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Echocardiography
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ECHOCARDIOGRAPHY (CARDIAC ULTRASOUND)
Echocardiography is a technique used to evaluate the heart's activity with ultrasounds.
PHYSICAL PRINCIPLE
Ultrasounds represent mechanical vibrations of an elastic medium with a frequency above
20000 Hz. These waves can be represented graphically as sinusoidal waveforms
characterized by: amplitude, length of wave and frequency.
Figure no. 98. Sinusoidal waveform (where: T - time (period) =1/F, A amplitude, λ – length of the wave).
In a homogeneous and elastic medium, ultrasounds propagate as a wave-front. When this
front will meet a surface of separations between two mediums with different density, it will
suffer two important physical processes: reflection (the wave will returns in the first medium)
and refraction (the wave will pass in the second medium). Both physical processes are
important in echography because the reflected wave will be transformed in image on the
screen and the refracted wave will pass into the depth of the tissues and will offer us
information about deeper structures.
Figure no. 99. Physical principles of wave propagation.
THE ECHOCARDIOGRAPH
This device has three main components: transducer (probe), amplification system and
recording system (or visualization system).
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1. The transducer (probe) – is one of the most important parts of the device as this is the
place were are ultrasounds are formed (produced) and recorded. This is possible due to the
piezoelectric effect.
The piezoelectric effect the piezoelectric effect is closely related to the
occurrence of electric dipole moments in solids. As a result of the application
of mechanical pressure an electric field will appear in certain non-conducting
crystals. Pressure polarizes some crystals, such as quartz, by slightly
separating the centers of positive and negative charge. The resultant electric
field is detectable as a voltage. The converse effect also occurs: an applied
electric field produces mechanical deformation in the crystal. Using this effect,
a high-frequency alternating electric current can be converted to an ultrasonic
wave of the same frequency, while a mechanical vibration, such as sound,
can be converted into a corresponding electrical signal.
Figure no. 100. The piezoelectric effect.
In cardiology transducers with a specific frequency are used:2.5- 3.5 MHz.
In time, many types of transducers were developed:
► monocrystal probe – is used today only in one-dimensional echocardiography
► mechanical probe – there is only one crystal that is moved along of an arc of circle
with 60-90 degrees or there are 4 crystals in an rotating system which will send
waves only when they arrive in a specific place (slit) placed on the surface of the
transducer
► linear probe – it is formed by 15-30 crystals placed in linear fashion and activated
together, the final image being the resultant of the component images
► electronic probe – there are many linear crystals but with a compound activation
(phased array)
60-90o
A
B
C
D
Figure no. 101. Schematic presentation of different types of
ehocardiographic probes: A - monocrystal probe, B - mechanical probe with
one crystal, C - mechanical probe with 4 crystals, D - linear probe.
Echocardiography
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2. Display (recording or visualization system) – the final image is presented on a screen
with high resolution .There are 3 modalities to present the ecographical image on the screen:
►A mode (A = amplitude): the resultant image is formed by vertical deflections
(spikes) according to the intensity of the echo
► B mode (B = brightness): the image is composed of points with different luminosity
in correlation with the intensity of the echo. The image is presented in shades of white
- grey – black. This modality can present the heart bi-dimensionally or tridimensionally. If the frequency of the frame on the screen will be over 15
frames/second we can observe the heart "in real-time".
► M mode (M = motion): the signal is obtained according to time. We have two
different coordinates: amplitude (vertical) and time (horizontal).
Figure no. 102. Normal anatomy of the heart (in the left), as perceived in Bmode (middle) and M-mode (right).
EXAMINATION METHOD
In order to avoid the bone (which reflects the signal) and the air from lungs (which can
disperse the beam of waves too much) we use specific positioning of the transducer on the
thorax. These positions on the thoracic surface are called echographic windows. Between
the probe and the skin we use echographic gel.
Standard sections used in echocardiography are (see also Figure no. 103 and Figure no.
104):
► longitudinal view: the probe is placed in the 2nd intercostal space, near the
sternum (parasternal position)
► four chambers view: the probe is placed in the 5th intercostal space, on the
medium clavicle line (apical position)
► short axis view: the probe is placed just below the sternum
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Figure no. 103. Main echographic windows (parasternal, apical, below the
sternum and suprasternal).
Figure no. 104. Main views used in transthoracic echocardiography.
ECHOGRAPHY OF THE MITRAL VALVE
The mitral valve (also known as the bicuspid valve or left atrioventricular valve) is a dual-flap
valve in the heart that lies between the left atrium and the left ventricle. The mitral valve is
connected through chordae tendineae to the papillary muscles.
The examination is made with the probe placed in the parasternal position, 1-2 cm from the
left border of the sternum (mitral section).
The aspect in M mode is presented in Figure no. 105.
► during diastole – the mitral valve presents movements "in mirror": the anterior cusp
realizes the aspect of "M" whereas the posterior cusp creates a "W"
► during systole – both cusps are represented as a single echo (line) because they
are cleaved
Quantitative echocardiography allows calculating parameters of the mitral valve (see Figure
no. 106 and Table no. 6).
Echocardiography
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PAVD
ECG
SIV
E A
D
F
VMA
C
VMP
PPVS
Figure no. 105. Schematic representation of M-ECO of the mitral valve.
PAVD = anterior wall of the right ventricle, SIV = interventricular septum,
VMA = anterior cusp of the mitral valve, VMP = posterior cusp of the mitral
valve, PPVS = posterior wall of the left ventricle, D = the opening of the
mitral valve, E = maximal opening of the anterior cusp, F = protodiastolic
closing of the anterior cusp, A = atrial systole, C = closing of the mitral valve.
Table no. 6. Echocardiographic parameters of the mitral valve.
Parameter
Notation
Maximum amplitude of D-E ( mm)
leaflets opening
Value
20 - 30 mm
E-F slope
(protodiastolic closing)
A-C slope
( systolic closing)
E-F ( mm/s)
50 - 150 mm
A-C ( mm/sec )
140-370 mm
A-C (echo) - P-R (ECG)
interval
(A-C) - (P-R) <0.06 sec.
(sec)
Significance
Related to the mobility of
the valve and the output
through the valve.
Decreases
in
mitral
stenosis
Related to the enddiastolic pressure from
left ventricle.
Related to the enddiastolic pressure from
left ventricle.
Figure no. 106. Method to calculate echocardiographic parameters of the
anterior cusp of the mitral valve (VMA). The opening of the VMA is the
distance measured between D and E. The speed of protodiastolic closing is
the tangent of the angle created by EF segment with the horizontal line.
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ECHOGRAPHY OF THE AORTIC VALVE
The aortic valve has three cusps: the left coronary cusp and the right coronary cusp are
placed in an anterior plane whereas the non-coronary cusp is situated in a posterior plane.
The examination is performed using a transducer placed in parasternal position, with a
posterior-medial orientation towards the right clavicle of the patient.
VD
Ao-perete ant.
VAo
Ao-perete post.
AS
Figure no. 107. Schematic representation of M-ECO of the aortic valve. VD =
right ventricle, Ao = aorta, VAo = aortic valve, AS = left atrium.
The aorta (see also Figure no. 108) is easily recognized as two parallel signals (anterior and
posterior wall) with a sinusoidal movement (anterior during systole and posterior in diastole).
Between the aortic walls we can observe the aortic valve (during systole two different parallel
lines and a single signal during diastole).
Ao
DAo
EIA
Figure no. 108. Calculation of echocardiographic parameters of the aorta
and the aortic valve. Ao = diameter of the aorta, DAo = opening of the aortic
valve, EIA = systolic movement of the aortic root.
Also we can use quantitative echography to calculate specific parameters (see Table no. 7).
Table no. 7. Echocardiographic parameters of the aortic valve.
Parameter
Systolic opening of
the aortic valve
Diameter of the aortic
root
The systolic motion of
aortic root
Diameter of the left
atrium
Ratio of LA and DAo
Notation
DAo (mm)
Value
17 - 25 mm
Significance
Decreases in aortic stenosis.
Ao (mm)
20 - 37 mm
EIA or
Ao during S
LA (mm)
5 - 15 mm
Increases with age and in
aortic aneurism.
Related with systolic volume.
LA/DAo
0.07 - 1.1
23 - 44 mm
Related with the end-diastolic
pressure of the left ventricle.
Increased
in
valvular
diseases.
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ECHOGRAPHY OF THE LEFT VENTRICLE
For the examination the probe has to placed in the parasternal standard position, with an
inferior and lateral orientation. The aspect of the left ventricle in M mode is presented in
Figure no. 109. Left ventricle appears as a free space between interventricular septum
(anterior) and the posterior wall of the left ventricle (PWLV). The anterior and posterior walls
move closer to each other in systole and aloof in diastole.
VD
SIV
DTDVS
VS
DTSVS
PPVS
Figure no. 109. Schematic representation of M-ECO of the medioventricular
section. VD = right ventricle, SIV = interventricular septum, VS = left
ventricle, PPVS = posterior wall of the left ventricle. The method to calculate
quantitative parameters of the left ventricle is also shown: DTDVS = enddiastolic diameter of the left ventricle, DTSVS = end-systolic diameter of the
left ventricle. The thickness of the wall is always measured during diastole.
Table no. 8. Echocardiographic parameters of the left ventricle.
Parameter
Thickness
of
the
interventricular septum
Thickness of the posterior
wall of the left
End-diastolic diameter of
the left ventricle (EDD)
End-systolic diameter of
the left ventricle (ESD)
Value
6 - 11 mm
Significance
Increases in ventricular hypertrophy.
6 - 11 mm
Increases in ventricular hypertrophy.
24 - 40 mm
Increases in ventricular dilatation.
35 - 57 mm
Analyses ventricular performance.
Quantitative echocardiography permits us to calculate diameters of the ventricle and the
ventricular wall thickness. Using geometric models we can approximate the volumes of left
ventricle during cardiac cycle (Figure no. 110 and Table no. 9).
Figure no. 110. Geometric model of the left ventricle (ellipsoid with axial
diameter twice the cross-sectional diameter).
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Table no. 9. Performance parameters of the left ventricle calculated using M mode.
Parameter
Notation
Left
ventricular Sf
shortening fraction
Mean
velocity
of mVcf
shortening
of
the
circumferential fibers
Ejection fraction
Ef
Stroke volume
SV
Cardiac output
CO
Formula
( EDD  ESD) x 100
EDD
EDD  EDS
ejection time x EDD
SV x 100
EDD 3
ESD 3  EDD 3
SV x HR
Value
28 - 41 %
0.85 - 1.4 circ/sec
50 - 80 %
70 - 80 ml
5-6l
ECHOGRAPHY OF THE RIGHT VENTRICLE
We examine the right ventricle in the same standard window as the left ventricle. Dimensions
of the right ventricle are calculated in B mode using the four chambers view (Figure no. 111).
VS
AS
VD
AD
Figure no. 111. Echocardiographic aspects as recorded using the four
chambers view. VS = left ventricle; VD = right ventricle; AS = left atrium; AD
= right atrium.
ECHOGRAPHY OF THE RIGHT AND LEFT ATRIUM:
The left atrium is examined in aortic standard view. We can notice the left atrium as a free
space posterior from the aorta. A foreign signal detected within this compartment can mean
an atrial tumor or an atrial thrombus.
It is difficult to examine the right atrium in M mode. Because of its retrosternal position, we
examine this structure in B mode and four chambers view.