What is a mural thrombus?

Mural Thrombus: Definition, Clinical Significance, and Management

A mural thrombus is a blood clot that forms and adheres to the inner wall (endothelium) of a blood vessel or cardiac chamber without completely occluding the lumen. These thrombi typically develop in areas of blood stasis, endothelial injury, or hypercoagulable states, following Virchow's triad of thrombogenesis 1.

Locations and Types of Mural Thrombi

Mural thrombi can occur in various locations:

1. Left Ventricular (LV) Thrombus

   • Most commonly forms after anterior myocardial infarction (MI)
   • Typically located at the cardiac apex where wall motion abnormalities create blood stasis
   • Occurs in up to 24% of anterior MI patients as detected by cardiac MRI 2
   • More common in patients with severely reduced ejection fraction (<30%) 1

2. Aortic Mural Thrombus

   • Can form in the thoracic or abdominal aorta
   • May develop even in non-aneurysmal or minimally atherosclerotic vessels 3
   • More frequently located in the descending aorta, less commonly in the aortic arch 4

Pathophysiology

Mural thrombi form due to:

• Blood stasis - Particularly in areas of poor contractility (e.g., akinetic myocardial segments after MI)
• Endothelial injury - Following plaque rupture or inflammation
• Hypercoagulable states - Various prothrombotic conditions

In myocardial infarction, the pathophysiology involves:

• Plaque rupture leading to coronary thrombosis and myocardial injury 2
• Resulting wall motion abnormalities creating areas of blood stasis
• Formation of thrombus that adheres to the damaged endocardium, typically at the apex 2

Clinical Significance

Mural thrombi are clinically significant because:

1. Embolic Risk: They serve as a source of systemic emboli

   • Without anticoagulation, approximately 10% of patients with LV thrombus develop clinically evident cerebral infarction 1
   • Aortic mural thrombi can cause peripheral arterial embolization with high complication rates 3

2. Diagnostic Challenge: Often asymptomatic until embolization occurs

   • May be found incidentally on imaging studies
   • Require high-resolution imaging for accurate detection

Detection Methods

The detection of mural thrombi requires appropriate imaging:

• Transthoracic Echocardiography (TTE): Standard initial test but relatively insensitive
• Contrast Echocardiography: Significantly improves detection of LV thrombus
• Cardiac MRI: Highest sensitivity for LV thrombus detection (detected LV thrombus in 12.3% of patients compared to 6.2% with standard TTE) 2
• CT Angiography: Useful for detecting aortic mural thrombi

Management

Management of mural thrombi depends on location and clinical context:

Left Ventricular Thrombus:

• Anticoagulation: Primary treatment for LV thrombus
  • Vitamin K antagonists (VKAs) with target INR 2.0-3.0 for approximately 3 months 2
  • Reduces the risk of embolism by 86% and results in resolution of LV thrombus in 68% of cases 2
  • DOACs (direct oral anticoagulants) have shown variable results compared to warfarin 2

Aortic Mural Thrombus:

• Anticoagulation: Often used as first-line therapy but associated with 25-50% embolic recurrence rate 3
• Surgical Intervention: May be necessary for mobile thrombus, recurrent embolism, or contraindication to anticoagulation
• Endovascular Approaches: Emerging as effective options for covering aortic thrombi 3

Special Considerations

• Recurrence Risk: After resolution of LV thrombus, patients with persistent wall motion abnormalities remain at risk for recurrence 2
• Imaging Follow-up: Serial imaging is recommended to confirm thrombus resolution
• Duration of Therapy: Typically 3 months for LV thrombus, but may need to be extended in cases of persistent risk factors 2

In summary, mural thrombi represent a significant clinical entity with potential for serious embolic complications. Early detection with appropriate imaging and prompt initiation of anticoagulation therapy are essential for reducing morbidity and mortality associated with these thrombi.