Parameters of Right Ventricular Dysfunction on Echocardiography in Acute Pulmonary Embolism

Parameters of Right Ventricular Dysfunction on Echocardiography in Acute Pulmonary Embolism

Acute pulmonary embolism (PE) can produce a sudden increase in pulmonary vascular resistance, resulting in acute right ventricular (RV) pressure overload, RV dilatation, impaired RV contractility, and eventually hemodynamic collapse.

Echocardiography therefore plays an important role in identifying RV dysfunction, assessing the hemodynamic consequences of acute PE, and supporting risk stratification. Importantly, echocardiographic abnormalities should be interpreted in the overall clinical context because no single echocardiographic finding is sufficiently sensitive or specific to establish or exclude acute PE in most patients.

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Why Does the Right Ventricle Fail in Acute Pulmonary Embolism?

When a significant portion of the pulmonary arterial circulation becomes obstructed, pulmonary vascular resistance rises abruptly.

The thin-walled right ventricle is poorly adapted to a sudden increase in afterload. As RV pressure rises:

RV dilatation develops → RV wall stress increases → RV systolic function deteriorates → interventricular septum shifts toward the LV → LV filling decreases → cardiac output and systemic blood pressure may fall.

Severe RV dysfunction is therefore an important marker of adverse prognosis in acute PE.

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1. Right Ventricular Dilatation

RV enlargement is one of the most recognizable echocardiographic manifestations of significant acute PE.

Measurements should preferably be obtained from an RV-focused apical four-chamber view.

Important measurements include:

RV end-diastolic diameter >30 mm in some PE criteria.

RV basal diameter >42 mm indicates RV dilatation according to standard echocardiographic chamber quantification criteria.

RV enlargement reflects acute pressure and volume loading of the right ventricle.

However, RV dilatation is not specific for acute PE. It can also occur in pulmonary hypertension, chronic lung disease, congenital heart disease, significant tricuspid regurgitation, and chronic RV cardiomyopathy.

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2. RV/LV Diameter Ratio

The RV-to-LV diameter ratio is particularly useful when assessing a patient with suspected or confirmed pulmonary embolism.

Abnormal finding:

RV/LV ratio >0.9–1.0

An enlarged RV relative to the LV indicates significant RV pressure overload.

An RV/LV ratio ≥1.0 is commonly used as an important marker of RV dilatation in acute PE and is also frequently assessed on CT pulmonary angiography.

The greater the RV enlargement, particularly when accompanied by impaired systolic function, the greater the concern for hemodynamically important PE.

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3. TAPSE

Tricuspid Annular Plane Systolic Excursion (TAPSE) measures longitudinal systolic motion of the lateral tricuspid annulus.

It is simple, reproducible, and widely available.

Reduced TAPSE:

TAPSE <1.6–1.7 cm indicates impaired RV longitudinal systolic function.

A reduced TAPSE in acute PE supports the presence of RV systolic dysfunction.

However, TAPSE evaluates primarily longitudinal RV contraction and is load dependent. It should therefore not be interpreted in isolation.

Other measures of RV systolic function may include:

Tissue Doppler S′ velocity

RV fractional area change

RV free-wall longitudinal strain

3D RV ejection fraction where available

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4. Pulmonary Artery Acceleration Time

Pulmonary artery acceleration time (PAT or PAAT) is measured using pulsed-wave Doppler in the RV outflow tract.

It represents the interval from the onset of pulmonary flow to peak pulmonary flow velocity.

In pulmonary hypertension:

PAT becomes shortened.

A pulmonary acceleration time <90 ms suggests elevated pulmonary artery pressure, although thresholds vary according to methodology and clinical context.

In acute PE, a markedly shortened acceleration time reflects the abrupt increase in pulmonary vascular resistance.

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5. Tricuspid Regurgitation Velocity

The peak velocity of the tricuspid regurgitation jet can be used to estimate the RV-to-right atrial systolic pressure gradient using the simplified Bernoulli equation:

ΔP = 4V²

where V is the peak TR velocity.

For example, a TR velocity of 3 m/s corresponds to an RV–RA systolic gradient of approximately:

4 × 3² = 36 mmHg

Adding estimated right atrial pressure provides an estimate of RV systolic pressure, which approximates pulmonary artery systolic pressure when there is no RV outflow obstruction or pulmonary stenosis.

An elevated TR velocity can support the presence of increased pulmonary pressure, but it is not specific for acute PE.

Importantly, a very high pulmonary artery pressure may suggest pre-existing pulmonary hypertension rather than purely acute PE because a previously normal right ventricle may be unable to acutely generate extremely high pressures.

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6. McConnell’s Sign

McConnell’s sign is a classic echocardiographic pattern associated with acute RV pressure overload.

It consists of:

Hypokinesia or akinesia of the mid RV free wall with relative preservation of apical motion.

This produces the characteristic appearance of a poorly contracting RV free wall while the apex continues to move.

Clinical significance

McConnell’s sign may raise suspicion for acute pulmonary embolism, particularly when accompanied by RV dilatation and other signs of acute RV pressure overload.

However, it is not pathognomonic for PE.

Similar regional RV wall-motion abnormalities can occur in other conditions, particularly RV myocardial ischemia or infarction.

Therefore, McConnell’s sign should be interpreted together with clinical probability, hemodynamic status, other echocardiographic findings, and definitive imaging when appropriate.

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7. The 60/60 Sign

The 60/60 sign is particularly interesting because it combines two Doppler findings:

Pulmonary acceleration time <60 ms

AND

Peak systolic TR pressure gradient <60 mmHg

This combination reflects severe acute RV afterload without the extremely high pulmonary pressures more commonly associated with longstanding pulmonary hypertension.

Why is it useful?

In acute PE, pulmonary vascular resistance rises abruptly, but the previously normal RV usually cannot generate extremely high systolic pressures.

Therefore, the combination of:

Very short pulmonary acceleration time + only moderately elevated TR gradient

can suggest an acute rather than chronic pulmonary vascular obstruction.

The 60/60 sign is relatively specific when present but is not sufficiently sensitive to exclude PE when absent.

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Additional Echocardiographic Findings in Acute PE

Several other findings may strengthen the diagnosis of acute RV pressure overload.

Interventricular septal flattening

RV pressure overload pushes the interventricular septum toward the LV.

On the parasternal short-axis view, this produces a D-shaped left ventricle.

Septal flattening predominantly during systole suggests RV pressure overload.

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Dilated Inferior Vena Cava

An enlarged inferior vena cava with reduced inspiratory collapse suggests elevated right atrial pressure.

This may accompany significant RV failure in acute PE.

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Right Atrial Enlargement

Acute RV pressure overload may also produce right atrial enlargement, particularly in severe cases.

Marked right atrial and RV enlargement, however, should also raise consideration of pre-existing pulmonary hypertension.

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RV Free-Wall Strain

RV longitudinal strain can identify RV dysfunction even when conventional parameters are borderline.

Reduced absolute RV free-wall longitudinal strain indicates impaired RV myocardial deformation.

Speckle-tracking assessment may therefore provide additional prognostic information in selected patients with acute PE.

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The Most Important Echocardiographic Findings to Remember

For practical clinical and examination purposes, remember the following:

RV basal diameter >42 mm → RV dilatation

RV/LV ratio >0.9–1.0 → RV enlargement relative to LV

TAPSE <16–17 mm → impaired RV longitudinal systolic function

Short pulmonary acceleration time → increased pulmonary vascular resistance

Elevated TR velocity → increased RV/pulmonary pressure

McConnell’s sign → RV free-wall hypokinesia with relative apical sparing

60/60 sign → PAT <60 ms with TR systolic gradient <60 mmHg

Septal flattening → RV pressure overload

Dilated IVC with reduced collapse → elevated right atrial pressure

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Role of Echocardiography in Hemodynamically Unstable PE

Echocardiography becomes particularly important when a patient with suspected PE is hemodynamically unstable and immediate CT pulmonary angiography cannot safely or rapidly be performed.

Evidence of severe acute RV pressure overload in an appropriate clinical setting can strongly support the diagnosis and assist urgent management decisions.

Conversely, the absence of RV pressure overload in a profoundly unstable patient makes massive PE as the cause of shock less likely.

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Echocardiography Does Not Rule Out Pulmonary Embolism

A crucial clinical point is that a normal echocardiogram does not exclude acute PE.

Patients with small or intermediate clot burdens may have completely normal RV size and systolic function.

Therefore, in a hemodynamically stable patient, CT pulmonary angiography remains the principal imaging test when PE requires definitive imaging diagnosis.

Echocardiography is particularly valuable for assessing the cardiovascular consequences of PE rather than simply detecting the thrombus itself.

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Acute PE Versus Chronic Pulmonary Hypertension

Differentiating acute RV pressure overload from chronic pulmonary hypertension can sometimes be challenging.

Features favoring acute PE include:

Relatively mild RV wall thickness despite marked RV dilatation

McConnell’s sign

60/60 sign

Abrupt RV enlargement

Short pulmonary acceleration time

Features favoring chronic pulmonary hypertension include:

RV hypertrophy

Marked right atrial enlargement

Very high pulmonary artery pressures

Longstanding RV remodeling

Severe chronic tricuspid regurgitation

These findings should always be integrated with the patient's clinical history and other imaging.

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Clinical Take-Home Message

The central echocardiographic abnormality in hemodynamically significant acute pulmonary embolism is acute RV pressure overload.

Think of the sequence:

Acute pulmonary arterial obstruction

↓

Increased pulmonary vascular resistance

↓

RV dilatation

↓

Reduced RV systolic function

↓

Septal displacement

↓

Reduced LV preload

↓

Reduced cardiac output

↓

Hypotension and obstructive shock

No individual echocardiographic sign should be used alone to diagnose or exclude pulmonary embolism. The strongest assessment comes from combining RV size, RV/LV ratio, systolic function, pulmonary Doppler findings, TR-derived pressure estimates, septal configuration, IVC findings, and the overall clinical presentation.

For doctors and medical students, the highest-yield findings to remember are RV dilatation, increased RV/LV ratio, reduced TAPSE, McConnell’s sign, shortened pulmonary acceleration time, and the 60/60 sign.

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