Subxiphoid Four-Chamber View
The subxiphoid view is the most useful view for emergency ultrasound. It usually does not interfere in resuscitative measures such as thoracostomy, CPR, subclavian line insertion, or intubation. It is easily learned, repeated, and performed as part of both the cardiac and trauma ultrasound evaluations.
The subxiphoid view should be performed at the subxiphoid position of the abdomen (Figure 6-6A). The probe should be held at a 15° angle to the chest wall and aimed toward the left shoulder. The probe marker should be aimed toward the patient's left flank (using a cardiac preset). The transducer should be angled up or down depending on the depth of the chest cavity to obtain images of the beating heart. The depth should then be adjusted to visualize the atria at the bottom of the monitor screen. Poor quality initial images may be improved upon by using an appropriate amount of ultrasound gel, using a shallow angle to the chest wall, moving the transducer to the right to use the left lobe of the liver as a window, and moving off the xiphoid and over to the lower intercostal spaces to image the barrel-chested patient with a larger anterior–posterior diameter.
Probe position for subcostal 4 chamber view (A). Subcostal four-chamber diagram (B). Subcostal four-chamber normal ultrasound (C). RA = right atrium, RV = right ventricle, LA = left atrium, LV = left ventricle. (Courtesy of Hennepin County Medical Center for (C))
The subxiphoid four-chamber view should be seen as primarily a diagonal view for the ventricles, atria, pericardium, and the left lobe of the liver (Figure 6-6B and 6-6C). If the transducer is angled at a more acute angle toward the abdomen, the left lobe of the liver, inferior vena cava, and the hepatic veins should be visualized.
Subxiphoid Short-Axis View
The subxiphoid short axis view can be achieved by rotating the ultrasound probe 90° counterclockwise from the four-chamber view (using a cardiac preset) and aiming the probe toward the patient's left arm (Figure 6-7A). This orientation will resemble the parasternal short axis (“doughnut”) view of the left ventricle and may provide virtually all of the same information (Figure 6-7B and 6-7C).
Probe position for subcostal short axis view (A). Subcostal short axis diagram (B). Subcostal short axis normal ultrasound (C). L = liver, RV = right ventricle, LV = left ventricle. (Courtesy of James Mateer, MD, for (C))
Subxiphoid Long-Axis View
The subxiphoid long axis view uses a sagittal body axis and the probe marker can be aimed toward the patient's feet (using a cardiac preset) (Figure 6-8A). This will place the atrium/diaphragm on the left side of the screen as is the standard for abdominal longitudinal imaging. Echocardiographers (who are envisioning the longitudinal view from the patient's left side) often orient this image with the probe marker pointing cephalad and the atrium/diaphragm on the right side of the screen. A sagittal section of the body views the heart, the left lobe of the liver, the IVC, and hepatic veins (Figure 6-8B). This view allows evaluation of the proximal IVC during expiration and inspiration (Figure 6-8C and 6-8D). The anterior–posterior diameter of the proximal IVC usually measures about 1.5–2.0 cm during expiration and collapses with inspiration. Collapse of less than 50% during inspiration indicates elevated right-sided heart pressures.
Probe position for subcostal long axis view (A). Subcostal long axis diagram (B). Proximal IVC during expiration (C) and inspiration (D). IVC = inferior vena cava, RA = right atrium. (Courtesy of Hennepin County Medical Center for (C,D))
Parasternal Long-Axis View
The parasternal long axis view can be best obtained by accepting the long axis of the heart to be roughly from the right shoulder to the left hip (Figure 6-5). The transducer should be placed perpendicular to the chest wall at the 3rd or 4th intercostal space immediately to the left of the sternum with the probe indicator directed toward the right shoulder (using a cardiac preset) (Figure 6-9A). The following structures can be visualized from anterior to posterior on the monitor: right ventricular free wall, right ventricular cavity, interventricular septum, left ventricular cavity, and the posterior left ventricle (Figure 6-9B). On the basal side of the image, the aortic valve with its inflow and outflow tracts, the mitral valve with its inflow and outflow tracts, the left atrium, the posterior pericardium, and possibly the descending aorta should be seen (Figure 6-9C). The probe should be rotated to obtain the best axis to view these structures. Angling and tilting may be needed, but less so than for the short axis view. A reduction in size of the image may be needed to focus on certain structures or enlargement of the field of view to see the entire left ventricle and left atrium.
Probe position for parasternal long-axis view (A). Note: May require left lateral decubitus position. Parasternal long-axis diagram (B). Parasternal long-axis normal ultrasound (C). RV = right ventricle, Ao - aorta, LV = left ventricle, LA = left atrium.
Parasternal Short-Axis View
The imaging plane for the parasternal short axis view of the heart stretches from the left shoulder to the right hip (Figure 6-5), and should be obtained in the left 3rd or 4th intercostal space next to the sternum (Figure 6-10A). If the parasternal long axis view has already been obtained, the parasternal short axis views should be obtained by rotating the probe marker 90° clockwise toward the left shoulder (using a cardiac preset). With the probe in this position, several different short axis views can be obtained by sweeping the image from base to apex (Figure 6-10B). Parasternal short axis views can be obtained at the base of the heart, the level of the mitral valve (Figure 6-11A and 6-11B) the level of the papillary muscles, and at the apex. The short axis view at the level of the papillary muscles is an important view because it allows identification of the different walls of the left ventricle (Figure 6-12A and 6-12B). An ideal short axis view at the base of the heart (Figure 6-13A and 6-13B) visualizes the left atrium, right atrium, tricuspid valve, right ventricle, and pulmonary valve encircling the aortic valve (“Mercedes Benz sign”) in cross section in the middle of the view (Figure 6-14).
Probe position for parasternal short-axis view (A). Note: May require left lateral decubitus position. Diagram of short axis views from apex to base (B).
Parasternal short-axis diagram at mitral valve (A). Parasternal short-axis normal ultrasound at mitral valve (B).
Parasternal short axis diagram at papillary muscles (A). Parasternal short axis normal ultrasound at papillary muscles (B). RV = right ventricle, LV = left ventricle. (B: Courtesy of Hennepin County Medical Center)
Parasternal short axis diagram at aortic valve (A). Parasternal short axis normal ultrasound at aortic valve (B). RV = right ventricular outflow tract, RA = right atrium, LA = left atrium, PA = pulmonary artery, Ao V = aortic valve.
Mercedes Benz sign. Parasternal short axis at aortic valve demonstrates closure of all 3 cusps. (Courtesy of Lori Sens and Lori Green, Gulfcoast Ultrasound)
The apical 4-chamber view is a coronal view of the heart that images all four chambers in one plane. Alterations of this view include the apical two-chamber view, the apical three-chamber view, and the apical five-chamber view. Regardless of the number of chambers, the view is best observed by obtaining the window at the apex of the heart, usually where the point of maximal impulse (PMI) for the heart is located (Figure 6-15A). Alteration of this position may be required to adjust for breast tissue, emphysema, chest deformities, and other anatomic changes. Whenever possible, the patient should be rotated toward their left side to reduce lung artifact and bring the heart closer to the chest wall. The transducer should be placed at this position, generally in the 5th intercostal space or lower, and aimed toward the right shoulder with the marker directed toward the left lateral chest wall (using a cardiac preset). Some rotation may be needed to allow for all four chambers to be viewed. A rounded, foreshortened heart is usually artifactual. To correct this, the transducer should be aimed in a more anterior direction and/or a lower rib interspace should be used. On this view, the right ventricle with its lateral wall, the interventricular septum (septal wall), the left ventricle with the lateral wall, the two atria, the interatrial septum, and the pulmonary veins should be visualized (Figure 6-15B and 6-15C). This view is advantageous for assessing right ventricular function and the left ventricle for function and presence of blood clots. Doppler studies are often best obtained with apical views as blood flow is parallel to the transducer with this position. Intra-atrial abnormalities, such as myxoma, may be well visualized. When the image sector is swept more anteriorly from the four-chamber view, the left ventricular outflow and aortic valve come into view (five-chamber).
Probe position for apical 4 chamber view (A). Note: May require left lateral decubitus position with left arm elevated. Apical 4 chamber diagram (B). Apical 4 chamber normal ultrasound (C). RV = right ventricle, LV = left ventricle, MV = mitral valve, LA = left atrium, RA = right atrium, TV = tricuspid valve.
For the apical two-chamber view, the ultrasound probe should be placed in the same orientation as for the apical four-chamber view but the transducer should be rotated 90° counterclockwise (using a cardiac preset) until the marker is directed toward the left mid clavicle or head of the patient (Figure 6-16A). This view evaluates anterior and inferior walls, thus complementing the apical four-chamber view of the left ventricle for wall motion and function (Figure 6-16B and 6-16C). Further counterclockwise probe rotation from the two-chamber view (additional 30°) would create the apical long axis (three-chamber) view.
Probe position for apical two-chamber view (A). Note: May require left lateral decubitus position with left arm elevated. Apical two-chamber diagram (B). Apical two-chamber normal ultrasound (C). LV = left ventricle, LA = left atrium.
The suprasternal view provides a glimpse of the aortic arch with its three main branches: the brachiocephalic artery, the left carotid artery, and the left subclavian artery. The ultrasound probe should be placed in the sternal notch with the transducer marker pointed toward the patient's left shoulder (using a cardiac preset) and probe aimed as far anteriorly as possible (Figure 6-17A). While it is difficult to obtain in many patients, this view may provide a confirmation of aortic aneurysm or dissection in the patient with an optimal window. The right pulmonary artery in cross section can be viewed below the aortic arch. If the transducer is rotated 90° to visualize the aortic arch in cross section, the left pulmonary artery may be seen. Occasionally, the superior vena cava may be viewed lateral to the ascending aorta. The left atrium lies inferior to the pulmonary arteries and, in an optimal window, all four pulmonary veins may be viewed (Figure 6-17B and 6-17C).
Probe position for suprasternal view (A). Suprasternal diagram (B). Suprasternal normal ultrasound (C). The branch arteries may be closely approximated as in the diagram or spread apart for some patients as in the ultrasound example. Asc Ao = ascending aorta, Desc Ao = descending aorta.