Parasternal short axis (PSAX) view is the cross-sectional view of the heart. The image acquisition, sonographic anatomy and the key pathologies seen in this view are discussed below.
How is the exam performed?
The transducer selection and the principles of image orientation are essentially the same as discussed in the previous post.
The PSAX view is obtained by rotating the transducer 90 degrees clockwise from the parasternal long axis (PLAX) view, which positions the beam perpendicular to the longitudinal axis of the heart and slices it transversely. Probe marker should point toward the patient’s left shoulder (approximately 2o’clock). This view consists of three levels of visualization obtained by tilting the probe superiorly and inferiorly. Aortic valve level is obtained by tilting the probe face slightly upward and looking towards patient’s right shoulder. Mitral valve level is obtained when the probe is almost perpendicular to the chest wall and the papillary muscle level comes into view when the face of the probe is slightly tilted down toward the patient’s left flank [Figure 1]
Anatomy of the PSAX view
Aortic valve level
At the aortic valve level [Figure 2, Figure 3], the PSAX view demonstrates all three aortic valve leaflets: right, left, and the non-coronary cusps. In systole, the aortic leaflets open to a near-circular orifice and in diastole, the typical Y-shaped arrangement of the three leaflets looks like ‘Mercedes Benz’ emblem.The pulmonary valve and right ventricular outflow tract are seen anterolaterally, adjacent to the left coronary cusp of the aortic valve, and portions of the septal and anterior tricuspid valve leaflets are seen anteriorly and slightly medially, adjacent to the right coronary cusp. Posteriorly, the right atrium, interatrial septum, and left atrium lie in proximity to the non-coronary cusp of the aortic valve.In a good quality image, the origins of the coronary arteries may be seen adjacent to the aortic valve.
Mitral valve level
At the mitral valve level of PSAX [Figure 2, Figure 4], the left ventricle is round and the mitral leaflets are seen as they open nearly to the full cross-sectional area of the left ventricle in diastole and close in systole. Their motion resembles ‘fish mouth’. Occasionally, aberrant chordae tendinae to the ventricular septum or other structures may be seen in an otherwise normal individual.
Papillary muscle level
In this view [Figure 2, Figure 5], the left ventricle appears round and the right ventricular cavity appears semilunar similar to the mitral valve level. The two papillary muscles can be identified as round structures that bulge into the left ventricular cavity. The anterolateral papillary muscle is seen on the right of the image and the posteromedial papillary muscle on the left. This view is often called the ‘home base’ of the PSAX and provides useful information regarding the size and radial function of the left ventricle. In addition, abnormalities of the interventricular septum can be identified.
In a good image, the round left ventricle should be in the center of the image. If you are seeing a pear-shaped left ventricle, try scanning one intercostal space higher. If the left ventricle appears asymmetric, rotate the probe clockwise or anti-clockwise till it becomes round before drawing conclusions about left ventricular aneurysm or increased right sided pressures. Figures 6 and 7 demonstrate PSAX views obtained from the same patient that appear abnormal due to erroneous image acquisition. A formal echocardiogram revealed normal left ventricular structure as well as right ventricular pressures in this case.
Next month we will focus on common abnormalities seen on the Parasternal Short Axis View