What is the most appropriate next step in evaluating a 66-year-old woman with hypertension and recent knee replacement who presents with acute left-sided chest pain, shortness of breath, tachycardia, mild hypoxemia, normal troponins, sinus tachycardia on ECG, and new left leg discomfort?

CT Pulmonary Angiography (CTPA)

The most appropriate next step is CT pulmonary angiography (CTPA) to evaluate for pulmonary embolism, as this patient has multiple high-risk features including recent orthopedic surgery, acute chest pain with dyspnea, tachycardia, hypoxemia, and new leg pain that collectively create a high clinical probability for PE. 1

Clinical Reasoning

This patient presents with a classic constellation of findings highly suspicious for pulmonary embolism:

• Major risk factor: Knee replacement 3 weeks ago (recent major orthopedic surgery is a well-established VTE risk factor) 1
• Cardinal symptoms: Acute onset chest pain and shortness of breath 1
• Objective findings: Tachycardia (pulse 110), hypoxemia (O2 sat 91%), and new left leg discomfort suggesting possible DVT 1
• Exclusion of ACS: Normal troponins and sinus tachycardia on ECG make acute coronary syndrome less likely 2, 3

Why CTPA is the Correct Next Step

High Clinical Probability Assessment

The 2014 ESC Guidelines explicitly state that in patients without shock or hypotension, the diagnostic approach should be based on clinical probability assessment combined with appropriate imaging. 1 This patient's presentation places her in a high clinical probability category given:

• Recent major surgery (within 3 weeks) 1
• Acute cardiopulmonary symptoms 1
• Objective signs of physiologic compromise 1

Bypassing D-dimer in High-Risk Patients

The ESC Guidelines specifically note that D-dimer should NOT be measured in patients with high clinical probability, as it would not change management—these patients should proceed directly to CT angiography. 1 The guideline states: "D-dimer should not be measured in patients with a high clinic[al probability]" because a negative D-dimer cannot safely exclude PE in this population, and a positive result (which is expected) would not add diagnostic value. 1

CT Angiography as First-Line Imaging

CT angiography has become the main thoracic imaging test for investigating suspected PE, though it should not be used indiscriminately in all patients with chest pain. 1 In this high-probability scenario, CTPA is the definitive diagnostic test that will:

• Directly visualize pulmonary emboli if present 1
• Provide alternative diagnoses if PE is absent 1
• Guide immediate therapeutic decisions 1

Alternative Considerations and Why They Are Suboptimal

Compression Venous Ultrasonography (CUS)

While CUS of the lower extremities can detect DVT in 30-50% of patients with PE, and finding a proximal DVT is sufficient to warrant anticoagulation without further testing 1, this approach has limitations:

• Lower sensitivity: Only detects DVT in 30-50% of PE cases, meaning a negative CUS does not exclude PE 1
• Delays definitive diagnosis: Would still require CTPA if negative 1
• Less efficient: In a hemodynamically stable patient with high PE probability, proceeding directly to CTPA is more efficient 1

Echocardiography

Bedside echocardiography is reserved for patients with shock or hypotension (high-risk PE), where it can rapidly identify RV dysfunction and guide immediate reperfusion therapy. 1 This patient is hemodynamically stable (BP 124/75), making echocardiography less appropriate as the initial diagnostic test. 1

Common Pitfalls to Avoid

• Do not order D-dimer in high-probability patients: This wastes time and resources without changing management 1
• Do not delay imaging for lower extremity ultrasound first: In stable patients with high clinical probability, CTPA provides definitive diagnosis 1
• Do not assume normal troponins exclude all serious pathology: PE can present with normal cardiac biomarkers 2, 3
• Do not be falsely reassured by absence of leg edema: DVT can be present without obvious physical findings, and PE can occur without detectable DVT 1

Management After CTPA

If CTPA confirms PE, immediate anticoagulation should be initiated. 1 If CTPA is negative, alternative diagnoses should be pursued based on clinical presentation, though the high clinical suspicion in this case makes PE the primary concern requiring exclusion. 1