Methods of echocardiography

Echocardiography technique

Sensor positions

Since the heart is surrounded by ribs and air lung tissue, which make it difficult to transmit ultrasound waves, it is best to perform the examination during full exhalation from several positions. For the greatest expansion of the acoustic windows, the examination is performed with the patient lying on the left side, with the upper body slightly elevated. In this position, the heart is opposite the anterolateral chest wall and is least covered by lung tissue, especially during full exhalation. Due to the relatively small acoustic window, it is best to use a sector transducer, which allows you to get a slice of the heart in the form of a "piece of pie". Standard acoustic windows for echocardiography are as follows: parasternal in the 2nd-4th intercostal space, apical in the 5th-6th intercostal space, suprasternal in the suprasternal notch, and subcostal - below the xiphoid process.

Scanning planes

By rotating and tilting the transducer, the physician can use all the acoustic windows and scan the heart in several planes. According to the American Society of Echocardiography guidelines, three mutually perpendicular scanning planes are established: the long axis of the heart, the short axis, and the four-chamber plane. The position of the transducers in all these planes is based on the axes of the heart itself, not the patient's body.

The long axis plane is parallel to the major axis of the heart, defined by a line running from the aortic valve to the apex of the heart. The transducer is positioned in a parasternal, suprasternal, or apical position. The short axis is perpendicular to the long axis, and its plane represents a transverse image. Scanning from an apical or subcostal position produces a four-chamber image, showing all four chambers of the heart in a single slice.

The transducer can be tilted in both directions to obtain additional fan-shaped images of the heart. Such planes are used in particular to evaluate cardiac anomalies. For an accurate analysis of the anatomy and function, the heart should always be examined in several planes with different transducer positions. In this way, pathological structures are visible from different angles, they can be assessed and distinguished from artifacts.

The images below were obtained in three standard planes: the parasternal long-axis plane, the parasternal short-axis plane, and the apical four-chamber plane.

Parasternal plane of the true axis

For parasternal long-axis imaging, the transducer is positioned in the 3rd or 4th intercostal space anterior to the heart. The scanning plane extends from the right shoulder to the left iliac crest. The structures visible in the anteroposterior direction are the anterior wall of the right ventricle, the right ventricle (outflow tract), the interventricular septum, the left ventricle, and the posterior wall of the left ventricle. Cranial to the left ventricle are the aortic valve, ascending aorta, mitral valve, left atrium, and, posteriorly, the descending aorta. A correct image is obtained when all of these structures are visible simultaneously and the interventricular septum is nearly horizontal. Structures close to the transducer (right ventricle) are displayed at the top of the image, and cranial structures (aorta) are displayed at the right. Thus, the image appears as if the observer were looking at the heart from the left.

Cardiac cycle

Echocardiographic image series can be correlated with the ECG and demonstrate the movements of cardiac structures during individual phases of the cardiac cycle.

At the beginning of diastole (end of the T wave), the mitral valve opens wide and blood moves rapidly from the left atrium into the left ventricle, which expands. The aortic valve is closed. In mid-diastole (between the T and P waves), the pressure in the atrium and ventricle is equalized. Atrioventricular blood flow is insignificant or absent, the mitral valve cusps are in an intermediate position. At the end of diastole, atrial contraction (P wave) again causes rapid blood flow into the ventricle, the mitral valve opens wide. At the beginning of systole (apex of the R wave), ventricular contraction causes the mitral valve to close. The aortic valve remains closed during isovolumetric contraction until the pressure in the left ventricle reaches the level of the aortic valve. When the aortic valve opens, the ejection phase begins and the left ventricle decreases in size. At the end of the ejection phase, the aortic valve closes and the left ventricle reaches its smallest volume during the cardiac cycle. The mitral valve remains closed until the end of isovolumetric relaxation.

Parasternal plane along the short axis

To obtain a parasternal short-axis image, the transducer is again positioned in the 3rd or 4th intercostal space anterior to the heart. The scanning plane is perpendicular to the long axis and is displayed as shown below. The transducer should be tilted to obtain different anatomical planes.

In the vascular plane, the aortic valve is visualized in the center of the image, with its three cusps forming a stellate pattern. The curved area anterior to the valve is the right ventricular outflow tract, connecting the inflow tract and tricuspid valve to the pulmonary valve and main trunk of the pulmonary artery. Below the aorta is the left atrium.

In the plane of the mitral valve, the anterior and posterior cusps of the mitral valve and the outflow tract of the left ventricle are defined. During the cardiac cycle, the cusps of the mitral valve move like a "fish mouth".

In the plane of the papillary muscles, the right ventricle forms a shell-like region at the top left in front of the almost round left ventricle at the bottom right. Behind, on both sides, two papillary muscles are visualized.

In this plane, the concentric contraction of the left ventricle can be observed during the cardiac cycle. The image in diastole shows a rounded left ventricle with the interventricular septum and posterior wall. During systole, the left ventricular cavity decreases, which is accompanied by thickening of the septum and posterior wall.

Apical four-chamber plane

Four-chamber plane images with the transducer in the 5th or 6th intercostal space with the patient lying on the left side can be obtained even in obese patients with a poor acoustic window. The beam is directed to the left shoulder, crossing the heart from the apex to the base. Holding the breath during a full exhalation allows the acoustic window to be widened. The four-chamber plane is perpendicular to the planes along both the long and short axes. The physician views the heart from below, so the right and left sides in the image are seen in the opposite position.

The apex of the heart is positioned at the top (close to the transducer) in the image. The right atrium and ventricle are on the left. This plane allows both the atria and ventricles to be imaged in addition to the interatrial and interventricular septa and both atrioventricular valves. The transducer must be positioned precisely over the apex and then rotated and tilted to obtain a suitable section that shows all four chambers.

Five-chamber plane

Images in this plane are obtained by tilting the transducer anteriorly and rotating it clockwise from the apical four-chamber plane. This allows visualization of the left ventricular outflow tract and the aortic valve. The scanning plane is parallel to the blood flow to the aorta, creating optimal conditions for Doppler examination of the left ventricular outflow tract (aortic valve and ascending aorta). It is not always easy to identify all the structures of the right heart and obtain images of them in this plane.

Transesophageal echocardiography

A poor acoustic window due to obesity or emphysema of the patient may not provide adequate visualization of all cardiac structures during transthoracic echocardiography. In such cases, transesophageal echocardiography is performed, which provides excellent imaging of the atria, ventricles, and atrioventricular valves. It is especially useful in the operating room and in the intensive care unit in the early postoperative period after cardiac interventions. A special endoscope with a biplane or multiplane transducer is inserted through the pharynx into the esophagus and advanced until visualization of the heart is achieved. Good image quality of the left atrium, located near the transducer, allows visualization of thrombi in it or on the mitral valve and identification of any atrial septal defects.

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