A 58-year-old man with acute onset dyspnea and pleuritic chest pain is suspected of having pulmonary embolism. His D-dimer is elevated at 0.8 μg/mL. Chest X-ray is normal. Which is the investigation of choice to confirm the diagnosis?

Explanation

## Investigation of Choice for Suspected PE **Key Point:** CT pulmonary angiography (CTPA) is the gold standard and first-line imaging modality for diagnosis of acute pulmonary embolism in hemodynamically stable patients with high clinical suspicion. ### Why CTPA is Preferred **High-Yield:** CTPA offers: - High sensitivity (94–98%) and specificity (95–98%) for PE detection - Rapid acquisition (< 1 minute scan time) - Ability to visualize thrombus directly in pulmonary arteries - Assessment of right ventricular strain and alternative diagnoses - Widely available and reproducible - Can detect subsegmental and segmental emboli ### Clinical Context **Clinical Pearl:** In this patient: - Elevated D-dimer + clinical suspicion warrants imaging confirmation - Normal CXR does not exclude PE and makes CTPA interpretation easier (no confounding parenchymal disease) - Hemodynamic stability allows time for CTPA rather than emergent angiography ### CTPA Technique | Feature | Detail | |---------|--------| | **Contrast timing** | Bolus tracking to main pulmonary artery | | **Slice thickness** | ≤ 1 mm for optimal thrombus visualization | | **Sensitivity for** | Main, lobar, segmental emboli (>95%) | | **Subsegmental PE** | Sensitivity ~80–85% (clinical significance debated) | | **Right heart strain** | Can assess RV/LV ratio, guide prognosis | **Warning:** CTPA requires IV contrast — assess renal function and allergy history before ordering. ### Diagnostic Algorithm ```mermaid flowchart TD A[Suspected PE]:::outcome --> B{Clinical probability?}:::decision B -->|High| C[D-dimer often not needed]:::action B -->|Intermediate/Low| D[D-dimer test]:::action D -->|Negative| E[PE excluded]:::outcome D -->|Positive| F[Proceed to imaging]:::action C --> F F --> G{Hemodynamically stable?}:::decision G -->|Yes| H[CTPA]:::action G -->|No/Contraindication| I[Bedside echo ± angiography]:::urgent H --> J[Thrombus visualized?]:::decision J -->|Yes| K[Anticoagulation]:::action J -->|No| L[Alternative diagnosis]:::outcome ``` [cite:Harrison 21e Ch 297]