Chapter 29. Cardiac Ultrasound

Pericardial tamponade is arguably the most dramatic ultrasound (US) finding for the Emergency Physician (EP). The diagnosis is difficult to make without cardiac US, and acute intervention can be lifesaving. Cardiac US has proven to be an invaluable tool for identifying critical pathology and directing decision making in the Emergency Department (ED).1 A quick bedside US can assess a patient's cardiac activity, global cardiac function, presence or absence of effusion, and volume status. Cardiac US is an essential part of the evaluation of the trauma patient,2 the cardiac arrest patient,3,4 and the patient with undifferentiated hypotension.5,6

Cardiac ultrasonography can be one of the most challenging areas of emergency US. The EP must have a keen grasp of the spatial anatomy of the heart to properly perform and interpret the US examination. An EP can become competent in basic cardiac ultrasonography with practice. This tool can be utilized to gain great insight into the body's most vital organ. This chapter will cover basic cardiac anatomy, the indications for emergency echocardiography, techniques, and image interpretation.

General Anatomy and Physiology

It is essential to know the anatomy of the heart before performing any US examination (Figure 29-1). The heart lies obliquely in the middle of the chest. It consists of four chambers: the left atrium, the right atrium, the left ventricle, and the right ventricle. The atria are thin-walled muscular structures. The ventricles are more voluminous and muscular, with the left ventricle having the thickest wall. The base of the heart is the superior portion. It is formed by the left atrium, and to a lesser extent the right atrium. The apex of the heart consists of the inferolateral portion of the left ventricle. The anterior surface of the heart abuts the chest wall and is mainly formed by the right ventricle. The left ventricle forms the majority of the inferior surface, with the inferior portion of the right ventricle making a minor contribution. The heart has two axes; both are used extensively in ultrasonography. The long axis extends from the base to the apex, roughly along a line from the right shoulder to the left hip. The short axis slices the heart transversely and perpendicular to the long axis, roughly along a line from the left shoulder to the right hip.

The right heart delivers blood to the lungs to be oxygenated, and the left heart distributes it to the rest of the body. The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava. Blood flows from the right atrium through the tricuspid valve and into the right ventricle during diastole. Blood is pumped from the right ventricle through the pulmonary valve and into the pulmonary artery during systole. The blood is oxygenated by the lungs then flows into the left atrium via the pulmonary veins. Blood flows across the mitral valve into the left ventricle during diastole. It is then pumped by the left ventricle for distribution to the body via the aorta during systole.

The heart is contained within the two-layered pericardial sac. The visceral pericardium is a single layer of cells in direct approximation with the epicardium. The tougher outer fibrous parietal pericardium surrounds the visceral pericardium. The two layers form a potential space that contains a small volume of fluid of approximately 20 to 50 mL.7 This pericardial fluid allows the heart to freely move within the fibrous pericardium. Larger volumes of fluid can collect in this potential space in pathologic states.

Pericardial Effusion

A pericardial effusion is a collection of fluid in the space between the visceral and parietal pericardium. Effusions can be due to trauma, uremia, infection, neoplasm, connective tissue disorders, iatrogenic complications, idiopathic conditions, chyle, and numerous other rare causes.8 Cardiac tamponade occurs when the fluid collects rapidly, such as in the setting of trauma, where it can cause collapse of the ventricles and decreased cardiac output.8,9 Fluid that collects more slowly will allow the parietal pericardium to expand accordingly and usually does not lead to cardiovascular collapse.9

Cardiac Arrest

Cardiac arrest is the end result of numerous different pathologic states. Asystole is the complete absence of cardiac activity, or akinesis of the heart.10 While atrial twitching may be visualized on US, the lack of ventricular activity is uniformly seen in asystole. Pulseless electrical activity (PEA) describes the state in which no pulses are palpable, but cardiac electrical activity is visible on ECG monitoring. Cardiac activity may or may not be present upon US of a heart in PEA. Cardiac arrest can occur from nonperfusing tachyarrhythmias and bradycardias. Cardiac motion is present in the case of ventricular fibrillation but is unorganized, preventing adequate cardiac filling and ejection of blood. Severe bradycardia causes the heart to beat at a rate too slow to provide adequate perfusion of the heart and other tissues.

Congestive Heart Failure

Congestive heart failure (CHF) is an increasingly common condition that distorts normal cardiac anatomy.11 Dilation of the left ventricle, decreased ejection fraction, and decreased cardiac output are seen in systolic heart failure.12 With a loss of healthy contractility and enlargement of the left ventricle, dilation of the other cardiac chambers generally ensues. Diastolic failure is due to prolonged exposure to high cardiac afterload as seen with aortic stenosis and uncontrolled hypertension.13 This results in hypertrophy of the left ventricular myocardium. The thickened myocardium cannot relax appropriately to allow ventricular filling during diastole. Diastolic and systolic heart failure both result in a heart that appears globally enlarged. The point of maximal impulse (PMI) is lateralized due to enlargement of the left ventricle from either dilatation or hypertrophy. Both disease states can be visualized on US.

US for Suspected Pericardial Fluid

Pericardial fluid appears as an anechoic collection between pericardium and myocardium (Figure 29-2). Small effusions may layer posteriorly or appear as thin black stripes under the pericardium. Larger effusions extend anteriorly to surround the heart entirely. Epicardial fat may be confused for pericardial fluid but can usually be differentiated because it appears as an isolated thin hypoechoic layer along the anterior aspect of the heart (Figure 29-3).18 Fluid generally appears anechoic and not hypoechoic like the epicardial fat. Loculated effusions are usually spherical or lenticular collections with echogenic borders and septae.

US for Traumatic Hemopericardium

Cardiac US has been used to diagnose hemopericardium in the setting of trauma, particularly penetrating injuries.2,19 US is a rapid and noninvasive means of determining the need for operative intervention. The physical exam is generally unreliable in diagnosing a hemopericardium.20 A subxiphoid pericardial window is invasive and unwarranted in low-risk patients.2 Rozycki et al. evaluated the use of US performed by Surgeons, Cardiologists, and technologists for diagnosing a hemopericardium due to penetrating torso trauma. This study revealed a sensitivity of 100%, specificity of 96.9%, and an accuracy of 97.3%.2 Plummer et al. demonstrated that a rapid sonographic evaluation of the heart performed by EPs expedites lifesaving management for victims of penetrating trauma.19 Both length of time to operative intervention and mortality were significantly improved by ED cardiac US.

The Focused Assessment with Sonography for Trauma (FAST) exam is the cornerstone of trauma ultrasonography.17 This study consists of four views: three abdominal views and a single cardiac view. The incidence of hemopericardium is significantly lower for blunt trauma than for penetrating injuries. Substantial blunt force to the chest or deceleration injuries may result in myocardial or aortic tears and a hemopericardium.21 Refer to Chapter 5 for the complete details of the FAST exam.

US for Nontraumatic Effusions

The clinical suspicion for a pericardial effusion should prompt the EP to perform bedside ultrasonography. The diagnosis of pericardial effusion should be considered in any patient presenting with shortness of breath, chest pain, and decreased exercise tolerance. Hypotension, distended neck veins, pulsus paradoxus, a pericardial rub on physical examination, and low voltage or electrical alternans on ECG are all consistent with a pericardial effusion. Unfortunately, most of these findings are neither sensitive nor specific for a pericardial effusion or cardiac tamponade.20 Hence, cardiac US is critical in making the diagnosis. It is important to note that chronic pericardial effusions are generally better tolerated than acute effusions. Pericardial compliance over time allows for a greater volume that exerts less pressure upon the cardiac chambers (Figure 29-4).9

Mandavia et al. investigated the ability of EPs to diagnose a pericardial effusion with US.1 Of the 515 patients enrolled, 103 had pericardial effusion identified by the EPs for a sensitivity of 96% and a specificity of 98% according to the comparative standard.

US in Cardiac Arrest

US is useful for guiding the management of patients in cardiac arrest. Confirmation of asystole helps the EP in deciding to terminate resuscitation efforts. The sonographic findings of an arrested heart include still ventricular walls, sporadic nonperfusing twitches of the valves or myocardium, and at times a “smoky” appearance to the intracardiac blood without forward motion. Blaivas and Fox evaluated the predictive value of cardiac US in cardiac arrest.4 Of 136 patients with cardiac standstill on US, 71 had an identifiable rhythm on the monitor. No patient with PEA and cardiac standstill survived to leave the ED.

PEA refers to a state in which the heart generates electrical activity on the ECG monitor but is unable to perfuse a palpable pulse. The spectrum of etiologies for this condition can be visualized with US, from “subpalpable hypotension” with contracting ventricles to terminal erratic cardiac twitches. In an observational study performed by Tayal and Kline, PEA patients without sonographic cardiac activity all died.3 Several patients with sonographic motion of the myocardium had reversible causes such as a pericardial effusion survived. US has value in diagnosing several other etiologies of PEA including: cardiac tamponade,1 myocardial infarction,22 cardiogenic shock,5,6 pulmonary embolism (PE),23 aortic rupture,24 hypovolemia, and hemorrhagic shock states.14

Circumstance may arise when ventricular fibrillation is not appreciated on the ECG monitor but is diagnosed by US. Fine ventricular fibrillation can look like asystole on the ECG monitor. Ultrasonography of fine ventricular fibrillation appears as rapid trembling of the ventricular myocardium versus the lack of any motion for asystole.

US for Left Ventricular Failure

The high prevalence of CHF makes the assessment of left ventricular (LV) function particularly valuable in the ED. New-onset CHF is generally a clinical diagnosis for the EP. However, cardiac US allows for direct evaluation of LV function. Cardiac US may aid in distinguishing CHF from other causes of dyspnea such as chronic obstructive pulmonary disease, pneumonia, pericardial effusion, and PE.25,26 US can help differentiate cardiogenic shock from other types of shock in a patient with unexplained hypotension.6

Moore and Agur investigated the use of bedside US for estimations of LV function in hypotensive patients.27 They concluded that EPs can make accurate determinations. Randazzo et al. conducted a study in which EPs performed bedside cardiac US examinations on 115 patients.28 Overall agreement between EP categorization of LV ejection fraction and formal Cardiologist echocardiogram was 86.1%.

Complex statistical calculation packages exist in echocardiography for determining the function of the left ventricle. However, the echocardiographer's estimation of LV ejection fraction has been shown to be quite accurate.29 Rapid general assessment of LV function is suited for the EP. LV function can be categorized as hyperdynamic, normal, moderately impaired, and severely impaired for practical purposes in the ED. The more cardiac US's one performs, the more comfortable one becomes categorizing a patient's LV function. A hyperdynamic heart is seen in the setting of hypovolemia or distributive shock. The tachycardic contractions cause the ventricular walls to nearly approximate or “kiss” each other. Hypokinetic contractions appear stiff. Patients with impaired LV function generally have dilated cardiac chambers, limited contractility, and limited inward movement of the ventricular walls during systole (Figure 29-5).

US for Pulmonary Embolism

Patients with a large PE and hemodynamic compromise are often too unstable for conventional diagnostic imaging such as computed tomography and ventilation–perfusion scans. US can provide clues at the bedside for the diagnosis of a PE. The deep veins of the extremities can be assessed for clot.30 A large obstructive PE will produce signs of right heart strain on cardiac US.31,32 Dilation of the right ventricle should raise concern for a PE (Figure 29-6). Paradoxical bulging of the septum toward the left ventricle during diastolic filling is a sign of right heart strain (Figure 29-7).32 Numerous other conditions such as emphysema, pulmonary hypertension, and right ventricular infarction cause right heart strain.25,26 Konstantinides et al. showed that in hemodynamically stable patients with a PE and cardiac US findings of right heart dysfunction, administration of thrombolytic therapy reduced the need for escalation of treatment but did not affect mortality.33

US to Assess Shock States

Bedside US is a valuable tool in the management of patients with undifferentiated shock. US provides a direct view into the cardiovascular system and allows the EP to make determinations about the hemodynamic status of a patient. Shock due to heart failure, cardiac tamponade, and PE was described previously. Hypovolemic and distributive shock generally presents with a tachycardic hyperdynamic heart. Rose et al. presented a protocol for the sonographic evaluation of the heart, peritoneal space, and aorta for undifferentiated hypotension.5 Jones et al. concluded that implementing a similar protocol resulted in a more focused differential diagnosis and a more accurate ultimate diagnosis for patients in shock.6

Central venous pressures (CVP) and right atrial pressures can be estimated by US evaluation of the inferior vena cava (IVC) and the internal jugular veins, respectively.16,34 An IVC diameter of 1.5 to 2 cm is considered normal (Figure 29-8).16 A larger diameter indicates elevated CVP while a smaller diameter is indicative of depressed CVP. The diameter of the IVC varies with respiration. Negative intrathoracic pressure produced by inspiration causes the IVC to collapse (Figure 29-9). A collapse of 50% is considered normal, with greater collapse indicative of low CVP and negligible collapse indicative of high CVP.14–16 Simply stated, “fat” great veins are consistent with an elevated CVP and “flat” great veins are consistent with a low CVP.

The list of indications for cardiac US in the ED is continually expanding (Table 29-1). The two indications first described for ED US were for the identification of pericardial fluid (traumatic and nontraumatic) and the evaluation of cardiac activity.17 These are still the primary examinations the EP must gain comfort in performing. Additional echocardiographic studies can be undertaken once these two have been mastered. This includes, but is not limited to, evaluation for left ventricular failure, chamber dilatation, myocardial wall motion defects, PE, evaluation of shock states, cardiac valve thrombus or vegetations, valvular dysfunction, procedural guidance (i.e., pericardiocentesis and transvenous pacer placement), and estimation of CVP by great vein measurements.

Numerous other indications exist for emergency US. EPs have begun to use cardiac US to evaluate wall motion defects in the setting of myocardial infarction.22 Valvular abnormalities such as stenosis, regurgitation, thrombus, and vegetations (Figure 29-10) can also be assessed by emergency cardiac US.35 The evaluation for cardiac myxomas, cardiac tumors, septal defects, dynamic function, and pediatric echocardiography are other cardiac US considerations in the future for the EP.

US is a noninvasive diagnostic modality. It is contraindicated only if it would delay and negatively impact a clinically obvious need for emergent operative intervention. The cardiac US exam should not be performed unsupervised by providers who have not been adequately trained.

• US machine
• US gel
• Phased array low frequency US probe
• US probe cover or glove

A complete discussion of US equipment is beyond the scope of this chapter. Decisions regarding machines and probes depend on the user, cost, and intended applications. The cardiac US exam can be performed with a good quality low frequency probe. Probes with smaller footprints allow for easier viewing between the ribs.

The vast majority of cardiac US examinations performed by EPs are performed via the transthoracic approach. The preferred probe for transthoracic imaging is a small footprint, low frequency, phased array, or microconvex probe (Table 3-2). Curved sequential probes can be used and may produce superior images. The large footprint of these probes can be cumbersome when trying to image between ribs or in a small subxiphoid space.

The US probe is generally used directly against the patient's skin, with gel between them. Place the probe in a probe cover or glove to prevent contamination of the probe if the patient's skin is covered with blood, urine, feces, or other substances. Place US gel in the probe cover or glove before inserting the probe. Squeeze out any air in the space between the tip of the probe and the probe cover or glove.

Little to no preparation is required to perform the cardiac US exam. Wipe any debris and liquids from the patient's skin in the areas to be scanned. Place the US probe in a probe cover or glove, as described above, if the patient's skin is contaminated with blood, vomit, other body fluids, or other substances that may contaminate or damage the probe.

Echocardiography is a complex field. US is a dynamic tool that is well suited to imaging an organ in motion such as the heart. Much information about cardiac function and flow can be gained from complicated statistical calculation packages, advanced Doppler, and M-Mode measurements. This section focuses on the primary views most relevant to the EP with the hope of providing a foundation for more in-depth study of advanced cardiac US techniques in the future.

Orientation Indicator

The probe orientation indicator in echocardiography is conventionally set to the right side of the screen. In Radiology, the probe indicator is set to the left side of the screen. Some controversy exists in EM as to which side of the screen to have the probe indicator for cardiac US. The approach preferred by the present authors is to set the orientation indicator on the left side of the screen, consistent with its location for other emergency US indications. It is impractical to switch the location of the indicator in the middle of a FAST exam or when performing multiple studies in a hypotensive patient. To obtain the conventional echocardiographic views, the probe must be rotated 180° from the conventional emergency US position. The left–right reversal of the indicator and the rotation of the probe result in the same image displayed on the screen. Most modern machines have a cardiac preset that automatically adjusts a number of factors to maximize cardiac imaging. It is important for the sonographer to be aware that this preset places the orientation indicator on the right side of the image. Left–right inversion is easily achieved on most machines.

Subxiphoid View

The subxiphoid view is probably the most commonly used view by EPs. It provides visualization of the four heart chambers and allows for a superior evaluation for pericardial fluid. It can be performed without interruption of cardiopulmonary resuscitation or the insertion of chest tubes and subclavian central venous lines. The subxiphoid view is often the easiest view to incorporate into the FAST exam. This view can be limited in patients with a protuberant abdomen, abdominal pain, abdominal injuries, free air below the diaphragm, and/or nausea.

Place the probe in the subxiphoid space. Angle the probe cephalad into the patient's chest with the marker aimed to the patient's right (Figure 29-11A). Hold the probe with your fingers out from the underside or topside to allow for a shallow angle (approximately 20°) between the probe and the patient. The shallow angling of the transducer risks breaking contact between the footprint and skin. Apply an adequate amount of gel and firm pressure into the subxiphoid space to maintain contact.

To obtain a complete view of the heart, the US beam depth must be increased beyond that typically used for most other cardiac and abdominal imaging. To grasp the spatial orientation of this view, bear in mind that the probe is aimed from the inferior aspect of the heart. The US beam first traverses the left lobe of the liver, and hence, liver tissue is seen at the top of the image (Figures 29-11B & C). The plane of the beam then slices through the right-sided chambers, the septum, and then the left-sided chambers (Figures 29-11B & C). The echogenic pericardium is seen surrounding the myocardium.

Adjustments in a number of planes may improve the quality of the image. First, try to increase or decrease the steepness of the angle of the probe. While the heart lies more to the patient's left, so does the stomach, which contains air that scatters the US beam. The liver, on the other hand, serves as a good “acoustic window” or a transmitter of the beam allowing for better image acquisition. Taking advantage of imaging through the liver often involves veering from just right of midline, a slight counter clockwise rotation of the probe, and angling toward the patient's left shoulder. Ask the patient to take a deep breath to bring their heart inferiorly and into the scanning plane to improve the image.

Parasternal Long Axis View

The parasternal long axis view may not be familiar to most EPs. It often is easier to obtain, provides clearer images, and is better tolerated by the patient. Place the probe to the left of the sternum, along the long axis of the heart (Figure 29-12A). Hold the probe perpendicular to the chest wall with the marker aimed toward the apex of the heart or the PMI. This is roughly toward the patient's left hip. Unfortunately, shadowing from bone and scattering from air in the lung surrounds the heart. Place the probe between two ribs and just lateral to the sternum, but not over lung tissue. The third or fourth intercostal space affords the best view.

The right ventricle sits underneath the probe and is visualized in the near field of the screen (Figures 29-12B & C). This view also provides an excellent glimpse into the left side of the heart. The left ventricle lies beneath the right ventricle. The interventricular septum is well visualized and extends to the apex of the heart on the left side of the screen. The base of the heart can be visualized on the right side of the screen (Figure 29-12C). The left ventricle empties into the aortic outflow tract, with the aortic valve and root usually visible. The left atrium lies deep, and the mitral valve can be seen opening into the left ventricle (Figures 29-12B & C). To visualize the apex of the heart in the center of the screen, slide the probe in the direction of the marker (toward the PMI) and in the opposite direction to the center of the base of the heart. The descending aorta may be visualized in a transverse slice along the underside of the heart and is an important landmark in distinguishing pericardial from pleural fluid. Pericardial fluid collects posteriorly and will appear as a black stripe separating the myocardium from the pericardium and descending aorta (Figure 29-13). Pleural fluid, on the other hand, will reside outside of the bright pericardium and tapers to a stop at the descending aorta.

Adjustments on the tilt of the probe may optimize the view. Place the patient in the left lateral decubitus position to bring the heart closer to the chest wall and improve the image. Slide the probe laterally, to a more cephalad intercostal space, or open its rotation with a counter-clockwise turn to better optimize the view for patients with CHF. Move the probe to a more caudal intercostal space, close the angle of the probe with a clockwise rotation, or use the subxiphoid view to better optimize the view for patients with emphysema and an inferiorly displaced heart.

Parasternal Short Axis View

The parasternal short axis view slices through the heart transversely. Place the probe similar to the parasternal long axis view, but with the probe rotated 90° to rest along the heart's short axis (Figure 29-14). Aim the marker toward the patient's right hip. The left ventricle appears as a prominent circle in the center of the screen, with the right ventricle resting atop it as a flatter or a crescent-shaped chamber (Figures 29-14B & 29-15). Tilting or sliding the probe along the heart's long axis toward the patient's left hip allows visualization of the apex of the heart. Tilting or sliding the probe toward the patient's right shoulder allows visualization of the base of the heart. The ventricles should cone down to a tip at the apex. When tilting back up from the apex through the heart, the papillary muscles (Figure 29-15) and mitral valve with its “fish-mouth” appearance (Figure 29-16) will come into view. Continue tilting the probe upward toward the base of the heart. The three leaflets of the aortic valve will be seen centrally (Figure 29-17). At this point, the scan is beyond the left ventricle, allowing the atria to be visualized as well as the right ventricle emptying into the pulmonary artery.

Apical Four-Chamber View

The apical four-chamber view is obtained by placing the probe at the PMI, just inferior to the left nipple and angling up through the heart (Figure 29-18). Aim the marker toward the patient's right. This study is relatively simple to perform by transitioning from the parasternal short axis view. Slide the probe down to the apex of the heart and then tilt it upward toward the base of the heart (Figure 29-18A). The image reveals a side-by-side view of the ventricles in the near field and the atria in the far field (Figures 29-18B & C). The lung adjacent to the heart impedes imaging. Place the patient in the left lateral decubitus position to alleviate scattering. The left ventricle appears larger and has thicker walls than the right ventricle. The mitral valve sits slightly lower than the tricuspid valve. Ventricular function, flow across the valves, and septal defects can be assessed with this view. This view allows for comparing chamber size and evaluating for right ventricular dilatation if there is concern for an obstructive PE.

Subcostal Inferior Vena Cava View

Sonographic evaluation of the IVC can provide valuable hemodynamic information to the EP.14,15 This view is also referred to as the subxiphoid long axis view. Place the probe in the subxiphoid space, perpendicular to the patient's abdominal wall and with the marker aimed toward the patient's head (Figure 29-19A). The longitudinal IVC will appear posteriorly, beneath the liver and the bowel, as a long black cylinder. It is important to distinguish the IVC from the aorta. The aorta lies on the patient's left side, is more “pipe-like” in appearance, is noncompressible when pressure is applied by the US probe, and has a recognizable pulsatility. The IVC is compressible when pressure is applied by the US probe and varies in diameter with respiration (Figures 29-19C & D). It may be beneficial to start in the transverse plane in which both the IVC and the aorta are visualized (Figure 29-20). Starting with the transverse view, rotate the US probe 90°, maintaining the IVC in the center of the screen to obtain the longitudinal view (Figure 29-19). Tilt the probe cephalad to visualize the IVC entering the right atrium (Figures 29-19C & D).

Measurements of the IVC proximal to its entrance into the right atrium allows for a noninvasive estimate of CVP. The negative pressure generated in the chest by inspiration draws blood cephalad and decreases the diameter of the IVC (Figures 29-19C & D). Normal dimensions for the IVC include a diameter of 1.5 to 2.0 cm and an inspiratory collapse of 50%.14,15 A smaller diameter and greater inspiratory collapse are indicative of a low CVP.14–16 A larger diameter and lesser inspiratory collapse reflect a high CVP.14–16 Obtain estimates by having the patient sniff deeply and freeze the image postinspiration. Use the cine-rewind feature on the US machine to identify images or frames that allow for the measurement of the maximal and minimal IVC diameters through the respiratory cycle (Figure 29-19). M-Mode tracing of the respiratory cycle allows for precise measures of the inspiratory and expiratory IVC diameters (Figure 29-21).

US Guidance for Pericardiocentesis

US-guided pericardiocentesis has proven to be safe and is the method of choice for most institutions.36 A brief description of the procedure is provided in this section. Please refer to Chapter 36 for the complete details regarding pericardiocentesis.

Emergent pericardiocentesis can be guided by US using either a static or a dynamic approach. For the static approach, visualize the effusion by US and determine the best approach for needle placement. Remove the probe from the patient and proceed with the pericardiocentesis procedure. For the dynamic approach, the heart is visualized throughout the procedure to guide needle placement. Sterile technique is required for the US probe and cord. The availability of a second ultrasonographer or an assistant for dynamic guidance is helpful, particularly if an agitated-saline injection is attempted.

The pericardiocentesis site depends on the patient's body habitus, the location of the maximal visualized effusion, and the US views obtainable. The two most common sites for needle insertion are the subxiphoid space and left anterior parasternal chest wall.

For the static approach, visualize the path of needle penetration with the corresponding US image. Measure the distance from the top of the image to the pericardial space to determine the depth of needle insertion. It is important to note that the liver is often visualized in the anticipated needle trajectory with the subxiphoid US view. Use the parasternal long axis view because the pericardium is more superficial in this view. This author prefers the parasternal long axis approach for these reasons. Proceed with the pericardiocentesis procedure.

For the dynamic approach, insert the needle directly adjacent to the transducer. Angle the probe to interface with the plane of needle insertion (Figure 29-22). Aim the US probe marker cephalad and between the ribs to provide good visualization of the intercostal space. Insert the needle over the superior edge of the rib and along the plane of the US beam. It is optional to use color Doppler in the near field to ensure the intercostal and internal mammary arteries are not punctured. Advance the needle while aspirating with the syringe as the needle is advanced. The pericardium may “tent” as the echogenic needle presses upon it (Figure 29-23A) and then enters the pericardial space (Figure 29-23B).

Injection of agitated saline may be attempted to confirm needle placement in the pericardial space. Agitate the saline by rapidly injecting saline back and forth from one syringe into another through two ports of a three-way stopcock: with the third port connected by sterile tubing to the pericardiocentesis needle. Once microbubbles have formed, inject the agitated saline into the pericardial space. The fluid will appear on US as a bright white scattering within the pericardial sac.

US Guidance for Cardiac Pacing

US can be used to confirm capture of transcutaneous (Chapter 31) or transvenous (Chapter 33) cardiac pacing.37,38 It is difficult to appreciate mechanical capture by simply looking for electrical changes on the ECG monitor. Transcutaneous cardiac pacing discharges often cause simultaneous jerking of the patient that masks a palpable pulse. Cardiac US evaluation during cardiac pacing allows visualization of mechanical contractions of the heart. During placement of the transvenous cardiac pacing wire, it can be visualized passing through the right atrium and tricuspid valve into the right ventricle. A subcostal view of the IVC can confirm errant passage of the wire down the IVC.

Limited ED cardiac ultrasonography provides real-time information to answer specific questions. It is not intended to replace formal cardiac echocardiography. There is a body of evidence that shows non-Cardiologists can accurately and safely perform limited cardiac US exams. The use of cardiac US in the ED has risen from a few basic examinations into a sophisticated series of exams in a very short time. This chapter provides an introduction to ED cardiac ultrasonography. The EP can become very comfortable with cardiac US as a supplement to the evaluation and management of patients. ED cardiac ultrasonography is a very valuable tool that can easily be incorporated into the daily clinical practice of Emergency Medicine.