## Investigation of Choice for PE Confirmation **Key Point:** CTPA (Computed Tomography Pulmonary Angiography) is the gold standard and first-line imaging modality for confirming or excluding pulmonary embolism in patients with intermediate to high clinical probability. ### Why CTPA is Preferred | Feature | CTPA | V/Q Scan | Pulmonary Angiography | |---------|------|---------|----------------------| | Sensitivity | 94–98% | 60–90% (depends on probability) | 99% | | Specificity | 95–98% | 90–95% | 99% | | Speed | Rapid (minutes) | Slow (hours) | Invasive, time-consuming | | Radiation dose | Moderate | Low | High | | Availability | Widely available | Limited | Rarely used | | Operator dependent | No | Yes | Yes | | Can diagnose alternative pathology | Yes | No | No | **High-Yield:** CTPA is the imaging test of choice because it: 1. Has excellent sensitivity and specificity for PE detection 2. Can identify alternative diagnoses (pneumonia, aortic dissection, pneumothorax) 3. Is rapid and non-invasive 4. Is widely available in most hospitals 5. Allows assessment of RV size and function ### Clinical Context **Clinical Pearl:** In this patient with intermediate Wells probability and normal CXR, CTPA is indicated. If CTPA is contraindicated (e.g., renal insufficiency, iodine allergy), then V/Q scan or compression ultrasound of lower limbs would be alternatives. ### Role of Other Investigations - **V/Q scan:** Used when CTPA is contraindicated or in patients with low-intermediate probability and normal CXR; less specific than CTPA - **Pulmonary angiography:** Invasive gold standard; reserved only for cases where CTPA is inconclusive and clinical suspicion remains very high - **Echocardiography:** Useful for assessing hemodynamic consequences (RV strain) but cannot confirm PE diagnosis
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