Tamponade
Pericardial Effusions
2D and M-mode can be used to assess the size of an effusion.
Tiny amounts of pericardial fluid may be present normally. Any effusion visible in diastole is abnormal.
Measurement is done at the largest point.
<5mm = mild
5-20mm = moderate
>20mm = large
In very large effusions the heart will be very mobile, swinging around in the effusion.
Effusions are usually circumferential and dependent but may be localised. It is important to assess multiple views.
High suspicion should prompt a TOE if TTE is negative (eg post cardiac surgery).
Pericardial fluid will usually appear black but may have hyperechoic elements - blood, clot, pus, fibrous stranding. Purulent effusions are associated with a thick, shaggy pericardium.
Pericardial fat may be seen and should not be confused with an effusion. It will only be small, move with the synchronously with the myocardium and will only be visible anteriorly.
Pericardial effusions are easily confused with pleural effusions.
In the PLAX view the 2 are distinguished by the aorta. A left pleural effusion will be behind the aorta while a pericardial effusion will be visible between the LA and descending aorta.
An effusion present only behind the LA is likely to be pleural.
The 2 can be difficult to distinguish in the A4C view.
Ascites can be mistaken for an effusion in the subcostal view.
This is why it is important for the critical care physician to have at least a basic knowledge of lung and abdominal US which easily demonstrate fluid collections.
Very large pleural effusions can reportedly cause cardiac tamponade.
Tamponade
Tamponade occurs when pressure in the pericardial space exceeds pressure in the cardiac chambers enough to impair cardiac filling and therefore output.
If acute due to ventricular perforation then only a small amount of fluid is needed to cause tamponade. If pericardial builds up slowly (malignant effusion) then an effusion can be very large without the pressure increasing much as the pericardium has time to stretch.
The lowest pressure areas are affected 1st - RA then RVOT then whole RV then LA then LV.
Compression of the RA will be seen in (ventricular) systole when the chamber should be filling.
Inversion of the RA free wall for >⅓ systole has a high sensitivity and specificity for tamponade.
Collapse of the RVOT occurs in early diastole and is best seen in the PLAX view.
RAP will be high so the IVC will be dilated with little or no respiratory variation. This is a sensitive but not specific sign.
In spontaneous ventilation, inspiration increases flow of blood into R heart (sucks it in) and reduced flow into L heart (pulm vessels expand). This is exaggerated in tamponade (pulsus paradoxus). Remember that this is the opposite if positive pressure ventilation. This effect can be assessed with PW doppler
Assess RV and LV inflow in A4C. Measure max and minimum E wave velocities for each valve.
Size variation with respiration (%) of | Normal | Tamponade |
TV E wave | <25 | >25 |
MV E wave | <15 | >15 |
RVOT and LVOT Vmax or VTI | <10 | >10 |
Assess outflow of RVOT and LVOT by measuring Vmax and/or VTI.
It is important to note that this is only validated in spontaneously breathing patients. With IPPV pulsus paradoxus is reversed and is usually of smaller magnitude. As we have already seen it can be caused by other pathology such as hypovolaemia, ventricular failure and also of course by airway narrowing (asthma, COPD, upper airway obstruction).
Practically speaking tamponade should be diagnosed by a combination of 2D echo appearance and clinical context (shocked patient).
Pericardiocentesis
Echo guided pericardiocentesis is safe with a low complication rate as long as the operator is proficient.
The site of needle entry is at the location where the effusion is largest (rather than the traditional blind subcostal approach). This can be anterior, lateral or subcostal. A perpendicular angle is easiest to duplicate for needle insertion which favours an anterior or lateral approach. Often the best approach is by the A4C view.
As with all US guided needle insertion careful note should be taken of the depth and angle of insertion.
Real time insertion is not necessary but catheter and wire position should be confirmed with US. A few mls of agitated saline can be useful to confirm the presence of the catheter in the pericardium.
Follow up echos will be needed to ensure tamponade does not reoccur.