Chest x-ray is a staple in the evaluation of the trauma patient. While not ordered for the specific purpose of detecting pericardial effusions, signs of effusion may be evident on chest film. The cardiac silhouette may be widened; however, a normal silhouette does not rule out effusion. In fact, pericardial effusions of 200 to 500 mL are necessary for the cardiac silhouette to appear enlarged on chest film. Other signs suggestive of effusion are a dilated azygous vein and increased pulmonary venous markings.4 Importantly, chest x-ray can show other injuries such as fractures, pneumothorax, and hemothorax, which may assist with the utility of echo or management of the unstable patient (Table 23–2 and Figure 23–1).
TABLE 23–2Chest X-ray Findings of Tamponade |Favorite Table|Download (.pdf) TABLE 23–2Chest X-ray Findings of Tamponade
Widened cardiac silhouette
Increased pulmonary venous markings
Others signs of chest trauma (pneumothorax, hemothorax, sternal or rib fractures)
Chest x-ray showing widened cardiac silhouette.
In stable patients at centers where ultrasound is unavailable, CT may identify pericardial effusion. CT can also show some of the signs of tamponade such as distension of the superior vena cava (SVC) and inferior vena cava (IVC) or IV contrast refluxing into the azygous vein. Given the heart motion, ECG-gated CT provides the best resolution of the cardiac chambers. An ECG-gated CT can also show deformity of the cardiac chambers and bowing of the interventricular septum with tamponade physiology.14 However, ECG-gated CT is not commonly employed in the trauma setting (Table 23–3 and Figure 23–2).
TABLE 23–3CT Findings of Tamponade |Favorite Table|Download (.pdf) TABLE 23–3CT Findings of Tamponade
Contrast refluxed into azygous vein
Bowing of interventricular septum
Axial CT scan of the chest showing circumferential pericardial effusion (arrow).
Echocardiography has the greatest utility in the diagnosis of tamponade. In performing a cardiac ultrasound, it is important that the correct probe is selected. A phased array probe is best, and settings should be adjusted for the proper depth and gain for optimal image quality.15 Surgeons should familiarize themselves with the basic views and be able to acquire these images. Generally, the most useful views are the subcostal four-chamber, parasternal long-axis, parasternal short-axis, and apical four-chamber views.
The subcostal view is the most useful for rapid diagnosis of a pericardial effusion and is employed as part of the FAST examination. This view is acquired by placing the probe just below the xiphoid and aiming toward the heart. The marker dot should face the patient’s left (unfortunately, this is opposite to what is often taught for FAST examinations). The probe should be adjusted until all four chambers can be seen. The probe can then be rotated, so that the marker points toward the patient’s head and tilted perpendicular to the floor to reveal the subcostal view of the inferior vena cava (IVC) (Figure 23–3).
Normal subcostal four-chamber view. The liver edge will be visible first, and the cardiac chamber closest to the probe is the right ventricle. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
The parasternal long axis is acquired by placing the probe at the second intercostal space just to the left of the sternum. With the marker dot pointing toward the patient’s right shoulder, the probe should be moved caudally until the view is obtained. The short axis is simply perpendicular to the long axis; the probe should be rotated so that the marker is pointing toward the left shoulder. Tilting the probe will show the left ventricular apex, left ventricular mid-papillary, mitral valve, and aortic valve views (Figures 23–4 and 23–5).
Normal parasternal long-axis view. The right ventricle (RV) is visible closest to the probe. Beneath the right ventricle is the left ventricle (LV), the left ventricular outflow tract (LVOT), aortic valve (AV), and ascending aorta (Ao). The left atrium (LA) and mitral valve (MV) are at the bottom right of the image.
Normal parasternal short-axis view, left ventricular mid-papillary level. The right ventricle (RV) is crescent shaped at the top right of the screen. The muscular wall of the left ventricle (LV) is round, and the papillary muscles (white arrow) are visible inside the chamber. The interventricular septum (yellow arrow) separates the two ventricles.
The apical views are obtained by placing the probe on the lateral left chest at the point of maximal impulse. The marker dot is directed to roughly the 3 o’clock position. It is often helpful to place patients on their left side for this view as it brings the heart closer to the chest wall (Figure 23–6).
Normal apical four-chamber view. The apex of the left ventricle is closest to the probe, and the anterolateral wall of the left ventricle (LV) is seen on right side of the image. The mitral valve (MV) is seen separating the left ventricle from the left atrium (LA). The right ventricle (RV), tricuspid valve (TV), and right atrium (RA) are seen on the left side of the image.
A pericardial effusion is often easily detectable with a subcostal four-chamber view as is used in a FAST examination. Blood or fluid is identified as an echolucent or anechoic (black) area within the pericardium. Heart swinging or a decrease in motion of the parietal pericardium may also be observed.10 Other views may assist in the diagnosis of an effusion and may be particularly useful in differentiating pericardial and pleural effusions. In the parasternal long-axis view, a pleural effusion will be noted as posterior to the descending aorta, while a pericardial effusion is anterior (Figures 23–7, 23–8, and 23–9).
Echocardiogram showing a subcostal four-chamber view with a large pericardial effusion.
Apical four-chamber view showing large circumferential pericardial effusion.
Echocardiogram showing a parasternal long-axis view. This patient has both a pleural effusion and a pericardial effusion. Note the descending aorta (arrow). Fluid collections posterior to the descending aorta are pleural (Pl), while those anterior are pericardial (Pc). LA, left atrium; LV, left ventricle; LVOT, left ventricular outflow tract.
Findings suggestive of tamponade are generally seen in the right ventricle and atrium before any changes are seen on the left side of the heart. The right ventricle will be compressed, and early diastolic collapse is associated with tamponade with a high degree of specificity.11 The right atrium will also show systolic collapse, which is most specific when collapse is present for greater than 30% of the cardiac cycle. Left atrial systolic collapse is less common, but when it is seen it is highly specific.4 M-mode imaging can be useful in detecting cardiac chamber collapse. With M-mode, a line is placed through the image and a temporal representation of the image is created by rapidly sampling along this line over time (Table 23–4 and Figures 23–10 and 23–11).
TABLE 23–4Echocardiographic Findings of Tamponade |Favorite Table|Download (.pdf) TABLE 23–4Echocardiographic Findings of Tamponade
Right ventricular diastolic collapse
Right atrial systolic collapse
Decreased left ventricular filling on inspiration
Subcostal four-chamber view echocardiogram with M-mode in a patient with tamponade. The green line indicates the path of the M-mode cursor. Note the arrow showing diastolic collapse of the right ventricle. LV, left ventricle; RV, right ventricle.
Subcostal four-chamber view in a patient with tamponade. There is a large effusion, and collapse of the right atrium is seen during systole. LV, left ventricle; RA, right atrium; RV, right ventricle.
Further echocardiographic findings may be necessary to support the diagnosis of tamponade. This evaluation is beyond a focused examination and may require a more experienced sonographer or cardiologist. In general, the heart will have a circumferential fluid layer compressing all chambers. To maintain cardiac output, tachycardia and high ventricular ejection fractions will be present.4 Echocardiographic signs of pulsus paradoxus are seen on views of the IVC and with Doppler evaluation across the mitral valve. The IVC may collapse on inspiration as negative thoracic pressure fills the right ventricle. Later in tamponade, the IVC will be dilated with little respiratory variation.
M-mode views of the IVC are especially useful in measuring IVC changes. On the left side of the heart, the reverse is seen. Pulse-wave Doppler of the mitral valve will show decreased velocities on inspiration, correlating with poor left ventricular filling and hypotension.6 This can also be shown with views of the interventricular and interatrial septa. Both septa will deviate left on inspiration as the right heart fills, with the reverse occurring on exhalation.
Sometimes echocardiography can also be used to identify the site of cardiac injury. Transesophageal echocardiography is best, but some cardiac injuries, such valve injuries, ventricular septal defects, and focal systolic hypokinesis, are evident on transthoracic echo as well14 (Figure 23–12).
Subcostal view of the inferior vena cava (IVC). The IVC is dilated (arrow) and exhibits no respiratory variation (not seen). Note the large pericardial effusion as well. RA, right atrium; RV, right ventricle.