PSAX (8)

DMST 253: Echo 1 - Parasternal Short Axis Anatomy and 2D Protocol

Overview

  • Course: DMST 253

  • Focus: Understanding the Parasternal Short Axis (PSAX) views used in echocardiography.

  • Publisher: SAIT Polytechnic, 2026.

  • Frequency: Patient Scans.

  • Frequency Response: 1.7 MHz/3.3 MHz.

Critical Thinking Case Study

  • Patient Profile: 32-year-old with transient vision loss and word-finding difficulties.

Parasternal Short Axis (PSAX) Imaging

  • PSAX Overview:
      - Imaged at 6 different levels.
      - The beam is swept from the base to the apex of the heart.
      - From the Parasternal Long Axis (PLAX) view, the probe is rotated 90 degrees clockwise.

Levels of PSAX Imaging

  • 1. PSAX Base (Aortic Valve Level):
      - Structures Visible: Aortic Valve (AV) (Right Coronary Cusp - RCC, Left Coronary Cusp - LCC, Non-Coronary Cusp - NCC), Left Atrium (LA), Left Atrial Appendage (LAA), Interatrial Septum (IAS), Right Atrium (RA), Septal Tricuspid Valve (TV) leaflet, Right Ventricle (RV), Pulmonary Valve (PV), Main Pulmonary Artery (MPA).

  • Appearance and Technique Notes:
      - Depth should extend slightly past LA.
      - AV must be centered with clear visibility of TV and PV.
      - RVOT and PA diameter may be taken as measurements in 2D.

  • 2. PSAX - Pulmonary Valve (PV) View (Bifurcation):
      - Patient rolled to Left Lateral Decubitus (LLD) position.
      - Structures Visible: Right Ventricular Outflow Tract (RVOT), PV, MPA, Right Pulmonary Artery (RPA), Left Pulmonary Artery (LPA).

  • 3. PSAX - Mitral Valve (MV) Level:
      - Structures Visible: Right Ventricle free wall, Right Ventricle chamber, Interventricular Septum (IVS), Anterior Mitral Valve Leaflet (AMVL), Posterior Mitral Valve Leaflet (PMVL), MV annulus.
      - Important to assess symmetry of MV opening to ensure the view is on-axis.

  • 4. PSAX - LV Base Level:
      - Structures Visible: Posteromedial Papillary Muscle, Anterolateral Papillary Muscle, Chordae Tendinae.
      - Important to check LV wall motion but not routinely done at all sites.
      - LV appears round and assesses LV wall motion.

  • 5. PSAX - Mid (Papillary Muscle) Level:
      - Contraction of all LV walls is evaluated simultaneously.
      - Structures: both papillary muscles should be attached to LV wall (avoid over-rotation).

  • 6. PSAX - Apex Level:
      - Must slide toward apex, with LV appearing as a smaller circle.
      - Structures usually include the IVS and RV only as a sliver.

PSAX Pitfalls

  1. If uncertain of the view while capturing PSAX, revert back to PLAX for centering.

  2. Over-rotation:
      - Ensure the AV is round and symmetrical at baseline and not opening sideways.
      - Check MV across levels to confirm roundness and symmetry, avoid mis-centering.

PSAX Measurements

  • RVOT Diameter Measurement:
      - Normal diameter is less than 2.7 cm, measured from medial to lateral sides of the RVOT.

  • Pulmonary Artery Diameter Measurement:
      - Associated with RVOT and may sometimes be measured distal to the PV.

Coronary Arteries

  • General Information: Two primary branches originate from the aorta:
      - Left Coronary Artery (LCA): Includes LAD (Left Anterior Descending artery) and Left Circumflex artery (Cx).
      - Right Coronary Artery (RCA): Travels rightward along the AV sulcus towards the posterior heart, gives rise to the Right Marginal Artery and PDA (Posterior Descending Artery), often from the RCA, supplying the posterior inter-ventricular sulcus.

Perfusion Territories

  • Purpose: Each wall of the heart is perfused by corresponding arteries, which helps in indirectly diagnosing ischemia or infarctions based on wall motion.

  • Examples:
      - Anterior wall perfused by LAD, inferior walls by RCA, etc.

LV Segments in Planes

  • Segmentation Details: Must memorize levels and respective arteries that supply each segment.

  • Common Segmentation Names:
      - Base: Septal and Lateral Segments.
      - Mid & Apex: Should specify LV anterior, inferior, and lateral segments.

Comprehension Questions

  • To reinforce learning, practical questions might include:

  1. Draw and label the 3 levels of the LV in PSAX.

  2. Create a diagram of PSAX base view with AV leaflet names.

  3. Identify which view best shows right and left pulmonary arteries.

  4. Describe coronary artery perfusion territories.

Conclusion

  • The PSAX provides essential insights into cardiac structure and function through various levels and careful orientation.

  • Mastery of techniques and identification of anatomical features are critical for effective echocardiography.