Parasternal long axis view (PLAX)

How to acquire it?

The parasternal long axis (PLAX) view is usually the first view used at the beginning of the examination. The patient is positioned in the left lateral decubitus position, lying on his left with his arm tucked under his head. 

• Place the transducer in the 3rd or 4th intercostal space at the left parasternal border.
• The index marker should be pointing to the patient’s right shoulder at the 9 – 10 o’clock position.
• The left ventricle should appear perpendicular to the US beam. The apex is not seen on PLAX in the majority of patients, so the appearance of “false apex” needs to be eliminated by tilting, angling or rotating of the transducer. 
• If the LV is not horizontal enough, try moving to a higher parasternal window or tilt the patient more on his left side.
• Place the mitral valve (MV) and aortic valve (AV) in the centre of the image by tilting the probe away from sternum and make the atrioventricular (AV) cusps appear symmetric by rotating the probe .

What is visualized in PLAX? : Left atrium, Mitral valve, Left ventricle, Left ventricular outflow tract, Aortic valve, Right ventricle, Interventricular septum

‍Image 1 PLAX - marker should be pointing to the patient’s right shoulder at the 9 – 10 o’clock position.

‍Video 1 Normal PLAX view

Image 2 PLAX view anatomy

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2-dimensional measurements 

The PLAX view should be used for linear measurements of the left ventricle, RVOT diameter, LA diameter and aortic annulus and ascending aorta measurements. 

Routine linear M-mode measurements for quantification are not recommended!

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1) Left ventricle measurements

The LV wall thickness and internal diameter are measured in PLAX during end-diastole and end-systole. 

End-diastole = the first video frame immediately after mitral leaflet closure or it may be identified as the peak of the R wave on the ECG.

End-systole = usually the frame preceding the initial early diastolic opening of MV or the frame after aortic valve closure, obtained at the smallest cavity dimension of LV. On ECG identified at the end of the T wave.

Take care to only include the compacted myocardium and avoid papillary muscle, MV apparatus and septomarginal trabeculation.

LV internal diameter (LVID)

The diameter is measured immediately below the MV leaflet tips, perpendicular to the long-axis of the LV. Position the caliper at the inner edge of IVS and extend the line to the compacted myocardium of the posterior wall.

If isolated thickening of the basal septum (septal bulge, sigmoid septum) is present, the measurement should be moved towards the LV apex just beyond the septal bulge to avoid overestimation of the LV mass.

LV enddiastolic diameter (LVEDD) 

• Inner edge to inner edge, perpendicular to the long axis of the LV, at or immediately below the level of the mitral valve leaflet tips. 
• Perform at end-diastole (the largest LV dimensions/volume)

LV endsystolic diameter (LVESD) 

• Inner edge to inner edge, perpendicular to the long axis of the LV, at or immediately below the level of the mitral valve leaflet tips. 
• Perform at end-systole 

Image 3 Correct measurements of internal diameteres

2) LV wall thickness 

The Interventricular Septum (IVSd) and Posterior Wall (PWd) should be measured at end-diastole at the same time and position as the LVIDD. This measurement may be repeated at the end-systole.

IVSd

• Measure at end-diastole
• Only compacted tissue is included, avoid RV trabeculae, TV apparatus or insertion of the moderator band
• Place the caliper where RV meets the compacted septum and extend to the inner edge of LV cavity.

PWd

• Measure at end-diastole
• Place the caliper at the border of LV with compacted myocardium and extend to the LV posterior wall-pericardial interface. 
• Avoid MV apparatus – advance frame by frame to differentiate PW from papillary muscles, chordae tendineae and leaflets.

‍Image 4 Normal end-diastolic diameter of the LV, interventricular septum diameter and inferolateral wall diameter 

Image 5 Normal end-systolic diameter of the LV (LVESD)

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3) RVOT

RVOT diameter in PLAX (proximal part of RVOT)

• Measure at end-diastole
• Place the caliper at the inner edge of the anterior RV wall and extend to the junction between IVS and aortic valve. 

‍Image 6 RVOT diameter in PLAX

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4) LVOT and Aorta measurements

Image 7 Aortic root and ascending aorta diameters

Use the zoom function in the PLAX view for optimal visualization of LV outflow tract (LVOT) and the aortic valve with visualization of AV cusp insertion points (annulus).

‍Both MV leaflets and 2 of the 3 aortic leaflets should be visible in good quality.

a) LVOT diameter

• PLAX zoomed to LVOT and AV
• Measure in mid-systole = maximal opening of the AV
• The caliper line should be parallel to the aortic valve, placed approx. 3-10mm beneath the AV annulus.
• From  inner edge to inner edge.

Image 8 Normal LVOT measurement in mid-systole

b) Aorta measurements

4 measurements are taken in the PLAX view zoomed AV and ascending aorta and all are taken perpendicular to the long axis of aorta at their largest dimension. 

• Try to move the transducer 1-2 interspaces higher or reposition the patient to obtain complete view of the Asc Ao
• Freeze the image and scroll to a frame with closed AV and check if the image quality is suitable for measurement. 
• Two approaches to measurement of aortic dimensions may be used:
• inner edge-to-inner edge method - where you place the caliper on the interface of the aortic wall and the aortic cavity and extend to the other inner edge of the aortic wall, this is represented by the black arrow on picture below (this method is recommended by British Society of Echocardiography)
• leading edge-to-leading edge method - where you place the caliper on the outer interface of the aortic wall and extend to the interface between aortic wall and aortic cavity (this measurement comes from the M mode measurements, where it is easier to capture the leading edge, it is still a recommended method by the American Society of Echocardiography)

Image 9 Aortic root dimensions

Adapted from: Lang RM, Badano LP, Mor-Avi V, Afilalo J, Armstrong A, Ernande L, Flachskampf FA, Foster E, Goldstein SA, Kuznetsova T, Lancellotti P, Muraru D, Picard MH, Rietzschel ER, Rudski L, Spencer KT, Tsang W, Voigt JU. Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. J Am Soc Echocardiogr. 2015 Jan;28(1):1-39.e14. doi: 10.1016/j.echo.2014.10.003. PMID: 25559473.

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I) AV Annular diameter 

• PLAX zoomed to LVOT and AV
• measure in mid-systole = largest LVOT diameter
• Place the caliper at the inner edge of insertion point of the right cusp and extend to the inner edge of noncoronary/left leaflet

Image 10 Aortic anular diameter 

II) Sinus of Valsalva (SoVAo)

• Measure in end-diastole
• Use the inner edge-to-inner edge method and measure the maximum diameter of the sinus.

Image 11 Normal sinus of valsalva diameter in end-systole

III) Sinotubular Junction (STJ)

• Measure in end-diastole
• Place the caliper at the inner edge at the junction of the distal sinuses and origin of the tubular aorta and extend to the other inner edge.

Image 12Normal sinotubular junction diameter = 30 mm

IV) Ascending Aorta diameter (AscAo)

• Measure in end-diastole
• AscAo is measured at the largest dimension above the aortic sinuses
• Use the inner edge-to-inner edge method to measure the maximum diameter of Asc Ao
• The first few cm of aorta should be visible
• If the visibility is poor, try a higher parasternal window or ask the patient to remain in expiration

Image 13 Normal ascending aorta diameter

Image 14 Aortic root and ascending aorta diameters

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5) Left Atrial Measurements

• The LA is measured in end-systole using a leading-edge-to-leading edge method
• place the caliper at the sinus of valsalva of the aortic root and extend to the leading edge of the posterior LA wall (inner edge to inner edge - British Society of Echocardiography). 
• M mode measurement of LA diameter may be used – cursor is perpendicular to the aortic root and LA at the level of the aortic sinus. Then measure between the leading edge of the posterior wall of the aortic sinus and the leading edge of the posterior LA wall.

Image 15 Normal left atrial diameter 

6) PLAX zoomed MV 

• Parasternal window, PLAX view
• Adjust ROI to zoom on the MV
• Use this view to assess MV morphology and to show full range of motion of both leaflets, proximal chordae, and annulus.
• PLAX in standard position goes through the centre of the MV showing the A2 and P2 scallops. You can also see the postero-medial papillary muscle extending from the inferolateral (posterior) LV wall.
• To view the additional scallops simply change the angulation of the transducer: a) inferior tilt towards the RV inflow and Tri valve shows A3/P3 scallops, b) superior tilt towards RV outflow and pulmonary view shows A1/P1 scallops

7) PLAX zoomed AV 

• Zoom on the AV to demonstrate valve cusps. From a parasternal view, two cusps are seen: the right coronary cusp (RCC) is positioned anteriorly and extends from the ventricular septal aspect of AV annulus. However, the more posterior cusp in view may be either the non-coronary (NCC) or the left-coronary (LCC) cusp depending on the degree of beam tilt.

8) MV and AV colour flow assessment

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PLAX RV inflow view

• Obtain PLAX view
• Tilt the face of the transducer inferiorly towards the right hip
• Rotate slightly anticlockwise to visualize two of the TV leaflets – anterior with septal leaflet (if septum is visible) or posterior leaflet (if not).
• Centre on the TV, on the upper right is the RV anterior wall, the RV inferior wall on the left
• Coronary sinus (CS), Eustachian valve, Eustachian ridge or inferior vena cava (IVC) may be seen
• Apply CFD to the tricuspid valve to assess presence of any regurgitant jets

‍Video 2 Normal RV inflow view

Image 16 RV inflow view anatomy

‍Video 3 Colour Doppler of RV inflow tract with mild TR

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PLAX RV outflow view

• From PLAX, tilt the transducer towards the left shoulder and rotate slightly clockwise
• Better visualization of the RVOT
• Pulmonary valve (PV) with the main pulmonary artery (PA)
• Bifurcation of the PA may be seen

‍Video 4 PLAX RV outflow view

Image 17 PLAX RV outflow view anatomy

‍Video 5 Colour Doppler in PLAX RV outflow view

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References

1. Cheitlin MD, Alpert JS, Armstrong WF, Aurigemma GP, Beller GA, Bierman FZ, Davidson TW, Davis JL, Douglas PS, Gillam LD. ACC/AHA Guidelines for the Clinical Application of Echocardiography. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Clinical Application of Echocardiography). Developed in collaboration with the American Society of Echocardiography. Circulation. 1997 Mar 18;95(6):1686-744. doi: 10.1161/01.cir.95.6.1686. PMID: 9118558.
2. Mitchell C, Rahko PS, Blauwet LA, Canaday B, Finstuen JA, Foster MC, Horton K, Ogunyankin KO, Palma RA, Velazquez EJ. Guidelines for Performing a Comprehensive Transthoracic Echocardiographic Examination in Adults: Recommendations from the American Society of Echocardiography. J Am Soc Echocardiogr. 2019 Jan;32(1):1-64. doi: 10.1016/j.echo.2018.06.004. Epub 2018 Oct 1. PMID: 30282592.
3. Ayan R Patel, MD (2021). Transthoracic echocardiography: Normal cardiac anatomy and tomographic views. In I. Susan B Yeon, MD, JD, FACC (Ed.), UpToDate. Retrieved August 4, 2021 from https://www-uptodate-com.ezproxy.is.cuni.cz/contents/transthoracic-echocardiography-normal-cardiac-anatomy-and-tomographic-views?search=echocardiography%20chambers&source=search_result&selectedTitle=5~150&usage_type=default&display_rank=5
4. CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press
5. http://pie.med.utoronto.ca/tte/TTE_content/standardviews.html#introduction

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