What are the key echo findings in a patient suspected of having pulmonary embolism?

Echo Findings in Pulmonary Embolism

Primary Echocardiographic Signs of Acute PE

The key echocardiographic findings in pulmonary embolism include right ventricular dilatation and hypokinesis, abnormal interventricular septal motion, tricuspid regurgitation with specific velocity patterns, and dilated proximal pulmonary arteries. 1, 2

Right Ventricular Findings

• RV dilatation with RV/LV diameter ratio >0.5 is a cardinal sign, with ratios ≥1.0 indicating more severe disease and worse prognosis 1, 2
• RV hypokinesis is present in approximately 90% of patients with hemodynamically significant PE 1
• McConnell sign (hypokinesis of the RV free wall with sparing of the apex) has 77% sensitivity and 94% specificity for acute PE, distinguishing it from other causes of RV dysfunction 1
• Decreased TAPSE <16 mm indicates RV systolic dysfunction and correlates with adverse outcomes 2

Interventricular Septal Abnormalities

• Paradoxical septal motion with bulging into the left ventricle occurs due to RV pressure overload 1
• This finding reflects acute RV afterload stress and is characteristic of hemodynamically significant PE 1

Tricuspid Regurgitation and Pressure Estimates

• Tricuspid regurgitant jet velocity of 2.5-3.5 m/s is typical in acute PE, corresponding to pulmonary artery systolic pressure (PAsP) of 40-50 mmHg 1
• PAsP ≤60 mmHg suggests acute PE, as the RV can only generate this level of pressure acutely 1
• PAsP >60 mmHg suggests chronic or recurrent PE rather than acute presentation, indicating repeated embolic episodes or underlying chronic pulmonary disease 1

Additional Structural Findings

• Dilated inferior vena cava with decreased collapsibility (<40% inspiratory change) is present in 82% of clinically important PE 1
• Dilated proximal pulmonary arteries reflect acute pressure overload 1
• Right heart thrombi are detected in 4-18% of PE patients and indicate high early mortality risk 2

Doppler Flow Patterns

• Disturbed RV outflow tract flow velocity pattern is characteristic 1
• Severely disturbed RV ejection pattern (acceleration time <60 ms) combined with trans-tricuspid gradient <60 mmHg has 98% specificity for acute PE 1

Clinical Indications for Echocardiography

High-Risk PE (Hemodynamically Unstable)

Bedside TTE should be performed immediately in patients with suspected high-risk PE presenting with shock or hypotension, particularly when CT is unavailable or the patient is too unstable for transport. 1, 2

• The absence of RV overload or dysfunction virtually excludes massive PE as the cause of hemodynamic instability 1, 2
• Unequivocal echocardiographic evidence of RV dysfunction is sufficient to prompt immediate reperfusion treatment without further testing in highly unstable patients 2
• TTE helps differentiate PE from other causes of shock including pericardial tamponade, acute valvular dysfunction, severe LV dysfunction, and aortic dissection 2, 3

Non-High-Risk PE (Hemodynamically Stable)

• TTE is NOT recommended as part of routine diagnostic workup in hemodynamically stable patients with suspected PE due to limited sensitivity 1, 2
• TTE is valuable for risk stratification in confirmed non-high-risk PE to identify intermediate-risk patients who may benefit from intensive monitoring 1, 2
• Evidence of RV dysfunction in normotensive patients identifies intermediate-risk PE with 2.29-fold increased short-term mortality 2

Differential Diagnosis

• TTE is useful when clinical and laboratory findings are ambiguous for distinguishing cardiac versus non-cardiac causes of dyspnea 1, 2
• Echocardiography can identify alternative diagnoses such as myocardial infarction, pericardial disease, aortic dissection, or hypovolemic shock 3, 4

Prognostic Value

• RV dysfunction on echocardiography is found in ≥25% of unselected acute PE patients and correlates with elevated short-term mortality risk 2
• Patients with submassive PE (normotensive with RV dysfunction) have worse survival than those with normal RV function 1
• Patent foramen ovale and right heart thrombi detected on echo are associated with increased mortality 2, 5, 6
• Serial echocardiography allows monitoring of treatment response and resolution of RV dysfunction 5, 6

Critical Pitfalls and Caveats

• Small PE without hemodynamic impairment may show normal echocardiography, limiting sensitivity for excluding PE 7
• Echocardiographic parameters are difficult to standardize, with positive predictive value for PE-related death <10% in stable patients 2
• Poor acoustic windows may necessitate transesophageal echocardiography, which can directly visualize thrombi in main pulmonary arteries 3, 7
• TTE cannot definitively confirm or exclude PE and should not replace CT angiography in stable patients where imaging is feasible 1