What are the diagnostic and treatment steps for a patient showing signs of a pulmonary embolism (PE)?

Signs and Clinical Presentation of Pulmonary Embolism

The most critical initial determination is whether the patient presents with hemodynamic instability (shock or systolic blood pressure <90 mmHg), as this immediately defines them as high-risk PE requiring urgent bedside echocardiography and emergency reperfusion therapy. 1

High-Risk PE: Hemodynamic Instability

In patients presenting with shock or hypotension, perform bedside transthoracic echocardiography (TTE) immediately as the first diagnostic step to differentiate suspected high-risk PE from other acute life-threatening conditions including cardiac tamponade, acute coronary syndrome, aortic dissection, and acute valvular dysfunction. 1

Key Echocardiographic Findings:

• Right ventricular (RV) dysfunction with RV/LV diameter ratio >1.0 is the primary finding that confirms high-risk PE in an unstable patient. 1
• In a critically unstable patient, echocardiographic evidence of RV dysfunction alone is sufficient to initiate immediate reperfusion therapy without further testing. 1
• Visualization of right heart thrombi, though rare, strengthens the diagnosis. 1

Ancillary Bedside Tests:

• Transesophageal echocardiography (TEE) may directly visualize thrombi in the pulmonary artery and main branches, though it should be used cautiously in hypoxemic patients. 1
• Bedside compression ultrasonography (CUS) can detect proximal deep vein thrombosis (DVT), confirming venous thromboembolism. 1

Critical Pitfall: Once the patient is stabilized with supportive treatment, obtain confirmatory CT angiography for definitive diagnosis. 1

Non-High-Risk PE: Hemodynamically Stable Patients

Step 1: Clinical Probability Assessment

Use either a three-level scheme (low, intermediate, high probability) or two-level scheme (PE unlikely vs. PE likely) to assess clinical probability. 1, 2

The clinical probability assessment should be based on:

• Past medical history of venous thromboembolism
• Clinical symptoms (dyspnea, tachypnea, chest pain)
• Physical examination findings (tachycardia, signs of DVT)
• Alternative diagnoses likelihood 3, 4

Step 2: D-Dimer Testing (Selective Use)

Measure D-dimer ONLY in patients with low or intermediate clinical probability, or those classified as "PE unlikely." 1, 2

Do NOT measure D-dimer in patients with high clinical probability because the negative predictive value is too low in this population (Class III recommendation). 1

Important Caveats:

• D-dimer measurement is of limited usefulness in hospitalized patients due to high false-positive rates from concurrent conditions (infection, cancer, inflammation). 1
• A negative D-dimer (<500 μg/L) in low/intermediate probability patients safely excludes PE with a 3-month thromboembolic risk <1%. 1, 4
• The negative predictive value of D-dimer combined with low clinical probability reaches 99.5%. 4

Step 3: Imaging Studies

CT pulmonary angiography (CTPA) is the imaging test of first choice for patients with elevated D-dimer levels or high clinical probability. 1, 2

CTPA Interpretation:

• Accept the diagnosis of PE if CTPA shows a segmental or more proximal filling defect in patients with intermediate or high clinical probability (Class I recommendation). 1, 2
• Reject the diagnosis of PE without further testing if CTPA is normal in patients with low or intermediate clinical probability. 1
• If CTPA shows single subsegmental PE, consider the possibility of a false-positive finding and discuss with radiology or seek a second opinion to avoid unnecessary anticoagulation. 1

Critical Pitfall: In patients with high clinical probability and negative CTPA, consider further investigation before withholding PE-specific treatment, though this situation is infrequent. 1

Alternative Imaging:

• Ventilation-perfusion (V/Q) scintigraphy is a valid option when CTPA is contraindicated (renal failure, contrast allergy, pregnancy). 1, 2
• Reject the diagnosis of PE without further testing if the perfusion lung scan is normal (Class I recommendation). 1
• Do NOT perform CT venography as an adjunct to CTPA (Class III recommendation). 1, 2
• Do NOT use MR angiography to rule out PE (Class III recommendation). 1, 2

Step 4: Compression Venous Ultrasonography

Finding a proximal DVT on CUS in a patient suspected of PE is sufficient to warrant anticoagulant treatment without further testing. 1

CUS is particularly useful:

• Before CT in patients with contraindications to CT (renal failure, contrast allergy, pregnancy) 1
• CUS shows DVT in 30-50% of patients with PE 1
• Sensitivity >90% and specificity ~95% for symptomatic proximal DVT 1

Immediate Treatment Considerations

Institute anticoagulation therapy as soon as possible while the diagnostic workup is ongoing, unless the patient is bleeding or has absolute contraindications (Class I recommendation). 1

For Hemodynamically Unstable Patients:

• Initiate intravenous unfractionated heparin (UFH) with weight-adjusted bolus injection immediately upon suspicion of high-risk PE. 1
• Administer systemic thrombolytic therapy to patients with confirmed high-risk PE (Class I recommendation). 1

For Hemodynamically Stable Patients:

• Prefer low molecular weight heparin (LMWH) or fondaparinux over UFH if anticoagulation is initiated parenterally. 1
• When oral anticoagulation is initiated, prefer a novel oral anticoagulant (NOAC) such as apixaban, dabigatran, edoxaban, or rivaroxaban over traditional LMWH-VKA regimen. 1

Critical Exception: Do not use NOACs in patients with severe renal impairment or antiphospholipid antibody syndrome. 1

Common Diagnostic Pitfalls to Avoid

• Never delay anticoagulation to obtain imaging in patients with intermediate or high clinical probability. 1
• Do not routinely measure D-dimer in hospitalized patients where the number needed to test for a clinically relevant negative result is prohibitively high. 1
• Avoid misdiagnosing subsegmental filling defects on CTPA as definite PE without radiologist confirmation, as false-positives can lead to unnecessary anticoagulation. 1
• Do not assume a normal lung scan or CTPA rules out massive PE if the patient remains hemodynamically unstable—search for alternative causes of shock. 1