What is the most helpful investigation for a patient presenting with shortness of breath and chest pain, with a high D-dimer (Elevated D-dimer), stable vital signs, and electrocardiogram (ECG) findings of peaked P wave in lead II and right deviation with right bundle branch block?

CT Pulmonary Angiography (CTPA) is the Most Helpful Investigation

In this patient with shortness of breath, chest pain, elevated D-dimer (800), and ECG findings highly suggestive of acute pulmonary embolism (peaked P wave in lead II, right axis deviation, and right bundle branch block), CT pulmonary angiography is the definitive diagnostic test that should be performed immediately. 1

Clinical Reasoning

High Clinical Probability of Pulmonary Embolism

• The ECG findings of peaked P wave in lead II (P pulmonale), right axis deviation, and new right bundle branch block are classic signs of acute right heart strain, which strongly suggests pulmonary embolism 1
• The combination of acute dyspnea, chest pain, and these specific ECG changes places this patient in a high clinical probability category for PE 1, 2
• The elevated D-dimer of 800 μg/L (above the 500 μg/L cutoff) further supports the diagnosis, though it cannot confirm PE alone 3, 4

Why CT Angiography is Superior in This Case

• For patients with high clinical probability of PE, proceed directly to CT pulmonary angiography without relying on D-dimer results alone, as the pretest probability is already sufficiently elevated to warrant definitive imaging 1, 2
• Thin collimation spiral CT with 1-2 mm image reconstruction has a sensitivity of 95% or higher for segmental or larger pulmonary emboli 1
• CTPA is particularly useful in patients who may have underlying cardiopulmonary disease that would make V/Q scanning nondiagnostic 1
• The test provides rapid, definitive diagnosis and can identify alternative diagnoses if PE is not present 1

Why Other Options Are Less Appropriate

Echocardiography (Option A)

• While echo can demonstrate right heart strain and is valuable for risk stratification in confirmed PE, it cannot definitively diagnose or exclude pulmonary embolism 1
• Echo findings of right ventricular dysfunction are not specific for PE and can result from other causes of right heart strain 1
• Echo is most useful after PE is confirmed to assess hemodynamic significance, not as the primary diagnostic test 1

V/Q Scan (Option B)

• V/Q scanning is recommended as an alternative to CTPA primarily in patients with contraindications to CT contrast (renal failure, contrast allergy) or to reduce radiation exposure in young patients 2
• Approximately 30-50% of V/Q scans are nondiagnostic and require additional testing 2
• In patients with potential underlying cardiopulmonary disease (which may be present given the clinical presentation), V/Q scans have a higher likelihood of being nondiagnostic 1
• V/Q scanning takes longer to perform and interpret compared to CTPA 1

MRA (Option D)

• MRA has limited sensitivity for PE and a high proportion of inconclusive scans, making it not ready for routine clinical practice 2
• Studies show up to 52% of MRA studies are technically inadequate 1
• MRA should only be considered at centers that routinely perform it well and only for patients with contraindications to standard tests 1

Critical Clinical Pitfall to Avoid

• Do not delay definitive imaging to obtain serial troponins or wait for additional testing - the combination of symptoms, ECG findings, and elevated D-dimer already establishes high probability requiring immediate CTPA 1, 2
• The magnitude of D-dimer elevation (800 μg/L) is moderately elevated; while extremely elevated D-dimers (>5000 μg/L) have higher positive predictive value for PE (up to 32%), any elevation above 500 μg/L in the context of high clinical probability warrants immediate imaging 5, 4
• A positive D-dimer alone cannot diagnose PE and must always be followed by confirmatory imaging 2, 6

Management Algorithm

1. Immediate CTPA given high clinical probability based on symptoms and ECG findings 1, 2
2. If CTPA confirms PE, assess hemodynamic stability and consider echocardiography for risk stratification 1
3. If CTPA is contraindicated (severe renal impairment, contrast allergy), proceed to V/Q scanning as alternative 2
4. Initiate anticoagulation immediately if PE is confirmed, without waiting for additional testing 1

Answer: C) CT angiogram