What are the echocardiography (echo) findings in pulmonary embolism?

Echocardiographic Findings in Pulmonary Embolism

In acute pulmonary embolism, echocardiography reveals indirect signs of right ventricular pressure overload including RV dilatation (RV/LV diameter ratio >0.6 or area ratio >1.0), RV hypokinesia with possible apical sparing (McConnell sign), abnormal interventricular septal motion, and tricuspid regurgitation with peak velocities typically 2.5-3.5 m/s (corresponding to pulmonary artery systolic pressure 40-50 mmHg). 1

Primary Echocardiographic Findings

Right Ventricular Changes

• RV dilatation is the most common finding, present in approximately 84% of patients with acute PE, manifested as an abnormal RV/LV diameter ratio >0.6 or RV/LV area ratio >1.0 1, 2
• RV hypokinesia occurs in 60-70% of cases, but characteristically may spare the RV apex while affecting the mid-free wall (McConnell sign), though this is not specific to PE as previously thought 1
• Paradoxical or abnormal interventricular septal motion is seen in approximately 70% of patients, reflecting RV pressure overload 1, 2
• Inferior vena cava dilatation with decreased collapsibility (<40% inspiratory change) occurs in 82% of clinically important PE 1

Doppler Findings

• Tricuspid regurgitation is frequent in intermediate-to-high-risk PE, with peak velocities typically 2.5-3.5 m/s in acute PE 1
• Pulmonary artery systolic pressure in acute PE is usually 40-50 mmHg; pressures >60 mmHg suggest chronic or recurrent PE rather than acute presentation 1
• The 60/60 sign (pulmonary ejection acceleration time <60 ms with tricuspid gradient <60 mmHg) is 98% specific for acute PE, though only 48% sensitive 1, 3
• Pulmonary artery acceleration time <60-80 ms suggests acute PE, while <105 ms indicates increased pulmonary vascular resistance 3

Direct Visualization (Rare but Diagnostic)

• Right heart thrombus is visualized in only 4% of unselected PE patients (up to 18% in ICU settings) but is pathognomonic when present and associated with high early mortality 4, 3
• Thrombus in main pulmonary arteries may be visible, particularly with transesophageal echocardiography 5

Diagnostic Performance

Sensitivity and Specificity

• Overall sensitivity of transthoracic echocardiography for PE diagnosis is approximately 50-60%, with specificity around 80-90% 1, 5, 6
• Right ventricular dilatation has a sensitivity of 50% but specificity of 98%, with a positive predictive value of 88% 7
• Undefined "right heart strain" shows sensitivity of 53% and specificity of 83% 6
• Echocardiography is normal in approximately 50% of unselected patients with acute PE, particularly those with small emboli causing minimal hemodynamic impairment 1, 5

Clinical Context and Indications

High-Risk PE (Hemodynamically Unstable)

• Bedside TTE is strongly recommended immediately in patients with suspected high-risk PE presenting with shock or hypotension, especially when CT is unavailable or the patient is too unstable for transport 1, 4
• The absence of RV overload/dysfunction virtually excludes massive PE as the cause of hemodynamic instability in shocked patients 1, 4
• Unequivocal echocardiographic evidence of RV dysfunction is sufficient to prompt immediate reperfusion treatment without further testing in highly unstable patients 4

Intermediate and Low-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 4
• TTE is valuable for risk stratification after PE diagnosis is confirmed, distinguishing intermediate-risk (RV dysfunction present) from low-risk (normal RV function) patients 1, 4
• Evidence of RV dysfunction in normotensive patients identifies intermediate-risk PE with 2.29-fold increased short-term mortality 4

Distinguishing Acute from Chronic Right Ventricular Dysfunction

Features Suggesting Acute PE

• RV free wall thickness ≤5 mm (chronic >5 mm) 3
• Tricuspid regurgitation gradient ≤46 mmHg (chronic >46 mmHg, corresponding to velocity ≤3.4 m/s vs >3.4 m/s) 3
• Right atrial size equal to left atrial size (chronic shows RA > LA) 3
• McConnell sign (mid-RV free wall hypokinesis with apical sparing) suggests acute process, though not entirely specific 1, 3, 7

Features Suggesting Chronic Process

• Pulmonary artery systolic pressure >60 mmHg suggests chronic or recurrent PE rather than acute presentation 1
• RV free wall thickness >5 mm indicates chronic adaptation 3
• Right atrial enlargement exceeding left atrial size suggests chronicity 3

Critical Pitfalls and Caveats

• McConnell sign is not specific for PE and can occur in other causes of acute RV dysfunction, contrary to earlier beliefs 1
• Severe tricuspid regurgitation may cause underestimation of pulmonary artery pressure by Doppler 1
• Echocardiographic parameters are difficult to standardize, with positive predictive value for PE-related death <10% in hemodynamically stable patients 4
• TTE may be technically limited in patients with hyperinflated lungs (COPD), though subcostal views usually provide adequate visualization 8
• Normal echocardiogram does not exclude PE, particularly in hemodynamically stable patients or those with small emboli 1, 5
• High specificity but low sensitivity makes echocardiography useful as a "rule-in" test in critical settings but inadequate as a "rule-out" test 6, 7

Prognostic Value

• RV/LV diameter ratio ≥1.0 and TAPSE <16 mm are key parameters for assessing prognosis in acute PE 4
• Presence of right heart thrombi is associated with RV dysfunction and high early mortality 4
• Patent foramen ovale with right-to-left shunt is associated with increased mortality 4
• Early and late mortality is significantly higher in patients with moderate to severe RV dysfunction on echocardiography 1