Ellen Woodcock - Cardiac Sonography Educator, Christchurch Hospital, Christchurch, New Zealand.
Is there a pericardial effusion?
A pericardial effusion is when there is abnormal accumulation of fluid within the pericardial cavity. It can result from a range of clinical situations, including inflammation of the pericardial (pericarditis), radiation and trauma. The size or amount of fluid should be assessed at end- diastole, when the ventricles are at their fullest.
Small <10mm
Moderate 10 -20mm
Large>20mm
A small (panel A), moderate (panel B) and a large (panel C) pericardial effusion are shown. Images were recorded from the parasternal long axis (PLAX), parasternal short axis (PSAX), apical 4 chamber view (A4Ch) and subcostal 4 chamber (sub 4Ch) views at end-diastole.
Pericardial vs Pleural effusion
A pleural effusion, especially on the left, can be easily mistaken for a pericardial effusion. The best view to distinguish the two is from the parasternal long axis. The image depth should be increased so that you can clearly see the relationship of the fluid to the descending aorta. In this view the pericardium will run between the descending aorta and the left atria, therefore pericardial fluid will accumulate between these two structures. A pleural fluid will be posterior of the descending aorta.
Parasternal long axis demonstrating both a pericardial and pleural effusion.
Is there cardiac tamponade?
The impact of the fluid on cardiac function relates to how quickly the fluid has accumulated rather than directly to the volume of fluid present. A moderate effusion that has accumulated rapidly is more likely to result in tamponade physiology than a large effusion that has formed slowly.
Cardiac tamponade is a clinical diagnosis resulting from compression of the heart which reduces its ability to fill. An echo can be used to confirm the presence and size of a pericardial effusion. Collapse of the cardiac chambers during diastole is a typical echo sign of cardiac tamponade. If there is a large volume of fluid the heart may also swing freely within it. An echo can also help to determine the distribution of the fluid and if pericardiocentesis can be used to drain it.