A 58-year-old woman presents to the emergency department with acute onset dyspnea and right-sided pleuritic chest pain. She underwent total abdominal hysterectomy 5 days ago. On examination, she is tachycardic (HR 118/min), tachypneic (RR 28/min), and hypoxic (SpO₂ 88% on room air). Her right calf shows mild swelling and tenderness. Chest X-ray is normal. ECG shows sinus tachycardia with T-wave inversions in leads V1–V4. D-dimer is markedly elevated at 2.8 μg/mL. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Pulmonary Embolism ### Key Clinical Features **Key Point:** This patient presents with the classic triad of PE: acute dyspnea, pleuritic chest pain, and hypoxemia in the setting of a major risk factor (recent surgery). ### Risk Factors Present - Recent major surgery (total abdominal hysterectomy 5 days ago) — immobilization + endothelial injury + hypercoagulability - Clinical signs of DVT: right calf swelling and tenderness - Prolonged immobilization post-operatively ### Diagnostic Findings | Finding | Significance in PE | |---------|-------------------| | Tachycardia (HR 118) | Compensatory response to hypoxemia and reduced cardiac output | | Tachypnea (RR 28) | Increased dead space ventilation; reflex hyperventilation | | Hypoxemia (SpO₂ 88%) | Ventilation-perfusion mismatch; right-to-left shunting | | Normal CXR | Typical in PE; rules out pneumonia/pneumothorax | | ECG: T-wave inversion V1–V4 | Indicates right ventricular strain (classic "anterior NSTEMI pattern" but in PE context) | | Elevated D-dimer (2.8 μg/mL) | Highly sensitive for PE (>95%); rules out PE if <0.5 μg/mL | **High-Yield:** The combination of normal chest X-ray + hypoxemia + tachycardia + elevated D-dimer is pathognomonic for PE until proven otherwise. ### Pathophysiology 1. **Acute obstruction** of pulmonary arteries by thrombus 2. **Ventilation-perfusion mismatch**: ventilated but unperfused alveoli → dead space 3. **Right ventricular strain**: increased afterload → RV dilatation → septal shift → ECG changes 4. **Hypoxemia** from: - V/Q mismatch (primary) - Right-to-left shunting through patent foramen ovale (if present) - Decreased cardiac output **Clinical Pearl:** ECG changes in PE mimic anterior MI but occur without coronary artery occlusion; troponin may be mildly elevated due to RV infarction, but the clinical context (recent surgery, DVT signs, normal CXR) points to PE. ### Next Steps in Management 1. Immediate CT pulmonary angiography (CTPA) — gold standard 2. Consider V/Q scan if renal impairment or contrast allergy 3. Anticoagulation (unfractionated heparin or LMWH) while awaiting confirmation 4. Oxygen supplementation to target SpO₂ >90% 5. Risk stratification for thrombolysis (hemodynamically stable → anticoagulation alone) **Mnemonic:** **PERC** (Pulmonary Embolism Rule-out Criteria) — if all are negative, PE is very unlikely: **P**ulse <100, **E**xygen sat >94%, **R**espiration <20, **C**hest pain absent, **C**linical DVT signs absent. This patient fails PERC (tachycardia, hypoxia, pleuritic pain, DVT signs) → PE must be ruled in. [cite:Harrison 21e Ch 297]