Pericardial effusions are usually an incidental finding on bedside echocardiogram—unless a patient shows clinical signs of tamponade physiology and obstructive shock. Echocardiogram is both sensitive and specific to detecting pericardial effusions.1 Although there are many causes of pericardial effusions, the most common causes of symptomatic effusions in the Western World are due to neoplasm, pericarditis, traumatic pathology, or idiopathic etiology. In developing countries, however, pericardial effusions are predominantly due to tuberculosis in an area where it is endemic.2,3 The size of the effusion is classified based on measurements of a fluid pocket during diastole. Mild effusion is defined as less than 10 mm; moderate effusion, 10 to 20 mm; and large effusion, greater than 20 mm.3
It is important to note that the pericardial space contains up to 50 mL of physiological fluid which may be seen on echocardiography during systole. Small effusions usually contain less than 100 mL of fluid; moderate effusions contain 100 to 500 mL of fluid; and large effusions, over 500 mL of fluid. Fluid of smaller effusions typically layer posteriorly, while the fluid of some moderate and most large effusions may be seen circumferentially.
Clinical Signs and Symptoms
Patients with large chronic effusions are often asymptomatic, and clinical symptoms usually correlate to the acuity of pericardial accumulation. Patients with symptomatic effusions present with dyspnea on exertion that is followed by orthopnea, chest pain, and sometimes dysphagia, hoarseness, or hiccups due to irritation of surrounding structures until they exhibit tamponade physiology leading to hypotension secondary to obstructive shock. The most recognized signs of tamponade physiology on bedside echocardiography are early diastolic collapse of the right atrium and right ventricle, as well as ventricular interdependence.4
Pericardial effusion and cardiac tamponade can be detected in any of the standard echocardiographic views, with fluid usually appearing as an anechoic stripe. The fluid will first appear in the dependent portion of the pericardial space, but may become circumferential as it grows (Figure 1).
After evaluating for signs of tamponade on examination, the next step is to evaluate the inferior vena cava (IVC). A simple way to identify the IVC on echocardiography is to visualize the heart in the subxiphoid view, then rotate the probe so that the marker is pointing toward the patient’s head. As demonstrated in Figure 5, the IVC should be seen entering the right atrium; if the patient is truly in obstructive shock, the IVC should be plethoric with minimal respiratory variation.