Author:
Keti Dalla
Updated:
3 October, 2024
Here, ultrasound of the heart—echocardiography—is described. The chapter covers, both in words and illustrations, the various views used with ultrasound to obtain a clear image of the heart's pumping function. It also includes the integrated examination FATE (Focused Assessment with Sonography for Trauma).
- Basic Principles of Echocardiography
- Doppler (Heart-ECHO)
- FATE (Focus Assessed Transthoracic Echo)
- LAX/ Parasternal Long-Axis View
- SAX – Parasternal Short-Axis View
- Apical Four-Chamber View (4Ch)
- Apical Two-Chamber View (2-Ch)
- Apical Two-Chamber View with Aorta (3Ch)
- Subcostal Four-Chamber View
- Hypovolemia
- Static Parameters (Fluid Responsiveness)
- Dynamic Parameters
- Reference Values UCG
Basic Principles of Echocardiography
In two-dimensional echocardiography (UCG), ultrasound waves are successively sent out in different directions from the examination probe (transmitter/probe). The ultrasound machine can calculate the depth of reflection by tracking how long the sound waves have been out in the body. The reflection points from each ultrasound beam together create an image, which is displayed on the ultrasound machine’s screen. The number of images displayed per second is called frame rate (FR). A frame rate of over 40 frames/second is required to examine the heart. The higher the FR, the better. FR is increased by reducing the depth and the sector width.
Doppler (Heart-ECHO)
When ultrasound waves are reflected off moving objects, e.g., red blood cells, the frequency of the sound changes. The reflected sound has a higher frequency than the transmitted sound if the object is moving toward the transmitter and a lower frequency if the object is moving away from the transmitter. The difference in frequency between the transmitted and reflected ultrasound is called the Frequency shift or Doppler shift (Df).
Df = 2f x V x cos-α/C
If the ultrasound beam has the same direction as the blood flow, the angle α = 0 degrees, and the cosine of 0 degrees is 1. As the angle increases, the cosine becomes less than 1, which results in an underestimation of the blood flow velocity.
With continuous Doppler (CW), all velocities along the Doppler beam are recorded. The strength of the continuous Doppler is that very high velocities can be recorded.
With Pulsed Doppler (PW), velocities are recorded within a specific area, e.g., LVOT.
FATE (Focus Assessed Transthoracic Echo)
LAX/ Parasternal Long-Axis View
The parasternal long-axis view cuts through the aorta, mitral valve, left ventricle, left atrium, and right ventricle. The left ventricle’s inner diameter, septal thickness, and posterior wall thickness are measured in end-diastole when the ventricle is largest. The measurement is made just below the mitral valve leaflets. Moving the probe slightly upwards can often visualize large parts of the ascending aorta.
SAX – Parasternal Short-Axis View
In the aortic valve plane, the parasternal short-axis view (SAX) cuts through the aortic valve, right and left atrium, right ventricular outflow tract (RVOT), pulmonary valve, and pulmonary trunk.
The view often needs adjustment by moving the probe caudally for the RVOT, pulmonary valve, and pulmonary trunk to be seen. The flow profile across the pulmonary valve with PW Doppler can reveal pulmonary hypertension (Fig 1). A short acceleration time < 95 ms and a “dip” in the flow profile during the second half of systole suggest increased pulmonary vascular resistance (PVR).
The tricuspid valve, parts of the right atrium, and atrial septum can also be seen in this projection.
In the mitral valve plane, the basal parts of the left ventricle are visible. At the papillary muscle level, the mid-portion of the left ventricle is visible. During systole, all parts of the ventricular wall should thicken, and the endocardium should normally move towards the center of the ventricle. In cases of right ventricular volume overload, the septum often bulges toward the left ventricle during diastole. With right ventricular pressure overload (pulmonary embolism, pulmonary hypertension), the septum bulges towards the left during systole.
Apical Four-Chamber View (4Ch)
The apical four-chamber view (4Ch) cuts through the central parts of the ventricles and atria as well as the mitral and tricuspid valves. Here, the septum, the left ventricle’s lateral wall, and the apex are visible. The left ventricle’s diastolic and systolic volumes and ejection fraction (EF ) can be calculated using Simpson’s method by drawing a line along the entire endocardium in diastole and systole when the ventricle is smallest. The mitral valve should be assessed for sclerosis, stenosis, prolapse, and SAM. The diastolic flow velocities across the mitral valve can be recorded with pulsed Doppler, providing information about the ventricular diastolic function. The sample volume is placed at the tips of the mitral valve leaflets.
Filling pressure can be estimated using pulsed Doppler (PW) in the mitral valve and pulmonary veins.
Mitral insufficiency (MI) can be assessed with color Doppler and continuous Doppler (CW).
The size of the left and right atria can be assessed by tracing the atrial wall in systole when the atrium is largest. The size of the left atrium is an important parameter in the assessment of diastolic function and the degree of mitral insufficiency.
The outflow tract and aortic valve open if the probe is tilted anteriorly. Blood flow velocity in the LVOT is recorded with pulsed Doppler (PW). If the PW curve area is traced, VTI (Velocity Time Integral) is calculated—the stroke length of blood cells during systole, a measure of contractility.
LVOT area ALVOT= π x r2
The equation for stroke volume is:
SV = ALVOTx VTILVOT.
Aortic insufficiency is seen with color Doppler. Grading of aortic insufficiency and aortic stenosis is done with continuous Doppler (CW).
The right ventricle is normally smaller than the left ventricle. In this view, right ventricular mobility and size can be assessed. The systolic pressure difference between the right ventricle and right atrium is calculated by recording the maximum velocity of tricuspid regurgitation with CW. ΔPmax = 4 x VTI
The systolic right ventricular pressure, which equals the systolic pulmonary pressure in the absence of pulmonary stenosis, is calculated if CVP is added to ΔPmax
PAsyst = ΔPmax + CVP
ΔP=4VTI2 (VTI is the maximum velocity of tricuspid regurgitation)
Apical Two-Chamber View (2-Ch)
This view appears if the probe is rotated about 60° relative to the apical four-chamber view (with the notch of the probe pointing towards the patient’s left shoulder). The left ventricle’s anterior and inferior walls as well as the mitral valve and left atrium, are visualized here.
Apical Two-Chamber View with Aorta (3Ch)
The apical two-chamber view with the aorta is obtained by rotating the probe about 120° relative to the apical four-chamber view (with the notch of the probe towards the patient’s right shoulder). The view cuts through the aortic valve, mitral valve, anterior part of the septum, and inferolateral wall of the left ventricle. With color Doppler and CW, mitral and aortic insufficiency can be studied. With PW in the LVOT, VTILVOT and stroke volume can be calculated.
Subcostal Four-Chamber View
This view cuts through the same parts as the apical four-chamber view (the notch of the probe towards the patient’s left side). The accumulation of pericardial effusion can be more easily assessed from the subcostal registration.
The inferior vena cava is seen by rotating the probe slightly counterclockwise (notch upwards). The following estimates can be made:
At Normal CVT < 5 mmHg, the inferior vena cava diameter is < 20 mm, and during the Valsalva maneuver (sniffing), the diameter decreases by > 50%.
At CVT around 10 mmHg, the inferior vena cava is < 20 mm, and during inhalation/sniffing, the diameter decreases by < 50%.
At high CVT > 15 mmHg, the inferior vena cava (IVC) is > 20 mm, and during inhalation/sniffing, the diameter decreases by < 50%.
Hypovolemia
Detecting patients in circulatory shock who are volume-dependent is an important issue in intensive care. Echocardiography should always be integrated into the overall clinical picture. From the Frank-Starling curve, one can see that fluid administration can be crucial for a patient in the early part of the curve (preload-dependent) or dangerous for another patient on the flat part (preload-independent). If hypovolemia is suspected, static parameters should be supplemented with dynamic measurements to distinguish “responders” from “non-responders.”
Static Parameters (Fluid Responsiveness)
Dynamic Parameters
- 20% variation in VTI (Velocity Time Integral) during a respiratory cycle discriminates responders from non-responders.
- If the VTI increases by more than 15% after a fluid bolus, it indicates that the patient is a responder.
- In spontaneously breathing patients or intubated patients who trigger the ventilator, an increase in SV > 12% after PLR (passive leg raising) predicts an increase in SV > 15% after fluid administration.
When does fluid administration become harmful? Examination with PW in pulmonary veins and the mitral valve with an estimation of filling pressure can aid the assessment.
Non-responders: An increase in mitral E or E/A by more than 10%, a decrease in the S/D ratio, and an increase in VTI < 10% after a fluid bolus. These measures indicate little change in stroke volume after fluid administration and a tendency towards elevated filling pressure.
Reference Values UCG
Women
Left ventricular diastolic diameter 4.1-5.1 cm
Left atrial area ≤ 21 cm2
VTI ≥ 15.5 cm
Men
Left ventricular diastolic diameter: 4.6-6.0 cm
Left atrial area ≤ 25 cm2
VTI ≥14.3 cm
S/D
40-59 years: 0.8-1.6
≥ 60 years: 0.8-2.0
References
- Otto: Textbook of Clinical Echocardiography
- Arne Olsson: Echocardiography
- Daniel de Backer: Hemodynamic Monitoring Using Echocardiography in Critically Ill
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