Estimation of Global Cardiac Function and Ejection Fraction

Multiple studies have shown the ability of emergency phy-sicians to accurately evaluate cardiac function and ejection fraction.^3,4 When compared with cardiologists, emergency physicians were found to have a correlation coefficient of 0.86 with cardiologists when assessing ejection fraction. Cardiologists had a similar coefficient of 0.84 among themselves.

Diagnosis of Pericardial Effusion

Emergency physicians have proved to be accurate in the diagnosis of pericardial effusion. Previous research has shown that emergency physicians have a sensitivity of 96%⁵ to 100%⁶ as compared with formal overreading by trained echocardiographers.

Probe Selection

Classic echocardiography requires the use of a phased-array probe, sometimes referred to as the thoracic probe. These probes have a small footprint and are ideal for achieving visualization with a small acoustic window between ribs.

Acoustic Windows

Bedside cardiac ultrasound is typically taught with the use of three separate acoustic windows and multiple orthogonal views within the windows. These acoustic windows include the parasternal, apical, and subcostal. Each window is then broken down into orthogonal views, including the parasternal long-axis, parasternal short-axis, apical four-chamber, apical two-chamber, apical long-axis, subcostal four-chamber, and subcostal long-axis views.

Probe Orientation

Echocardiography places the probe marker on the right side of the ultrasound screen so that when the ultrasound machine is in the cardiac mode, the right-hand side of the screen indicates the side of the probe with the marker on it (this is opposite any other scanning mode).

Specific Views

Parasternal Long Axis

The parasternal long-axis view seen in Figure 5.1 is obtained by placing the probe in the third to fourth intercostal space with the probe marker pointed toward the patient’s right shoulder (Figs. 5.2 and 5.3). The long axis of the heart should be horizontal on the screen with the apex pointed to the left. If the apex is pointed up, the probe is too low and should be moved up an interspace. This view allows visualization of the left ventricle, mitral valve, left atrium, right ventricular outflow tract, aortic valve, and aorta. The descending thoracic aorta is often visualized posterior to the left ventricle in transection.

Fig. 5.1 Parasternal long-axis view of a normal-appearing heart.

Fig. 5.2 Parasternal long-axis diagram.

Ao, Aorta; LA, left atrium; LV, left ventricle; RVOT, right ventricular outflow tract.

Fig. 5.3 Probe orientation for the parasternal long-axis view.

Parasternal Short Axis

The parasternal short-axis view is obtained by rotating the probe 90 degrees from the parasternal long-axis position so that the probe marker is pointed to the patient’s left shoulder (Figs. 5.4 and 5.5). The ultrasound beam is now transecting the heart in its short axis. If the physician tilts the probe so that it is pointing to the base of the heart, the aortic valve is visualized along with the “inflow and outflow” of the right heart. This view includes the right atrium, right ventricular outflow tract, and pulmonic valve. As the probe is tilted more apically, the aortic valve is lost and a cross-sectional view of the mitral valve is obtained (Fig. 5.6). At this point the right ventricle becomes more apparent and takes a position as a crescentic ventricle to the left and superficial to the mitral valve and left ventricle. Finally, as the probe is tilted more toward the apex, the mitral valve is lost and the muscular portion of the left ventricle is visualized. The posterior medial and anterior papillary muscles are visualized at this point, and the circular nature of the left ventricle can be appreciated (Fig. 5.7).

Fig. 5.4 Parasternal short-axis diagram.

LV, Left ventricle; RV, right ventricle.

Fig. 5.5 Probe orientation for the parasternal short-axis view.

Fig. 5.6 Parasternal short-axis view at the level of the mitral valve: the “fish mouth” view.

Fig. 5.7 Parasternal short-axis view at the level of the papillary muscles.

This is an athletic heart with an enlarged right ventricle.

Apical Four- and Two-Chamber Views

The apical window allows visualization of either all four chambers (Figs. 5.8 and 5.9) or just two chambers (the left atrium and ventricle) (Fig. 5.10). The apical windows are difficult to obtain in the emergency setting and often require the patient to be in the left lateral decubitus position, which is often impossible. The window is obtained by placing the probe at the location of maximal impulse with the probe marker pointed to the left axilla. The probe must be tilted so that the probe is pointed to the patient’s right shoulder (Fig. 5.11).

Fig. 5.8 Diagram of the apical four-chamber view.

LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Fig. 5.9 Probe orientation for the apical four-chamber view.

Fig. 5.10 Diagram of the apical two-chamber view.

LA, Left atrium; LV, left ventricle.

Fig. 5.11 Apical four-chamber view.

Notice the size of the left ventricle in comparison with the right ventricle in this normal heart.

The apical two-chamber view allows further evaluation of the left ventricle and mitral valve. The left atrial appendage can sometimes be see on the right side of the screen on the anterior side of the basal left ventricle.

Subcostal Four-Chamber View

The subcostal four-chamber view (Figs. 5.12 to 5.14) is obtained by placing the probe just inferior to the xiphoid and applying pressure downward on the abdomen with the probe horizontal. This view can be performed with either the curvilinear abdominal probe or the phased-array thoracic probe. The probe marker should be toward the patient’s left in cardiac mode and toward the patient’s right when using focused abdominal sonography for trauma (FAST) or abdominal protocols.

Fig. 5.12 Subcostal four-chamber window.

Note the liver at the top of the ultrasound imaging window. LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Fig. 5.13 Probe orientation for the subcostal four-chamber window.

The probe is placed in the subxiphoid space with the probe marker oriented to the patient’s left (cardiac mode) or to the patient’s right (abdomen/focused abdominal sonography for trauma mode). The apex of the heart should be pointing to the right of the screen as seen in Figures 5.8 and 5.7.

Fig. 5.14 Subcostal four-chamber window.

Pericardial Effusion

Evaluation of pericardial effusion is one of the first indications for cardiac ultrasound.⁶ Identification of pericardial effusion (Fig. 5.15) is achieved by visualization of the heart in multiple views. The subcostal window is the most commonly taught site because of the FAST examination. An effusion will appear as an anechoic stripe of fluid surrounding the heart. This stripe is most commonly located between the right ventricle and the liver. Ideally, all three acoustic windows should be used when attempting to rule out pericardial effusion.

Fig. 5.15 Pericardial effusion noted in the parasternal long-axis view.

Notice the location in reference to the descending thoracic aorta. Pericardial effusions track between the heart and the descending aorta, whereas pleural effusions can be seen posterior to the descending aorta.

The critical complication of pericardial effusion is cardiac tamponade (Fig. 5.16). Physiologically, cardiac tamponade occurs when the pressure inside the pericardial sac becomes elevated above right ventricular diastolic filling pressure. This leads to decreased filling of the right ventricle in diastole and reduced preload and cardiac output. Echocardiographic signs of cardiac tamponade are the presence of right ventricular free wall collapse as seen in Figure 5.16. Alternatively, a more sensitive, but less specific finding is the presence of right atrial collapse during ventricular systole (atrial diastole).

Fig. 5.16 Pericardial effusion with tamponade.

Note the right ventricular free wall collapse in diastole (arrow).

Cardiac Arrest

POC cardiac echocardiography can be invaluable during cardiac arrest. Typical uses include evaluation for tamponade, hypovolemia, and suggestions of PE (clot, right ventricular dilation); detection of aortic dissection; monitoring for pacer capture and the adequacy of compressions; and most important, evaluation for cardiac activity in patients with pulseless electrical activity (PEA) and asystole. Studies have shown cardiac standstill during arrest to be 100% predictive of mortality.⁷ Furthermore, cardiac ultrasound has been used in place of a pulse check in pediatric populations because of the inherent difficulty of finding a pulse.⁸ Typical algorithms use cardiac ultrasound to evaluate PEA and asystolic rhythms.⁹ If cardiac standstill is present, further resuscitation is futile.⁷

Acute Heart Failure

Emergency physicians have been shown to be accurate in estimating left ventricular ejection fraction (LVEF).³ LVEF is most easily separated into three categories: reduced, normal, and hyperdynamic. Although echocardiographers often report actual percentages, we can think of normal LVEF as 55% to 75%, reduced as less than 55%, and hyperdynamic as greater than 75%. Some authors add a fourth category in which severely reduced LVEF is less than 30%. This distinction can be useful when discussing cardiac function with consultants.

The ejection fraction is typically estimated by visual inspection of the “squeeze” of the left ventricle, although it can also be measured with algorithms in the cardiac package of many emergency ultrasound machines.

Pulmonary Embolism

Although cardiac ultrasound cannot identify a pulmonary embolus,¹⁰ several findings are suggestive of this diagnosis. Right ventricular dysfunction and dilation are typically visualized in the apical four-chamber window. Right ventricular dilation has been described in reference to the relative areas of the right and left ventricles at end-diastole. A right-to-left ventricular area ratio of greater than 0.66 has been shown to be 85% specific for PE.¹¹ Another finding is described as retained apical function in the setting of right ventricular free wall hypokinesis. This is called the McConnell sign and can be fairly specific for PE. McConnell et al. described this particular finding as being 94% specific for PE¹¹ (Fig. 5.17). An additional finding in acute PE is flattening of the interventricular septum. This is seen in the parasternal short-axis view and is due to either volume or pressure overload of the right heart (Fig. 5.18).¹²

Fig. 5.17 McConnell sign.

The apical contraction is denoted by the arrow.

Fig. 5.18 Parasternal short-axis view showing septal flattening associated with right-sided pressure or volume overload.

Volume Status

Assessment of the patient’s condition and the presence of hypervolemia or hypovolemia can be complicated. Through direct visualization of chamber size and evaluation of the great vessels, this clinical conundrum can often be overcome.

Echocardiographic evaluation of volume status starts with global assessment of the ejection fraction and filling of the right and left sides of the heart. Reduced filling of both the right and left heart chambers implies reduced preload and hypovolemia. Conversely, the presence of dilated right and left heart chambers with a poor ejection fraction suggests hypervolemia. Finally, a dilated right ventricle with a contracted left ventricle and an elevated LVEF suggests a forward flow problem of the right heart, such as PE, right-sided myocardial infarction, or cor pulmonale.

Additionally, a body of research has led to evaluation of the inferior vena cava as a surrogate marker for central venous pressure and thus volume status.¹³ The current recommendations are summarized in Table 5.1. The inferior vena cava should measured during both inspiration and expiration from the subcostal long-axis view as seen in Figure 5.19.

Fig. 5.19 Subcostal long axis of the inferior vena cava used to estimate central venous pressure.