A 62-year-old woman presents with acute dyspnoea and syncope. Investigations show right ventricular dysfunction on echocardiography and elevated BNP. Which single finding most reliably distinguishes massive PE from acute decompensated heart failure in this haemodynamically unstable patient?

## Distinguishing Massive PE from Acute Decompensated Heart Failure ### Clinical Challenge Both conditions present with acute dyspnoea, syncope, RV dysfunction, and elevated natriuretic peptides — making differentiation challenging. A single reliable laboratory discriminator is needed in the haemodynamically unstable patient. ### Why Option B is Correct: Markedly Elevated D-dimer with Normal Cardiac Troponin | Feature | Massive PE | Acute Decompensated HF | |---------|-----------|------------------------| | **D-dimer** | Markedly elevated (high sensitivity ~97%) | May be mildly elevated but not markedly so | | **Cardiac Troponin** | Usually normal or mildly elevated (RV strain only) | Often significantly elevated (myocardial injury/ischaemia) | | **BNP/NT-proBNP** | Elevated (RV strain) | Markedly elevated (chronic + acute) | | **Pulmonary artery pressure** | Acutely elevated (rarely >50 mmHg in acute PE) | Chronically elevated (can be very high) | | **Orthopnoea/PND** | Usually absent, but CAN occur with severe RV failure | Typically present in chronic HF | **Key Point:** A **markedly elevated D-dimer** has ~97% sensitivity for PE (Harrison 21e, Ch 273). In acute decompensated HF, D-dimer may be mildly elevated due to inflammation but is rarely markedly elevated. Conversely, **cardiac troponin** is significantly elevated in acute decompensated HF due to myocardial injury, whereas in massive PE, troponin elevation is typically mild and reflects RV strain rather than primary myocardial damage. The combination of markedly elevated D-dimer + normal/near-normal troponin is the most reliable single biochemical discriminator. **Clinical Pearl:** Absence of orthopnoea/PND (Option D) is an unreliable discriminator — severe RV failure in massive PE can cause pulmonary oedema and orthopnoea. Elevated pulmonary artery systolic pressure (Option A) occurs in both conditions. Acute onset without prior dyspnoea (Option C) is suggestive but not reliably distinguishing, as acute decompensated HF can also present de novo. **High-Yield:** D-dimer has a high negative predictive value for PE. In the haemodynamically unstable patient, a markedly elevated D-dimer with a normal or near-normal troponin strongly favours massive PE over acute decompensated HF, where troponin elevation is expected. Confirm with CTPA or bedside echocardiography (McConnell's sign). ### Diagnostic Approach - **Markedly elevated D-dimer + normal troponin** → Massive PE until proven otherwise → CTPA or empiric thrombolysis if too unstable - **Elevated troponin + mildly elevated D-dimer** → Acute decompensated HF more likely → Echocardiography, BNP trend, clinical history [cite: Harrison 21e Ch 273; ESC Guidelines on Pulmonary Embolism 2019]