CHAPTER 90 Echocardiography

The prevalence of heart disease will continue to increase in the United States as the population ages. The amount of heart disease managed by primary care clinicians will also continue to increase. In many cases, both the management and the prognosis of heart disease are based on the amount of remaining viable myocardium. This is especially true for patients with congestive heart failure (CHF), cardiomyopathy, arrhythmias, and ischemic heart disease. One method of quantifying the remaining viable myocardium is to assess the ejection fraction. In fact, the most common reason echocardiography is currently performed in the United States is to determine the ejection fraction.

Many common symptoms, signs, or diagnoses of heart disease (e.g., palpitations, cardiomegaly on electrocardiogram [ECG] or chest x-ray, atrial fibrillation, CHF) are evaluated or managed based on data from echocardiography (Table 90-1). In certain situations, the more readily available the echocardiogram, the better the management. For example, acute chest pain is managed differently when echocardiography is immediately available. Even extracardiac causes for acute chest pain, some of which can be life threatening (e.g., pulmonary embolus, aortic dissection), can be diagnosed with echocardiography. If an acute myocardial infarction (MI) is diagnosed, risk stratification can be performed immediately. Complications from an acute MI can also often be diagnosed early.

TABLE 90-1 Common Symptoms and Differential Diagnosis for Echocardiography

Reason for Echocardiography	Differential Diagnosis
Chest pain	Aortic dissection Coronary artery disease: acute myocardial infarction or angina Hypertrophic cardiomyopathy Pericarditis Pulmonary embolism Valvular stenosis
Heart failure	Dyspnea Hypotension Left ventricular diastolic dysfunction Left ventricular systolic dysfunction (global or segmental) Pericardial disease Right ventricular dysfunction Valvular heart disease
Palpitations	Congenital heart disease (e.g., atrial septal defect, Ebstein’s anomaly) Left ventricular systolic dysfunction Mitral valve disease Pericarditis Structural cardiac disease
Murmur: systolic	Aortic stenosis, subaortic obstruction, hypertrophic obstructive cardiomyopathy Flow murmur (valve abnormality) Mitral regurgitation Pulmonic stenosis Tricuspid regurgitation Ventricular septal defect
Murmur: diastolic	Aortic regurgitation Mitral stenosis Pulmonic regurgitation Tricuspid stenosis
Cardiomegaly on chest x-ray	Dilated cardiomyopathy Pericardial effusion Specific chamber enlargement (e.g., left ventricle in chronic aortic regurgitation)
Systemic embolic event	Aortic valve disease Left atrial thrombus (only diagnostic if seen, otherwise transesophageal echo needed) Left ventricular systolic function and segmental wall motion abnormalities (aneurysms) Left ventricular thrombus Mitral valve disease Patent foramen ovale

Adapted from Otto CM: Textbook of Clinical Echocardiography, 2nd ed. Philadelphia, WB Saunders, 2000.

Other common diagnoses that can be made or evaluated in the primary care clinician’s office with echocardiography include mitral valve prolapse, dilated left atrium (important for patients with atrial fibrillation), left ventricular hypertrophy, transient ischemic attack, and ischemic heart disease. Whether in the clinician’s office, the hospital, or the emergency department, a rapid diagnosis of pericardial tamponade or a pericardial effusion may be life-saving. Furthermore, if pericardiocentesis is needed, the risk of complications is significantly reduced if it is performed under ultrasonic guidance (see Chapter 214, Pericardiocentesis).

Improvements in image quality, portability, and affordability for real-time sonography have allowed it to become a valuable adjunct for the clinician in the office, in the hospital, or in the emergency department. Albeit not by much, the cost of echocardiography equipment has also decreased as the technology has expanded and improved. Consequently, echocardiography has seen some of the most rapid growth among procedures performed by primary care clinicians (see Chapter 94, Stress Echocardiography). For those clinicians with a large number of adult patients, two-dimensional (2D) and M-mode echocardiography may be a welcome addition to their practice. If the primary care clinician is uncomfortable performing echocardiography, contractors are available to provide sonographers. Over-reading services are also available (see the “Suppliers” section). This chapter predominately describes the performance of a 2D/M-mode echocardiogram with a brief summary of common findings. Since color and Doppler flow imaging are helpful for almost all echocardiograms, especially for those assessing the hemodynamic severity of an abnormality, they will also be discussed briefly. For a discussion of ultrasound principles and concepts, and for information regarding limited echocardiography, see Chapter 225, Emergency Department, Hospitalist, and Office Ultrasonography (Clinical Ultrasonography). Electromechanic dissociation, pericardial effusion, pericardial tamponade, and assessing intravascular volume status, right ventricular strain/dysfunction, and acute pulmonary hypertension (e.g., pulmonary embolism) are briefly discussed in that chapter. (Assessing for possible pulmonary hypertension is also discussed in the Interpretation section of this chapter.)

Two-dimensional echocardiography provides the clinician with cross-sectional, real-time images of various cardiac structures. Using 2D, cardiac chambers, walls, valves, and other structures can be observed as they move through the cardiac cycle. Freeze-framing and the use of calipers allow the clinician to measure certain structures, if needed, at various points during the cardiac cycle.

M-mode echocardiography produces graphic images in which time makes up the horizontal axis and the structures in motion being scanned compose the vertical axis. In other words, wherever the cursor is placed on the image, a linear beam of ultrasound is directed through the corresponding tissue and movement of the structures is graphically imaged over time. The resultant M-mode tracing can then be used to look at excursion and contraction patterns as well as to precisely measure distances from the various horizontal structures over time. Chamber dimensions, wall thicknesses, and valve excursions can be measured precisely throughout the cardiac cycle. From chamber dimensions, an ejection fraction can be estimated.

Doppler flow imaging is used to measure the velocity of blood flowing over certain structures. Using the Bernoulli equation, pressure gradients (e.g., across a valve) can also be determined. As with M-mode, time and the cardiac cycle are graphed along the horizontal axis while the vertical axis consists of blood velocity in meters per second. By convention, flow toward the transducer is depicted above the baseline and flow away from the transducer is depicted below the baseline. Pulsed wave (PW) technology and measurements utilize tiny, three-dimensional sample volumes to detect the exact location of any abnormalities. However, PW Doppler is limited when there is high-velocity flow. Continuous wave (CW) technology utilizes two crystals (one continuously emitting sound waves, the other continuously listening for echoes) and can measure high velocities (e.g., stenotic valves). However, it is of limited use for localizing abnormalities. As a result of these limitations, both PW and CW should be utilized with every valve. Color flow Doppler is a special adaptation of PW technology. It uses thousands of sampling volumes to produce a color image of velocities. By convention, flow away from the transducer is blue and flow toward the transducer is red. The intensity of the color increases with the velocity.

Indications

• Determine ejection fraction (most common indication)

• Acute chest pain

• Acute or old myocardial infarction

• Atrial fibrillation

• Cardioversion preparation

• Cardiomegaly on chest radiograph

• Congestive heart failure

• Dyspnea (possibly due to cardiac origin)

• Embolus (systemic or pulmonary)

• Hypotension (possibly due to cardiac origin)

• Hypertensive heart disease

• Ischemic heart disease

• Mitral valve prolapse

• Murmur

• Palpitations

• Pericardial effusion, electromechanical dissociation, or suspected pericardial tamponade

• Suspected cardiomyopathy

• Suspected infectious endocarditis

• Suspected left ventricular hypertrophy (e.g., LVH on ECG)

• Transient ischemic attack

• Valvular defect, stenosis, regurgitation, or insufficiency

• Ventricular arrhythmias (with suspected cardiac structural abnormality)

Contraindications

• Patient too unstable or too uncooperative to be scanned

• Patient needs Doppler flow imaging or a color Doppler scan, and the equipment does not have this capability

Preprocedure Patient Preparation

Indications for the study and possible findings should be explained to the patient. The patient should be prepared to change positions, if possible, while being scanned. The patient should be prepared for adequate gel and pressure from the transducer to be applied to the parasternal, apical, suprasternal, and, possibly, subxiphoid areas of the chest and abdominal walls. The patient should be gowned and in the supine or left lateral decubitus position.

Technique

Two-Dimensional Echocardiography

Viewing the front of the chest, if the 12 o’clock position is considered cephalad and the 6 o’clock direction caudal, the axis of the heart is usually located in a line drawn between the 10 o’clock and the 4 o’clock positions. Placing the marker dot of the transducer at about the 10 o’clock position usually produces the long-axis view of the heart, especially if the probe is located parasternally. A line drawn between the patient’s right shoulder and left hip also approximates the long axis of the heart. The long-axis view is essentially the longitudinal view of the heart, if described in the conventional terminology of ultrasound for the remainder of the body. Rotating the marker dot almost 90 degrees or perpendicular to the long axis, to the 2 o’clock position, produces the short-axis view of the heart. This is essentially a transverse view of the heart (Fig. 90-1). A line drawn between the left shoulder and the right hip also approximates this axis.

Figure 90-1 Parasternal short-axis view at the level of the mitral valve (MV). LV, left ventricle; RV, right ventricle.

(From Reynolds T: The Echocardiographer’s Pocket Reference, 2nd ed. Phoenix, School of Cardiac Ultrasound at Arizona Heart Institute, 2000.)

Because the patient is usually lying in the left lateral decubitus position while being scanned and the transducer is placed on the anterior chest wall (or abdominal wall for the subxiphoid view), the transducer edge will be noted at the top of the image. Posterior cardiac structures will be located at the bottom (inferior aspect) of the image. With the usual orientation, if the directional marker is noted on the right side of the image, objects to the right of the screen will correspond to objects near the marker dot on the transducer.

1 With the patient in the left lateral decubitus position, attempt to scan by first placing the transducer in the parasternal location (third to fourth intercostal space, next to the sternum) or the apical location (inferolateral to the left nipple at the point of palpated maximal cardiac impulse [PMI]). These same two traditional auscultatory points are used for a stethoscope. If the best window is found at the apical location, skip to step 12.

2 When scanning parasternally, the probe will be rotated so that the marker dot is either in the 10 o’clock (long-axis) or the 2 o’clock (short-axis) position. The short-axis view at the level of the mitral valve is often a good view for assessing the adequacy of the window, since the mitral valve is usually prominent and easily located (see Fig. 90-1).

NOTE: Some ultrasound equipment places the marker dot 180 degrees away from this standard orientation (that is, the 4 o’clock position is what would typically be the 10 o’clock position). To determine the orientation of the probe, the directional marker on the image should be found. It corresponds with the marker dot on the probe and should be displayed on the right side of the display for cardiac imaging.

3 Small changes in patient position (e.g., rolling the patient further onto his or her left side) or working with the patient’s breathing may improve the quality of the image. These adjustments cause the lingula of the lung to fall away from the heart, often providing a better window.

4 For unresponsive patients, those who cannot be moved, patients with chronic obstructive pulmonary disease, or other technical difficulties impairing the use of ultrasound in the parasternal position, the subxiphoid position will often provide a good window. Place the transducer directly below the xiphoid and angle it toward the patient’s left shoulder with the marker dot toward the patient’s left side. If this is the only location where an adequate window can be obtained, skip to step 16.

5 If a good window can be found at the parasternal short-axis view, rotate the transducer 90 degrees to the parasternal long-axis view (Fig. 90-2). With this view, observe the anterior and posterior leaflets of the mitral valve as it is scanned lengthwise. With prolapse, the leaflets will close beyond 90 degrees or cross the plane of the mitral annulus. True prolapse is often associated with thickened valves. Also with this view, the right ventricle is seen at the superior portion of the image, and the interventricular septum is noted as the inferior border of the right ventricle. Beneath the interventricular septum to the left of the image is the left ventricular chamber bordered by its posterior wall. Note that the ventricular walls thicken during systole, reducing the size of the ventricular cavity. Very little of the apex can be visualized with this view, because it is beyond the left side of the image. The left atrium is to the right side of the image, immediately inferior to the aortic root. The left atrial diameter should be about the same as the aortic root diameter. If either is markedly larger than the other or more than 4 cm in their anteroposterior diameter, they are considered dilated. The descending thoracic aorta is noted behind the left atrium. Rotate the transducer slightly clockwise if a better longitudinal view of the aorta is desired.

6 To obtain the long-axis view of the right ventricular inflow tract (RVIT) view, from the parasternal long-axis view, tilt the transducer inferomedially or toward the right hip. This is a good view in which to study the tricuspid valve, right atrium, and the right ventricle (Fig. 90-3). The posterior and anterior tricuspid leaflets separate the right atrium from the right ventricle. In fact, this is about the only view where the posterior leaflet of the tricuspid valve can be seen. Liver tissue is usually noted adjacent to the diaphragmatic wall of the right ventricle.

7 After angling the probe back again to the parasternal long-axis view, rotate the transducer 90 degrees so that the marker dot is at the 2 o’clock position. This will produce the parasternal short-axis view again (see Fig. 90-1). Note the appearance in real time of the opening and closing mitral valve. Some have likened this image to that of a “fish mouth” opening and closing, especially if there is any stenosis. Without stenosis, the lateral and medial commissures of the valve are easy to distinguish. At this level, the ventricular wall can be divided into six segments, and the contractility of all of the segments should be observed (see step 10). In the normal heart, the segments should be contracting uniformly and symmetrically. The tricuspid valve may be seen above and to the left of the mitral valve.

8 Next, without actually moving or rotating the transducer, merely angle it more cephalad toward the base of the heart to observe the aortic valve (Fig. 90-4). In this transverse view of the aortic valve, it produces a characteristic “Y sign” when the leaflets are closed. If the valve itself is viewed as the face of a clock, the commissures are noted in the 2, 6, and 10 o’clock positions at the edges of the Y. When the valve is open in systole, it should produce a triangular shape. If it produces an oval shape with opening, the aortic valve is bicuspid. This is one of the most common abnormal findings on adult echocardiography, occurring in 1% to 2% of the population. If it is found the patient should also be scanned for coarctation of the aorta, because 50% to 80% of those with aortic coarctation will have a bicuspid aortic valve (see the suprasternal notch view, step 21). At this level of the parasternal short-axis view, the right ventricular outflow tract (RVOT) can be seen curving above and around the aortic valve. The tricuspid valve is noted to the left of the aortic valve and the pulmonary valve is located superiorly and to the right. The right ventricle is located between the two. The right atrium is located in the inferior portion of the image to the left of the aortic valve. The left atrial appendage can often be seen to the far right of the aortic valve, and the left atrium is noted inferior or posterior to the aortic valve. Part of the atrial septum can be noted between the atria. The three cusps of the aortic valve are labeled the right, left, and noncoronary cusps. The right cusp is located next to the right ventricular outflow tract, the noncoronary cusp closest to the right atrium, and the left coronary cusp next to the left atrium. In a normal heart, the corresponding right and left coronary arteries originate from the same-labeled cusps.

9 Tilting the transducer yet more superiorly, beyond the aortic valve, the aortic root can be visualized in its short axis (transversely). At this level, on the right side of the image of the aortic root, the pulmonary artery can often be noted to bifurcate into the right and left pulmonary arteries.

10 Next, angle the probe back through the mitral valve, down to the level of the papillary muscles (Fig. 90-5). This level provides an excellent view for assessing left ventricular wall motion and the severity of left ventricular hypertrophy if it is present. At this level, the left ventricular wall can again be divided into six segments—the anterior, anteroseptal, anterolateral, inferolateral (posterolateral), inferoseptal (posteroseptal), and inferior (posterior) segments—which are all visualized. This same segmentation system can be used on the parasternal short-axis view at the level of the mitral valve. Each of the segments should contract in a uniform manner. With coronary artery disease, determining which wall becomes hypokinetic with ischemia may predict which coronary artery is obstructed (see “Findings and Interpretation” section). Usually two papillary muscles are visualized at this level, one located anterolaterally and the other posteromedially. At this level, only part of the right ventricle can usually be visualized, and it will be to the left of the image.

11 Next, slide the transducer slightly toward the apex and obtain a short-axis view of the ventricles at the apex (Fig. 90-6). By convention, the left ventricular wall is divided into only four segments (anterior, lateral, septal, and inferior [posterior]) at this level. In the normal heart, all four segments will contract uniformly.

12 By moving the transducer to the apex, which can be located by palpating the PMI inferolateral to the left nipple, the apical four-chamber view can be obtained (Fig. 90-7). At this position, the majority of scanning is usually performed with the marker dot at the 3 o’clock position. Angle the transducer back up toward the base of the heart to obtain the best possible four-chamber image. To confirm the orientation while scanning, note that the septal leaflet of the tricuspid valve is closer to the apex than the anterior leaflet of the mitral valve. By convention, the tricuspid valve and the right ventricle should be on the left side of the image. The right ventricle can usually be distinguished from the left ventricle because the right ventricle has the echogenic moderator band extending from the apex to the septal wall. Again, the right ventricular wall is more trabeculated than the left ventricular wall. With this view, again observe the ventricular wall motion for uniformity of contraction. From this transducer position, observe the valves again for abnormalities.

13 Tilt the transducer slightly anteriorly, toward the anterior chest wall (tail of transducer is tilted downward slightly), from the apical four-chamber view to obtain the apical five-chamber view (Fig. 90-8). This view provides an excellent image of the left ventricular outflow tract as well as an excellent view to exclude hypertrophic obstructive cardiomyopathy.

14 Return to the apical four-chamber view and rotate the transducer 90 degrees counterclockwise and tip it slightly laterally to obtain the apical two-chamber view (Fig. 90-9). The left ventricle and atrium will be visualized, separated by the mitral valve. With this image, the full length of the inferior wall of the left ventricle can be visualized. Observe this wall, along with the anterior wall of the left ventricle, for uniform contractility.

15 Rotate the transducer counterclockwise so that the sector plane passes through the long axis of the heart to obtain the apical long-axis view (Fig. 90-10). The aortic root can be evaluated, while the aortic valve is noted to be contiguous with the base of the anterior mitral leaflet. This view is very similar to the parasternal long-axis view, but the apex is visualized from this position. With this image, the anterior interventricular septum and the inferolateral ventricular wall can be inspected for uniform contractility.

16 Moving the transducer to below the xiphoid, the subxiphoid (subcostal) four-chamber view (Fig. 90-11) can be obtained with the marker dot to the patient’s left side. Usually a portion of the liver is used as a window. The ventricles will be to the right side of the image and the atria to the left side. The left ventricle and atrium will be located behind (below) the right ventricle and atrium. Inspect both the mitral valve and the tricuspid valve, and observe wall motion for uniformity of contraction.

17 From the subxiphoid four-chamber view, by tilting the transducer anteriorly, visualize the aortic valve lengthwise. This will again provide an image similar to that seen with the parasternal long-axis view. This technique of imaging may be very valuable if the standard parasternal long-axis image cannot be obtained because of technical difficulties.

18 From the subxiphoid four-chamber view, it is also possible to angle the transducer to visualize the entire atrial septum. This position is the most reliable for evaluating patients for atrial septal defects and patent foramen ovale.

19 From the subxiphoid view, the inferior vena cava (IVC) can be imaged (Fig. 90-12) and its diameters measured. The diameter of the IVC can be used to estimate right atrial pressure (RAP). With the marker dot toward the patient’s feet and the transducer located in the midline, the long-axis view of the IVC can be obtained by angling slightly to the patient’s right side. Normally the IVC is less than 2 cm in diameter and collapses more than 50% with inspiration. It will also normally collapse with pressure from the transducer. If it does not collapse, the formula in the “Findings and Interpretation” section can be used to estimate RAP. The IVC is thin-walled compared with the aorta, and it may appear to pulsate as a result of pulsations transmitted through solid tissue from the aorta. When it collapses with inspiration, these pulsations will be minimized.

20 In addition to what has been described, almost all of the parasternal short-axis views can be obtained scanning from the subxiphoid position. However, because of the depth of tissue necessary to scan from this position, there is usually some loss of resolution. This is especially true when compared with scanning from the parasternal position.

21 Placing the transducer in the suprasternal notch with the marker dot to the patient’s left side, scan the aortic arch in its long axis (Fig. 90-13) to provide what some call the “candy cane” view. With this image, the ascending aorta, its horizontal arch, and the proximal descending thoracic aorta can often be visualized. The origins of the left subclavian and left carotid arteries off of the aorta can usually be visualized, and occasionally the origin of the brachiocephalic artery can be seen. The right pulmonary artery is usually noted in short-axis view beneath the arch. This is the best view for excluding coarctation of the aorta.

22 From the suprasternal view, by angling the transducer anteriorly and to the patient’s right, the aortic root can often be visualized.

23 Further clockwise rotation can be used to obtain short-axis views from the suprasternal notch (Fig. 90-14). The right pulmonary artery can often be visualized in this manner. The right pulmonary artery is located between the aorta and the left atrium. It may be possible to visualize where the pulmonary veins drain into the left atrium.