In imaging for pericardial effusion (see the images below), echocardiography and tomographic modalities (MRI, CT, EBT) are quite sensitive and can identify the presence of pericardial fluid even at the normal amount of 15-35 mL. Pericardial fluid is considered normal in the absence of pericardial disease if it appears as a homogeneous or echo-free space between visceral pericardium and parietal pericardium seen only during systole when the heart contracts inward, with less that 1 mm separation of the pericardial layers during diastole. Fat between the visceral and parietal layers may produce a false positive echo but is distinctive by MRI and CT.
Pericardial effusion can occur following a number of different conditions, primarily related to inflammation and cardiac surgery.
Echocardiography remains the imaging modality of choice because of its availability and because it can be used at the bedside. Standard views along with 2-dimensional, M-mode, and Doppler analysis are important in the routine analysis of pericardial effusion.
Effusion, pericardial. Pericardial effusion as seen with 2-dimensional (2D) echocardiography.
Effusion, pericardial. Pericardial effusion as seen with M-mode echocardiography.
Effusion, pericardial. ECG showing low-voltage QRS complexes, tachycardia, PR elevation, and ST changes in a patient with pericardial effusion.
Loculated pericardial effusion. Contrast-enhanced chest CT demonstrates a pericardial effusion. The effusion is loculated on the right side. An advantage of CT over echocardiography is demonstrating loculation.(Courtesy of Eugene Lin, MD Seattle, WA)
Asymptomatic effusions are typically first detected by radiography performed for other reasons. A minimum of about 250 mL of fluid collection is required for detection through radiography that augments the cardiac silhouette. Increased pericardial fluid can be hydropericardium (transudate), true pericardial effusion (exudates), pyopericardium (if purulent), hemopericardium (in presence of blood), or mixtures of the above.
The normal pericardium is frequently identified on a lateral plain chest radiograph as a thin, linear opacity between the anterior subxiphoid mediastinal fat and subepicardial fat. In the posteroanterior (PA) view, the pericardium may be seen along the left heart border.
Pericardial effusion is characterized by accumulation of excess fluid in the pericardial space surrounding the heart. Most commonly, the fluid is exudative and results from pericardial injury or inflammation. Serosanguineous effusions are seen mainly in patients with tuberculous cancers, but they may also be encountered in uremic and viral disease or following mediastinal irradiation.
Hemopericardium is most commonly seen with trauma, myocardial rupture following myocardial infarction, myocardial or epicardial coronary artery rupture, catheter manipulation, aortic dissection with rupture into the pericardial space, or spontaneous hemorrhage in the presence of anticoagulant therapy. Chylopericardium is a rare condition that results from leakage or injury to the thoracic duct.
The presence of pericardial effusion generally indicates underlying pericardial disease; however, the clinical significance of pericardial effusion is mainly associated with its hemodynamic impact. The latter depends on the rate of fluid collection in the pericardial space, the rate of rise in the intrapericardial pressure, and resultant development of pericardial tamponade. A rapidly accumulating effusion, such as that associated with hemopericardium due to trauma, may result in tamponade with collection of as little as 100-200 mL of fluid, while a more gradual accumulation of fluid may allow for compensatory stretching of the pericardium and may not show tamponade, despite collection of fluid even in excess of 1500 mL.
Pericardiocentesis is needed in patients with hemodynamic compromise, tamponade, hemopericardium, or pyopericardium. However, in the absence of these factors, drainage is rarely indicated. Large effusions can sometimes be drained to relieve symptoms due to compression of surrounding lung and other structures. Pericardial drainage may occasionally be required to make a diagnosis based on examination of the pericardial fluid or pericardial biopsy samples.
Echocardiography is the most widely used imaging technique for the detection of pericardial effusion and/or thickening. A major advantage of echocardiography is its portability to the bedside to examine critically ill patients. The technique is noninvasive and is quite sensitive in imaging fluid-filled structures.
Echocardiographic analysis using 2-dimensional, M-mode, and Doppler evaluation can assess the following
Quantity and quality of pericardial fluid
Collapse of cardiac chambers
Respiratory variation of the ventricular diameters
Inferior vena cava collapsibility
Flow patterns in atrioventricular valves
When the pericardial fluid volume is small, it may appear as an anterior hypoechoic or echo-free space behind the left ventricle (LV), which could also represent a fat pad or a posterior or circumferential hypoechoic or echo-free space (the latter is most likely effusion).
When the pericardial effusion is large, the pericardial hypoechoic zone may expand to encircle the right ventricular (RV) apex. Rarely, echocardiography may be unable to identify pericardial fluid, especially in the presence of constriction, tumor, or hemorrhage.
Echocardiography is also useful in assessing the hemodynamic impact of the effusion: right atrial inversion, right ventricle inversion, septal motion, and respiratory variation in Doppler transvalvular flow (>50% right, >25% left) indicate compromise.
If echocardiographic findings are inconclusive, CT or MRI can be helpful in detecting pericardial thickening, diffuse or loculated effusion, calcification, adjacent mediastinal and pulmonary disease, and neoplasm.
Electrocardiography (ECG) is of little or no diagnostic value. Sometimes, large pericardial effusions may exhibit electrical alternation of QRRS voltage or “pulsus alternans” reflecting free swing of the heart within the pericardial fluid with shifting electrical axis. Reduced ECG voltage is nonspecific. Nonetheless, massive effusions, such as those seen in severe myxedema, produce true “low” voltage that may parallel that seen with severe myocardial or hemodynamic abnormality. ECG may show diffuse PR depressions (often viewed as ST-T elevations), indicating pericardial or myocardial inflammation, diffuse T-wave inversions, and low voltage and suggesting effusion; the latter findings are not reliable.
MRI and CT
The extent of normal and abnormal pericardium is best appreciated with CT and MRI in most patients because of better resolution.
With both CT and MRI, the anterior, lateral, and posterior portions of the pericardium are clearly separated from mediastinal fat. In addition, discontinuous areas of pericardial thickening and loculated effusions can also be identified. While the pericardial recesses are clearly defined by MRI and CT, they may on occasion mimic aortic dissection or mediastinal lymphadenopathy.
MRI stripes can identify pericardial adhesion to underlying myocardium, and dynamic views of LV filling can identify constriction or restrictive disease. MRI strain maps can help confirm restrictive disease. MRI chemical sensitivity, by spatiospectral excitation and/or by inversion crossing, can distinguish fat from other materials in the pericardial space.
As pericardial fluid accumulates, the cardiac silhouette begins to enlarge and appears as flask-like, triangular, or globular in shape. The usual indentations and prominences normally seen along both the left and the right heart borders begin to diminish, such that the shape of the cardiac silhouette becomes globular and featureless.