Technical implementation of the method
Echocardiography is based on the principle of echolocation. Ultrasound waves have a short wavelength and can form narrow beams, acting analogously to light rays. The device transducer is equipped with a piezoelectric crystal with electrodes, which functions as both a signal emitter and receiver.
During the examination, the physician places the transducer on the chest wall. The ultrasound beam passes through tissues and is partially reflected from interfaces between structures of different densities (e.g., the myocardium-blood boundary). The reflection coefficient depends directly on the density difference between these media and the angle of incidence of the beam. Today, the introduction of computer processing and video recording has transformed these echoes into a high-precision diagnostic tool.
Classic imaging modes
The data obtained by the transducer are displayed on the screen (oscilloscope) in several graphic formats:
- A-mode (Amplitude): The signal is displayed as amplitude peaks. The X-axis represents pulse amplitude, and the Y-axis represents the distance from the transducer to the structure.
- B-mode (Brightness): The echo signal amplitude is converted into dot brightness (the stronger the reflected signal, the brighter the dot). This generates a real-time two-dimensional (2D) sector image of cardiac anatomy, visualizing chambers, valves, and great vessels.
- M-mode (Motion): Provides a time-motion display. The vertical axis represents depth, and the horizontal axis represents time. This mode records the motion of structures intersected by a strictly single beam (unidimensionality is its main disadvantage).
In M-mode, the beam can be directed at three standard levels:
- Through the aortic root and left atrium (motion of the aortic valve cusps).
- Through the mitral valve (clearly showing how its cusps move in opposite directions during opening).
- Through the ventricles (for measuring chamber dimensions and visualizing papillary muscles).
Transesophageal echocardiography and Doppler
When standard transthoracic access is insufficiently informative, transesophageal echocardiography (TEE) is used. It is indispensable for detecting intracavitary thrombi and atrial tumors, assessing vegetations in infective endocarditis, analyzing congenital heart defects, and monitoring myocardial function directly during surgery.
To assess hemodynamics, the Doppler effect is used—the shift in ultrasound frequency upon reflection from moving objects (erythrocytes or cardiac structures). If blood flows toward the transducer, the signal frequency increases; if away from it, the frequency decreases. Color Doppler flow mapping deserves special attention, as the two-dimensional image is synchronized with the Doppler signal. Flow velocity and direction are color-coded, greatly simplifying interpretation. Tissue Doppler imaging (TDI) is also used to measure the velocity and amplitude of motion of the myocardial walls and valve annuli themselves.
Assessment of left ventricular diastolic function
Pulsed-wave Doppler mode allows the analysis of the transmitral flow spectrum. The sample volume is placed above the coaptation point of the mitral valve cusps. Ventricular filling phases form two characteristic waves:
- Peak E (Early): early diastolic filling.
- Peak A (Atrial): late atrial systole.
Normally, the E wave is dominant (it is higher than the A wave). During diagnostics, the physician measures the peak velocities, their ratio (E/A), early filling deceleration time (DT), and isovolumic relaxation time (IVRT). Based on the severity of changes in these parameters, three types of diastolic dysfunction are distinguished:
- Impaired relaxation type (stiff).
- Pseudonormal type (pathology masked as a normal pattern).
- Restrictive type (most severe impairment).
Briefly: answers to topical questions
What are the classic echocardiographic features of mitral stenosis in M-mode?
The classic echocardiographic features of mitral stenosis in M-mode include specific changes in the pattern and velocity of cusp motion.
- Decreased closing velocity: significant reduction in the diastolic closing velocity of the anterior mitral leaflet (increased EF slope, flattening of the slope).
- Unidirectional motion: unidirectional motion of the anterior and posterior valve cusps during diastole (the posterior cusp moves in the same direction as the anterior one).
- Shape alteration: the diastolic motion curve of the anterior cusp flattens and acquires a B-like or square-rooted (or plate-like) character (instead of the normal M-shaped form).
- Reduced opening: a decrease in the maximum diastolic opening distance of the cusps.
Which echocardiographic parameters are used to calculate the left ventricular ejection fraction using Simpson's method?
To calculate the left ventricular ejection fraction using the biplane method of disks (Simpson's method), cardiac chamber volume measurements are used. These volumes are determined in two echocardiographic views: 4-chamber and 2-chamber.
Key calculation parameters:
- End-diastolic volume (end-diastolic volume): the volume of the ventricle at its maximum filling.
- End-systolic volume (end-systolic volume): the volume of the ventricle at its maximum emptying.
- Stroke volume (stroke volume): the difference between end-diastolic and end-systolic volumes.
Ejection fraction is calculated as the ratio of stroke volume to end-diastolic volume.
Class and exam questions
What does the intensity of the reflected ultrasound signal depend on?
It depends on the density difference between adjacent media (e.g., tissue and fluid) and the angle of incidence of the ultrasound beam on the interface.
What is the main disadvantage of M-mode?
M-mode provides only a one-dimensional study and a narrow field of view, as it records the motion of structures along a single beam only.
How to distinguish normal LV diastolic function on a Dopplergram?
Normally, when assessing transmitral flow, the early diastolic filling wave (peak E) should be higher than the atrial systole wave (peak A).
What else to study on this topic
- Normative criteria for cardiac chamber dimensions measured in M-mode
- Specific features of valve vegetations in infective endocarditis on TEE
- Differential diagnosis of pseudonormal and normal types of diastolic function
- Clinical significance of DT and IVRT parameters in heart failure
- Features of turbulent blood flow visualization in valvular stenosis
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