A 58-year-old man from Mumbai presents to the emergency department with acute onset dyspnea and right-sided pleuritic chest pain for 6 hours. He underwent total knee replacement 10 days ago. On examination, heart rate is 110/min, respiratory rate 28/min, blood pressure 128/82 mmHg, and oxygen saturation 92% on room air. Unilateral leg swelling is noted on the operated side. Chest X-ray shows a wedge-shaped opacity in the right lower lobe. ECG reveals sinus tachycardia with T-wave inversion in leads V1–V3. D-dimer is markedly elevated at 2.8 µg/mL (normal <0.5). What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Pulmonary Embolism with Infarction ### Key Clinical Features **Key Point:** The constellation of recent immobilization (post-operative state), unilateral leg swelling (DVT sign), acute dyspnea, pleuritic chest pain, and wedge-shaped opacity on CXR is pathognomonic for pulmonary embolism with pulmonary infarction. ### Pathophysiology of PE-Related Infarction Pulmonary infarction occurs in ~10% of PE cases and requires three conditions: 1. Occlusion of a peripheral pulmonary artery 2. Intact bronchial circulation compromise (usually pre-existing cardiopulmonary disease) 3. Alveolar hemorrhage leading to wedge-shaped consolidation **Clinical Pearl:** Wedge-shaped (Hampton's hump) opacities are highly specific for PE with infarction and are located at the lung periphery, typically in lower lobes due to gravity-dependent blood flow. ### Diagnostic Criteria Met | Finding | Significance | |---------|-------------| | Post-operative immobilization (10 days) | Major risk factor for VTE | | Unilateral leg swelling | Indicates DVT (source of embolism) | | Acute dyspnea + pleuritic pain | Classic PE presentation | | Wedge-shaped CXR opacity | Pathognomonic for PE with infarction | | ECG T-wave inversions V1–V3 | Right ventricular strain pattern | | Elevated D-dimer | Highly sensitive for VTE | | Hypoxemia (SaO₂ 92%) | Due to V/Q mismatch | **High-Yield:** The combination of **wedge-shaped opacity + pleuritic pain + DVT signs** makes PE with infarction the diagnosis. Isolated PE without infarction typically has normal or non-specific CXR findings. ### Why Infarction Occurred Here This patient likely has compromised bronchial circulation due to post-operative state and possible underlying cardiac stress, allowing the peripheral PE to cause tissue necrosis and hemorrhage—the hallmark of infarction. **Mnemonic: WEDGE** — **W**idth limited to one segment, **E**mbolism source (DVT), **D**yspnea acute, **G**radient opacity (peripheral), **E**levated D-dimer. ### Confirmation CT pulmonary angiography (CTPA) would show filling defect in segmental or subsegmental pulmonary artery with corresponding wedge consolidation on lung window. [cite:Robbins 10e Ch 15]