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Cardiac US

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The Views

PLAx

Parasternal Long Axis (PLAx) is usually the first echo window in the non arrested patient.

Probe placement:

  • 2-3rd Intercostal space, parasternal
  • Probe marker towards the patient's Right shoulder
  • Probe held vertically on the patient
Michael keeps his transducer parasternal, vertical on the patient's chest. Note how he stabilises the transducer with the outer fingers resting on the patient's chest. Also, the gel streak shows how he has moved around the intercostal spaces to find the best window.
Michael keeps his transducer parasternal, vertical on the patient's chest. Note how he stabilises the transducer with the outer fingers resting on the patient's chest. Also, the gel streak shows how he has moved around the intercostal spaces to find the best window.

An on-axis PLAx view has the heart lying on its side (horizontal) with the LV inferolateral wall and interventricular septum parallel to each other. The apex of the LV should not be seen. You should be able to see both the aortic valve (AV) and mitral valve (MV) opening and closing. 

Ideal PLAx image. Note the depth: descending aorta at the bottom of the screen

Adjust depth so the descending aorta is seen at the base of the screen 

PLAx should be reviewed systematically for pathology. I tend to go clockwise from the RV.

RV

Assess for size and contractility. RV should be the same size as the aorta and LA (approximately 3cm). This is the 1:1:1 rule you should always look for. The RV should also be smaller than the LV cavity (2/3 of LV cavity). The cavity should decrease with systole. 

AORTA

The aorta should be less than 3cm from outer edge to outer edge. The aortic valves should be thin and open fully.

LA

The height of the LA should be equal in size to the width of the aorta: approximately 3cm. The mitral valve should be thin and open fully into the LV. With normal LV function and an unrestricted MV, the anterior mitral leaflet should open to within 5mm of the interventricular septum. 

LV

The LV walls should be <1cm in diastole. The LV cavity should change in diameter by 30-50% with systole. The cavity width in diastole should be <6cm. In this view, the LV is bordered by the interventricular septum (between the RV and LV) and the inferolateral wall.

SEPTUM

The Interventricular septum should bow to the RV

PERICARDIUM

Hyperechoic and sits anterior to the descending aorta. In the normal heart, if there is any pericardial fluid, it should only be a trace and only seen during systole.

RV:LA:Ao in PLAx should be 1:1:1

TROUBLE SHOOTING FOR PLAx

HEART IS ON ITS HEAD

An on axis PLAx the heart sits horizontally in the screen (the heart on the left in the clip above). Or like i like to call it: the heart is lying on its side. Conversely, the heart on the right in the above clip seems to be doing a headstand (if you imagine the LA as the head and LV as the body). This happens when your intercostal window is too close to the apex of the heart. That is your transducer is too lateral and too low on the anterior chest. Slide/ sweep the transducer closer to the sternum and to a higher rib space to improve your image. 

This often happens when lung gets in the way in the high parasternal rib spaces and you keep sweeping the probe laterally to get rid of the lung. Turning the patient left lateral or getting them to hold expiration until you capture a clip can help with this.

LV WALLS SEEM TO BE CLOSING OFF

In an on axis PLAx, the LV walls should be parallel and the apex should not be seen. The LV walls should be coming together like they are clapping.  If the walls seem to be closing off and becoming circular, it means that you have rotated too much clockwise (ie towards the patient's left shoulder). The view is starting to become a short axis view of the heart - PSAx.

To fix this do a tiny rotation anticlockwise until you can open up the LV cavity again. 

RV INFLOW VIEW

In this case, you have fanned the transducer inferiorly towards the patient's toes (the tail of the probe is closer to the patient's chin) and you are slicing the beam of the US too superficially through the heart, thus getting the RV and RA. 

This view is great when looking for a TR jet, or for catching a clot in transit in the RA.

To get back to the on axis PLAx view, fan the transducer cranially or towards the patient's chin. 

RV OUTFLOW VIEW

This is the opposite of the inflow view. In this case you have fanned the transducer up the the patient's chin too much (the tail of the probe is now closer to the patient's nipple) and you start looking at the great vessels which are at the base of the heart, namely the pulmonary artery. This view is great for looking for PR, proximal PA clot etc.

To get back to the on axis PLAx fan the transducer slightly down towards the patient's toes, the tail of the probe will move closer to the patient's chin.

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PSAx