A 58-year-old man with acute dyspnoea and pleuritic chest pain is suspected of having pulmonary embolism. Which single clinical or investigative finding best distinguishes acute PE from acute myocardial infarction presenting with similar chest pain and dyspnoea?

Explanation

## Distinguishing PE from Acute MI ### Clinical Context Both PE and acute MI can present with chest pain, dyspnoea, and elevated cardiac biomarkers, making differentiation challenging. However, specific clinical and ECG findings can point toward PE. ### Key Discriminating Features | Feature | PE | Acute MI | |---------|----|-----------| | **Leg swelling/DVT signs** | Common (50–80% with DVT) | Absent unless cardiogenic shock | | **Troponin elevation** | Present in 30–50% | Present in >90% | | **S1Q3T3 pattern** | Classic but only 20% sensitive | Rare; indicates inferior MI | | **D-dimer** | Markedly elevated | Mildly elevated or normal | | **Source of thromboembolism** | DVT in legs/pelvis | Cardiac wall thrombus | **Key Point:** Unilateral leg swelling with calf tenderness indicates a source of thromboembolism (DVT), which is the hallmark of PE pathophysiology. This finding is virtually absent in acute MI unless cardiogenic shock develops. **Clinical Pearl:** The presence of DVT signs (asymmetric leg swelling, calf pain, Homan's sign) should immediately raise suspicion for PE and prompt imaging (CT pulmonary angiography or compression ultrasound of the legs). **High-Yield:** While troponin and D-dimer are elevated in both conditions, clinical DVT is a discriminator specific to PE—it represents the source of the embolus and is not expected in uncomplicated MI. ### Why This Matters Identifying DVT as the source of PE allows clinicians to: - Confirm the thromboembolism pathway - Assess for IVC involvement - Plan anticoagulation and consider IVC filter if needed [cite:Harrison 21e Ch 298]