General

RSE – The fifth acoustic window

Today’s post focuses on the “fifth” acoustic window to the heart, the right sternal edge (RSE). The right sternal edge , or right sternal border, allows improved visualization of the mid to distal ascending aorta and potentially an improved angle of incidence for assessing aortic stenosis. Whilst some consider this a routine component to the scan, other sonographers are quite unsure of how to approach this.

The aorta begins its course just to the left of the sternum, travelling superiorly from the heart towards the suprasternal notch. The normal aorta passes from the left side of of the sternum at around the 3-4th intercostal space (aortic valve), heading behind the sternum and continuing to the right of the sternum at approximately the 2nd intercostal space before curving at the aortic arch just below the suprasternal notch, then heading inferiorly and posteriorly down the chest cavity as the descending thoracic aorta. As we get older and/or the aorta dilates, the artery also becomes longer (think of it like when the elastic goes from your socks and there seems to be a lot more material). The base of the heart is fixed in place by the pulmonary veins, effectively anchoring the aorta at its origin. The aorta is also anchored at the aortic arch by the ligamentum arteriousum. This means the angle needs to change to accommodate the increased length of the artery and we see a rightward angulation of the aorta. In this case, the majority of the ascending aorta then lies behind or to the right of the sternum, making imaging of the full length from a left sternal approach often impossible.
The RSE approach is critical for comprehensive assessment of ascending aortic morphology.

Patient positioning and transducer orientation

Position the patient steeply on their right side with the right arm extended towards the head of the bed with the left arm down by their side (right lateral decubitus position). Start with the probe close to, but to the right of, the sternum in around the 3rd intercostal space. As a rule of thumb it will be an intercostal space higher than where you obtained your left parasternal images. You should see the mid ascending aorta at this point as two parallel lines, with the right pulmonary artery in short axis. If you can see the aortic valve, you are too low on the chest and need to be an intercostal space higher. The transducer will be rotated to about 11 o’clock, but this will depend a lot on the amount of rightward angulation (young patients will be closer to vertical, older patients are rotated anticlockwise back to ~ 10 o’clock). And always remember the Golden Rule for obtaining an on-axis image: tilt for the center and rotate for the sides (and always in that order). You will need to rotate the probe to open out the walls of the aorta as two parallel lines.

Still struggling to get a good image?? Most commonly you need to tilt the patient steeper, or try imaging with a full breath out (the patient, not you!!!).

When/how should we image from RSE?

I obtain 2D images of the aorta from the RSE in the following patients:

  • Dilated aorta measured in any other view, irrespective of image quality
  • Bicuspid aortic valve
  • Marfan’s syndrome
  • Mitral valve prolapse
  • Known aortopathy or other systemic condition associated with aortopathy
  • Hypertension
  • Aortic stenosis
  • When I haven’t seen the aorta well in the PLAX view. This includes when I can’t get high enough up the aorta or haven’t imaged the aorta as two parallel lines. Typically I aim to image / measure the mid ascending aorta at the point where we see the right pulmonary artery in short-axis. (Need image)
  • And anytime that I am just about to use the non-guided CW probe from that window (this will help you find the correct window and save heaps of time)

This is not an exhaustive list, but you will note that the list also doesn’t leave many patients that wouldn’t fall into one of these categories. It is pretty rare that I don’t perform a RSE view.

Non-guided CW (PEDOF) probe

Ped-hoff

Often incorrectly referred to as a pedof, pedoff or even a Ped-Hoff probe. It is actually spelled PEDOF and stands for Pulsed Echo Doppler Flowvelocity meter. PEDOF was originally developed in 1976 as a PW Doppler probe, which was later modified for CW Doppler. Thanks to David Adams for the recent history lesson.

Non-guided CW (PEDOF) probe is a must for proper interrogation of native aortic valve stenosis and for aortic valve replacement (AVR) assessment. There is a common misconception that modern advances in transducer and processor technology has removed the need for a dedicated CW probe. In other words, there is a misguided belief that velocities just as high can be obtained with the regular imaging transducer using guided CW. The primary benefit of the PEDOF probe is the small angled transducer face which can be placed more effectively between the rib spaces, improving the ability to reduce the Doppler angle of incidence. An experienced sonographer will always get at least as high a velocity with the non-guided, and most times will obtain a significantly higher velocity with the PEDOF (compared to imaging transducer). It is estimated that velocities may be underestimated by as much as 20% by only using the imaging Tx.

in other words… YOU MUST USE PEDOF FROM MULTIPLE WINDOWS TO ADEQUATELY ASSESS AORTIC STENOSIS!!
Check out this example of how multiple acoustic windows were needed to accurately estimate mean aortic gradient in this patient with severe aortic stenosis.

PEDOF_window_example

 

Most common mistake when obtaining the aortic signal from the RSE.

Inexperienced sonographers are sometimes so excited/relieved to obtain a Doppler signal above the baseline that they anxiously hit freeze and store the signal. Remind yourself what qualities of the signal tell you that you have the correct signal from the apex…strong, dense signal with a clear opening and closing click. This often gets forgotten about from the RSE and some people store the aortic flow, rather than the flow through the actual valve orifice… If you are in the right spot, you will get clicks.

Non-guided CW Doppler from RSE. There is a signal above the baseline which looks like the correct signal, but note the absence of valve clicks.

Non-guided CW Doppler from RSE. There is a signal above the baseline which looks like the correct signal, but note the absence of valve clicks.

Improved line-up through the aortic valve. Note the opening and closing clicks, indicating ultrasound is passing through the valve rather than the ascending aorta.

Improved line-up through the aortic valve. Note the opening and closing clicks, indicating ultrasound is passing through the valve rather than the ascending aorta. Much higher velocity.

 

Similarly, If you are in the right spot, you don’t need a lot of Doppler gains. If you find you are increasing the gains to fill out the signal (and the background is now full of echoes) then you are probably not in the right space.

 Practice, practice, practice…

RSE imaging, especially with the PEDOF probe, should be second nature. The addition of the RSE view should not add more than 1-2 minutes to the standard scan. Just keep practicing. I often hear people say that that you can only get a RSE view in patients with severe AS or a dilated aorta…this is simply not true. If you look you can get it in nearly everyone.

 

When do you use RSE imaging?? Got some tips for finding the perfect signal?? Add your experience to the comments below.


Update – 21/12/2015

A good RSE image will allow visualisation of the ascending aorta, at least up to the level of where the right pulmonary artery is in short-axis.

nice_RSE_overviewnice_RSE_zoom_label

In reality though, images this nice are rare… and more commonly look like this…

difficult_rse

 


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15 Comments

  • Reply Susan Spell April 11, 2015 at 6:48 pm

    Awesome, awesome, awesome !! I appreciate the way you always provide background knowledge along with the instruction. This allows us to truly understand “why” we are performing each step instead of merely memorizing them. This, of course, leads to much success.

    You truly have a gift and a calling !!
    Thank you so much for always providing information to our profession that is ALWAYS relevant on a daily basis !!

    • Reply echoguru April 11, 2015 at 9:25 pm

      Thanks for your support and really kind words Susan!!

  • Reply Dushyant April 12, 2015 at 2:38 am

    Thanks, that was very useful , RSE. You list hypertension (common reason for echo request) as a reason to better image the mid – distal aorta, Should this (RSE, better image mid-distal aorta) be added to the ‘regualr/routine’ echo.

    Could you address in a future topic, the IVC and its use assess RA pressure, how to best evaluate, exact focus point on the IVC ? 1cm dital to hepatic vein junction ,postion of patient, quiet breathing , sniff, M-mode of IVC , Thnx

    • Reply echoguru April 12, 2015 at 11:54 am

      I think the RSE should be imaged a lot more than most people are… I don’t think it necessarily needs to be in the routine examination but I personally image it more often than I don’t.
      IVC tips post is coming soon….

  • Reply Kyle April 12, 2015 at 8:02 pm

    Thank you, I’m going to be practicing the RSE a lot more now. This information is very helpful.

  • Reply Ron April 13, 2015 at 12:34 am

    I’m self taught so I had an idiot for a teacher 🙂 Kidding aside I am thankful for your insights they provide me with nuances which improve my studies and make me a better Echocardiographer. Thanks again for your help.

  • Reply Justin Gordon April 16, 2015 at 5:33 am

    The RSE should form part of the routine scan when assessing aortic gradients. The RSE examination should also be used routinely when assessing a patient for an ASD or suspected PFO / ASD. The RSE has proven to be helpful in assessing the atrial septum and in identifying both sinus venosus ASDs and partial anomalous pulmonary venous drainage in adult patients. Once the ascending aorta in visualised, slight righward and inferior angulation of the probe should allow for visualisation of the SVC as it enters the RA and the inter-atrial septum, with defects in this area readily appreciated. Further manipulation of the probe position on the patient should also show the IVC entering the RA and the inferior posterior portion of the atrial septum. This “forgotten view” will only add another minute or 2 to the standard scan but may indeed prove diagnostic for an ASD and save the patient from undergoing more invasive investigations.

    • Reply echoguru April 16, 2015 at 5:36 am

      Thanks for the great imaging tip Justin! I sense an additional RSE post on the “forgotten view” coming up!

  • Reply LITFL Review 177 April 26, 2015 at 4:42 am

    […] has some great advice on the uncommonly used right parasternal window for echocardiography. […]

  • Reply Steve November 4, 2015 at 1:12 am

    Nice article, very helpful. Could you please add a typical 2D image that we might expect to see from this view so that we know what we are aiming for?

    • Reply echoguru November 4, 2015 at 1:14 am

      Thanks Steve. Great idea…I’ll add one next week when I’m back in a hospital.

  • Reply trapullasPablo December 26, 2015 at 9:31 pm

    I am self taugth too, so same poor teacher…I found your post and started to use this view. I found it wonderful for aorta, but usually square to it, so unusefull to get gradients. Any trick? Thanks a lot for your sharing

    • Reply echoguru December 29, 2015 at 3:08 am

      Just because you are perpendicular to the aorta does not mean that it is a useless view for obtaining peak gradients. This is actually the point of using multiple windows. We want to find the view which gives the highest gradient by reducing the angle between the ultrasound beam and the direction of flow. The angle of the aorta is irrelevant, it is the angle of the flow passing across the valve that we are chasing.

  • Reply Pablo January 5, 2016 at 1:55 pm

    OK, thank you very much

  • Reply Syed Abid Raza October 20, 2017 at 12:15 am

    Excellent work, since many years I have been looking for the information of how to get right parasternal view and what is relative position of different structures seen. Millions of thanks

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