What is the role of an echocardiogram (echo) in diagnosing and managing a patient with suspected pulmonary embolism (PE)?

Role of Echocardiography in Pulmonary Embolism

Echocardiography is essential for immediate bedside evaluation in suspected high-risk PE with shock or hypotension, where it can justify emergency reperfusion treatment without further testing, but it should NOT be used as part of routine diagnostic workup in hemodynamically stable patients due to poor sensitivity (approximately 50-56%). 1, 2, 3

High-Risk PE (Shock or Hypotension)

Echocardiography is the most useful initial test in hemodynamically unstable patients and serves multiple critical functions: 1, 2

Diagnostic Role in Unstable Patients

• The absence of RV overload or dysfunction on echo virtually excludes massive PE as the cause of hemodynamic instability, making it an excellent rule-out test in this specific context. 1, 2

• Unequivocal echocardiographic signs of RV pressure overload and dysfunction alone justify emergency reperfusion treatment (thrombolysis/embolectomy) when CT is not immediately available or the patient is too unstable for transport. 1, 2

• Echo should be performed immediately at bedside when CT is unavailable or the patient's critical condition allows only bedside testing. 1, 2

Differential Diagnosis in Shock

Echo helps distinguish PE from other causes of hemodynamic collapse: 1, 2

• Pericardial tamponade
• Acute valvular dysfunction
• Severe LV dysfunction or myocardial infarction
• Aortic dissection
• Hypovolemia

Key Echocardiographic Findings in Acute PE

A typical picture of hemodynamically significant PE includes: 1, 2

• RV dilation with RV/LV diameter ratio >0.5 (ideally ≥1.0 for prognostic purposes) 1, 2
• RV hypokinesis with preserved apical contractility ("McConnell sign" - 77% sensitive, 94% specific) 1
• Interventricular septal bulging into the LV 1
• Tricuspid regurgitation velocity 3-3.5 m/s (or >2.5 m/s) 1, 2
• Dilated proximal pulmonary arteries 1
• Dilated IVC without inspiratory collapse 1
• TAPSE <16 mm indicates poor prognosis 2
• Disturbed RV outflow tract flow pattern (acceleration time <60 ms with trans-tricuspid gradient <60 mmHg is 98% specific for acute PE) 1, 2

Detection of Right Heart Thrombi

• Mobile right heart thrombi are found in <4% of unselected PE patients but up to 18% in ICU settings. 1, 2
• Their presence essentially confirms PE diagnosis and is associated with RV dysfunction and high early mortality. 1, 2
• Transoesophageal echo may directly visualize thrombi in the pulmonary arteries when transthoracic views are inadequate. 1

Non-High-Risk PE (Hemodynamically Stable Patients)

Echocardiography is NOT recommended as part of routine diagnostic workup in stable, normotensive patients with suspected PE. 1, 2

Why Echo Should Not Be Used for Diagnosis in Stable Patients

• Sensitivity is only 53-56% with specificity of 81-90%, meaning it misses approximately half of PE cases confirmed by angiography. 1, 3, 4
• The negative predictive value is only 40-50%, so a negative echo cannot exclude PE. 1
• RV dysfunction signs may be absent in hemodynamically stable PE or present due to pre-existing cardiopulmonary disease. 1

Appropriate Uses in Stable Patients

Risk stratification after PE is confirmed by CT: 1, 2

• RV dysfunction is found in ≥25% of confirmed PE patients and identifies intermediate-risk patients who may benefit from intensive monitoring. 1, 2
• RV dysfunction confers a 2.29-fold increase in short-term mortality risk in normotensive PE patients. 2
• Echo guides therapeutic decisions regarding escalation of care or consideration of advanced therapies. 2

Differential diagnosis of acute dyspnea when clinical presentation is ambiguous and other cardiac causes need exclusion (MI, endocarditis, valvular disease). 1, 2

Critical Pitfalls to Avoid

• Never use echo alone to rule out PE in any patient population - its sensitivity is too low. 1, 3, 4
• Do not delay CT in stable patients to obtain echo - CT angiography is the primary diagnostic test. 1
• Beware of false positives - RV dysfunction may be chronic from prior cardiopulmonary disease, not acute PE. 1
• In unstable patients, do not perform conventional pulmonary angiography if bedside echo shows RV dysfunction - proceed directly to treatment. 1
• Echocardiographic parameters are difficult to standardize, with positive predictive value for PE-related death <10% in stable patients. 2