What is the role of a 2D (two-dimensional) echocardiogram in diagnosing pulmonary embolism (PE)?

Role of 2D Echocardiography in Pulmonary Embolism

2D echocardiography is NOT recommended for diagnosing PE in hemodynamically stable patients, but is the first-line bedside test for suspected high-risk PE with shock or hypotension, where it can guide immediate life-saving treatment decisions. 1, 2

High-Risk PE (With Shock or Hypotension)

In hemodynamically unstable patients, bedside echocardiography should be performed immediately as the initial diagnostic test. 1, 2

Diagnostic Role

• 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 setting. 1, 2
• Unequivocal signs of RV pressure overload and dysfunction justify emergency reperfusion treatment (thrombolysis or embolectomy) if immediate CT angiography is not feasible. 1, 2
• In critically unstable patients who cannot be transported for CT, PE diagnosis may be accepted based on compatible echocardiographic findings alone. 1

Key Echocardiographic Findings

• RV dilation (RV/LV diameter ratio ≥1.0) 1, 2
• RV hypokinesis with preserved apical contractility (McConnell sign) - high positive predictive value even with pre-existing cardiopulmonary disease 1
• Abnormal interventricular septal motion 2
• Tricuspid regurgitation with elevated gradient 2
• Decreased TAPSE (<16 mm) 1, 2
• Right heart thrombi (detected in <4% of unselected PE patients, up to 18% in ICU settings) - confirms diagnosis and indicates high mortality risk 1, 2

Differential Diagnosis Utility

Echo helps distinguish PE from other causes of shock including:

• Pericardial tamponade 1, 2
• Acute valvular dysfunction 1
• Severe LV dysfunction or cardiogenic shock 1
• Aortic dissection 1
• Hypovolemia 1

Non-High-Risk PE (Hemodynamically Stable)

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

Why Echo Fails as a Diagnostic Test in Stable Patients

• Sensitivity is only 41-56% - missing approximately half of angiographically proven PE cases 3, 4, 5
• Negative predictive value of 40-50% - a normal echo cannot exclude PE 1, 4
• RV dysfunction may be absent in smaller emboli without significant hemodynamic impact 1, 6
• RV dysfunction can be present due to pre-existing cardiac or respiratory disease unrelated to PE 1

Prognostic Role in Confirmed PE

Once PE is confirmed by CT angiography, echo is valuable for risk stratification to identify intermediate-risk patients. 1, 2

• RV dysfunction on echo is found in ≥25% of unselected PE patients 1
• Presence of RV dysfunction identifies intermediate-risk patients who may benefit from intensive monitoring and consideration of escalated therapy 1, 2
• RV/LV ratio ≥1.0 and TAPSE <16 mm are the most validated prognostic parameters 1, 2
• However, the positive predictive value for PE-related death remains low (<10%) in normotensive patients 1, 2

Transesophageal Echocardiography

TEE may be considered in hemodynamically unstable patients when searching for emboli in the main pulmonary arteries, as it can directly visualize thrombi in the pulmonary arteries and has high diagnostic yield in bilateral central PE. 1

Common Pitfalls to Avoid

• Never use echo alone to rule out PE in stable patients - its low sensitivity makes this dangerous 1, 2
• Do not delay CT angiography in stable patients to perform echo - CT is the gold standard for diagnosis 1
• Beware of RV dysfunction from RV infarction mimicking the McConnell sign - look for additional signs of pressure overload 1
• Remember that echo parameters are difficult to standardize - interpretation requires expertise 1, 2
• In high-risk PE, a normal lung scan or CT should prompt search for another cause of shock, not reliance on echo findings alone 1