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PSAx

PSAx is exactly 90 degrees from the perfect PLAx. So if your PSAx is off axis, your PSAx will be too. In this case, go back to PLAx, make this view as good as you can and then rotate 90 degrees to your right (or the patient's left). Typically, the probe marker will be towards the patient's left shoulder. 

You can assess the entire heart from the base to the apex in the PSAx view. It's like cutting a cross section of the heart.

To get a perfect PSAx, rotate the transducer 90 degrees from the perfect PLAx while maintaining the same angle and tilt. In the early stages, it may be helpful to use your free hand to rotate the probe.

PSAx is great for comparing the LV and RV size. In an ideal image, the RV should be elliptical and the LV round. If the LV doesn't look round, it may be an imaging issue, so rotate, fan and rock the transducer until you can make the LV as round as possible. 

Alternatively, you knowyou are on axis when the papillary muscles look symmetrical. If you are off axis, one papillary muscle will look smaller than the other or the mitral valve leaflets will be seen on one side and not the other. 

PSAx - MITRAL VALVE - FISHMOUTH VIEW

Because the typical PLAx is at the level of the MV, when you rotate to PSAx in this plane, you will see the MV opening and closing. This is called the fishmouth view (as seen above). 

On axis PSAx at the level of the Mitral Valve. Note the round LV. The RV draped over the LV like a water balloon

PSAx BASE OF HEART

If you now fan the tranducer towards the patient's suptraclavicular notch, you will look at the base of the heart. In this view, the Aortic valve will be in the centre of the screen. The aortic valve is tri-leaftlet and when it closes, looks like the Mercedes Benx sign. This view is good for AV assessment and also to assess atrial size.

Fanning towards the supraclavicular notch 

PSAx at the level of the aortic valve: base of the heart. The tri-leaflet aortic valve when closed looks like the Mercedes Benz sign

PSAx - PAPILLARY MUSCLE VIEW

From the base of heart view, if you fan towards the patient's nipple, you will first look at the MV and then further down at the papillary muscles. This is the pap muscle view. This view is great to assess RWMA of the LV.

Fanning towards the apex or the patient's nipple:

PSAx Pap muscle view. Sometimes it's easier to look at RWMA of the LV in this view because of the absence of the MV opening and closing

PSAx - LV APEX

To look at the apex of the heart (LV only - no RV), you will need to sweep the transducer laterally towards the patient's nipple. Do this last as you will slide out of the perfect PSAx view. 

Apex in PSAx: note RV is not seen at all. The walls may normally appear hypertrophic in the apex view. 

Try and fan through the base, MV and pap muscle views every time you look at the PSAx view of the heart. Things to look for in this view:

RV

Smaller than LV, the RV is usually about 2/3 of the LV size. Being a low pressure chamber, it has a triangular shape and seems to drape over the LV, kind of like an underfilled water balloon. A dilated, pressure overloaded RV on the other hand will appear like a round rock sitting on and pushing into the LV.

IV SEPTUM

Domes into RV

LV

The LV has a robust round shape with the IV septum doming into the RV cavity. Its walls thicken symmetrically during systole. The best way to assess for RWMA is to focus on the centre of the LV cavity and allow your eyes to passively take in the LV walls moving into the cavity. The area which isn't contracting will soon become clear. 

MITRAL VALVE

"Fishmouth" appearance. Anterior mitral leaflet opens to within 5mm of interventricular septum. 

PERICARDIUM

Bright white around the LV. 

TROUBLE SHOOTING FOR PSAx

With genuine RV pressure overload, the LV starts to look oblong and the IV septum is flat or bows into the LV. But off axis imaging can also create this. The way to know it is off axis instead of real pathology is by looking at the pap muscles. If both pap muscles are seen symmetrically on either side, you know your imaging is not the problem. 

However, if you can clearly see one pap muscle, but the other side shows chordae or MV leaflet, you know you're just off axis. in this case, go back to PLAx, make that view perfect and then carefully rotate without fanning or rocking. 

LV is oblong shaped. The pap muscle on the left (posterior) is smaller and shows some chordae: suggesting the imaging is off axis

LA OPENING INTO LV

The LA may open into the LV from the left inferior or right inferior of the screen. 

Opening from the right may be because you're fanning too much towards the base of the heart and getting the AV view intermittently. In this case, to get rid of the AV, fan towards the patient's nipple. 

The LA may also open from the right because you haven't rotated clockwise enough and you're getting a cross between the PLAx and the PSAx. Just a tiny bit more rotation towards the patient's left shoulder will close off the LV completely. 

If the LA is opening from the left inferior screen, you have rotated clockwise too much and started opening the heart into a four chamber view. Rotate anticlockwise a bit and your axis will improve. 

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