All that follows are quotes from Reference (1) in Resources:
Take Care In Imaging The Root and Ascending Aorta From the Parasternal Long Axis
“An imaging plane aligned parallel to the long axis of the left ventricle will not, in most cases, be exactly parallel to the left ventricular outflow tract and aortic root. This is illustrated in figure 5.11, which demonstrates that slight counterclockwise rotation of the transducer is needed to follow the long axis of the vessel left ventricle into the long axis of the aorta. In this illustration, the true dimensions of the proximal aorta are underestimated in the left panel which shows a properly aligned para sternal long axis view. By slightly rotating the transducer (right panel), the aortic root is “opened up” and the true long axis of the aortic is demonstrated. In most patients, some angulation of the scan plane from medial to lateral is required to obtain a complete interrogation of the aortic valve, including the leaflets, annulus, and sinuses.” (* p 96)
“Because transthoracic echocardiography visualizes only a limited area of the ascending aorta, it generally is not considered an adequate diagnostic tool for the exclusion of aortic dissection. [However, for a different view of the utility of transthoracic echocardiography in the diagnosis of acute proximal aortic dissection, please see the second reference in resources.] Only a minority of ascending aortic dissections will be detected from the transthoracic window. However, when an intimal flap is detected on transthoracic imaging a dissection of the proximal aortic is most likely present. . . . Proximal aortic dilatation is usually present in patients with ascending aortic dissection. Identification of normal aortic dimensions and geometry and the absence of aortic insufficiency from a transthoracic echocardiogram are evidence against the presence of an aortic dissection in the acsending aortic, but do not fully exclude the diagnosis.” (* p 646)
“The primary use of the suprasternal views is to examine the great vessels. Extending and rotating the patient’s head allows positioning the transducer so that the aortic arch is readily recorded. This can be uncomfortable for the patient and care should be taken to minimize pressure on the patient’s throat. Orientation of the scan plane is based on the position of the arch relative to the ultrasound beam. Although a variety of terms have been used to define the various transducer positions, describing the imaging plane as either parallel or perpendicular to the arch is most intuitive.” (* pp 107 + 108)
” When the plane is oriented parallel to the aortic arch, it is often possible to visualize both the ascending and descending segments of the aorta as well as the origin of the inominate, left common carotid, left subclavian, and right pulmonary arteries (Fig 5.43). Because of the proximity of the aortic arch to the transducer, a 90 degree sector may not be wide enough to simultaneously record both the ascending and descnding segments of the aorta. Angulation of the transducer is necessary for complete recording in such patients. From this position, the transducer can be rotated 90 degrees to provide the perpendicultar plane, which demonstrates the arch in short-axis orientation. From this view, the right pulmonary artery and left atrium can usually be recorded. By adjusting the scan plane leftward and slightly anteriorly, the superior vena cava can also be visualized. Fig 5.44 illustrates the suprasternal short axis view, demonstrating the aortic arch in cross section, and, below it, the right pulmonary artery and left atrium can be seen.” (* p 108)
(1) *Feigenbaum’s Echocardiography, 7th Ed, 2010. WF Armstrong, T Ryan.
(2) **Feasibility and accuracy of bedside transthoracic echocardiography in diagnosis of acute proximal aortic dissection. Cardiovasc Ultrasound. 2015 Mar 25;13(1):15. doi: 10.1186/s12947-015-0008-5 [PubMed Abstract] [Full Text HTML] [Full Text PDF]