Higher embolic risk if pedunculated or mobile
More common in valvular AF compared to non-valvular AF.
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2. Classification Based on Mobility
1. Mural (Non-mobile) Thrombus
Attached along LA wall
Broad-based
Lower embolic potential compared to mobile thrombi
2. Pedunculated / Mobile Thrombus
Attached by a stalk
Oscillates within LA cavity
High embolic risk
May mimic atrial myxoma
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3. Classification Based on Morphology (Echocardiographic Appearance)
A. Fresh (Recent) Thrombus
Hypoechoic or isoechoic
Soft appearance
May be associated with dense spontaneous echo contrast
B. Organized (Chronic) Thrombus
More echogenic
Firm and well-defined
May show layered appearance
Chronic thrombi may partially endothelialize.
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4. Classification Based on Underlying Etiology
A. Non-Valvular AF
Mostly LAA thrombus
Associated with CHA₂DS₂-VASc risk factors
B. Valvular AF (e.g., Rheumatic MS)
LA body thrombus more common
Larger clot burden
C. Post-Cardiac Surgery or Device-Related
Around prosthetic valves
Along LA walls or closure devices
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5. Special Classification: Type I vs Type II LA Thrombus (Rheumatic MS Context)
Type I: Confined to LAA
Type II: Extends into LA cavity
Type II carries higher embolic risk and procedural complications during balloon mitral valvotomy.
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Imaging Modalities for Classification
Transthoracic Echo (TTE): Limited sensitivity for LAA
Transesophageal Echo (TEE): Gold standard
Cardiac CT: Useful when TEE contraindicated
Cardiac MRI: Tissue characterization
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Key Clinical Implications
Presence of LA thrombus = defer elective cardioversion
Requires therapeutic anticoagulation (usually ≥3–4 weeks before reassessment)
Repeat TEE to confirm resolution
Persistent thrombus may require long-term anticoagulation
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Summary Table
Basis of Classification Types
Location LAA, LA body
Mobility Mural, Mobile
Morphology Fresh, Organized
Etiology Valvular, Non-valvular, Device-related
Rheumatic MS subtype Type I, Type II
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Left atrial thrombus classification is not merely academic—it directly influences embolic risk assessment, anticoagulation strategy, and procedural planning in atrial fibrillation and rheumatic mitral stenosis.
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