Comprehensive Diagnostic Transthoracic and Transesophageal Echocardiography

Parasternal Long-Axis View

For the left parasternal window, the patient is placed in a left lateral decubitus position with the transducer in the third or fourth left intercostal space. The LV long-axis view is obtained with the transducer index marker facing toward the patient’s right shoulder at approximately the 10-o’clock position (see Fig. 8.2C ). This view allows visualization of the LV, left atrium (LA), MV, AV, and proximal ascending aorta ( Fig. 8.3 ). The LV should lie perpendicular to the ultrasound beam, with the anterior (AMVL) and posterior (PMVL) mitral valve leaflets and the right and noncoronary cusps of the AV visualized ( Table 8.2 ). With increased depth in the imaging sector, the parasternal long-axis view (PLAX) allows differentiation of pericardial and pleural effusions: the oblique pericardial sinus lies between the LA and the descending thoracic aorta, and a pericardial effusion lies between these two structures, whereas a pleural effusion tracks posterior to the descending thoracic aorta (see Fig. 8.3B ). The size of a pericardial effusion does not necessarily correlate with hemodynamic impact. In this view, the true LV apex is not visualized; rather, the “apex” is typically an oblique image plane through the anterolateral wall.

RV Inflow View

The RV inflow view is obtained by tilting the transducer inferomedially from the PLAX and rotating it slightly clockwise. In this view, the right atrium (RA), TV, and RV are visualized in a long-axis plane. The TV anterior leaflet is present along with the posterior leaflet. The coronary sinus enters the RA adjacent to the posterior tricuspid annulus, and the inferior vena cava (IVC) enters the RA inferior to the coronary sinus ( Fig. 8.4 ).

Parasternal Short-Axis Views

The parasternal short-axis (PSAX) views are obtained by rotating the transducer 90 degrees clockwise from the PLAX, with the transducer index marker pointed toward the left supraclavicular fossa at approximately the 2-o’clock position, placing the ultrasound beam perpendicular to the LV long-axis plane. By tilting the transducer superiorly or inferiorly, different cross-sectional views of the heart may be visualized.

When the transducer is tilted superiorly, a transverse view of the heart is recorded at the level of the great vessels. In this view, the AV, LA, interatrial septum (IAS), RA, TV, and RV outflow tract (RVOT) are visualized. The right, left, and noncoronary cusps of the AV are seen, with the IAS attached just adjacent to the noncoronary cusp. The right coronary cusp is positioned anteriorly and abuts the RVOT; the left coronary cusp is adjacent to the proximal pulmonary artery (see Table 8.2 ). The origins of the left main and right coronary arteries can often be identified in this view.

For the MV short-axis view, the transducer is tilted inferiorly so that the ultrasound beam transects the heart at the level of the mitral leaflets. In this view, the AMVL and PMVL are seen en face. Each leaflet is segmented into three major scallops, called lateral (A1 and P1), middle (A2 and P2), and medial (A3 and P3), respectively ( Fig. 8.5A ). If the transducer is tilted further inferiorly, a cross-sectional view is obtained at the mid-ventricular (papillary muscle) level. In this view, a normal LV appears circular in shape, and the anterolateral and posteromedial papillary muscles are present at approximately the 3- and 8-o’clock positions, respectively (see Fig. 8.5B ).

Apical 4-Chamber View

The apical window is obtained by placing the transducer at the point of maximal impulse, with the patient in the left lateral decubitus position. Rotation of the transducer allows for acquisition of the apical views. For the apical 4-chamber view, the ultrasound beam is directed medially and superiorly toward the patient’s right scapula, with the transducer index marker at approximately 3 o’clock. In this view, all four chambers of the heart, the IAS, and the interventricular septum (IVS) are visualized ( Fig. 8.6 ; see Table 8.2 ). The LV appears as a truncated ellipse with visualization of the anterolateral wall, apex, and inferoseptum. The AMVL is adjacent to the septum, and the PMVL is adjacent to the lateral wall.

The tricuspid annulus is more apically positioned than the mitral annulus, with insertion of the septal TV leaflet up to 1 cm displaced relative to the AMVL insertion. This anatomic distinction aids in the identification of cardiac chambers if there is ambiguity in the orientation of the heart. The atria and the IAS are also visualized in this view; however, ultrasound resolution is often limited due to their distal positions relative to the transducer. Rotation of the transducer from the apical window allows visualization of all 17 myocardial segments ( Fig. 8.7 ). Slight counterclockwise rotation of the transducer produces the RV-focused view ( Fig. 8.8 ). RV size and function parameters obtained from the RV-focused view are more reproducible than those measured from the apical 4-chamber view.

Apical 2-Chamber and Long-Axis Views

Rotating the transducer counterclockwise approximately 60 degrees from the apical 4-chamber view provides the apical 2-chamber view. The anterior LV wall and the P1 scallop of the MV are seen on the right of the display, whereas the inferior wall and P3 scallop are seen on the left (see Fig. 8.7 ). Ejection fraction is calculated with the use of geometric assumptions based on the areas traced from end-diastolic and end-systolic frames in the apical 4-chamber and 2-chamber views ( Fig. 8.9 ).

Longitudinal strain is another measurement used for the evaluation of LV function ( Fig. 8.10 ; see Chapter 2 ). By convention, strain percentages are reported as negative for shortening. Averaged values from multiple regions provide global measures of LV function such as global longitudinal strain (GLS) (see Fig. 8.10B ).

An additional 60 degrees counterclockwise rotation of the transducer yields the apical long-axis view, which is analogous to the image plane for the PLAX but with the transducer now positioned at the point of maximal impulse (see Figs. 8.6 and 8.7 ). Although the LV apex is now visualized in the apical long-axis view, image resolution for the AV, MV, and LV outflow tract (LVOT) is now relatively poorer because of the greater imaging depth from the transducer.