Ultrasonography is a valuable recent addition to the diagnostic armamentarium of emergency physicians. Bedside sonography allows for more rapid diagnosis and treatment of patients with potentially life-threatening illnesses while using a noninvasive modality. Because of advances in the quality of the imaging and in the portability of ultrasonography, the use of echocardiography by emergency physicians is now standard practice in the management of various acute cardiovascular disease processes (1).

Limited emergency cardiac ultrasound performed at the bedside can provide valuable life-saving information in seconds. Studies have demonstrated that with little formal training emergency physicians are capable of using ultrasound to diagnose specific emergent conditions and that they display acceptable technical skill and interpretive acumen (2). The optimal amount of training required to accurately detect such conditions and the frequency of examinations necessary to maintain proficiency for emergency physicians have not yet been definitively determined. However, using recorded photographic images or hard copy and videotaped examinations provides a means of quality assurance (see Chapter 132). Emergent echocardiography is most useful in pediatric patients to confirm the diagnoses of cardiac tamponade, pulseless electrical activity, and cardiac trauma (3,4).

Cardiac tamponade results from the accumulation of fluid, pus, or blood within the pericardial sac. This restricts cardiac filling, limits stroke volume, and reduces blood pressure. If tamponade remains uncorrected, it can result in cardiovascular insufficiency, shock, and eventually death.

Infection is the most common cause of pericarditis and the accumulation of pericardial fluid in children. Bacterial etiologies are more likely to result in cardiac tamponade. Up to 15% of patients develop pericardial effusions 1 to 3 weeks following cardiac surgery in a condition known as postpericardiotomy syndrome (5). Trauma, both penetrating and blunt, is increasingly seen as a cause of tamponade in older children and adolescents. Other causes include collagen vascular and oncologic disease.

Pulseless electrical activity (PEA) or electromechanical dissociation (EMD) is said to exist in the patient who displays electrical cardiac activity on a monitor but has no detectable pulse. PEA in children has multiple causes, including severe hypovolemia (e.g., blood loss), cardiac tamponade, severe hypoxemia, tension pneumothorax, hypothermia, and ingestions. Detection of cardiac motility in the setting of PEA is crucial for determining the prognosis, underlying causes, and possible therapeutic interventions.

Impediments in adult echocardiography such as obesity, difficulty with positioning, and chronic obstructive pulmonary disease are less likely to pose limitations to ultrasound scanning in children. However, the smaller size of the child may present more of a problem in gaining access to the chest without interrupting ongoing management.

For purposes of ultrasound evaluation, the heart can be divided into three planes: the long-axis plane, the short-axis plane, and the four-chamber plane. The long-axis plane transects the heart parallel to the long axis of the left ventricle. The short-axis plane is obtained by transecting the heart perpendicular to the plane of the long axis. The four-chamber plane is a special coronal plane that transects the heart nearly parallel to the dorsal and ventral surfaces of the body (6).

The pericardium is a dense tissue that forms a sac completely surrounding the heart and a proximal part of the aorta and pulmonary artery. This tissue is highly echogenic and is
visualized as the outer border of the heart on ultrasound. The pericardium is composed of two layers—the visceral pericardium and the parietal pericardium. Fluid between these layers is seen on ultrasound as an anechoic space between the two more reflective echoes. A small amount of fluid is normally present in this potential space and serves to lubricate the membranes. Generally, fluid is not visible anteriorly or in the nondependent areas of the supine patient. Any anterior displacement of the parietal pericardium represents an abnormal collection of fluid. Effusions tend to collect initially around the more dependent and mobile ventricles and later in the area of the less mobile atria. The minimal quantity of fluid detected with echocardiography varies with the size of the patient and the frequency of the probe; however, the amount of fluid required to produce hemodynamic changes is very easily visualized. Pericardial fat, pleural effusions, and subdiaphragmatic fluid may be confused with pericardial fluid. These anechoic stripes are not circumferential and do not demonstrate the normal variation in size between systole and diastole seen with pericardial fluid.

Hemopericardium is the most common feature of cardiac injury and is also seen as a circumferential echo-free space within the pericardium. An acute hemopericardium may present as a pericardial hematoma that has echogenic components. Any significant intrapericardial collection—either echo-free or echodense—in the setting of penetrating injury is presumed to represent penetrating cardiac injury.

Myocardial rupture is a rare complication of blunt chest trauma. Most patients die at the scene. In patients entering the emergency medical services (EMS) system alive, however, rapid diagnosis and treatment is essential for survival. Usually the pericardial sac contains the rupture, and these patients present with hemopericardium and some degree of cardiac tamponade.

The role of pediatric cardiac ultrasound by the emergency physician is restricted to a few specific conditions in which it can provide immediate and unequivocal findings. It is in no way intended to supplant the role of a comprehensive echocardiographic examination. Currently, this procedure has three main applications: (i) detection of a pericardial effusion in the appropriate clinical setting, (ii) detection of a hemopericardium or cardiac rupture associated with chest trauma, and (iii) detection of the presence of any cardiac motion associated with PEA.

Suspicion of cardiac tamponade must be acted on within seconds. In an adolescent who has sustained a penetrating chest wound, an emergent echocardiographic examination can provide information regarding the extent of injury before a patient deteriorates. Emergent cardiac ultrasound gives the physician the ability to immediately look inside the chest to confirm or refute the diagnosis at the bedside.

Cardiac tamponade in a child may present with a number of physical findings. Hypotension, especially when associated with evidence of increased central venous pressures; the presence of a pulsus paradoxus; chest pain; poor peripheral perfusion; and distended neck veins may all be signs of tamponade. However, no clinical findings associated with tamponade are 100% sensitive or specific. The classic triad of distant heart sounds, hypotension, and elevated central venous pressure are rarely present in a child, making tamponade a difficult clinical diagnosis.

Standard available tests also are nonspecific in diagnosing cardiac tamponade. ECG changes or increased heart size on a chest radiograph may suggest pericardial fluid; however, normal results do not exclude its presence. The size of the cardiac silhouette on chest radiograph depends on the amount of fluid in the effusion and the distensibility of the pericardial sac. Effusions of acute onset generally do not result in a significant increase in the cardiac shadow. Echocardiography is therefore the procedure of choice in detecting the presence of a pericardial effusion (7). Limited ultrasound in the ED may provide important additional information, especially when there is limited time available before the need for intervention.

Ultrasound also may be useful in the setting of blunt or penetrating chest trauma in cases of suspected hemopericardium or cardiac rupture. Its role may be restricted to those patients with symptoms or extended to those with a significant mechanism of injury in an attempt to anticipate potential deterioration. The Focused Assessment with Sonography for Trauma (FAST) has been shown in one small study to be 100% sensitive and specific in determining cardiac injury in patients with pericardial effusions following penetrating chest trauma (see Chapter 138) (8).

Using ultrasound to diagnose cardiac trauma is not intended to replace other standard tests currently available. It should be used as a noninvasive, rapidly available modality to complement other clinical tools and to determine the presence of specific cardiac injury in a patient who has suffered chest trauma (9). Two-dimensional echocardiography performed in the ED for identifying penetrating cardiac injuries has decreased the time to diagnosis and has improved the survival rate and neurologic outcome of survivors (10).