A 68-year-old man with atrial fibrillation and a recent myocardial infarction is found to have a mural thrombus on echocardiography. What is the most common site of origin of systemic arterial emboli in such patients?

Explanation

## Most Common Source of Systemic Arterial Emboli ### Pathophysiology of Cardiac Thrombus Formation **Key Point:** The left ventricular apex (particularly following anterior wall myocardial infarction) is the most common site of mural thrombus formation and the leading cardiac source of systemic arterial emboli. ### Why the LV Apex in Anterior MI? 1. **Akinetic/dyskinetic segment**: Anterior wall MI causes transmural necrosis and loss of contractility at the apex, creating a stasis zone. 2. **Endocardial injury**: Myocardial necrosis exposes thrombogenic tissue factor and collagen, triggering coagulation. 3. **Blood stasis**: The non-contractile apex allows blood pooling, satisfying Virchow's triad (stasis, endothelial injury, hypercoagulability). 4. **Frequency**: LV apical thrombus occurs in ~5–15% of anterior MI cases (higher with large, anterior infarcts and reduced ejection fraction). ### Cardiac Sources of Systemic Emboli — Frequency Ranking | Source | Frequency | Clinical Context | | --- | --- | --- | | **LV mural thrombus (anterior MI)** | Most common | Acute anterior MI, akinetic apex | | **Left atrial appendage thrombus** | Common | Atrial fibrillation (AF), dilated LA | | **Dilated cardiomyopathy** | Moderate | Severe LV dysfunction, EF <20% | | **Rheumatic mitral stenosis** | Moderate | AF + mitral stenosis | | **Prosthetic valve** | Less common | Mechanical prosthesis | | **Endocarditis vegetations** | Less common | Infective endocarditis | | **RV thrombus** | Rare | RV infarction, PE source | **High-Yield:** While the left atrial appendage (LAA) is the most common source of emboli in **atrial fibrillation alone**, the LV apex is the most common overall cardiac source of systemic arterial emboli when considering all cardiac pathology, especially in the acute post-MI setting. ### Clinical Implications **Clinical Pearl:** Anticoagulation (warfarin or DOAC) is indicated for: - LV thrombus detected on echo post-MI (3 months minimum, longer if EF remains <35%) - Atrial fibrillation (CHA₂DS₂-VASc score ≥1 for men, ≥2 for women) - Dilated cardiomyopathy with EF <35% ### Mechanism Diagram ```mermaid flowchart TD A[Anterior Wall MI]:::outcome --> B[Transmural myocardial necrosis at apex]:::outcome B --> C{Virchow's Triad}:::decision C -->|Stasis| D[Akinetic apex, blood pooling]:::action C -->|Endothelial injury| E[Exposed TF, collagen, phosphatidylserine]:::action C -->|Hypercoagulability| F[Post-MI inflammatory state]:::action D --> G[Mural thrombus formation]:::outcome E --> G F --> G G --> H[Systemic arterial embolism]:::urgent H --> I[Stroke, limb ischemia, mesenteric infarction]:::urgent ``` [cite:Robbins 10e Ch 4]