Justin B. Joines
Cedric Lefebvre
Chest radiographs are the most commonly performed diagnostic radiographs in emergency departments. A chest radiograph can help identify cardiovascular emergencies and other medical problems such as pneumothorax, pulmonary edema, aortic dissection, pneumonia, perforation of the gastrointestinal tract, fractures, masses, and foreign bodies (Table 3.1).
MEDICAL CONDITIONS AND ASSOCIATED FINDINGS ON CHEST RADIOGRAPH
| Diagnosis | Important Finding |
|---|---|
| Pulmonary edema | Vascular congestion, increased cephalization of vascular flow |
| Pneumothorax | Absence of lung markings, deep sulcus sign, mediastinal deviation |
| Aortic dissection/aneurysm | Abnormal mediastinum, aortic knob or cardiac contour; pleural effusions, displaced intimal calcification, tracheal deviation |
| Pneumonia | Focal or lobar consolidation, localized infiltration, patchy opacifications |
| Cardiac tamponade | Possible presence of enlarged cardiac silhouette |
| Pulmonary embolus | Westermark sign, Hamptons hump, atelectasis |
| Esophageal rupture | Widened mediastinum, free air |
A radiograph, or “x-ray,” is customarily performed by a trained radiologic technician. The x-ray apparatus typically consists of x-ray film or a special plate that digitally records the picture and an x-ray tube. The x-ray film is positioned next to the patient while the x-ray tube is located at a distance of about 6 feet from the patient. Two views are taken for a conventional chest radiograph: a posterior–anterior (PA) view, in which the x-ray beam passes through the chest from the back, and a lateral view such that x-rays pass through the chest from one side to the other. When the clinical scenario mandates a portable radiograph at the bedside, an anterior–posterior (AP) view can be obtained with the patient in a seated position. The technician may use a lead apron to protect certain parts of the patient’s body (eg, reproductive organs) from radiation. The amount of radiation used in a chest radiograph is relatively small and confers approximately 0.1 milli-severts (1/10,000 Sv) to the patient.
Most chest radiographs today are viewed and stored in a digital format. Chest radiographs use the ionizing radiation of x-rays to produce images of the structures within the human torso. Visual contrast is achieved by the different degrees to which various tissue types absorb radiation. Lungs are air-filled structures that appear dark, whereas bony structures are dense and appear white. The interpretation of a chest radiograph should be approached in a consistent and stepwise fashion. Consider the following format: review identifying patient information, observe the trachea for midline position and caliber, view the lungs and pleura for abnormal appearance, screen the pulmonary vasculature for enlargement or cephalization of flow, and investigate the hila for masses or lymphadenopathy. Next, examine the heart-to-thorax ratio and mediastinal contour, identify bony lesions or fractures, inspect soft tissues for swelling or air, and confirm supporting medical apparatus when applicable (eg, tubes and intravenous [IV] lines).
The patient must take a deep breath and hold it for an adequate image. The diaphragm should be found at about the level of the eighth to tenth posterior rib or fifth to sixth anterior rib.
The AP view will magnify the size of the cardiac silhouette.
Adequate penetration is required for a good study. For a point of reference, the thoracic spine disc spaces should be barely visible through the heart on a PA film.
Rotation of the patient may cause the mediastinum to look abnormal. Ensure that the clavicular heads are at equal distances from the spine.
Casey Glass
Bedside echocardiography can assist the emergency physician in narrowing the differential diagnosis and improving treatment decisions for a number of clinical scenarios. Common Emergency Department (ED) applications include assessment of global left ventricular (LV) function, investigation of acute right-sided heart failure or symptomatic pericardial effusion, and evaluation of volume status through measurement of the inferior vena cava (IVC). The measurement of ejection fraction, the assessment of diastolic dysfunction, and Doppler evaluation of valvular function can also be obtained using bedside echocardiography.
The quality of images obtained is greatly dependent on the quality of the ultrasound equipment and the skill of the operator. Generally, point-of-care machines produce images inferior to their dedicated echocardiography counterparts. Ideally, a phased array probe will be used for cardiac ultrasound. However, images can be obtained with a curved linear array probe as well. The ultrasound probe is oriented to produce images of the same screen appearance as formal echocardiography studies. Typically a bedside echocardiogram will include a four-chamber subcostal view, a long axis view of the vena cava, parasternal long and short axis views, and an apical four-chamber view.
The subcostal view is obtained by placing the ultrasound probe in the subxiphoid space with the indexed side of the probe to the patient’s right and the beam aimed at the left shoulder. This view visualizes all four chambers of the heart as well as the anterior and posterior pericardium. A pericardial effusion appears as a dark stripe around the heart. Portions of the chambers may be out of plane and chamber size may be distorted. Caution should be exercised when deciding if there is abnormal chamber size.
The probe is then rotated 90° clockwise so that the indexed side of the probe is oriented toward the patient’s head. The right upper quadrant (RUQ) is swept from midline to the right flank to locate the vena cava, which appears as an anechoic tube connecting to the right atrium. In this position, an M-mode tracing can be performed approximately 2 cm caudal to the diaphragm to evaluate for respiratory movement of the IVC and IVC diameter. The ratio of the inspiratory and expiratory diameter of the IVC (the caval index) correlates with central venous pressure (CVP). A diameter greater than 1.5 to 2 cm with little change during respiration correlates with an elevated CVP (>20 cm H2O), and a small or collapsed IVC <1 cm with more than 50% collapse with respiration correlates with a low CVP (<10 cm H2O).
Parasternal views are obtained when the probe is placed in the third or fourth intercostal space along the left side of the sternum. The probe is first oriented with the indexed side to the lower left costal margin producing an image of the heart in the long axis. The parasternal long axis view visualizes the LV and left atrium as well as the aortic outflow tract. The RV is only partially imaged and the right atrium is excluded. This view is helpful for assessing volume status and global cardiac function as well as aortic root diameter.
The parasternal short axis view is obtained by rotating the probe 90° clockwise until it is oriented toward the lower right costal margin producing an image of the LV in the short axis. The probe should be angled or moved laterally to image the LV at the level of the papillary muscles. In cases of acute pulmonary hypertension, the septum may deviate toward the LV producing a “D-shaped” ventricle. The short axis view is also useful for assessing global LV function.
FIGURE 3.12
The parasternal long axis view gives a good representation of the LV, left atrium (LA), interventricular septum (IVS), and aortic outflow tract (AO). The mitral (MV) and aortic (AoV) valves are seen. Aortic root measurements are performed at the level of the aortic valve (arrows). The descending aorta is also imaged posterior to the heart (DAo).
The apical four-chamber view is obtained when the probe is placed over the point of maximal impulse with the indexed side of the probe aimed anteriorly and toward the patient’s right. The beam is aimed at the right shoulder producing a four-chamber image of the heart. This view is helpful for assessing RV size, global function, and the presence of effusion. To measure ventricle size, the ventricles are measured at the level of the tricuspid or mitral valve from the outer wall to the middle of the septum at end diastole.
Clinical scenarios where bedside echocardiography is often employed include evaluation of unexplained hypotension, possible aortic dissection, and for estimation of ejection fraction.
Advanced skills include evaluation for systolic dysfunction by evaluating the degree of E-point septal separation and measured ejection fraction, evaluation for diastolic dysfunction through measurement of the E to A ratio and E wave duration, and measurement of cardiac output. These studies require significant additional ultrasound skill and an understanding of their limitations.
FIGURE 3.15
E-point septal separation is a useful surrogate for impaired ejection fraction due to systolic dysfunction, valvular dysfunction, or ventricular septal defect. The probe must be perpendicular to the heart to ensure an axis view. The maximal excursion of the anterior mitral leaflet is measured with reference to the interventricular septum (arrowheads). A normal measurement is less than 4 mm.
FIGURE 3.16
When patients have known systolic dysfunction without significant regional wall motion abnormalities, ejection fraction can be estimated by comparing the systolic (small arrows) and diastolic (large arrows) diameters of the LV. This measurement is usually obtained in the parasternal short axis view at the level of the papillary muscles.
The left lateral decubitus position is helpful for improving the parasternal and apical views.
Positive pressure ventilation can reduce or eliminate the normal respiratory variation in IVC size.
Cardiac views may be improved by having the patient hold their breath at end expiration.
Pleural and peritoneal fluid can be mistaken for a pericardial effusion if several views of the heart are not assessed.
FIGURE 3.17
Simpson’s method of disks is a more accurate estimation of ejection fraction, is appropriate for all patients and is necessary for those with significant regional wall motion abnormalities. The ventricle is imaged in the apical four- or two-chamber view and the endocardium is traced at end diastole and end systole.
Joseph Yeboah
Bharathi Upadhya
Transthoracic echocardiography (TTE) has evolved into a diagnostic cornerstone in cardiovascular emergency management. It is safe, noninvasive, highly accurate, and offers a quick assessment of the heart and a portion of the aorta. A crystal-containing TTE probe projects ultrasound waves at the organ of interest and these waves are reflected back to the probe. The reflected waves are processed and reconstituted into images. TTE imaging includes M-mode, in which the ultrasound beam is aimed manually at selected cardiac structures, as well as color and Doppler imaging by which the direction and velocities of moving objects can be measured. More recently, strain/speckle tracking imaging has been developed for noninvasive assessment of myocardial deformation. Standardized imaging protocols have been established for TTE of the heart and thoracic aorta. These standardized views include parasternal long and short axes, apical long and short axes, subcostal and suprasternal notch views.
The scope of the diagnostic capabilities of TTE includes evaluating the cause of chest pain, investigating the etiology of hypotension/shock, and exploring the source of dyspnea. In the setting of chest pain, TTE can help differentiate between myocardial ischemia/infarct during which wall motion abnormalities may be noted, and acute pericarditis during which wall motion is normal but a small amount of pericardial effusion may be seen. Stress-induced cardiomyopathy, or Takotsubo cardiomyopathy, is another cause of chest pain that can be investigated by TTE. In Takotsubo cardiomyopathy, characteristic apical ballooning and hyperdynamic movement of the base of the LV is noted. Thoracic aortic dissection is another etiology of chest pain that can be found on TTE.
When investigating the cause of severe hypotension/shock, TTE can accurately identify cardiac emergencies contributing to hemodynamic instability. In cases of cardiogenic shock due to massive myocardial infarction (MI), TTE will often reveal reduced LV ejection fraction with wall motion abnormalities. In cases of cardiac tamponade, an accumulation of fluid in the pericardial sac with evidence of hemodynamic compromise can be observed with TTE. TTE can also detect hypovolemia as the cause of hypotension by identifying underfilling of the cardiac chambers.
When evaluating a patient with acute shortness of breath, TTE can help identify causes such as massive pulmonary embolism (PE), congestive heart failure, and chronic obstructive pulmonary disease (COPD) exacerbation. It is the ideal tool for identifying complications such as free wall rupture, ventricular septal defects, and papillary muscle rupture. Identification of cardiac masses, such as tumors and thrombi, can be achieved with TTE as well. TTE can be used as an adjunct to therapy during cardiovascular emergencies such as pericardiocentesis.
TTE during cardiovascular emergencies should be performed by a qualified echocardiography technician or physician. Images from TTE should be interpreted by a qualified physician. A systematic review of the TTE images (overall anatomy, chamber sizes and function, and valve morphology), evaluation of color and Doppler flow velocities (pressure gradients), and careful consideration of patient’s history and hemodynamic status are always recommended. In many cardiovascular emergencies, however, time is restricted and only a focused exam is feasible. Therefore, interpretation of TTE must be made with limited information at times. Limitations of TTE imaging include inadequate resolution of images and poor echocardiographic windows. These can occur in patients on mechanical ventilation and in obese patients. Assistance from other providers may be necessary to help position the patient for adequate imaging. Misinterpretation of TTE images can lead to the misdiagnosis of critical cardiovascular emergencies and a delay to therapeutic measures.
In patients with chest pain not relieved by nitroglycerin and with no obvious ST-segment elevation on electrocardiogram (ECG), be certain to visualize the aorta (root, arch, and descending). The patient may have an aortic dissection.
Beware of image artifact. If image artifact is suspected, check to see whether a structure is visible in multiple views. If it is not, artifact is likely and should not be included in the interpretation of the TTE.
A large pericardial effusion does not always result in cardiac tamponade. Cardiac tamponade is a clinical diagnosis that can be assisted by findings on TTE. If a patient with a pericardial effusion is hemodynamically unstable, one should investigate TTE evidence of tamponade such as RV collapse in early diastole, right atrial inversion in late diastole, and respiratory variation of mitral/tricuspid inflow velocity.
Min Pu
Transesophageal echocardiography (TEE) is a semi-invasive procedure that provides real-time imaging of the heart. To overcome the shortcomings of TTE, TEE was developed after miniaturization of the echocardiographic probe. Indications for TEE include the need for real-time data about cardiac function that will help guide clinical and therapeutic strategies. The information obtained by TEE includes valvular function, pericardial conditions, aortic anatomy, and heart wall motion. Severe esophageal disease (cancer or obstruction) is an absolute contraindication to performing TEE.
Moderate sedation of the patient is required to perform TEE. Clinical practice guidelines for safe and effective conscious sedation should be followed. Benzocaine spray and/or gargled lidocaine preparations may be used for local anesthesia. The patient is positioned in the lateral decubitus position and a bite guard is used. The TEE probe is introduced into the mouth and down the esophagus. The probe is manipulated to acquire images and to optimize picture quality. With the probe in the mid-esophagus, multiple mid-transesophageal views can be obtained. In order to acquire transgastric images, the probe is advanced into the stomach, flexed anteriorly, and slowly withdrawn while monitoring the images. With biplane views, short and long axis images of the LV and RV can be simultaneously obtained. The descending aorta can be imaged by rotation of the probe to near 180˚ facing the back of the patient. Slow withdrawal and rotation of the probe enables visualization of the thoracic aorta.
A complete or targeted TEE examination can be performed depending on the clinical question and the patient’s condition. Although serious complications are rare, the risks of TEE include injury to laryngeal structures and rupture of the esophagus. The potential side effects and risks associated with sedation must also be considered and disclosed to the patient or consenting party. Postprocedural management includes monitoring of vital signs for at least 30 minutes and until the patent returns to baseline. Patients should not eat or drink for at least 2 hours after the procedure or until oral sensation and swallowing function return to normal. General postprocedural sedation precautions should be observed.
FIGURE 3.27
(A) The TEE probe can be flexed anteriorly, posteriorly, and laterally via manipulation of the control knob. (B) Short and long axis views of the LV are demonstrated here. (C) TEE images of the descending aorta and aortic arch are displayed.
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