Video
clip 1:David P. Bahner, M.D., RDMS, FAAEM, FACEP
I. Introduction and Indications
Cardiac ultrasound is a valuable skill set for medical professionals in
multiple clinical scenarios including trauma, hypotension and cardiac arrest. The
proper techniques to image the heart can be mastered with practice and
familiarity with the ultrasound machine. Familiarity with the common
echocardiographic “windows” provides a foundation upon which
to interrogate these structures and make clinical decisions. As technology
continues to improve, the education of future clinical providers becomes
the rate-limiting step to fully implement the true potential of ultrasound. The
twenty first century emergency physician may soon utilize bedside ultrasound
to differentiate critical cardiac patient presentations by answering focused
questions such as: Is there a pericardial effusion? Is
tamponade present? What is the cardiac contractility? What
is the intravascular volume status of my patient?
This chapter will attempt to guide an emergency department medical provider in
the necessary skills to acquire and interpret sonographic images of the heart
and great vessels in the emergency medicine setting.
II. Anatomy
The appearance of cardiac anatomy on ultrasound can sometimes be confusing.
It is difficult to derive a three-dimensional mental construct utilizing
2 dimensional images. The best way to learn anatomy is by
reviewing the sonographic shapes and patterns displayed in 2 dimensions
and continuously relate that to the 3 dimensional configuration. It
is important to find sonographic landmarks to provide spatial orientation
when viewing the heart from multiple planes. Echocardiography is
a dynamic assessment and it is important to examine structures through
the entire cardiac cycle. The normal heart sits in the left chest
with its base anchored by the great vessels: the aorta, superior
vena cava, and main pulmonary artery. The cardiac apex points anterior
inferior and about 60 degrees to the left. The heart consists of
two thicker walled ventricles, two thinner walled atria and four valves
that separate flow between the chambers. The left heart is filled
by 4 pulmonary veins draining into the left atrium. Blood
flows between the anterior and posterior leaflets of the mitral valve
into the thick walled left ventricle.
The left ventricle (LV) is thicker walled and is the largest of the four chambers in the normal heart. The LV is by far the main focus in echocardiography and learning nuances of its appearance aids the experienced sonographer. The cardiac apex provides a distinctive landmark from which to orient the image. In the longitudinal (long) parasternal (LPS) view the cardiac apex is on the left side of the screen while the apex is on the right side of the screen in the subxiphoid (SUX) view.
From the LV, blood flows into the tubular ascending aorta and into the systemic circulation. The ascending aorta, otherwise known as the Left Ventricular outflow tract (LVOT), is shaped like a tube on long axis. The aortic valve can be seen in this plane as two of the three aortic leaflets (typically the non coronary cusp and right coronary cusp) mark diastole (closed) and systole (open). Occasionally the left coronary cusp is seen in this imaging plane. In the short axis parasternal view, tilting the probe cephalad can image the aortic valve in cross section. This is the so-called “Mercedes Benz” sign where all three valves are displayed at the ascending aortic root.
Superior and inferior vena cava drain into the right atrium and can help orient the sonographer. These structures lead the operator to the right side of the heart. In the subxiphoid view of the heart, the left lobe of the liver is used as an “acoustic window” to image the three hepatic veins draining into the IVC as it passes through the diaphragm and drains into the right atrium. From there, blood flows through the tricuspid valve into the triangular shaped right ventricle. The right ventricle size is determined by forces influencing preload (e.g. intravascular volume, right atrial and tricuspid function) and afterload (e.g. pulmonary artery pressure). It can assume many shapes depending on the disease state. The pulmonary arteries are difficult to see yet can be visualized in the short axis parasternal view. The right heart normally carries deoxygenated blood to the lungs and is separated from the left heart by the interatrial septum and the thick walled interventricular septum.
A variety of congenital cardiac malformations are common and should be considered when normal patterns deviate. Cardiac anomalies have varying prevalence among differing populations. The normal heart will change morphology and function with age and comorbid conditions.
III. Scanning Technique and Normal Sonographic Findings
Probe selection: Typically, cardiac
imaging requires the use of intercostal acoustic windows. This
necessitates the use of probes with small “footprints.” Phased
or microconvex arrays are utilized for this reason. Imaging in
adults requires the use of lower frequencies (typically 2-4 MHz). Curvilinear
probes can be used to image the heart, especially in the subxiphoid view. However,
rib shadows impede the use of these larger footprint probes with transthoracic
imaging.
Orientation: To image the heart utilizing ultrasound, one must approach the acquisition and interpretation of the heart from various orthogonal planes based on the heart’s position within the chest. Traditional imaging planes for anatomic structures are transverse (short axis) and sagittal (long axis) planes. The picture on the monitor is essentially a displayed version of the ultrasound “beam” that emanates from the transducer face. Structures closest to the transducer are displayed at the top of the image deemed the near field. The deeper structures are displayed at the bottom of the screen in the far field. The focal zone is that area of greatest resolution (usually marked with a carat) that indicates the transition from the near to far field. All probes have an indicator that demarcates the leading edge of the beam that corresponds to a mark on the monitor. This orientation in cardiac imaging has created much controversy on how to position the probe on the chest wall to obtain the necessary standard images of the heart. Standard cardiology teaching positions the probe “pointing” to the right shoulder in the long parasternal view or to the left shoulder in the short parasternal view with the indicator on the right side of the monitor. Other methods have been described such as rotating the probe 180 degrees and reversing the image on the monitor so the indicator is on the left side of the image (standard for abdominal presets). The confusion in the cardiac display is best explained and clarified at the bedside by touching one side of the probe and watching the resultant image on the display. Standard display of cardiac anatomy in the long and short axis, subxiphoid and apical views are the goal for cardiac imaging.
Scanning Methods: Scanning the patient incorporates the 3 P’s, Patient, Probe and Picture. The anatomy of the patient is interrogated with an ultrasound probe that then displays the returning echoes (ultrasound beam) on a picture display according to the probe’s orientation. The chest can be imaged from a series of acoustic windows and tissue planes. First of all, make sure to document the right patient and medical record number. Ensure that there is a recording device (analog-thermal paper, Super VHS, or digital- Picture Archiving Communication System-PACS) and set the correct cardiac preset application. Cardiac settings enhance the image for optimal motion detection. Scan the patient from the patient’s right and hold the probe comfortably as a pen or gently in a cupped hand. Apply generous amount of warm gel and position the patient in left lateral decubitus if tolerated. The heart sits in the chest at an angle and can be approached through the intercostal muscles. These intercostals and structures such as the liver (gray or black structures in the near field) act as acoustic windows to allow sound waves to penetrate to the underlying heart and chest cavity. Comparatively, strong reflectors such as ribs or gas in the stomach obscure visualization into the far field. The ribs obscure the beam from penetrating, therefore it is important to rotate the cardiac probe to align the beam parallel to the ribs in the space and eliminate rib shadows.
Common Cardiac Ultrasound Windows
Illustration 1: Probe direction for subxiphoid and parasternal views.
Long Axis Parasternal: The
heart sits obliquely in the left chest with the apex pointing toward the
left hip. To obtain
the long parasternal view, begin to sweep the probe across the parasternal
area in the third or fourth intercostal space. If the mark on the monitor
is on the left, than point the probe to the left hip, if the mark on the
monitor is on the right, point the probe to the right shoulder. Either
way the image is displayed in the same manner for convenience with the
curved apex on the left side of the monitor (See
Illustration 1,2, and 3 and Figures 1 and 2). Look for the landmark
mitral valve and rotate the probe to image the aortic and mitral valve
in the same long axis plane.
Illustration 2: Drawing illustrating sonographic capture of a long axis parasternal view.
Figure 1: Long axis parasternal view of the left ventricle (LV), aorta (Ao), mitral valve (MV, closed) and interventricular septum (S).
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Figure 2 |
Illustration 3 |
Figure 2 and Illustration 3: This split screen shows a long axis parasternal view of the heart. It displays the change in left ventricular (LV) size during systole and diastole. Sonographically watching the beating heart can demonstrate systolic and diastolic function marked by the opening and closing of the mitral and aortic valves.
Video clip 1: Heart in long axis parasternal view.
Short Axis Parasternal: The short axis is in plane ninety degrees from the long axis and points the probe toward 8 o’clock (mark on left) or the left shoulder (mark on right). After adjusting the probe to obtain a circular short axis view of the left ventricle, the structures along the endocardial border help to determine the segmental position of the heart (Mitral Valve = base, Papillary Muscle = mid section, small diameter = apex).
The short axis focuses on obtaining an image of the LV in a circular pattern and then angling through the various positions to interrogate the respective wall segments. (See Figure 3-5, Illustration 3). Angling through the short axis views allows the operator to visualize the LV from the smaller caliber apex past the base to the aortic valve in the superior mediastinum. The short axis beam can be aimed cephalad to image the aortic valve in cross section. This image can provide insight into the right ventricular outflow tract, as it is oriented anterior to the aorta (Figure 7).
Figure 3: Short Axis view of left ventricle (LV) at the mitral valve (base). The hyperechoic mitral valve (MV) spans the left ventricle unlike the mid level papillary muscles that abut the left ventricle (Figure 4)
Figure 4: Short axis parasternal image at papillary muscle mid section (PM) of the left ventricle.
Figure 5: In this image the various short axis segments of the cardiac wall are labeled. Very often the lateral wall of the ventricle can be obscured by lung tissue. Using a probe with a smaller footprint (e.g. phased array instead of curvilinear) or positioning the patient in left lateral decubitus, may provide better image quality.
Illustration 4: Diagram outlining the wall segments of the left ventricle. There are typically 15 or 16 wall segments with the apex partitioned into 3 or 4 segments. In this 16 segment model displays the base and mid section of the heart 6 segments each while the apex has four segments. The areas of the left ventricle (anteroseptal 1,7,13, anterior free wall 2,8,14, lateral wall 3,9, posterior 4,10,15, inferior 5,11,16, and inferoseptal 6,12) are then demarcated according to sonographic landmarks, notably the presence of the MV (base) or the papillary muscles (mid).
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Figure 6a |
Figure 6b |
Figure 6a: This shows a cardiac short axis view
at the level of the aortic root in diastole. It displays the circular
aorta (Ao) in the center with the left atrium (LA) directly posterior and
the right ventricle (RV) anteriorly. The egress of the right ventricular
outflow tract into the pulmonary arteries can sometimes be seen, yet in
this image is obscured by artifact from air in adjacent lung tissue. Figure 6b: The image displays the aortic root
(Ao) in systole.
Figure 6c: A parasternal short axis view is shown
at the level of the apex with some visible papillary muscles (PM).
Video clip 2: Heart in short parasternal axis view.
Subxiphoid: A common approach to critically image the heart is the subxiphoid view. Unlike other cardiac views, this view is dependent on the left lobe of the liver as an acoustic window in the near field. With the probe aimed to the right, angle cephalad toward the thorax and then center the heart onto the screen with a rock and slide maneuver. The operator should first identify the “starry sky” appearance to the liver. Next the anechoic IVC in the far field abuts the hyperechoic diaphragm. As the operator angles up into the chest, the IVC will transition into the right atrium. Measurements taken at this IVC/RA junction have been described as rough estimates of central venous pressure (Table 1). (1)
Table 1
IVC measured |
Percent collapse (IVC) during inspiration |
CVP (mm Hg) |
<1.5 cm |
>50% |
0-5 |
1.5-2.5 cm |
>50% |
5-10 |
1.5-2.5 cm |
<50% |
10-15 |
>2.5 cm |
Little phasicity |
15-20 |
Relation Between IVC/RA junction and Central Venous Pressure
(CVP)
Adapted from Jones Handbook of Ultrasound in Trauma and Critical Care
Illness, 2003 (9).
Figure 7: Note the operator is holding the probe from a cephalad position. This allows for a flattening of the probe face to image up into the chest.
Figure 8: This sonographic image demonstrates the three hepatic veins (HV) emptying into the posterior located anechoic IVC. The heart will come into view on the right side of the screen (heart). The key to the subxiphoid view is to fill the near field with liver tissue by aiming toward the right shoulder, identifying the IVC posteriorly, and then aiming superiorly as the IVC empties into the right atrium.
Figure 9: The atrial (AS) and ventricular septum
(VS) is seen clearly oblique to the beam. The right heart structures
are juxtaposed to the liver. The left heart structures are in the
far field as the beam is angled under the rib cage. The apex (yellow)
is a morphological landmark with its curved surface and hyperechoic pericardial
lining.
Figure 10: The same subxiphoid view is shown with the four heart chambers labeled. Adjacent to the liver are the right atrium (RA) and right ventricle(RV), while the left heart (left ventricle LV, left atrium LA) lies in the far field and right side of the screen.
Video clip 3: Subxiphoid view of the heart.
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Figure 11: This long axis view of the IVC shows an example of a hepatic vein (HV) draining into the inferior cava, which then immediately drains into the right atrium (RA). Standard measurements of the IVC caliber at this juncture and its response to respiration can help the clinician to determine volume status. (Table 1).
Figure 12: This is a split screen image of a B-mode and corresponding M-mode ultrasound. The B-mode shows a long axis view of the IVC entering the right atrium (RA). The dotted green line depicts the area of measurement for the M-mode. On the right, these measurements (e.g. IVC width) are shown over the course of time. (HV = hepatic vein).
Apical: On physical exam the point of maximal intensity on the chest wall demarcates the cardiac apex. An ultrasound probe can be placed lateral to the nipple line there and rotated between the three apical views (Apical four chamber, apical two chamber, apical long). The apical four-chamber view displays the ventricular septum in the middle with the right heart displayed on the left side of the screen and the larger left heart on the right of the screen. The atria are seen in the far field (Figure 13).
Figure 13: This is a phased array sector image displaying all four heart chambers. The probe is placed over the tip of the heart and shows an apical four-chamber view (apex on top of the image). By convention, the left heart is displayed on the right side and the right heart is on the left side. The atria and AV-valves are in the far field.
IV. Pathology
Indications: If the technology is available at the bedside, the following patients can benefit from cardiac ultrasound: the trauma patient, the hypotensive patient, and the patient in cardiopulmonary arrest. Chest pain and pulmonary embolism are attractive diagnoses to experienced sonologists, but are difficult to interpret without advanced training. A focused approach to the patient in shock can utilize ultrasound to provide key information on the critically ill patient (1). Differentiating between the presence/absence of effusion, state of contractility (absent/poor/normal), and chamber size (large/small) can provide key bedside data in a variety of critical patient scenarios.
Trauma and Tamponade: The trauma patient may have injury to the chest that can be interrogated with ultrasound. Specifically penetrating trauma has a high likelihood of having a pericardial effusion and resultant tamponade. Remember, cardiac pressure rises quicker over smaller volumes during “acute” time periods and thus develops tamponade physiology earlier than in chronic effusions that develop over a longer time period. Sonographic tamponade is a combination of pericardial effusion and right heart diastolic collapse. The heart usually moves inward at systole and expands during diastole. During this time of low pressure, increased pressures around the heart (pericardial effusion) can cause paradoxical wall movement (collapse). In the presence of a pericardial effusion, observing the right heart for diastolic collapse is diagnostic of tamponade physiology.
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Figure 14 |
Figure 15 |
Figure 14: In this image a large circular pericardial
effusion (black) is distinguished from the left ventricle (LV, blue). Figure 15: This patient has a moderate amount of
pericardial fluid (PE). The effusion is anterior to the descending
thoracic aorta, which acts as a landmark to differentiate pericardial (anterior)
from pleural (posterior) effusions.
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Figure 16 |
Figure 17 |
Figure 16 and 17: These subxiphoid images display
additional samples of circular pericardial effusions (PE). The right
heart chambers do not exhibit diastolic collapse (LA = left atrium, LV – left
ventricle, LVOT = left ventricular outflow tract, RA = right atrium, RV
= right ventricle).
Video clip 4: This clip shows a significant pericardial effusion with diastolic collapse of the RV and pendulum movement of the heart (Courtesy of B. Hoffmann, MD).
Shock: Shock is a common presentation to many disease states and can be classified according to etiology (e.g hypovolemic, obstructive, cardiogenic, distributive). The hypotensive patient can be a conundrum as far as fluid resuscitation and timely administration of pressors. The circulatory collapse of a patient has many patterns from the elderly patient with urosepsis, to the accident victim with ruptured spleen and hypovolemic shock. Bedside echocardiography makes it easier for clinicians to differentiate shock etiology. Ultrasound of the patient in shock can be used to interrogate the heart (contractility and effusion), search for blood loss (FAST exam), and interrogate the great vessels for aneurysm. The patient in shock with or without pericardial effusion, with or without normal cardiac contractility, and with or without evidence of adequate preload (2), can be quickly differentiated using common echographic views of the heart.
Video clip 5: Shows hyperdynamic cardiac activity. The patient presented with hemodynamic shock secondary to bloodloss (Courtesy of B. Hoffmann, MD).
Video clip 6: This patient is in cardiogenic shock. Note the hypoactive heart with significantly decreased LV function (Courtesy of B. Hoffmann, MD).
Figure 18: A synthesized hypotensive protocol (3) uses common acoustic windows into the torso to image those structures important in maintaining blood pressure. Probe placement at area 1-long axis parasternal, 2-short axis parasternal and 3- subxiphoid, allow common windows into imaging the heart during hypotension. Views 4 and 5 image the aorta, while images 6-8 encompass a modified FAST exam.
Cardiac Motion and Contractility: Clearly the first step is to image the heart and determine if there is cardiac wall motion. There are 15 to 16 wall segments described within the left ventricle and each can be scored individually or globally for wall motion (4) (Table 2). Moore et al described emergency physicians accurately utilizing echo to predict LV ejection fraction in three broad terms (Normal >55%, depressed 30-50%, severely depressed <30%) in those patients presenting with hypotension. (5) Cardiac ultrasound allows the operator to assess depressed cardiac function by investigating thickening of the myocardium and further elucidating the hypotensive state.
Table 2
Score |
Cardiac Wall Motion |
0 |
Hyperkinesis |
1 |
Normal |
2 |
Hypokinesis |
3 |
Akinesis |
4 |
Dyskinesis |
Adapted from Otto. Echocardiography. 2004 (4)
Cardiac Arrest: Advanced cardiopulmonary life support systematically assesses and manages patients in arrest with energy (joules) and pharmacology (epinephrine, atropine, vasopressin, etc.) while monitoring the electrical rhythms of the heart. Echocardiography enables the bedside clinician to image the heart during a pulse check (subxiphoid or parasternal view) and objectively assess cardiac function, chamber size and the presence of effusion. In a study of 169 cardiac arrest victims presenting without a pulse, cardiac standstill on ultrasound was predictive of death (6). Another study looked at adding end tidal CO2 to focused cardiac ultrasound in patients in arrest to predict resuscitation outcome. The investigators found that cardiac motion was associated with survival, as was capnography > 16 torr, however in combination there was no statistical enhancement.(7) Ultrasound can be useful to determine if there is cardiac motion or no motion in the arrest patient (8,9) and combined with clinical parameters can help define futility of resuscitation efforts.
Video clip 7: This video shows a heart in severe cardiogenic shock with futile contractions. The patient did not have a pulse on exam (Courtesy of B. Hoffmann, M.D.).
Cardiac motion or lack of motion can be documented using M-mode (Figure 19 and 20).
Figure 19:
Split-screen image of B-and M-mode ultrasound. The subxiphoid view
shows a patient in cardiac arrest. M-mode is activated within the
B-mode image (dotted green line).
The different gray tones of the M-mode waveform correspond (orange arrows)
to the anatomic structures detected. Their change in position is shown
in the morphology of the waveform. Here a flat line represents no
cardiac activity (no motion of the underlying anatomy).
Figure 20: This displays an ultrasound B/M-mode screen captured during simulated cardiac activity. The chest compressions during CPR cause a displacement of the cardiac chambers, changing the flat line to a significant waveform.
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VI. References
- Hendrickson RG, Dean AJ, Costantino TG.
A Novel use of ultrasound in pulseless electrical activity: The diagnosis of an acute abdominal aortic aneurysm rupture. J Emerg Med.2001;21:141-144.
- Kircher BJ, Himelman RB, Schiller NB.
Noninvasive estimation of right atrial pressures from the inspiratory collapse of the inferior vena cava. Am J Cardiol.1990;66:493-496.
- Bahner DP.
Trinity, A hypotensive ultrasound protocol. JDMS.2002;18:193-198.
- Otto CM.
Textbook of Clinical Echocardiography.W.B. Saunders: Philadelphia,3rd ed. 2004.
- Moore CL, Rose GA, Tayal VS, Sullivan DM, Arrowood JA, Kline JA.
Determination of left ventricular function by emergency physician echocardiography of hypotensive patients. Acad Emerg Med.2002;9:186-193.
- Blaivas M, Fox JC.
Outcome in cardiac arrest patients found to have cardiac standstill on the bedside emergency department echocardiogram. Acad Emerg Med.2001;8:616-621.
- Salen P, O'Connor R, Sierzenski P, Passarello B, Pancu D, Melanson S, Arcona S, Reed J, Heller M.
Can cardiac sonography and capnography be used independently and in combination to predict resuscitation outcomes. Acad Emerg Med.2001;8:610-615.
- Varriale P, Maldonado JM.
Echocardiographic observations during in hospital cardiopulmonary resuscitation. Crit Care Med.1997;25:1717-20.
- Jones R, Blaivas M.
The handbook of ultrasound in trauma and critical illness. Ohio ACEP,2003.