What is the best initial imaging test to rule out pulmonary embolism (PE) in a patient with exertional dyspnea and chest pain?

CT Pulmonary Angiography Should Be Ordered Now

In this hemodynamically stable patient with intermediate pretest probability of PE, CT pulmonary angiography (CTPA) is the appropriate next test to rule out pulmonary embolism. 1

Clinical Context and Risk Stratification

This 64-year-old patient presents with exertional dyspnea and chest pain, which are classic symptoms of PE, though nonspecific 2, 3. His clinical profile places him at intermediate pretest probability:

• Age >50 years (fails PERC criteria) 4
• Tachycardia (pulse 95/min, approaching the 100/min threshold) 4
• Recent major surgery (CABG 5 years ago is remote, but post-operative state is a risk factor) 2
• No hemoptysis, leg edema, or obvious DVT signs 4

The oxygen saturation of 96% is borderline but above the PERC threshold of 94% 4. However, PERC criteria cannot be applied here because the patient is >50 years old and has tachycardia, which violates at least two PERC criteria 4.

Why D-Dimer Is Not the Answer

D-dimer testing (Option A) would be appropriate only if this patient had LOW pretest probability AND met all PERC criteria, or had intermediate probability in an outpatient emergency department setting. 1, 4, 5 However, several factors make D-dimer less useful here:

• D-dimer has limited utility in hospitalized patients because it is frequently elevated due to comorbid conditions, recent surgery, and other factors 1, 4
• This patient has significant cardiovascular disease (CAD, prior CABG, hypertension), which increases the likelihood of false-positive D-dimer results 1
• In patients with high clinical suspicion or intermediate-to-high probability, proceeding directly to imaging is more appropriate 1, 4

Why CTPA Is the Correct Choice

CTPA has become the primary imaging modality for investigating suspected PE in hemodynamically stable patients 1:

• Sensitivity >95% for segmental or larger emboli 5
• Can be performed immediately without waiting for D-dimer results 1
• Provides alternative diagnoses if PE is not present (pneumonia, aortic pathology, cardiac issues) 1
• Most cost-effective strategy when included in diagnostic algorithms 1

The 2014 ESC Guidelines explicitly state that MDCT angiography is the second-line test in patients with elevated D-dimer and the first-line test in patients with high clinical probability 1. The 2017 and 2022 ACR Appropriateness Criteria confirm that CTPA is indicated in the evaluation of patients suspected of having PE 1.

Why V/Q Scan Is Not First-Line

Ventilation-perfusion scanning (Option B) is reserved for specific situations 1:

• Contraindications to CT (renal failure, contrast allergy, pregnancy) 1
• Younger patients where radiation exposure to breast tissue is a concern 1
• When CT is unavailable 1

This patient has none of these contraindications, and V/Q scanning is diagnostic in only 30-50% of cases, often yielding non-diagnostic results that require further testing 1.

Why No Further Testing Is Wrong

Option D is incorrect because this patient has clear symptoms requiring investigation, intermediate pretest probability, and no definitive alternative diagnosis on initial evaluation 1, 4. The pending troponin results are relevant for evaluating ACS but do not exclude PE, as both conditions can coexist 1.

Critical Pitfalls to Avoid

• Do not wait for troponin results before ordering PE imaging—the differential diagnosis includes both ACS and PE, and they are not mutually exclusive 1
• Do not use D-dimer as a "screening test" in patients with intermediate-to-high probability—it has low negative predictive value in this population 1, 4
• Do not delay imaging in a patient with active symptoms and intermediate probability—time to diagnosis affects outcomes 1

Algorithmic Approach

For this specific patient:

1. Clinical probability assessment: Intermediate (age, symptoms, tachycardia) 4
2. PERC not applicable: Age >50, tachycardia present 4
3. Skip D-dimer: Limited utility given clinical context 1
4. Proceed directly to CTPA: First-line imaging for intermediate-high probability 1
5. If CTPA positive: Initiate anticoagulation 1, 2
6. If CTPA negative: Consider alternative diagnoses (ACS given troponin pending, other cardiac/pulmonary pathology) 1

The answer is C: CT pulmonary angiography.