Methods of echocardiography

The technique of echocardiography

Sensor Positions

Since the heart is surrounded by ribs and airy lung tissue, making it difficult to transmit ultrasonic waves, it is best to perform the test with a full expiration of several positions. To maximize the expansion of acoustic windows, the study is carried out in the patient's position on the left side, while the upper part of the body is slightly elevated. In this position, the heart is located opposite the anterolateral thoracic wall and is least of all covered by the tissue of the lungs, especially when exhaled. Because of the relatively small acoustic window, it is best to use a sector sensor, with which you can get a cut of the heart in the form of a "piece of pie". Standard acoustic windows for echocardiography are as follows: parasternal in the 2-4th intercostal space, apex in the 5-6th intercostal space, supragastral in the supragranular suture and subcostal below the xiphoid process.

Scanning planes

Rotating and tilting the sensor the doctor can use all the acoustic windows and scan the heart in several planes. According to the leadership of the American Echocardiography Society, three mutually perpendicular scanning planes are established: a long axis of the heart, a short axis and a four-dimensional plane. The position of the sensors in all these planes is based on the axes of the heart itself, not the patient's body.

The plane of the relatively long axis is parallel to the main axis of the heart, defined along the line going from the aortic valve to the apex of the heart. The sensor is installed in the parasternal, suprasternal or apical position. The short axis is perpendicular to the length, and its plane is a transverse image. Scanning from the apical or hypochondrium position gives an image in a four-chamber position that displays all four chambers of the heart in one cut.

The sensor can be tilted in both directions to get extra fan-shaped images of the heart. Such planes are used in particular to assess cardiac abnormalities. To accurately analyze anatomy and function, the heart should always be examined in several planes at different positions of the sensor. Thus, pathological structures are seen at different angles, they can be assessed and distinguished from artifacts.

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

Parasternal plane of the original axis

To obtain images in the parasternal plane along the long axis, the sensor is placed in the 3rd or 4th intercostal anterior to the heart. The scanning plane is located along the line from the right shoulder to the left iliac crest. In the anteroposterior direction the following structures are visualized: the front wall of the right ventricle, the right ventricle (the outgoing tract), the interventricular septum, the left ventricle and the posterior wall of the left ventricle. Cranial to the left ventricle are the aortic valve, the ascending aorta, the mitral valve, the left atrium and, behind, the descending aorta. A correct image can be said when all these structures are visible simultaneously, and the interventricular septum is located almost horizontally. The structures near the sensor (right ventricle) are displayed at the top of the image, and the cranial structures (aorta) are in the right. Thus, the picture looks as if the observer were looking at the heart on the left.

Heart cycle

A series of echocardiographic images can be correlated with the ECG and demonstrate movements of the heart structures during the individual phases of the cardiac cycle.

At the beginning of the diastole (end of the T wave), the mitral valve opens wide and the blood rapidly moves from the left atrium to the left ventricle, which expands. The aortic valve is closed. In the middle of the diastole (between the teeth T and P), the pressure in the atrium and ventricle is equalized. Atrial-ventricular blood flow is negligible or absent, the mitral valve flaps are in an intermediate position. At the end of diastole, the contraction of the atria (tooth P) again causes a rapid flow of blood into the ventricle, the mitral valve opens wide. At the beginning of the systole (apex of the R wave), contraction of the ventricle causes closure of the mitral valve. The aortic valve remains closed during isostolytic contraction until the pressure in the left ventricle reaches the aortic level. When the aortic valve is opened, the ejection phase begins and the size of the left ventricle decreases. At the end of the ejection phase, the aortic valve closes, and the left ventricle reaches the smallest volume during the cardiac cycle. The mitral valve remains closed until the end of isovolytic relaxation.

Parasternal plane along the short axis

To obtain an image in the parasternal plane along the short axis, the sensor is again placed 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 sensor should be tilted to produce different anatomical planes.

In the vascular plane, the aortic valve is visualized in the center of the image, where its three leaves form a stellate picture. The curved area anterior to the valve is the outward tract of the right ventricle, which connects the inflow pathway and the tricuspid valve with the pulmonary artery valve and the main pulmonary artery trunk. The left atrium is located below the aorta.

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

In the plane of the papillary muscles, the right ventricle, in the upper left, anterior to the almost circular left ventricle, on the lower right, is a region in the form of a shell. Two papillary muscles are visualized behind both sides.

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

Apical four-chamber plane

Images in the four-chamber plane when the sensor is in the 5th or 6th intercostal space in the patient's position on the left side can be obtained even in obese patients with a poor acoustic window. The ray is directed to the left shoulder, crossing the heart from the tip to the base. Holding the breath at full expiration allows you to expand the acoustic window. The four-chamber plane is perpendicular to the planes both along the long and short axes. The doctor sees the heart from below, so the right and left sides of the image are visible in the opposite location.

The top of the heart in the image is located on top (near the sensor). The right ventricles of the ventricle are on the left. This plane allows to display both the atrium and the ventricles in addition to the interatrial and interventricular septa and both atrioventricular valves. The sensor must be precisely positioned above the tip, and then rotated and tilted to get a suitable cross-section on which all four cameras will be visible.

Five-chamber plane

Images in this plane are obtained by tilting the sensor anteriorly and rotating it clockwise from the apical four-chamber plane. This achieves visualization of the outflow tract of the left ventricle and the aortic valve. The scanning plane is located parallel to the blood flow to the aorta, creating optimal conditions for the dopplerographic examination of the outflow tract of the left ventricle (the aortic valve and the ascending aorta). Determining all the structures of the right heart and getting their images in this plane is not always easy.

Transesophageal echocardiography

A poor acoustic window due to obesity or emphysema can not provide adequate visualization of all heart structures for transthoracic echocardiography. In such cases, transesophageal echocardiography is performed, providing an excellent image 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. Through the pharynx, a special endoscope with a two-plane or multi-plane sensor is inserted into the esophagus and advances until the heart is vul- vascularized. Good image quality of the left atrium, located next to the sensor, allows visualization of thrombi in it or on the mitral valve and detect any defects of the interatrial septum.

[1], [2], [3], [4], [5]