CT Pulmonary Angiography (CTPA) is the Most Appropriate Investigation
In this patient with elevated D-dimer (800 ng/mL) and ECG findings highly suggestive of acute pulmonary embolism—including peaked P waves in lead II, right axis deviation, and right bundle branch block—CT pulmonary angiography (CTPA) should be performed immediately without delay. 1
Clinical Presentation Indicates High Probability of Pulmonary Embolism
This patient's constellation of findings creates a high pretest probability for PE that mandates direct imaging:
ECG findings are classic for acute right heart strain from PE: The combination of peaked P wave in lead II (P pulmonale), right axis deviation, and new RBBB represents acute right ventricular pressure overload, which occurs in 40% of PE patients and indicates hemodynamically significant disease 2, 1
The elevated D-dimer of 800 ng/mL (above the 500 ng/mL threshold) has 96% sensitivity for PE but only 35% specificity, meaning it effectively rules out PE when negative but cannot diagnose it when positive—confirmatory imaging is mandatory 3, 1
In patients with high clinical probability based on symptoms plus ECG changes, a negative D-dimer cannot safely exclude PE, and proceeding directly to CTPA without D-dimer testing is the recommended approach 1, 4
Why CTPA is Superior to Other Options
CTPA has become the primary imaging modality for investigating suspected PE in hemodynamically stable patients, with sensitivity >95% for segmental or larger emboli 1:
CTPA provides definitive diagnosis by directly visualizing thrombus in the pulmonary arterial tree 1, 4
CTPA offers alternative diagnoses if PE is not present, such as pneumonia, aortic pathology, or cardiac issues 1
CTPA is the most cost-effective strategy in diagnostic algorithms for PE 1
Why Other Options Are Inferior
Echocardiography (Option A) has limited utility as a primary diagnostic test:
- Echo can show right ventricular dysfunction and is useful for risk stratification in confirmed PE, but it cannot definitively diagnose or exclude PE 2
- Regional wall motion abnormalities are not specific for acute conditions and may represent old infarction or ischemia 2
- Echo is reserved for hemodynamically unstable patients when CTPA is not immediately available 1
V/Q scan (Option B) is now second-line imaging:
- V/Q scanning is diagnostic in only 30-50% of cases, often yielding non-diagnostic results that require further testing 1
- V/Q is reserved for patients with contraindications to CT (severe contrast allergy, renal failure), younger patients to minimize radiation, or when CT is unavailable 1
- In this stable patient without contraindications to CT, V/Q would delay definitive diagnosis 1
MRA (Option D) has no established role in acute PE diagnosis and would represent inappropriate testing 1
Critical Management Points
Do not wait for additional testing before ordering CTPA—the combination of symptoms, ECG changes, and elevated D-dimer constitutes sufficient indication for immediate imaging 1, 4
Initiate anticoagulation immediately if CTPA confirms PE, as the ECG findings suggest hemodynamically significant disease requiring urgent treatment 1
If CTPA is negative despite high clinical suspicion, consider lower extremity venous ultrasound to detect DVT, which is found in 70% of PE patients and would justify anticoagulation 1
Common Pitfalls to Avoid
Never use D-dimer as a "screening test" in patients with intermediate-to-high probability—it has low positive predictive value (35-50%) and cannot confirm PE 3, 4
Do not delay imaging in a patient with active symptoms and ECG changes suggesting acute right heart strain, as time to diagnosis directly affects outcomes 1, 5
Recognize that extremely elevated D-dimer (>5000 ng/mL) is uniquely associated with severe disease including VTE, sepsis, or cancer, though this patient's level of 800 ng/mL is only modestly elevated 6