Suprasternal Notch Views (SSN)
©Walter Rasmussen, R.D.C.S.
Aortic Arch and Descending Aorta
For assessment of the aortic arch, the patient should assume a supine position with the chin elevated so that there is more room to place and manipulate the transducer. To locate the suprasternal notch window, place the transducer at the slight depression located anterior and just superior to the sternum, where the neck attaches to the chest.
Above: Suprasternal notch window.
Above: Suprasternal Notch View (SSN) with imaging of the transverse aorta and a large portion of the descending thoracic aorta.
Position the transducer index mark initially toward the left shoulder and point the transducer downward, adjusting the transducer plane through experimentation, while looking for a dark, curved vessel which is relatively horizontal, then bending downward, becoming the descending aorta.
Imaging the aorta from the suprasternal notch can be difficult due to poor acoustic properties of the surrounding tissue(cartilage and bone) and the sometimes narrow or deep features of the fossa, as well as the distance the aorta may be from the transducer.
If the arch does not become immediately visible with the index mark oriented toward the left shoulder, slowly rotate the transducer a few degrees counter-clockwise or clockwise to see if it comes into view. If visualization is still difficult, it may help to lower the transducer frequency. Color Doppler can be of immense help in locating the descending aorta and subsequently, the aortic arch.
Above: Dual image of the transverse and descending thoracic aorta demonstrating color Doppler with 2-D only.
The transducer can be moved and angled slightly in any direction and even off the suprasternal notch if it makes the aortic arch easier to image. In tall persons and those whose heart is displaced downward due to lung disease or previous thoracic surgery, the transverse aorta can appear quite distant from the suprasternal notch and so it will look much smaller than expected.
In rare cases, the aortic arch may be impossible to image. This most often happens when a patient is intubated or has bandages or penetrating catheters in the area that block ultrasonic energy or prevent access to the window.
In adults, the ascending and right portions of the aortic arch are typically not easily visualized however, when they are visible, they can be recorded with and without color Doppler.
Once the aortic arch and descending aorta are located, adjust the depth so that it occupies most of the sector image. Record a clip with and without the Color Doppler box placed within the descending aorta. The color Doppler display will usually reveal a pulsing, primarily blue color, indicating that blood is moving away from the transducer, thus confirming its identification. If a dominantly red or orange Color Doppler signal is found during systole, it is an indication that the ascending aorta or some other vessel is actually being imaged.
Once the two-dimensional and color Doppler images have been obtained, the PW Doppler cursor is placed within the descending aorta, where it is at its brightest for the assessment of systolic and diastolic blood flow. It is important to place the sample volume beyond the termination of the aortic arch where once-again, the blood is moving in a relatively straight line in order to avoid recording the eddy currents produced by the curved portion of the vessel. Adjust the scale of the PW Doppler so that the velocity profile both above and below the baseline are clearly seen. Make certain that the PW Doppler filter is not set so high that it erases the diastolic blood flow recorded nearest the baseline.
Continuous Wave Doppler of the descending thoracic aorta from the same SSN window is used to assess for coarctation of the aorta. From the same cursor position as was used for the PW Doppler exam, switch the Doppler mode to CW Doppler. Tilt the transducer slightly in all directions within the lumen of the descending aorta in order to assure that the area has been thoroughly investigated.
The aortic arch can also be imaged in its short axis, which is very valuable when dilation or dissection is suspected. This is achieved by rotating the transducer counter-clockwise from where the arch was imaged until it appears as circular as possible. For the best images, decrease the depth and adjust the focus to the level of the aortic arch.
Both the long and short axes of the aortic arch provide valuable information concerning the diameter and integrity of the vessel. Pulsed Doppler can provide velocities at various points at the descending aorta for grading the severity of aortic valve insufficiency. Caliper measurements of the arch and descending aorta can aid in the assessment for suspected aortic dilatation, aneurysm and dissection.
Color Doppler can provide mapping of flow reversal or turbulence in order to help distinguish between moderate and severe aortic insufficiency, coarctation of the aorta and a false lumen found in aortic dissection.
The SVC ascends parallel to the ascending aorta. For this reason, it can also be found from the suprasternal notch position or the right supraclavicular window. Activate Color Doppler and from the aortic arch view, rotate the transducer approximately 90 degrees counter-clockwise so that the short axis of the aortic arch is within view. From the aortic arch, the face of the transducer is angled a few degrees toward the right side of the body. Color Doppler greatly aids in finding the SVC, revealing a streaming blue color, often faint, when its scale is adjusted to approximately 30 cm/sec, or as required. It may be necessary to increase the color Doppler gain in order to see the SVC blood flow better. In adults, the color Doppler signal is often the only way to visualize this vessel. Place the PW Doppler sample volume within the brightest blue portion of the color flow signal and record the Spectral Doppler displayed.
The Spectral Doppler recording of the SVC will look very closely like a recording of the IVC or hepatic vein in the subcostal view.
The suprasternal notch window is usually the final step in a routine Echocardiogram.
If the patient is being evaluated for aortic stenosis or prosthetic aortic valve, further examination with the Pedoff probe would begin at the suprasternal notch.
Right Supraclavicular View:
Closely related to the suprasternal view, the supraclavicular view is obtained with the transducer placed just above the collar bone immediately adjacent and the the right side of the suprasternal window.
From the supraclavicular window, a sometimes better view of the superior vena cava can be obtained. This view is also used for CW Doppler interrogation of the aortic valve. See the Pedoff probe section of this guide for more information.