In an earlier post we looked at how to obtain the perfect on-axis image. I focused on the golden rule of “tilt for the centre and rotate for the sides”. But what happens if we aren’t in the right intercostal space to start with?!?!? Today’s post looks at how you can identify the correct intercostal space for imaging the parasternal long axis view (PLAX).
The intercostal space provides an acoustic window for the ultrasound to image the heart. We can’t see through bone (ribs or sternum) so we are completely reliant on being able to get the transducer between the ribs to obtain a view. The challenge is that there is usually more than one available intercostal space (window) for looking at the heart, but not all windows are the ideal window for that particular view. Student sonographers are often nervous to explore other windows, and are just happy that they found the heart at all.
Have confidence in yourself that if you found a window once, you can find it again…
The following tips take the guesswork out of how to find the correct window when imaging a PLAX view.
There are usually three distinct windows (or intercostal spaces) that we can image a PLAX view from. Too high, too low, or just right. The echo texts say to place the probe in the 3rd or 4th intercostal space, but there is too much individual anatomical variation in patients for that to be overly helpful. So, I suggest placing the probe on the chest, just to the left of the sternum in about the 3rd space to see how it looks.
If we are too high on the chest wall, the aorta is the predominant feature of the image. Often the LV is not well seen at this point, but very nice views of the mid ascending aorta can be obtained. This is useful for measuring the aorta, but it isn’t what we want for looking at the LV.
Here is the standard PLAX view. Note how the LV is in view, as well as the ascending aorta. The walls of the LV are seen as parallel with one another and the apex of the LV is not included in this view. This is the “ideal” intercostal space.
Often though, we are too low on the chest wall and the image more resembles an apical long axis view tilted onto its side. In this example the heart looks tilted up and the apex is more on view.
This should not be confused with rightward angulation of the aorta which can give a similar appearance. The key to differentiate between rightward angulation of the aorta (aka unfolded aorta, senile septum) and too low a transducer position is the relative angle of the LV major axis to the aorta. See example below; Note that the angle of the aorta is quite different to the normal heart.
Don’t be afraid of trying a rib space higher and lower. It is worth the effort to obtain the correct data.
Hope it helps!