Echocardiography is a method for studying the structure and function of the heart, based on recording the reflected pulse signals of ultrasound generated by a sensor with a frequency of about 2.5 – 5.0 MHz. Wave reflection occurs at the interface between two media with different acoustic densities if the object is larger than the ultrasonic wavelength (1–1.5 mm). The higher the oscillation frequency of ultrasound (i.e., the shorter the wavelength), the higher the resolution the instrument has, but the depth of signal penetration in the tissue decreases. Therefore, in the study of the heart in adults use sensors with a frequency of 2.5 – 3.5 MHz, and children – 5.0 MHz. A slightly different principle is used in Doppler echocardiography (DehoKG). The Doppler effect is that the ultrasonic beam directed at any moving object is reflected from it and is sent back to the sensor, but with a different frequency. Knowing the frequency of the reflected ultrasound, you can determine the speed of movement of particles (blood cells). It should be remembered that ultrasound practically does not pass through the gas environment and does not penetrate into the organs containing gas (lungs, intestines)
In the study of the heart and blood vessels, usually three modes of operation of the device are used: one-dimensional (M – modal), two-dimensional (sectoral, B- or 2D-mode) and Doppler (EchoKG) modes.
M-mode (Motion-movement) allows you to get an idea of the movement of various structures of the heart, which crosses the ultrasonic beam. In this mode, the vertical axis is the distance from one or another structure of the heart to the sensor, and the horizontal axis is time. It is usually used to measure the chambers of the heart, the lumen of large vessels, calculate the wall thickness, some hemodynamic parameters. Although one-dimensionality is its disadvantage, however, the image quality and measurement accuracy of intracardiac structures are higher than when using other modes.
In or 2D mode (Two dimensional) allows you to get on the screen a planar two-dimensional image of the heart, which clearly shows the mutual arrangement of individual structures and their movement in real time. To some extent, the two-dimensional EchoCG is simpler for perception than one-dimensional, because it is more realistic reflects the anatomy and structure of the heart in a particular sectional plane (a kind of tomogram of the heart).
DehoKG – Doppler mode is used for qualitative (laminar or turbulent flow) and quantitative (speed) characteristics of intracardiac blood flows. The Doppler signal is depicted on the screen as a graph (time is plotted on the horizontal axis, and flow velocity on the vertical axis). The isoline divides the screen into two parts – blood particles moving to the sensor form a curve above the isoline, and from the sensor – below the isoline. Such curves are obtained using a constantly wave (LDPE) or pulsed (IVD) doppler. The difference between them is that in the pulse-wave mode we can estimate the blood flow at an arbitrarily chosen depth, i.e. at the level of a “control” or “gated” volume, and with a constant-wave one we obtain the character of the flow throughout the entire ultrasonic beam, which makes it possible to measure flows at high speeds and at a greater depth.
One of the varieties of DehoKG is color Doppler research (CDS). The principle of the method is based on the fact that different directions of the blood flow and its nature (turbulent or laminar) are coded in different colors, the intensity of which varies depending on the flow velocity. CDI greatly facilitates the study (especially for heart defects) and reduces the possibility of errors, since the color identification of the blood flow is very clear.
It is not possible to answer the question which of the three EchoCG techniques is the most important, since any one may be the most important in the diagnosis of various forms of pathological conditions of the heart . In this section, I would like to highlight some of the erroneous ideas that exist about the method of echocardiography among general practitioners.
Healing doctors tend to overestimate the value of echocardiography (as well as other modern diagnostic methods – the effect of novelty). It should be determined immediately – the doctor of ultrasound diagnosis does not make a diagnosis. The EchoCG specialist gives a conclusion on the basis of which, like on the basis of other data, a clinical diagnosis is established by a doctor.
It must be emphasized that EchoCG is a rather subjective technique, and the interpretation of the same data by different specialists is often different. You should not pay much attention to the images attached to the protocol – the image directly depends on the device and printer settings, on the section angle and other factors, so even experienced specialists try not to advise on them. Moreover, using acoustic phenomena and artifacts, one can sometimes get a picture of what the patient does not have.
In some clinics (usually where EchoCG refers to the functional diagnostics department) in conclusion, one can read about whether the patient has “focal myocardial changes” or “myocardial fibrosis”, although an echocardiographer can only assume the nature of the histological changes.
Consequently, the accuracy and reliability of echoCG research depends not only on the experience and knowledge of the doctor, but also on the following factors:
the quality of the ultrasonic device, the set of sensors and programs, the size of the monitor screen (for example, some devices have measurement resolutions of up to 0.2–0.3 mm, and others only 1.0 mm; with a low resolution of the sensor, the back may not be visible) left ventricular wall, which significantly increases the size of its cavity; a small screen does not allow viewing small structures, for example – small vegetations on the valve);
constitutional features of the patient, the presence of concomitant pathology of the lungs (more than 20% of the studied cannot obtain a high-quality image due to the lack of an echo window due to the pathology of the lungs, displacement of the mediastinal organs, etc.);
the specialist’s awareness of this patient (the attention of the researcher is unevenly distributed, and the identification of small changes is sometimes determined by random factors, and often interpreted differently. Therefore, in the direction of the study, it is necessary to put specific questions to the doctor EchoCG diagnosis);
the quality of the protocol (in the protocol it is necessary to indicate not only absolute numbers, but at least an approximate degree of their changes). However, it should be taken into account that many regulatory indicators have not yet been developed, and those that have already been published often differ from different authors. There are changes that cannot yet be accurately quantified, for example, the volume of effusion in the pericardium;
It is desirable that the ultrasound control when evaluating the dynamics of the process is carried out by the same doctor, since the evaluation is carried out on the basis of not only dimensions, but also subjective perception.