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TAMPONADE

The echo features of tamponade are:

1. Plethoric IVC

2. RA systolic collapse

3. RV diastolic collapse

4. >40% variation in TV inflow velocities; >25% variation in MV inflow velocities with respiration

Echo features of tamponade occur because the pressure caused by the accumulation of pericardial fluid causes collapse of chambers when they are at their lowest pressure. Decreased intravascular volume or peripheral vasodilation causes the heart to be at increased risk of tamponade physiology.

Cardiac tamponade is a clinical diagnosis: hypotension in the presence of a pericardial effusion with no other cause for deterioration. Howeverm hypotension is usually the terminal event in the clinical trajectory of pericardial effusion. I prefer to use echo to find signs of tamponade in the normotensive patient, so I can identify the patients at increased risk of deterioration. Echo will often shows features of tamponade without hypotension (1,2). 

If I see features of tamponade in ED (in the normotensive patient)I will titrate filling so the cardiac chambers can withstand external compressive forces from the pericardial fluid and I will flag these patients as being at increased risk of deterioration on the ward and thus requiring close monitoring in CCU or ICU. 

ECHO FEATURES OF TAMPONADE

IVC

A plethoric IVC (dilated >2.1cm with no inspiratory collapse) is the most sensitive feature of tamponade and is present in 92% of cases (3). However, it is not very specific. Therefore, I use it as a rule out test. If I consider that the pericardial effusion is causing tamponade, but the IVC is small and collapsing, I will go looking for another cause for the hypotension.

RA COLLAPSE

A pericardial effusion exerts greatest pressure on the low pressure chambers of the heart: the right atrium and the right ventricle. 

RA collapse occurs when the intrachamber pressure is lowest: late diastole- early systole (during chamber filling). Collapse of the RA free wall for more than one third of the cardiac cycle is highly sensitive and specific for tamponade (4). 

Timing of diastole and systole can be done on 2D by looking at AV valve opening. The start of diastole is the opening of the valve, the start of systole is the closing of the valve.

RA collapse is best seen in A4C and the subxyphoid view. 

A4C: RA free wall collapse

RV COLLAPSE

RV collapse occurs during diastole as this is when the intrachamber pressure of the RV is at its lowest. Initially the apex of RV collapses and then the base. RV apical collapse tends to accentuate the triangular shape of the RV (especially in the subxyphoid view). 

Subxyphoid: RV collapse. Note the accentuated triangular shape of the RV

Sometimes, it may be difficult to pick the RV collapse. I look for undulation in the RV free wall in PLAx, PSAx and subxyphoid. M mode on the RV free wall can also help you see the collapse. 

In the subxyphoid view, the alternating RA and RV collapse is called the "sea-saw" sign. 

It is important to note that a hypertrophied RV may not show signs of collapse, but tamponade physiology may still exist. 

RV free wall is thickened and RV is 1:1 with LV suggesting RV pressure overload. There is no RV collapse because the increased RV intrachamber pressure is able to withstand the pressure of the pericardial fluid - kind of like a submarine underwater. 

DOPPLER TV and MV INFLOW VELOCITIES

The normal RV and LV alternate preferential filling during inspiration and expiration. That is: negative intrathoracic pressure on inspiration increases venous return causing increased RV filling during inspiration. Expiration causes increased venous return to the LA from the pulmonary vasculature causing increased LV filling during expiration. This is accentuated in tamponade so that you see a significant drop in RV filling on ex a drop in LV filling on expiration. 

This can be quantified by looking at the pulsed wave doppler velocities on the MV and TV during respiration. >40% difference in velocities inspiration to expiration in the TV and >25% (5,6) difference in velocities inspiration to expiration in the MV is usually present in tamponade physiology. This is the echo representation of the pulsus paradoxus sign drop in blood pressure by >10mmHg on inspiration. 

pulsed doppler inflow velocities of the MV showing 23% variation from inspiration to expiration

LA COLLAPSE

Localised effusions (eg post cardiac surgery) will cause LA systolic collapse. This is highly specific for tamponade. This will be seen best in A4C or PLax.

LV

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REFERENCES

1. Hoit BD. Pericardial Effusion and Cardiac Tamponade in the New Millennium. Curr Cardiol Rep. 2017 Jul;19(7):57. doi: 10.1007/s11886-017-0867-5. PMID: 28493085

2. Alerhand S, Carter JM. What echocardiographic findings suggest a pericardial effusion is causing tamponade? Am J Emerg Med. 2019 Feb;37(2):321-326. doi: 10.1016/j.ajem.2018.11.004. Epub 2018 Nov 17. PMID: 30471929

3. Himelman RB, Kircher B, Rockey DC, Schiller NB. Inferior vena cava plethora with blunted respiratory response: a sensitive echocardiographic sign of cardiac tamponade. J Am Coll Cardiol. 1988;12:1470-7

4. Gillam LD, Guyer DE, Gibson TC, King ME, Marshall JE, Weyman AE. Hydrodynamic compression of the right atrium: a new echocardiographic sign of cardiac tamponade. Circulation. 1983;68:294-301.

5. Wann S, Passen E: Echocardiography in pericardial disease. J Am Soc Echocardiogr. 2008, 21: 7-13. 10.1016/j.echo.2007.11.003.

6. Leeman DE, Levine MJ, Come PC. Doppler echocardiography in cardiac tamponade: exaggerated respiratory variation in transvalvular blood flow velocity integrals. J Am Coll Cardiol (1988) 11:572–8.