Transthoracic Echocardiography Tomographic Views

Parasternal Window

The parasternal window provides the parasternal long-axis, right ventricular (RV) inflow and outflow, and short-axis views. The parasternal long-axis (PLAX) view is typically the first image acquired in a transthoracic study ( Fig. 9.1 ). A high-depth image should be obtained to exclude pleural and pericardial effusion (see Fig. 9.1C ) and other pathology posterior to the heart. A low-depth image should be subsequently obtained to assess the cardiac anatomy (see Fig. 9.1D and Video 9.1 ). From this view, the left atrium (LA), left ventricle (LV), right ventricular outflow tract (RVOT), and aortic root are visualized. The right and either noncoronary cusps or left coronary cusp, depending on the cut-plane, of the aortic valve are seen, as well as the anterior and posterior mitral valve leaflets. Occasionally, the right coronary artery can be seen ( Fig. 9.2 ). If the image is obtained from a high rib space, the LV will point apically resulting in a “booted” heart. This can be corrected by moving the transducer down a rib space. In some patients, visualization of the LV and the aorta in the same plane is not possible, so an image of the LV should be obtained at a lower rib space and then the transducer moved up a rib space to image the aortic root and proximal ascending aorta. In the PLAX view, the mitral valve and aortic valve should be inspected and interrogated with color Doppler to identify the presence of regurgitation or stenosis.

Video 9.1. Two-dimensional (2D) transthoracic echocardiogram (TTE) parasternal long-axis image.

Although no longer recommended, the linear left atrial anteroposterior dimension can be measured in this view. It is measured from the trailing edge of the aortic root to the leading edge of the LA at end-systole, when the LA is largest. Also, from this view, M-mode measurements of the aortic root and LV are obtained, although measurements directly from the 2D images are preferred. If M-mode LV measurements are being obtained, the 2D targeted M-mode cursor should be placed at the level of the papillary muscle tips, oriented perpendicular to the LV walls. Left ventricular internal dimensions should be measured at end-diastole (LVIDd) and end-systole (LVIDs). The leading edge–to–leading edge convention should be used. ^, From these measurements, the fractional shortening can be computed as:

Intraventricular septal (IVS) and posterior wall thicknesses (PWT) (see Fig. 9.1D ) are measured at end-diastole. LV mass can be estimated using the formula:

in which PWTd is posterior wall thickness at end-diastole and IVSd is interventricular septal wall thickness at end-diastole.

From the parasternal long-axis window, the RV inflow view is obtained by tilting the end of the transducer toward the patient’s head (see Fig. 9.1E ). This allows imaging of the RA, RV, and tricuspid valve. This view is primarily used for visualizing the anterior and either the posterior (if no coronary sinus or septum is seen) or septal tricuspid valve leaflets if the coronary sinus or septum is seen). This view also allows assessment for the presence of tricuspid valve regurgitation with color Doppler. In contrast, by tilting the transducer toward the patient’s feet, the RVOT comes into view (see Fig. 9.1F ). From this perspective, the pulmonic valve and the bifurcation of the pulmonary artery are visualized. A patent ductus arteriosus may be seen in this view using color Doppler. By rotating the transducer 90 degrees from the parasternal long-axis view, the parasternal short-axis (PSAX) views are obtained. With angulation of the transducer superiorly, structures at the aortic valve level are imaged ( Fig. 9.3 ). These structures include cusps of the aortic valve, pulmonary artery, pulmonic valve, RVOT, septal and anterior leaflets of the tricuspid valve, RA, LA, and interatrial septum. The left main coronary artery and bifurcation can be seen in this window ( Fig. 9.4 ). The left upper pulmonary vein is closest to the left atrial appendage in this view with flow away from the transducer. The left lower pulmonary vein will be closer to the descending aorta with flow toward the transducer. By tilting the transducer anteriorly, the RVOT can be seen (see Fig. 9.2B ). The mitral valve can be inspected by returning to the short-axis view of the aortic valve and then directing the transducer inferiorly (see Fig. 9.2C ). Continued inferior angulation of the transducer allows acquisition of multiple short-axis cuts of the LV from the base to the apex, allowing assessment of overall LV performance, wall motion, and papillary muscle position (see Fig. 9.2D and E ; Video 9.2, Video 9.3, Video 9.4 ). For patients with increased LV septal wall thickness on the PLAX images, LV wall thickness may be measured in the short-axis images for confirmation. It is also in the short-axis images that identification of an increased ratio of noncompacted to compacted myocardium should be assessed.

Video 9.2. Two-dimensional (2D) transthoracic echocardiogram (TTE) parasternal short-axis image at the basal left ventricle by the mitral valve leaflet tips.

Video 9.3. Two-dimensional (2D) transthoracic echocardiogram (TTE) parasternal short-axis image at the mid left ventricle by the papillary muscles.

Video 9.4. Two-dimensional (2D) transthoracic echocardiogram (TTE) parasternal short-axis image at the apex.