Download Abnormal Echocardiogram

ULTRASONIC EXAMINATION
Ultrasonic examination is a very method in the clinical diagnosis of diseases.
Recently, Ultrasound, isotopic scanner, and X-ray (including computerized
tomography) comprise the three important imaging diagnostic techniques in modern
medicine. Ultrasound has many advantages, it is a non-invasive diagnostic technique
which can be used in the detection of many human organs, operated easily, not
dangerous and not harmful to the patients. It can be repeated many times in the short
period, and obtain the results very soon. Moreover, it is the most cheap among the
three techniques.
Section Ⅰ.Basic physics of ultrasound
The nature of sound waves
1. Basic conception
Sound is a mechanical vibration that is propagated through matter which is also
called medium. It cannot travel through a vacuum. Sound waves are produced by
vibrating sources that are calls “sound source”. One of the simplest example of the
sources is a tuning fork vibrating in the air. The ultrasound is one kind of the sound.
2. The formula about the sound
There are three elementary parameters about the sound:
Velocity(C) frequency (f), and wavelength( ).
These three parameters of sound are related in the following equation:
C=f*
For and given material, the velocity of sound is constant. Therefore, if the
frequency is increased, the wavelength must decrease proportionally.
3. Types of waves
1) Longitudinal wave. It is the predominant type in the human body.
2) Transverse wave. Only solid can support transverse wave. With the
exception of compact bone, the longitudinal waves are the only type
observe within the body.
4. Sound velocity
Table 1. acoustic velocity in various tissues
Tissues of material
Acoustic velocity(m/sec)
Air
331
Fat
1450
Water
1495
Soft tissue (mean value)
1540
Kidney
1561
Muscle
1585
Bone
4085
The average sound velocity for soft tissues is 1540 meters per second, and this
value is uses in the calibration of clinical ultrasonic instruments.
5. Wavelength
The wavelength of a sound eave is the distance from one wave peak to the
successive peak. Wavelength ranging from 0.1 to 1.5mm is utilized in medical
applications. The wavelength is important because it determines the theoretical
limit of resolution. Under on circumstances are structures that are closer
together than one wavelength identifiable as two distinct entities.
6. Frequency
The frequency of a sound wave is defined as the number of the associated
pressure wave that pass a given point in one second. The unit of frequency is the
hertz (Hz). One Hz means 1 cycle per second. One Kilohertz (KHz) equals 1000
1
Hz and 1 megahertz (MHz) equals 1,000,000Hz.
Table 2. Categories of sound
Category
Frequency range (Hz)
Ultrasound
>20,000
Audible sound
16-20,000
Infra-sound
<16
The human ear is sensitive to sonic frequencies from 20 to 20,000 Hz. This
provides a convenient classification of sound into three categories as listed in Table 2.
Sound frequency employed in medical applications ranges from 1 to 15 MHz
and therefore they are in the ultrasonic range.
The choice of frequency used in any medical application is a compromise
between resolving capability and penetration. The higher the frequency, the more
rapidly sound is absorbed, and the smaller the distance it can penetrate into tissue. The
lower the frequency, the poorer is the resolving capability.
II. Production of ultrasound
The ultrasound comes from the probe, which is made of piezoelectric crystals.
The piezoelectric effect is the generation of an electric voltage when a crystal is
compressed. The voltage generated is proportional to the amount of compressing.
According to the principle of the reverse piezoelectric effect the crystal, which is in
the high frequency alternative electric field, induces the successive composing and
stretch in the certain direction, in other words, it induces the vibration. If the
frequency of the alternative electric field is higher than 20,000 Hz the ultrasound is
produced. Meanwhile, the crystal possesses also the direct piezoelectric effect. It is
able to receive the echo signals and convert sonic energy into the electric signals, then
through the detective instruments the echo signals are showed on the screen in
different forms. That is called “ultrasonogram”.
III. The properties of the ultrasonic waves
1.Directional property to the ultrasonic waves
The directional property of ultrasound is related to the diameter of the crystal of the
probe and its vibrating frequency. It is according to the ratio of the probe diameter and
the wavelength. While the probe diameter is more large than the wavelength, the
ultrasonic waves, produce by the probe, possess the property that they are propagated
through a special direction. We can use the ultrasound to correctly detect the certain
tissue, organ, and lesion in the body, because the ultrasound has the perfect directional
property.
Sound beams are classified as divergent, sollimated or focused. At the near part to
the soundsource (probe), which is called “near field”, the diameter of the sound beam
is same, but through the narrowest part of the sound beam it becomes a divergent one
that likes a circular cone. The latter part is called “far field”. In the near field besides
the main lobe (main sound beam) there are some additional lobes in the different
directions that are called side lobes. If the side lobes meet the reflecting interface the
echoes are produced. These echoes are the “pseudo” echoes and they often induce the
difficult problem to the diagnostic analysis. Ultrasound width different frequencies
has different wavelength in the soft tissues.
Table 3. The wavelength in the soft tissues
Frequency (MHz)
1.00
2.25
2.50
3.50
5.00
Wavelength (mm)
1.54
0.68
0.60
0.44
0.31
1.Reflection, refraction and scatter
Acoustic impedance. The product of density of a material and the speed of sound in
that material is a quantity alwwed the characteristic acoustic impedance. The
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significance of this quantity is its role in determing the amplitude of reflected and
transmitted ways at an interface.(see table 4). There is a fomula : Z=P*C Not Z is the
impedance, P is the density of the medium and C is the speed of sound.
Reflection.
Whenever an ultrasound beam is incident on an interface formed by two materials
having different acousicic impedances, in general, some of the energy in the beam
will be reflected and the remainder transmitted. The amplitude of the reflected wave
depends on the difference between the acoustic impedances of the two materials
forming the interface, and the intensity of the incident ultrasound. According to the
Snell law, the reflecting direction to the Snell law, the reflecting direction of incident
ultrasound from the interface is related to the incident angle. When the incident angle
is 0 degree, the reflecting echoes return to the probe, and the ultrasonogram is showed
on the screen. If the ultrasonic beams are not perpendicular to the interface, there are
part or whole reflecting echoes that cannot reach to the probe. So the screen does not
show the Table 4. The acoustic velocity and impedance of human normal organs.
Tissue or organ
Velocity (m/sec)
Impedance/square 5 (cmec*10)
Fat
1,450
1.38
Soft tissue (mean)
1,540
1.63
Liver
1,549
1.65
Kidney
1,561
1.62
Spleen
1,566
1.63
Blood
1,570
1.61
Muscle
1,585
1.70
Bone
4,080
7.80
Air
331
0.0004
Water
1,498
1.48
Sonogram. When the interface is not smooth or its diameter is less than the diameter
of ultrasonic beam, the incident ultrasound ontl induce the nonspecular reflection or
scatter. These echo signals are difficult to be received by probe.
The acoustic impedance of the air is biggest and its reflecting coefficient is 1.
When the ultrasound propagates from air to another medium, it will induce “whole
reflection” that is the ultrasound cannot transmit the air.
3.Absorption and attenuation
Absorption is the transfer of energy from the sound beam to the tissue. It is
proportional to frequency. In addition to frequency, the amount of absorption
depends on the viscosity of the tissue through which the sound travels. In general,
the more rigid the tissue, the greater the absorption.
Attenuation. The intensity a sound beam constantly decreases as it travels through
tissue. This decrease in intensity is called attenuation. It is due to three factors: (a)
divergence of the sound beam, (b )absrption of sound energy by the tissue, and (c)
reflection of sound out of the beam.
4.Resolution and penetrability
Resolution is the ability ultrasound can distinct and show two different interfaces
which intervals the least. There are two kinds of resolution: longitudinal and
transverse resolution. The higher the frequency, the better the resolution, but the less
the penetrability.
5. Doppler effect
Dr any sound beam, whenever there is relative motion between the source and the
listener, the frequency heard by the listener will differ from that produced by the
source. The perceived frequency will be either greater or less than that transmitted by
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the source depending on whether the source and the listener are moving toward or
away from one another. Such a shift in the perceived frece ency relative to the
transmitted frequency is called a Doppler shift. A Doppler frequency shift can occur
for a moving source and ctatinary listener., a moving listener and stationary source, or
a moving source and listener. The ultrasound Doppler effect is employed in detection
of the heart and its movement of the valves, fetal heart sound, fetal movement and
blood flow.
Ⅳ.The principles of ultrasonic diagnosis
1.Measurement of the echo distance
2.Identification of property of the tissue, organ and lesions.
Solid organ: homogeneous or non-honogeneous
Liquid organ: sonolucent, liquid dark area
Hollow organ with gas: full reflection
Acoustic shadow
Constrast echogram
3.Absorption by the tissue and attenuation
4.Dynamic and functional examination of the organs
Section Ⅱ. Mode and properties of ultrasonic Diagnosis
A-mode:echogram
It is mostly used to measure the distance, e.g. the brain midline.
B-mode: sonogram or echotomogram
Bright spot imaging,
Static B-mode imaging,
Real time B-mode imaging,
Gray scale display,
Across sectional echocardiography or two dimentional echocardiography
M-mode: echocardiogram
Time-space curve
It is uses to observe time change of the movable interface.
D-mode: Doppler effect
Section Ⅲ. Clinical Application of Ultrasonic Examination
Ⅰ. Brain Midline echo
Ⅱ. Obstetrics and gynecology
1.Uterus. Normal and myoma.
2.Pregnancy.
3.Hydatideform mole.
Ⅲ. Abdominal mass
1. Properties
Table 5. Mass lesions: +sonograghic characterization
Cystic
Complex
Sclid
Features
Internal echoes
No
Yes
Yes
Wall sharpness
Yes
Yes
Yes
Beam attenuation
No
No
Yes
Typical causes
Symple
Infected
Solid
cyst
cyst
tumor
Abscess
tumor
2.Site (Location)
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3.Benigh or malignant
Ⅳ.Hydrops in the body cavity
1.Hodrothorax
2.Ascites
3.Hydropericardium
Ⅴ. Liver and spleen
1.Normal liver and spleen
2.Measurement of liver and spleen and normal values.
Liver: left libe, the up-down length is 4-8cm;
The oblique thickness of right lobe is less than 14.6cm.
Spleen: the thickness at the hilus of spleen is 1.7-3.6cm.
Portal vein: diameter of main PV is less than 1.6cm.
3.Liver cancer
A. High reflecting type, local giant bright lump, non-homogeneous distribution,
“bull’s eye sign”
B. Lower reflecting type
C. Mixed reflecting type
D. Enlargement of liver with irregular contour; other signs: necrosis and
liquefaction, cancer embolus
4.Liver abscess
5.Liver cirrhosis
Surface of liver uneven, intrahepatic echoes increase, non-homogeneous
distribution, dilated portal and splenic veins
Ⅵ.Gallbladder
1.sonolucent Iblong structure
A-P diameter is 2-4cm
Long diameter is 4-9cm
Thickness of GB wall is less than 3.5cm
2.abnormal gallbladder
acute cholecystitis
chronic chloecystitis
gall stone: (a) stone reflection
(b) shift with position changes
(c) acoustic shadow
gallbladder tumor
3.Billiary system and its diseases
Common bile duct, left and right hepatic ducts, intrahepatic bile ducts, stone in the
CBD
4.Differentiation of obtructice jaundice intrahepatic bile stasis,
Obstruction of extrahepatic bile duct
Ⅶ. Limitation
1.Ultrasound is a non-specific method. On many conditions, it cannot give an
etiologic diagnosis.
2.Ultrasound beam cannot penetrate gas and bome. When the sound beam
transverses tissue interface of widely different acoustic impedance most of the
beam is reflected back and racorede as useless noise. At a bone-tissue boundary a
70% reflected occurs a gas-tissue interface reflects 99% of the beam. Thus,
sonography through aerated lungs or the bony pelvis are not feasible to detected,
and it has been estimated up 25% of abdominal examinations are unsatisfactory
because of intestinal gas.
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3.It is difficult to the early diagnosis, if the lesion is less than 1-2cm or the
impedance difference is too small.
4.It is interfered by many factors, for instance, the type and property of the
machine, the experience and skill of examiner, the condition of the patient. In
addition, there may be some false positive or negative results.
Echocardiography
The term echocardiography refers to a group of tests that utilize ultrasound to
examine the heart and record information in the form of echoes. It is composed of
M-mode
echocardiography,
two-dimensional
echocardiography,
Doppler
echocardiography, Doppler color flow mapping, contrast echocardiography etc.
Echocardiography can be used in the following respects: (1) to diagnose the
valvular heart diseases. (2) to diagnose cardiac masses, vegetations, thrombosis and
pericardial effusion. (3) to detect constrictive pericarditis, dilated and hypertrophic
cardiomyopathy and coronary heart disease. (4) a useful method to differentiate most
congenital heart diseases, such as atrial septal defect, ventricular septal defect, patent
ductus arteriosus, tetralogy of Fallot, etc. (5) to follow up the functional status of
prosthetic valves. (6) to measure the dimensions of cardiac chamber and detect
ventricular performance. (7) to explain and differentiate the origin of abnormal heart
sound and cardiac murmurs.
Examination Of The Normal Heart
M-Mode Echocardiography
An M-mode recording is sometimes called a one-dimensional or an “ice pick”
view of the heart. However, since time is the second dimension on M-mode tracings,
this display is not truly one-dimensional. The M-mode presentation permits recording
of amplitude and of the rate of motion of moving objects with great accuracy. The
sampling rate is essentially 1000 pulses/sec. With the transducer placed along the left
sternal border in approximately the third or fourth intercostal space, the ultrasonic
beam can be swept in a sector between the apex and the base of the heart:
1.When the transducer is pointed toward the apex of the heart, the ultrasonic beam
traverses the left ventricular cavity at the level of the papillary muscles and passes
through a small portion of the right ventricular cavity (position 1).
2.Tilting the transducer superiorly and medially causes the ultrasonic beam to
traverse the left ventricular cavity at the level of the chordae tendae(position 2a) or at
the edges of the mitral valve leaflets (position 2b). The beam again passes through a
small portion of the right ventricle. In this position the distance between the left side
of the interventricular septum and the posterior left ventricular endocardium is largest,
so the diastolic and systolic dimensions of the left ventricle can be measured in this
position. Septal and posterior wall thickness can also be measured.
3.By directing the transducer more superiorly and medially, more of the anterior
leaflet of the mitral valve can be recorded and the beam may traverse part of the left
atrial cavity (position 3).
The curve of the anterior mitral valve leaflet can be traced in position 2b and
position 3. At the onset of left ventricular diastole, the anterior mitral valve leaflet
moves abruptly forward (toward the transducer) as the valve opens. The E point is the
maximum opening of the very early diastole—rapid filling stage. At the end of this
stage, the anterior mitral leaflet moves rapidly backward to a semiclosed position to
form the descending part of the E wave. The later diastolic phase is related to atrial
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systole, which produces a rapid forward motion of the anterior leaflet as the valve is
reopened at the A point. Following atrial systole, the mitral valve begins to close
before ventricular systole. The point of complete mitral valve closure is the C point.
The D point is the end systolic point. It is common to see segment CD gradually move
forward during the whole systolic stage. The characteristic M-shaped configuration of
the anterior mitral leaflet is made by the large E point and the relatively smaller A
point. The echogram of the posterior mitral leaflet is the approximate mirror image of
anterior leaflet and has a W-shaped configuration.
4.Further tilting of the transducer superiorly and medially directs the beam through
the root of the aorta, the leaflets of the aortic valve, and the body of the left
atrium(position 4). The curve of the aortic root can be traced in this position: The
anterior and posterior aortic walls are seen moving synchronously with each heart
beat in two parallel echoes. Both wall of the aorta move forward during systole and
backward during diastole. The aortic valve leaflets are recognized by a thin echogram
midway between the two parallel aortic walls during diastole and by their abrupt
opening motion at the onset of ventricular ejection. Normally, the two commonly
visualized cusps (right coronary cusp and non-coronary cusp) open to the periphery in
systole, producing a boxlike pattern with opening and closing of the valve leaflets
during each cardiac cycle. Left atrial measurements are also commonly made in this
position.
Two-Dimensional Echocardiography
The ultrasonic beam now moves in a sector so that a pie-shaped slice of the heart is
interrogated. Most commercial 2-D echocardiographs move the ultrasonic beam so
that approximately 30 slices/sec are obtained. The ultrasonic beam can be moved
mechanically by oscillating a single transducer or by rotating a series of transducers.
The ultrasound can also be steered electronically using the so-called phased array
principles. An infinite number of slices of the heart can theoretically be obtained using
2-D echocardiography. Three standard planes are the long-axis, short-axis, and
four-chamber views.
1.The long-axis plane is the imaging plane that transects the heart perpendicular to
the dorsal and ventral surfaces of the body and parallel to the long axis of the heart.
The parasternal long axis view can be obtained with the transducer in the third or
fourth intercostal space adjacent to the left sternal border. The leaflets of mitral valve
can be seen to open in their full excursion during diastole. The left atrium is posterior
to the posterior wall of the aorta. The cusps of the aortic valve can be seen to co apt in
a single line during diastole. The right ventricular outflow tract is anterior to the aorta.
The left ventricular cavity is seen in its long axis. The interventricular septum and
right ventricle are located anteriorly, and the left ventricular posterior wall and
posterior papillary muscle are located posteriorly. The apex of the left ventricle is
identified as the round tip at the left of the image, but it may not be easily visualized
in this view. This picture is the most fundamental view in 2D echocardiographic
examination.
2.The plane transecting the heart perpendicular to the dorsal and ventral surfaces of
the body, but perpendicular to the long axis of the heart, is defined as the short-axis
plane. Such an examination can be obtained with the transducer in the parasternal
position or in the subcostal (subxiphoid) position. Various short-axis examinations are
commonly obtained at the level of the apex, the papillary muscles, the mitral valve,
and the base of the heart. Short-axis views cut across the heart so that the left ventricle
resembles a circle. The right ventricle can be seen curving around the left ventricle.
The short-axis view at the base of the heart can examine aortic valve, the pulmonary
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valve, the atrial and the pulmonary artery with its bifurcation. It is also possible to
record the origins of the coronary arteries and the left atrial appendage.
3.The plane that transects the heart approximately parallel to the dorsal and ventral
surfaces of the body is referred to as the four-chamber plan. Such a view permits the
examination of all four cardiac chambers simultaneously. This type of examination
can be obtained with the transducer over the cardiac apex or with the transducer in the
subcostal position.
Doppler Echocardiography
M-mode and 2-D echocardiography essentially create ultrasonic images of the heart.
Doppler echocardiography utilizes ultrasound to record blood flow within the
cardiovascular system. Doppler technique can also provide useful information
concerning intracardiac pressure and pressure gradients across the stenotic orifice.
The principle of the Doppler effect is represented by Doppler equations that relate
Doppler frequency (fd) and the velocity of the moving target (v):
fd = 2f·v·cosθ/c
fd is the Doppler shift or Doppler frequency represents the difference between the
reflected and transmitted frequencies. If the ultrasonic beam is reflected by a
stationary object, the fd equals to zero. However, if the target reflecting the ultrasonic
energy is moving toward the transducer, the reflected frequency is greater than the
transmitted frequency, fd is positive. When the target is moving away from the
transducer, the reflected frequency is less than the transmitted frequency, fd is
negative. f is the transmitted frequency; θ is the angle between the paths of the
ultrasonic beam and moving target; c is the velocity of sound in the medium being
examined; in Doppler echocardiography the targets are the red blood cells. By this
equation, one can calculate the velocity(v) of the moving target.
There are two kinds of Doppler waves: the continuous-wave Doppler and the
pulsed Doppler. Significant differences exist between continuous wave and pulsed
Doppler. The velocity that can be recorded using pulsed Doppler is limited. Thus, if
the blood is moving very rapidly, as might occur when it is passing through a stenotic
valve, continuous-wave Doppler is necessary for recording very high velocities.
Although the pulsed Doppler can not be used to quantitate the high velocity, it is
useful to locate the sampling volume where the stenosis occurs.
The Doppler recording is a spectral display using fast Fourier analysis of the
audible Doppler signal. The recording is usually on strip chart paper or videotape and
is commonly referred to as spectral Doppler. There are two kinds of flow pattern: The
laminar flow is supposed to be normal blood flow, it has a totally different quality in
spectrum than that which originates from stenotic orifice, named disturbed or
turbulent flow.
Normal spectral Doppler recordings are basically of three types. There is the
venous, ventricular inflow and ventricular outflow pattern of Doppler flow. Venous
flow has both systolic and diastolic components. There will be some slight variation
whether the recording is from systemic or pulmonary veins. Ventricular inflow is
totally diastolic. There is an early component that peaks at the E wave and a late
component following atrial contraction that peaks with an A wave. Ventricular
outflow is entirely systolic in nature. The systolic flow moving away from the
transducer during systole. Doppler flow patterns on the right side of the heart are
essentially the same except the velocities are lower. The peak mitral velocity is about
100 cm/sec, and the aortic velocity is about 120 cm/sec.
Color Doppler
Doppler information from the cardiovascular system can also be
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recorded in a spatially correct format superimposed on an M-mode or 2-D
echocardiogram. The direction of the blood is displayed in color. With this particular
instrument blood moving toward the transducer is depicted in shades of yellow and
red, whereas blood moving away from the transducer is in shades of blue. Turbulent
flow can be displayed as green or as a mosaic of colors.
Abnormal Echocardiogram
Mitral Stenosis
The detection of mitral stenosis (MS) was the first clinical application of
echocardiography. It remains an important technique in the evaluation of suspected
mitral valve disease because echocardiography can allow visualization of the mitral
valve in a manner not possible with any other procedure. The M-mode examination
provides a sensitive assessment of the motion and thickness of the valve leaflets,
while the 2-D technique provides a spatial image of the valve and allows direct
measurement of the valve orifice. Doppler echocardiography provides hemodynamic
assessment of the stenotic orifice.
M-mode echocardiogram of a patient with calcific MS shows the motion of the
mitral valve is considerably altered from the normal pattern. The normal M-shaped
configuration during diastole is no longer present, since the presence of a
holodiastolic atrioventricular pressure gradient (diastasis) prevents rapid closure of the
valve in mid-diastole. Although sinus rhythm was present, there was no reopening of
the valve with atrial contraction and no A wave. Thus, the M-mode echocardiographic
hallmark of MS is the absence of valve closure in mid-diastole and of reopening in
late diastole.
In addition to the change in motion of the valve, the number of echoes originating
from the valve is increased when it is fibrotic or calcified, and another
echocardiographic sign of MS is increased thickness of the valve leaflets. Inadequate
separation of the anterior and posterior leaflets of the valve occurs during diastole.
Normally the two leaflets move in opposite directions during diastole, but when fused,
as in MS, they do not separate widely and may actually appear to move in the same
direction. The M-mode findings of reduced diastolic slope, increased thickness, and
decreased separation of the valve leaflets provide a sensitive and accurate method for
detection of MS---Great Wall-like picture.
The diagnosis of MS by 2-D echocardiography is made by noting thickening,
doming, and restricted motion of the leaflets. In long-axis view, doming of any valve
on 2-D echocardiography is a characteristic sign of stenosis. This distortion in shape
indicates that the tips of the leaflets are restricted in their ability to open, whereas the
bodies of the leaflets still wish to accommodate more blood flow; thus the leaflets are
curved, or domed. The presence of doming distinguishes a valve that is truly stenotic
from one that opens poorly because of low flow. Two-dimensional echocardiography
in short-axis view provides an opportunity to measure the flow-restricting orifice of
the stenotic mitral valve directly, which assumes the shape of a funnel.
Two-dimensional echocardiography is also the procedure of choice for assessing
the fibrosis, the degree of calcification and pliability of the mitral valve apparatus,
especially when subvalvular adhesions are present.
Doppler echocardiography provides another means of quantitating the degree of
MS. Pulsed Doppler recording of a patient with MS and atrial fibrillation
demonstrates there is no A wave. The peak velocities are increased, and the fall in
velocity in early diastole is decreased. The technique for quantitating the degree of
MS depends on the rate of velocity decrease in early diastole. The time interval
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required for the peak velocity to reach half of its initial level is related directly to the
severity of the obstruction of the mitral orifice. This pressure half-time correlates
reasonably well with the mitral valve area.
Secondary effects of mitral stenosis, such as left atrial, right ventricular dilatation
and pulmonary hypertension, can be detected with various echocardiographic
examinations.
Mitral Valve Prolapse With Mitral Regurgitation
Echocardiography is particularly useful in the diagnosis of this condition. The
principal M-mode finding is a fairly abrupt posterior (downward) motion of the mitral
valve apparatus in mid or late systole. This motion often commences simultaneously
with the mid or late systolic click, a typical auscultatory and phonocardiographic
finding in this condition.
Several findings on 2-D echocardiography have been suggested for the diagnosis of
mitral valve prolapse, including the recording of buckling or herniating of one or both
mitral leaflets into the left atrium during systole.
Other echocardiographic findings in patients with mitral valve prolapse include
excessive amplitude of motion of the valve during diastole that can be appreciated in
both M-mode and 2-D examinations. Thickening of the leaflets is common and is
presumably due to myxomatous degeneration. The leaflets may also be redundant and
seem to fold on themselves in diastole.
Doppler echocardiography is the specific procedure of choice for detection of
mitral regurgitation in mitral prolapse patient. Pulsed Doppler echocardiography can
detect mitral regurgitation spectrum in systole that is high velocity and marked
broadening. Color flow Doppler can detect the regurgitant blood flows into the left
atrium during ventricular systole. The velocity is very high, and a mosaic
multicolored pattern is recorded because of aliasing.
Echocardiography is also helpful in assessing the hemodynamic consequences of
the MR. The left atrium is invariably dilated, and left ventricular stroke volume
increases with frequent left ventricular dilatation.
Aortic Stenosis
M-mode and 2-D echocardiography have always provided an excellent qualitative
diagnosis of AS. Doppler echocardiography now provides an opportunity for the
quantitative diagnosis. The M-mode echocardiographic diagnosis of a stenotic aortic
valve include thickening of the valve leaflets as demonstrated by multiple echoes
coming from the leaflets. If one measured the distance between the leaflets, it would
be below normal, which is approximately 1.5 to 2.5cm in adults. The 2-D
echocardiographic diagnosis of valvular aortic stenosis is doming, thickening, and
restricted motion of the leaflets. The valve may be heavily calcified and immobile.
The best ultrasonic technique for quantifying AS utilizes continuous-wave Doppler.
Using the modified Bernoulli equation, it is possible to measure the pressure gradient
across the aortic valve. The higher the pressure gradient, the more severe the stenosis.
There are secondary signs of AS that can be noted on the echocardiogram. Both
M-mode and 2-D echocardiography can detect left ventricular hypertrophy with
increased thickness of the left ventricular walls.
Left Aatrial Myxoma
Left atrial myxoma is by far the most common cardiac tumor, and
echocardiography has proved to be an extremely important diagnostic technique for
its recognition. M-mode echocardiography was the first technique utilized to detect
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left atrial myxomas. One sees a cloud of tumor echoes behind the anterior leaflet of
the mitral valve, the echo-producing mass almost completely fills the mitral valve
throughout diastole. Directing the ultrasonic beam into the left atrium, one can follow
the echo-producing mass into the left atrium and see how it practically fills the entire
left atrial cavity. The spatial 2D examination provides additional useful information,
and the size and shape of the mass are apparent. In addition, the site of attachment of
the mass to the cardiac structure can frequently be detected.
Pericardial Effusion
Since the acoustic properties of fluid differ significantly from those of cardiac
muscle, the effusion surrounding the heart is less echogenic than is the myocardium.
Accordingly, the detection of effusion was one of the first and has remained one of the
most useful applications of echocardiography.
The size of the effusion is estimated by the amount of echo-free space surrounding
the heart. Frequently with small effusions one sees only a posterior echo-free space
and very little fluid anteriorly. As the fluid increases it distributes both anteriorly and
posteriorly. With large effusions, one usually sees more anterior fluid than posterior
fluid as the heart tends to sink posteriorly.
There are several echocardiographic signs for cardiac tamponade. One of the most
frequent findings is collapse of the anterior right ventricular free wall. Right atrial
collapse is slightly more sensitive but less specific than right ventricular collapse.
With very large effusions one can detect excessive motion of the heart within the
pericardial sac. This excessive motion has been noted as a “swinging heart.” If the
motion is such that the heart does not resume its original position before the next
electric depolarization occurs, then the axis of the QRS is altered and one notes
electrical alternans on the electrocardiogram.
CARDIOMYOPATHIES
Hypertrophic Cardiomyopathy(HCM)
Echocardiography is an important diagnostic tool in patients with HCM. An early
echocardiographic abnormality to be noted was systolic anterior motion of the mitral
valve (termed SAM), which appeared to be related to and was correlated with the
presence of obstruction to left ventricular outflow. The shorter the distance between
the septum and the leaflet and the longer the duration of apposition between these two
structures, the more severe the obstruction.
A second echocardiographic finding in patients with obstructive HCM is
midsystolic closure of the aortic valve. However, as noted earlier, this sign is not
specific for HCM and is also present in patients with discrete subaortic stenosis.
The basic abnormalities of HCM, and a key echocardiographic finding is
disproportionate hypertrophy of the septum in relation to the posterior wall of the left
ventricle, so that the ratio of thickness of the septum to the free wall exceeds 1.3:1.0
and the motion of the hypertrophied septum is reduced. There are patients with
asymmetrical septal hypertrophy who do not show SAM and therefore do not have
obstruction to left ventricular outflow. These patients may be considered to have
HCM without obstruction.
Two-dimensional echocardiography provides additional information by indicating
the shape and location of the hypertrophied myocardium in patients with known or
suspected HCM. Some patients have hypertrophied septum limited to the basal
two-thirds of the septum, while the apex is virtually free of muscular hypertrophy.
Other patients exhibit an apical form of hypertrophy with the proximal septum being
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relatively thin. Concentric hypertrophy is also a fairly common form of hypertrophic
myopathy. Cavity obliteration with ventricular systole is almost always present with
this type of disease. An intriguing observation is that the echoes from the diseased
septum in HCM are more reflective or “speckled”than those from the free posterior
wall.
Doppler echocardiography may also be helpful in evaluating hypertrophic
cardiomyopathy. The Doppler recording of the left ventricular outflow may show an
abnormal pattern with the abnormally high velocity occurring in late systole. The
systolic gradient can be estimated using the Doppler technique. The left ventricular
hypertrophy and reduced left ventricular compliance alter the Doppler recording of
mitral valve flow. The early diastolic velocity or E point is reduced, and the late
velocity with atrial systole is increased. Color Doppler provides spatial visualization
of the altered blood flow in patients with obstructive HCM.
Congestive (Dilated) Cardiomyopathy
The echocardiogram characteristically reveals a dilated poorly contracting left
ventricle in patients with congestive cardiomyopathy. Signs of reduced cardiac output
include a poorly moving aorta, slow closure of the aortic valve, and reduced opening
of the mitral valve. In M-mode tracing, the size of the opening of the mitral valve is so
small compared to dilated left ventricle that it is like the shape of a “diamond”. The
left atrium is dilated, and the abnormal closure of the mitral valve indicative of
elevated left diastolic pressure is frequently noted. Incomplete closure of the mitral
valve or papillary muscle dysfunction and subsequent mitral regurgitation are
common. Left ventricular filling on Doppler echograms changes as the disease
progresses.
CONGENITAL HEART DISEASE
Atrial Septal Defect
Echocardiography is an accurate means of detecting atrial septal defects of all types.
Atrial septal defects are classified according to the involved region of the atrial
septum. The most common type is the secundum defect, comprises approximately
70% of atrial septal defects. Abort 15% of atrial septal defects are of the ostium
primum type, and 15% are of the sinus venosus type.
The M-mode echocardiographic abnormality associated with an atrial septal defect
is that of a right ventricular volume overload. The two components of this
echocardiographic finding are a dilated right ventricle and abnormal septal motion.
The 2-D echocardiographic examination, especially from the subcostal position,
provides an opportunity for direct examination of the interarterial septum. In a patient
with an ostium secundum atrial septal defect, a remnant of the interatrial septum can
be seen attached to the ventricular septum. In contrast, in a patient with an ostium
primum defect, there is no residual septum attached to the ventricular septum. Thus,
the 2-D technique not only helps to identify the presence of an atrial septal defect, but
it is also an excellent means of differentiating a secundum from a primum type of
abnormality.
Color flow Doppler can be used to demonstrate atrial septal defects. One can see
the red-encoded blood passing from the left atrium to the right atrium through the
defect. Pulsed Doppler can detect diastolic turbulent flow with upward spectrum.
Tetralogy of Fallot
The Tetralogy of Fallot consists of a combination of a perimembranous ventricular
septal defect, overriding of the aorta over the ventricular septal defect, pulmonic
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stenosis and right ventricular hypertrophy/dilation. The M-mode detects the
discontinuity of the anterior aortic root and ventricular septum. The narrowed right
ventricular outflow tract can also be detected with M-mode echocardiography.
Because of right ventricular overload, the septal motion was abnormal.
Two-dimensional echocardiography allows direct visualization of the intracardiac
anatomy and documentation of the presence of a perimembranous ventricular septal
defect and degree of aortic overriding. Additionally the degree of narrowing of the
right ventricular outflow tract can be determined accurately. Doppler
echocardiography can detect turbulent flows at the sites of the ventricular septal
defect and pulmonic stenosis.
Infective Endocarditis
Echocardiography provides a means for visualizing the vegetations of infective
valvular endocarditis, which appear as echo-producing masses attached to the infected
valve. They are usually asymmetrical, commonly involving one leaflet more than
another, but may be present on more than one valve. If the vegetation is associated
with destruction of the valve or if it is on a long “stalk,”it can be readily imaged; its
excessive motion can be appreciated on both M-mode and 2-D echocardiography.
Transesophageal echocardiography is proving to be much more sensitive than
transthoracic echocardiography in detecting valvular vegetations.
One of the major applications of echocardiography in patients with endocarditis is
in the identification of complications. When the valve is damaged to the point that it is
grossly incompetent, echocardiography can both detect and assess the hemodynamic
importance of the valvular regurgitation.
Special Echocardiography
Transesophageal Echocardiography
Transesophageal echocardiography has been available for many years. With the
technical advances in placing a 2-D transducer at the end of a flexible endoscope, it is
now possible to obtain high-quality 2-D images via the esophagus in multiple planes
Transesophageal echocardiography is useful in patients in whom the examination
from the usual transthoracic approach is technically difficult or impossible. This
approach is particularly helpful in assessing prosthetic valves, vegetations, aortic
disease, and intracardiac masses. Another major application for esophageal
echocardiography is in the patient undergoing surgery. The esophageal ultrasonic
probe can be used to monitor cardiac left ventricular function throughout the surgical
procedure and into the postoperative state. Transesophageal echocardiography is
being used in the operating room during open-heart surgery and to monitor
myocardial ischemia during noncardiac surgery. Cardiac surgeons are finding
echocardiography helpful in assessing cardiac morphology and function before,
during, and after surgical repair of valvular or congenital conditions.
Intravascular Ultrasound
The ultrasonic transducer can be placed in a small catheter so that a vessel can be
imaged via the lumen to provide an intravascular echocardiogram, a technique known
as intravascular ultrasound. Several intravascular ultrasonic devices are currently
being used. The techniques utilize a rotating transducer, rotating ultrasonic mirror, or
phased array multielement systems. These devices are generating considerable interest,
especially for the ability to evaluate atherosclerosis from within the arteries. Slightly
larger intravascular ultrasonic devices are being used to visualize the heart from
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within the cardiac chambers.
Contrast Echocardiography
Ultrasound is an extremely sensitive detector of intravascular bubbles. The
injection of almost any liquid into the intravascular spaces will introduce many
microbubbles that appear as a cloud of echoes on the echocardiogram. Contrast
echocardiography is a very sensitive technique for detecting right-to-left shunts. The
contrast agents that have been used include the patient’s blood, saline, indocyanine
green dye, agitated or sonicated angiographic contrast agents, and sonicated albumen.
In all cases the contrast effect originates from suspended microbubbles in the fluid.
Commercially manufactured microbubbles that traverse the pulmonary capillaries are
now available. The potential clinical uses for contrast echocardiography are
numerous.
Three-dimensional Echocardiography
A variety of approaches to recording echocardiograms that are oriented in
three-dimensional (3-D) space have been proposed. One technique orients a 2-D
transducer in 3-D space using spark gap sensors. Most investigators are creating 3-D
images of the heart using gated, reconstructed 2-D examinations.
Stress Echocardiography
Although echocardiography has been used primarily for evaluating the cardiac
chambers at rest, there is increasing interest in performing the ultrasonic
examination during or immediately after some form of stress. These studies
have utilized supineor upright bicycle exercise, immediate post-treadmill
exercise, pharmacological stress, and atrial pacing. This type of examination is
being done primarily for detecting exercise-induced regional wall motion
abnormalities in patients with coronary artery disease. Exercise studies using
Doppler measurements during exercise have also been used to assess global
changes in left ventricular function and hemodynamics in patients with valvular
heart disease or congenital heart disease.
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