Pleural * Effusion
Fig. 16. (A) Pericardial vs (B) pleural effusion. Parasternal long axis views showing the anatomical relationships of pericardial vs pleural effusions (arrows) and their relationship to the descending thoracic aorta (dtAo). Note the small pericardial effusion (arrow at upper left) in B.
Confusion between pericardial fluid and ascites can occur in the subcostal view, which can be resolved by defining the diaphragmatic border.
Quantitation of pericardial fluid by echocardiography is imprecise, although estimates can be made imaging in multiple planes. Small effusions (100-200 mL) are generally observed only posteriorly in the supine patient, and the echolucent space between the parietal and visceral percardium is generally less than 0.5 cm. Moderate effusions (200-500 mL) separate the pericardial layers by 0.5-2 cm in diameter, and are usually seen circum-ferentially. Large effusions (greater than 500 mL) extend more than 2 cm in diameter and almost always surround the heart. A swinging motion of the heart during the cardiac cycle may be seen, with electrical alternans as the ECG correlate (Fig. 17).
Loculated pericardial effusions require more careful echocardiographic inspection to identify and characterize. These typically occur in the setting of previous pericardial or cardiac surgery, severe or chronic inflammation, or neoplastic disease, all of which create adhesions and closed spaces within the pericardial sac (Fig. 18; please see companion DVD for corresponding video). Localized fluid collections, which cause compression of only a single cardiac chamber, may create severe hemodynamic embarrassment without classic features of cardiac tamponade (Fig. 19). A specific form of loculated pericardial fluid collection is a pericardial hematoma that can form after cardiac surgery or cardiac laceration. After cardiac surgery, such hematomas are usually located anterior and lateral to the right atrium, and may have a variable echocardiographic appearance, ranging from an echolucent collection to a highly echogenic mass. They are prone to cause cardiac compression, particularly of pliable chambers such as the atria, and it is important to distinguish them from intra-atrial thrombi (Fig. 20).
Once a pericardial effusion has been identified, it is important to assess its hemodynamic significance, i.e., to evaluate for the echocardiographic features of cardiac tamponade. It is important to emphasize that the diagnosis of cardiac tamponade is a clinical one, associated with elevated venous pressures, hypotension, and tachycardia, supported by appropriate imaging and laboratory findings.
There are several features on 2D echocardiography that suggest a hemodynamically significant pericardial effusion (Table 2). Most sensitive is cyclical compression, inversion, or collapse of the right atrium. This is first observed in late ventricular diastole and persists into early ventricular systole; the sensitivity of this sign for tamponade is between 90 and 100%. The specificity of this sign for tamponade is lower, ranging between 60 and 80%, but can be improved if the right atrial inversion time index is used. This is a quantitative measure of the amount of time in the cardiac cycle the right atrium is compressed or inverted as a fraction of the total cardiac cycle. If the right atrial inversion time index is more than 0.34, this sign has higher sensitivity and specificity for hemodynamically significant tamponade. Left atrial compression or inversion is less sensitive but more
Fig. 18. (Opposite page) Adhesions in chronic pericarditis. Images of chronic pericarditis showing effusions with adhesion strands bridging visceral and parietal pericardium (arrows) from three different patients (A-C). (Please see companion DVD for corresponding video.)
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