Parasternal Long Axis: What to Acquire and How to Measure
TTE Imaging Series, Part 1
Whether you're new to cardiac sonography or fine-tuning your technique, mastering the parasternal views is a fundamental part of every transthoracic echocardiogram. The parasternal long-axis (PLAX) view isn’t just an entry point—it’s packed with structural detail and critical for obtaining accurate measurements. This article walks you through a step-by-step mock protocol for acquiring and measuring these views with confidence, using standards based on ASE guidelines.
This article is the first in a five-part series on transthoracic imaging protocol. Each installment will break down a different window using practical scanning tips and guideline-based measurements. Part 2—focused on parasternal short-axis (PSAX) imaging—will be published on June 17, 2025.
Keep in mind that while this guide outlines a standardized approach, imaging protocols may vary by institution depending on clinical focus, workflow, or pathology-specific requirements. Always refer to your lab’s protocol to ensure your studies align with local documentation and measurement expectations.
Parasternal Long-Axis (PLAX) View
Patient Positioning and Probe Setup
Position the patient in the left lateral decubitus position. Place the transducer in the 3rd or 4th left intercostal space, just left of the sternum. The probe marker should be aimed toward the patient’s right shoulder, approximately the 10 o’clock position. Your goal is to image the left ventricle (LV) nearly horizontal to the screen — perpendicular to the ultrasound beam.
PLAX Increased Depth
Image 1: Use an increased imaging depth to visualize the LV cavity (known as the scout view), posterior pericardium, and beyond. This helps assess for pericardial or pleural effusion. (For more, see Pericardial Effusions)
Scanning Tip: In the majority of patients, the LV apex will not be seen in this view. If the LV apex is visualized, ensure that it isn’t a “false apex” and that the LV isn’t foreshortened or obliquely cut. Reposition the patient, adjust the transducer angle, rotation, or tilt to lengthen the LV cavity.
PLAX Optimized Depth
Image 2: Once the initial scout view confirms your axis, reduce the depth and adjust the focus position to the level of the posterior wall. Center the aortic valve (AV), mitral valve (MV), left ventricle (LV), and right ventricle (RV) in your field. You should see motion of both MV leaflets and two of the three AV cusps.
Left Ventricular Single Plane Dimensions
Image 3: Freeze image at end-diastole, ideally the first frame after MV closure when the chamber is at its largest. The LV should be imaged in its true long axis with no papillary muscles in view. The interventricular septum, left ventricular end-diastolic dimension, and posterior wall are measured in this still frame image through the mitral leaflet tips.
Image 4: Freeze image at end-systole, ideally the frame just before MV opening. The left ventricular end-systolic dimension is measured in this still frame image and the machine will calculate the single plane ejection fraction known as the “Teichholz method”.
In some cases, a septal bulge is seen on the basal interventricular septum. Measuring distal to this thickening towards the middle of the cavity is recommended. (For more, see Sigmoid Septum)
Aortic Valve Zoomed View
Image 5: Zoom in on the aortic valve and the left ventricular outflow tract (LVOT). To optimize visualization and measurements—slide the transducer superiorly toward the sinotubular junction until the best view is achieved.
Image 6: Freeze during mid-systole, measure the LVOT diameter just below the aortic valve from inner-edge-to-inner-edge. This should be taken 0.3-1.0cm from the valve orifice at the same location PW Doppler will be used in the apical 5 chamber view.
Image 7: Freeze during end-diastole, measure leading-edge-to-leading-edge, perpendicular to the aortic long axis to measure the following aortic structures…
Sinus of Valsalva or Aortic root (AoR)
Sinotubular junction (STJ)
Ascending aorta
Image 8: Apply color Doppler over the aortic valve and LVOT. Adjust the color box to avoid overgaining and ensure it includes the entire LVOT, annulus, and proximal ascending aorta. Evaluate for signs of aortic regurgitation or stenosis, such as diastolic flow reversal or aliasing through a narrowed valve. (For more, see Aortic Stenosis)
Mitral Valve Zoomed View
Image 9: Focus your zoom on the MV and left atrium (LA) to include both MV leaflets, the annulus, and inflow region.
Image 10: Freeze at end-systole, measure the left atrial diameter from leading-edge-to-leading-edge, the posterior wall of the sinus of Valsalva to the posterior LA wall, perpendicular to the LA axis.
Image 11: Apply the color Doppler box over the mitral valve, annulus, leaflet coaptation zone, and proximal inflow area. Evaluate for systolic flow reversal into the left atrium (mitral regurgitation) or aliasing flow through the valve opening (mitral stenosis).
Right Ventricular Inflow View
Image 12: To see the tricuspid valve (TV), right atrium (RA), and proximal IVC, tilt the probe inferiorly and rotate slightly counterclockwise. The coronary sinus and Eustachian valve (EV) may also be visible. Center the TV and try to image at least two of its leaflets.
Image 13: Apply color Doppler, align with flow through the tricuspid valve, extending from the right atrium into the right ventricle. Color Doppler in this view is particularly useful for evaluating tricuspid inflow during diastole and detecting tricuspid regurgitation (TR) during systole.
Image 14: CW Doppler through the TV in the RV inflow view is used to assess TR, which is essential for estimating right ventricular systolic pressure (RVSP). When the TR jet aligns well with the ultrasound beam, this view allows accurate measurement of its peak velocity. Although less commonly used, it can also help evaluate for tricuspid stenosis (TS) when present.
(For more, see Tricuspid Regurgitation)
Right Ventricular Outflow View
Image 15: From the standard PLAX, tilt anteriorly and rotate slightly clockwise to bring the pulmonic valve (PV), RVOT, and main pulmonary artery (PA) into view. In some patients, the PA bifurcation may be visible.
Image 16: Apply color Doppler over the RVOT and PV to assess for flow acceleration, pulmonic stenosis, or regurgitation.
Image 17: PW Doppler can be used to sample flow within the RVOT and just below the PV, helping assess timing and velocity of systolic outflow.
Image 18: CW Doppler through the RVOT and PV is essential when higher velocities are suspected, such as in pulmonic stenosis or elevated pulmonary pressures, and is also the preferred method for evaluating pulmonic regurgitation.
(For more, see Patent Ductus Arteriosus)
Support Our Mission
Thank you for reading this lesson! We hope it brought more clarity and confidence to your scanning routine—whether you’re just starting out or sharpening your skills.
Stay tuned for Part 2 of this series on parasternal short-axis imaging, coming out on June 17, 2025.
If you found this helpful, we’d be so grateful if you shared it with your network on LinkedIn and tagged us—your support helps our lessons and practice tests reach more echo fanatics just like you!
References
Dewitt, Susan King, et al. Echocardiography: ... From a Sonographer’s Perspective. S.K. DeWitt, 2018.
Mitchell, Carol, et al. “Guidelines for performing a comprehensive transthoracic echocardiographic examination in adults: Recommendations from the American Society of Echocardiography.” Journal of the American Society of Echocardiography, vol. 32, no. 1, Jan. 2019, pp. 1–64, https://doi.org/10.1016/j.echo.2018.06.004.
Otto, Catherine M. Textbook of Clinical Echocardiography. Elsevier/Saunders, 2019.
Palma, Richard A. Echocardiographer’s Pocket Reference. 2020.
Disclaimer