Pulmonary Embolism (PE), the Great Imposter, should be considered in virtually any ED visit related to weakness, shortness of breath, dizziness or syncope, pain, extremity discomfort, or nonspecific malaise or functional deterioration.

Key History

Key Physical Exam

Risk Factors for PE

Differential Diagnosis

Diagnostic Testing

1. Lab:
   • CBC: WBC count can be normal or elevated.
   • D-dimer — D-dimer is a degradation product of cross-linked fibrin.
     • MUST use ELISA test and not the latex agglutination tests (SimpliRed ®, etc) due to low overall sensitivity: 50-60%
     • ELISA tests are much more sensitive – but still miss up to 10% of patients with a PE. Overall, the negative predictive value of an ELISA D-dimer indicates that patients with a normal D-dimer have a 95 percent likelihood of not having PE.
     • The use of ELISA D-dimer assays for the diagnosis of PE have been extensively studied, and the test is noted to have a good sensitivity and negative predictive value, but a poor specificity. The best, validated strategy is to first quantify the patient’s pretest probability of having a PE. Patients with low pre-test probability (using a validated pretest instrument such as the Wells’ criteria) AND a negative quantitative D-dimer (ELISA or turbidimetric) have a 98-99% probability of not having a PE and the work-up can be safely stopped. The D-dimer is NOT sensitive enough to rule out PE in patients with intermediate or high-risk pretest probability, and these patients require further study.
     • Need further imaging if
       • The D-dimer is positive
       • The pretest probability for PE is intermediate or high Wells' criteria for PE
     • D-dimer is not as reliable in patients with active malignancy or recent surgery.
2. ECG
   • Usually normal and nonspecific
   • Most common ECG abnormality is sinus tachycardia
   • May show anterior/lateral T wave inversions
   • ST elevation in AVR
   • S1Q3T3 pattern – rare and nonspecific
3. Imaging
   
   CXR:
   • Usually normal, but may show atelectasis, infiltrates or a pleural effusion
   • Hampton's hump: opacity with rounded border pointing towards hilum (area of infarction)
   • Westermark's sign: increased lucency from clot interrupting blood flow
   • Fleischner's sign: large, sausage-shaped pulmonary artery
   
   V/Q scan
   • Used when CTA not available or patient has contraindication to CT or IV contrast
   • Should be used in conjunction with a validated pretest probability stratification scheme
   • Normal V/Q scan in 4% of patients will still have PE (PIOPED Study)
   • High-probability scan effectively rules in PE (87% with this pattern have PE)
   • Non-diagnostic scan - indication for definitive test, usually angiography
   
   High Resolution Spiral (Helical) CT Angiography (CTA)
   • Can typically resolve down to 3rd order vessels
   • Less invasive; no PA catheters
   • Sensitivity: 56-100%
   • May miss subsegmental artery PE
   • IV contrast; can provide alternate diagnosis
   • Can be used as an alternative to V/Q scan (ACEP level B)
   • Thin columnation spiral CT of thorax (1-2 mm)
   • Eventual role as screening modality or criterion standard test still controversial
   
   Pulmonary Angiogram
   • Still the gold standard for diagnosis
   • Negative angiogram essentially excludes PE (> 90%).
   • Positive angiogram is definitive proof of PE
   • Can be useful even if the study is abbreviated
   • Indications:
     • Other studies non-diagnostic
   • High risk of bleeding with treatment
   • Mortality: up to 0.3% (elderly, pulmonary HTN)
   • Complications: 2-4%
     • Some patients may exhibit hypersensitivity to dye
     • Arrhythmias, cardiac perforation
   
   Ultrasound/Echocardiography
   • Good for suspected massive PE performed at bedside, otherwise of limited accuracy
   • A positive US proves PE
   • Echocardiography can visualize clots, and show right ventricular strain
   • Transtracheal echocardiography is up to 85% sensitive in massive PE, Transesophageal sensitivity up to 90% with 100% specificity
   
   MRI
   • MRI has a sensitivity of 85% and specificity of 96% for central, lobar, and segmental emboli.
   • MRI is inadequate for the diagnosis of subsegmental emboli.

Wells Criteria & PERC Rule

Clinical Risk and Safety Pearls

• The literature now supports a risk stratification strategy as described above.
• Immediate full anticoagulation for patients suspected to have DVT and/or PE is suggested.
• Diagnostic testing should not delay empirical anticoagulant therapy.
• D-dimer is not helpful if the patient has an active malignancy or recent surgery.
• Up to 60% of patients with a PE have a normal Doppler study of lower extremity.
• The onset of SOB typically occurs a few days before the patient presents to the ED with complaints.
• Less than half of patients present with sudden onset of SOB or chest pain.

Treatment

1. For PE without associated cancer diagnosis, direct oral anticoagulants (DOACs) are recommended over warfarin therapy.
2. For patients with PE and no cancer who are not treated with DOACs, warfarin is recommended over LMWH.
3. Initial parenteral anticoagulation is given before dabigatran and edoxaban; is not given before rivaroxaban and apixaban; and is overlapped with warfarin therapy.
4. For patients with PE and cancer, either LMWH or DOACs are recommended.
5. For patients with acute PE and hypotension (massive PE), thrombolytic therapy may be appropriate.
6. Inferior vena cava filter is not recommended for patients with PE who are treated with anticoagulants.

Pregnancy

• If the patient has a low pretest probability for pulmonary embolism and a normal D-dimer test result, clinical exclusion from further investigations is recommended.
• If the clinical features are compatible with PE, CT scanning is performed; previous recommendations for VQ have been replaced by current studies, which suggest CT is safer in pregnancy.
• IF VQ scan is performed:
  • If the perfusion scan is normal, the diagnosis of PE is excluded.
  • If a segmental defect in perfusion with normal ventilation (high-probability lung scan) is seen, the diagnosis of PE is confirmed.
  • Patients with non-diagnostic lung scans should undergo CUS; if this is abnormal, PE can be diagnosed.
  • If CUS is normal, D-dimer, pulmonary angiography, or serial CUS should be considered, provided that the limitations of these tests are understood.