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CHAPTER
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E E E E Echocardiography
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Peter J. Cawley
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Ec Echocardiography (echho) iis ulltrasoundd technology ass applied to im- ti tissues of diffferennt densiity within the body. For example, thhere is s
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aging the heart and the associated great vessels. As cardiac catheter- a a diffferent density of the blood than of the myocardiuum. The
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ization and invasive angiography transformed our understanding of bo bounddary between the twwo tissues causess reflflection of the trans-
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mitted sound wave, which is then detected by the transducer. De-
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same opportunities noninvasively. Our clinical experience utilizing g pe p nding uppon the tiime it tookk for thee transducer to emit thhe
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echo for patient care is vast andd spans many decades. Echo is one of sound wave and detect the reflected sound wave, it will place that
the most widely used imaging modalities today within cardiology object at a certain distance (depth) on the image. 2
because of the following attributes: safe, fast, lacks exposure to ion- Attenuation is degradation of the sound wave as it propagates
izing radiation, noninvasive, and portable. from the transducer. Sound waves pass through tissues and attenu-
In the United States, the acquisition of echo images is most ate with greater distances from the transducer. This attenuation re-
commonly performed by sonographers (individuals who have sults in a finite ability of the transducer to capture reflected sound
completed specialized training programs in ultrasound), echocar- waves from greater depths. The greater the distance the transducer
diographers (cardiologists with training in echo), or cardiovascu- is from the heart, the greater the number of sound waves that will
lar anesthesiologists. As the field has expanded, other physicians be attenuated, and the result will be poor image quality. Examples
including those who practice emergency medicine, primary care, of sound wave attenuation for echo caused by greater depth (dis-
or critical care have received training in image acquisition. tance) include obesity and breast tissue. But depth is not the only
This chapter will focus on three general topics: (1) principles cause of sound wave attenuation in echo. Bone and air also result in
and techniques of echo, (2) echo examination, and (3) special ap- considerable attenuation. Because the heart is surrounded by the
plications of echo. sternum and ribs, imaging can be performed only in the rib spaces.
In patients with smaller ribs spaces, imaging can be particularly
challenging. Because the heart is in close proximity to the lungs and
trachea, these structures must also be avoided. In patients with en-
PRINCIPLES AND TECHNIQUES larged lung spaces (i.e., chronic obstructive pulmonary disease), im-
OF ECHO aging can be difficult. Pneumomediastinum, pneumothorax, and
subcutaneous air will all result in signal attenuation.
Sound Waves Experienced echocardiographers and sonographers should pos-
sess a thorough understanding of the impact of image artifacts.
Ultrasound is sound with a frequency above 20,000 Hz (cycles per
second) or 20 kHz. This sound is outside of the range of the hu- Inability to recognize artifacts could lead to false interpretation,
man ear. Diagnostic ultrasound for cardiovascular imaging uses some with significant consequences. Ultrasound can cause several
frequencies ranging from 2 to 30 MHz: adult transthoracic fre- different types of artifacts and an explanation of each is beyond
quencies range from 2 to 4 MHz, transesophageal frequencies the scope of this chapter. To reduce misdiagnosing artifacts, ab-
from 5 to 7 MHz, and intravascular ultrasound frequencies (coro- normalities should be visualized in more than one imaging win-
nary artery) from 20 to 30 MHz. dow, thus reducing the likelihood of false interpretation.
Sound waves are generated at the transducer, the hand-held
probe that is applied to the body part of interest. Today, trans- M-Mode
ducers contain a piezoelectric crystal, which when applied to an
electric current, will cause the crystal to deform. This deformation M-mode (motion) echo displays a narrow ultrasound beam of in-
results in the generation of a sound wave, which is transmitted to formation within the heart along the y-axis (vertical axis) and dis-
x
x
the body. Returning sound waves can also deform the crystal and plays it according to time on the x-axis (horizontal axis). Heart
2
thus be detected by the transducer. The transducer receives structures are displayed with respect to motion and time. M-mode
sound waves that are generated from the interaction of the trans- echo provides high temporal resolution and provides information
mitted sound waves and the tissues of the body. The transducer regarding both the structure and function of the heart. M-mode
generates and receives reflected sound waves. Interestingly, the echo predated the existence of two-dimensional (2-D) echo and
time the transducer is in receiver mode (i.e., listening mode) is far although it is not as commonly used as in the past, M-mode can
greater than when in transmitting mode (i.e., generating sound still be useful to describe motion of structures of the heart with re-
waves) with one exception—continuous wave Doppler, which will spect to the cardiac cycle (Fig. 13-1).
be explained further (See Doppler).
Sound moves through media in the form of waves and may in- 2-D
teract with the tissues in different ways. This chapter presentshh d ff h h
two of the more common interactions, reflection and attenuation. 2-D echo was developed from similar concepts of M-mode. Be-
Reflection occurs when a transmitted sound wave interacts with cause M-mode only allowed a very narrow and focused area of
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