Analysis of cardiac echocardiography

Doppler spectrum analysis

The diastolic Doppler spectrum of blood flow through the atrioventricular valves is recorded by placing the sample volume in the center of the blood flow near the edges of the valve cusps.

If the sample volume is too ventricularly biased, the spectrum will show an increase in early diastolic inflow and a decrease in the atrial component.

Precise setting of the trial volume provides a picture of the normal "M-shaped" Doppler spectrum of the atrioventricular valves. The higher initial peak characterizes the early diastolic inflow into the relaxed ventricles and is called the E-wave (from early ). The second, smaller peak is caused by the contraction of the atria and is called the A-wave (from atrial ).

The peak velocities of the E and A waves are used to calculate the E/A ratio. This velocity ratio is age-dependent, being high in young people and decreasing with age. It is also dependent on heart rate and cardiac output: as heart rate increases, diastole shortens and atrial contraction plays a greater role in ventricular filling. This is reflected in the Doppler spectrum by an increase in the A wave, resulting in a decrease in the E/A ratio. If the E/A ratio is abnormal with intact valves, this indicates a disturbance of diastolic ventricular function, such as impaired early diastolic relaxation or decreased ventricular compliance.

Left ventricular outflow tract and aorta

Blood flow through the LVOT and aortic valve is best visualized in the apical lateral chamber plane. The transducer should be positioned so that the beam is directed parallel to the flow into the LVOT as much as possible. After acquiring B-mode images, color mode is activated to provide information about the blood flow. During systole, laminar blood flow from the transducer into the LVOT and through the aortic valve is normally seen. High blood velocities may cause blurring if the frequency shift exceeds the Nyquist limit.

To record the Doppler spectrum, place the sample volume in the aorta just behind the valve. A normal spectrum from the aorta shows laminar systolic blood flow in the aorta with a sharp rise and fall in its velocity. In diastole, regurgitant blood flow through the valve should not be detected, either on the color image or on the Doppler spectrum.

The time integral of velocity is the integral of the spectral curve or the area under the spectral curve. It is determined by planimetric analysis. S stands for the perfused cross-section of the aorta and is determined by measuring the aortic diameter using the formula for the area of a circle. Since the radius is squared, even a small error in its measurement can lead to a large error in the result.

Right ventricular outflow tract and pulmonary artery

LVOT flow is assessed by examining the pulmonary trunk in the parasternal short-axis plane at the level of the aortic root. As with the aorta, orientation is by color mode and the Doppler sample volume is set to the center of flow, just behind the open valve. The spectrum is similar to that in the aorta, but peak velocities are lower.

Wall motion anomaly analysis

Automatic segmental motion analysis (ASMA) is a relatively new technique. Cardiac contraction abnormalities are detected automatically and related to their location on the cardiac wall. Using a high-resolution digital converter built into the system, endocardial contours are recorded every 40 ms during the cardiac cycle and mapped in real time with color coding on the display. This color representation of segmental wall contractions remains on the monitor throughout the cardiac cycle and is updated at the beginning of a new one.

Valve diseases

Aortic stenosis

The valve is thickened, markedly hyperechoic, and has significant limitation of its movement. Systolic image shows turbulent blood flow in the ascending aorta distal to the aortic valve. There is concomitant mild mitral regurgitation, identified by a small color jet below the closed mitral valve. Diastolic image additionally shows regurgitant flow (15 sec) in the LVOT, as a sign of aortic insufficiency. The patient is an elderly woman with severe degenerative aortic stenosis. Doppler pressure gradient is 65 mmHg.

Valve prosthesis

The metallic prosthesis is characterized by a hyperechoic signal and produces a reverberation artifact in the underlying atrium and acoustic shadows. Accelerated blood flow from the atrium to the ventricle can be seen to the left and right of the obliquely positioned valve disc.

Tissue Doppler ultrasound

Tissue Doppler is a new technique that allows the assessment of cardiac wall motion by color coding tissue motion in blue when moving away from the transducer and in red when moving towards it. This is achieved using various filters. This allows better detection of abnormal wall motion, for example, in coronary heart disease, when stressful effects, such as physical exertion or dobutamine administration, lead to a decrease in blood flow in the affected artery and, as a consequence, to regional myocardial dysfunction. Local wall contractions can be compared at rest and during stress tests, while simultaneously assessing the cardiac cycle at different stages of stress echocardiography (for example, at different dobutamine infusion rates).

Tissue Doppler can also be used to analyze longitudinal myocardial contractile function. It is a sensitive marker of early myocardial dysfunction. Longitudinal shortening is best detected in the apical four-chamber plane with the sample volume located in the free walls of the right and left ventricles and in the interventricular septum.

Critical assessment

Interest in echocardiography is due to the non-invasiveness of the method, the ability to perform it at any time and repeat it as often as necessary. Currently, echocardiography provides complete information about the anatomy and function of the heart. It can be used in outpatient settings, in an emergency situation and even in the operating room. This range of applications is limited only by the fact that echocardiography cannot be performed on all patients due to a poor acoustic window, obesity or the presence of pulmonary emphysema. Using new techniques, such as harmonic imaging, it is possible to significantly improve the image quality. Visualization of the heart walls is also improved by using ultrasound contrast agents.

Not all cardiac structures (e.g. coronary arteries and peripheral branches of the pulmonary arteries) can be adequately assessed by echocardiography. For these vessels, other techniques such as angiography, CT or MRI are required. On the other hand, echocardiography can provide additional functional information in the complex diagnosis of cardiac diseases using other techniques.

Recent advances in echocardiography.

Three-dimensional processing of echocardiographic images in real time is now available for the assessment of cardiac structures.

Blood flow in the coronary arteries can be assessed using echocardiography in power Doppler mode, and not only in the proximal parts of the left and right coronary arteries.

Color evaluation of wall contractions facilitates detection of the area of abnormal function. Distensibility can be determined independently of cardiac contractions. In this case, signs of myocardial deformation in the form of systolic shortening and diastolic lengthening can be detected. These data allow evaluation of the general and regional functions of the myocardium.

Further improvements in the potential of echocardiography for non-invasive assessment of cardiac morphology and function are expected.

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