Pericardial effusion by TTE
Estimate effusion size from the maximal end-diastolic echo-free space, then judge significance from chamber collapse, IVC, Doppler variation, and clinical context.
Clinically reviewed 27 May 2026 · EchoRapp clinical content
Simple approach
First decide whether pericardial fluid is present, then separate size from haemodynamic impact. Size alone is not tamponade.
| TTE size | Echo-free space | Practical report wording |
|---|---|---|
| Trivial | Seen only in systole | Trace/trivial effusion |
| Small | <10 mm | Small pericardial effusion |
| Moderate | 10-20 mm | Moderate pericardial effusion |
| Large | >20 mm | Large pericardial effusion |
| Very large | >25 mm | Very large effusion; assess drainage path and haemodynamics |
Measure the maximal echo-free separation at end-diastole and document the view and location. Use PLAX, PSAX, apical, and subcostal views because effusions can be loculated or unevenly distributed.
If an amount in mL is entered, treat it as an optional rough volume estimate, not the primary severity grade. The TTE category should still come from the maximal end-diastolic separation and the haemodynamic assessment.
Judge significance separately. Look for RA collapse, early RV diastolic collapse, plethoric IVC, mitral and tricuspid inflow respiratory variation, and hepatic vein expiratory diastolic blunting or reversal. Mark tamponade only when the imaging findings fit the clinical picture.
Detailed tutorial
What TTE is estimating
TTE does not reliably calculate a true pericardial fluid volume. It gives a semiquantitative size estimate from the echo-free space between the visceral and parietal pericardium. This is why the guideline language is millimetres, not millilitres.
Info
The existing report amount field records the current app value. For interpretation, think in TTE size bands and haemodynamic signs.
When an mL amount is needed
Some workflows still ask for an approximate pericardial effusion amount in mL. This is usually derived from the same end-diastolic echo-free space rather than from a true 3D volume calculation.
| Echo-free space | Optional rough amount | How to use it |
|---|---|---|
| <1 cm | about 300 mL | Small/mild by TTE size band |
| 1-2 cm | about 500 mL | Moderate by TTE size band |
| >2 cm | >700 mL | Large by TTE size band |
Use these values only as coarse equivalents. They assume a relatively free, circumferential effusion and become unreliable when fluid is loculated, post-operative, clotted, fibrinous, or distributed irregularly around the heart. In those cases, document the maximal separation, location, and distribution; leave mL blank or use it only as a deliberately approximate app value.
Do not use the mL number to diagnose tamponade; it is not a decision variable for tamponade. Tamponade depends on pericardial pressure, intracardiac pressures, volume status, and how quickly fluid accumulated. A small rapid effusion can cause tamponade, while a chronic large effusion may have little haemodynamic effect.
How to measure size
Measure at end-diastole where the adjacent cardiac chamber is largest. Record the largest separation and the location, for example posterior LV in PLAX, apical, lateral, or right-sided. Small and very large effusions may be unevenly distributed, so sweep multiple windows before choosing the final size band.
| Step | What to check | Why it matters |
|---|---|---|
| PLAX | Posterior LV, anterior aorta, and descending thoracic aorta relation | Helps separate pericardial from pleural fluid |
| PSAX | Circumferential extent and RV free-wall relation | Shows regional collections and RV collapse |
| Apical | RA/RV collapse and apical collections | RA collapse duration is easier to appreciate |
| Subcostal | Global extent, IVC, hepatic veins, drainage path | Best window for IVC and many effusions |
Size categories
| Category | Maximal end-diastolic separation | Typical meaning |
|---|---|---|
| Trivial | Only visible during part of the cardiac cycle | Usually small physiologic or minimal fluid |
| Small/mild | <10 mm | Often tolerated; context decides follow-up |
| Moderate | 10-20 mm | Requires systematic haemodynamic assessment |
| Large | >20 mm | Higher risk; assess urgently for tamponade signs |
| Very large | >25 mm | Often needs detailed drainage planning if clinically significant |
Haemodynamic significance
Tamponade is a physiology, not a size label. A rapidly accumulating small effusion can cause tamponade, while a chronic large effusion can be tolerated if the pericardium has stretched.
| TTE sign | What to look for | Pitfall |
|---|---|---|
| RA collapse | Collapse lasting more than a brief moment; duration increases specificity | Very brief RA inversion can occur without tamponade |
| RV collapse | Early diastolic RV free-wall indentation, initially inspiratory only | Pulmonary hypertension or RV hypertrophy can mask it |
| IVC plethora | Dilated IVC with reduced inspiratory collapse | Sensitive but not specific; also occurs with high right-sided pressures |
| Mitral inflow | Inspiratory fall in peak E velocity, usually >25% in tamponade physiology | Do not use Doppler variation alone |
| Tricuspid inflow | Expiratory drop / inspiratory rise, often >40% in tamponade physiology | Rhythm and respiration quality matter |
| Septal shift | Significant respirophasic change in interventricular septal position | Ventilation pattern and RV pressure affect interpretation |
| LVOT / aortic outflow VTI | Significant visual respiratory change in LVOT or aortic outflow VTI | Supportive sign; confirm with the whole pattern |
| Hepatic vein | Expiratory diastolic flow blunting or reversal | Hard to obtain in some patients |
Warning
Do not mark tamponade from one isolated sign. The diagnosis should fit the clinical state and the whole echo pattern.
Doppler technique
Use a slow sweep speed, usually 25-50 mm/s, with clear respiratory timing. Average several beats when rhythm or respiration is irregular. For mitral and tricuspid inflow, compare the first beats of inspiration and expiration because the largest variation occurs there.
Special situations
Loculated posterior effusions after surgery can be missed by standard TTE windows and may need TEE, CT, or CMR. Clot, fibrin strands, malignancy, and post-procedural collections should be described, not reduced to a single size label.
Pulmonary hypertension, RV hypertrophy, and severe LV dysfunction can reduce or delay right-sided collapse despite clinically important pericardial pressure. Hypovolemia can make chamber collapse appear earlier.
What to document
- Presence or absence of pericardial effusion.
- Maximal end-diastolic separation and the view/location.
- Circumferential versus loculated distribution.
- Whether haemodynamic signs are present.
- Whether tamponade physiology is suspected.
- Associated pleural effusion and side.
References
- Allan L. Klein et al. American Society of Echocardiography Clinical Recommendations for Multimodality Cardiovascular Imaging of Patients with Pericardial Disease. J Am Soc Echocardiogr 2013;26(9):965–1012. View guideline
- Yehuda Adler et al. 2015 ESC Guidelines for the diagnosis and management of pericardial diseases. Eur Heart J 2015;36(42):2921–2964. View guideline