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A pericardial effusion is diagnosed based on the echocardiographic finding of an echo-lucent area around the heart. Pericardial effusions are usually circumferential, with fluid filling the entire pericardial space around the right and left ventricles, although pericardial effusions may also be asymmetric due to adhesions resulting in areas of loculated fluid, especially in patients with prior cardiac surgical procedures.

The pericardial space extends to the origin of the great vessels, with the narrow transverse sinus of the pericardium extending posterior to the aorta and pulmonary artery, and adjacent to the left atrial appendage. Fluid in the transverse sinus is uncommon but may be seen on TEE as in the example here. The pericardial space also encloses the right atrium, with pericardial reflections at the junctions of the SVC and IVC with the right atrium, so that fluid adjacent to the right atrium is commonly seen. A small pocket of pericardial fluid also may be seen posterior to the left atrium, where the oblique sinus of the pericardium extends into the region between the four pulmonary veins.

A pericardial effusion is distinguished from a pleural effusion by its location. Pericardial fluid is seen posterior to the left ventricle and left atrium but anterior to the descending thoracic aorta, whereas pleural fluid extends posterior to the descending aorta. Fluid adjacent to the right atrium may be either pleural or pericardial, with the latter inferred from the presence of a pericardial effusion in other views. The presence of a compressed lung in the echo-lucent space helps confirm a diagnosis of pleural effusion.

Pericardial fluid may be well tolerated if the pressure within the pericardial space is low, for example with a chronic effusion that has accumulated slowly. Even very large chronic effusions may be associated with normal hemodynamics. However, if the pressure in the pericardial space exceeds the diastolic pressure in the cardiac chambers, hemodynamic changes are seen. When pericardial pressure exceeds right atrial pressure, the free wall of the right atrium inverts or “collapses” and right atrial filling volumes are reduced. Similarly, the left atrium and right ventricle can be compressed when pericardial pressure exceeds the pressure in that cardiac chamber. Tamponade physiology can even occur with loculated effusions if there is compression of one of the cardiac chambers. The diagnosis of tamponade due to a loculated effusion can be challenging. In addition, chamber collapse may not be seen, even when pericardial pressures are high, if the wall of the chamber is thickened or fibrotic.

Along with chamber collapse, a high pericardial pressure restricts the total cardiac volume. Thus, as the right-sided chambers increase in size with inspiration, due to negative intrathoracic pressures and increased venous return, the left-sided chambers are compressed with a reduction in forward cardiac output. These reciprocal inspiratory changes in right and left ventricular diastolic filling result in the drop in blood pressure seen with inspiration, or pulsus paradoxus. These changes are not reliable in patients receiving positive pressure ventilation.

Suggested reading

• 1.
  

  Welch T: Pericardial disease. In Otto CM, editor: The practice of clinical echocardiography, ed 5, Philadelphia, 2016, Elsevier.

  
  
• 2.
  

  Klein AL, Abbara S, Agler DA, et al: American Society of Echocardiography clinical recommendations for multimodality cardiovascular imaging of patients with pericardial disease: endorsed by the Society for Cardiovascular Magnetic Resonance and Society of Cardiovascular Computed Tomography, J Am Soc Echocardiogr 26(9):965–1012, e15, 2013.

  
  
• 3.
  

  Silbiger JJ, Garg V, Moss N, et al: Protruding fat from the posterior atrioventricular groove: a novel echocardiographic finding useful in distinguishing pericardial effusions from left pleural effusions, J Am Soc Echocardiogr 28(1):116–117, 2015.