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← Section III · Chamber Size and Function
III.H

Interatrial and Interventricular Septum

10 cards

Notes

Interatrial septum

  • Best imaged in the subcostal 4-chamber view (perpendicular to the septum → minimal drop-out).
  • Membranous fossa ovalis is thinner than surrounding muscular septum.
  • Lipomatous hypertrophy of the atrial septum: non-encapsulated fatty infiltration, characteristic dumbbell shape sparing the fossa ovalis. Benign; can be very echogenic.

PFO

  • Present in ~25 % of adults.
  • Right-to-left shunt on agitated saline contrast - bubbles appear in the LA within 3 cardiac cycles of RA opacification = intracardiac shunt (usually PFO or ASD).
  • Bubbles appearing after 3–5 beats suggest an intrapulmonary shunt (e.g., pulmonary AV malformation).
  • Valsalva release phase increases sensitivity for right-to-left shunt.

ASD types

  • Secundum - fossa ovalis defect; ~75 % of ASDs.
  • Primum - inferior AV septum; associated with cleft anterior mitral leaflet; part of AVSD spectrum.
  • Sinus venosus - SVC or IVC type; often associated with anomalous right PV drainage.
  • Coronary sinus - CS communicates with LA (unroofed CS).

Atrial septal aneurysm (ASA)

  • Excursion into either atrium > 10 mm from mid-plane, or 15 mm total excursion.
  • Associated with PFO and cryptogenic stroke.

Interventricular septum

  • Muscular vs membranous portions.
  • Membranous IV septum sits below the aortic valve, adjacent to the tricuspid septal leaflet.

VSD types

  • Perimembranous - most common; adjacent to the membranous IVS. Can be partially covered by TV septal leaflet → aneurysm formation ("windsock").
  • Muscular - trabecular part; may be single or multiple; often close spontaneously.
  • Inlet (AV canal) - associated with AVSD.
  • Outlet (supracristal / subpulmonary / infundibular) - often causes prolapse of the right coronary cusp of AV → AR over time.

Gerbode defect

  • LV-to-RA shunt through the membranous septum (sits between LV and RA, above the TV septal leaflet).
  • Rare complication of endocarditis, MI, or congenital.

Septal motion abnormalities on M-mode

  • RV pressure overload (PAH, PS): septum flattens in systole.
  • RV volume overload (ASD, severe TR/PR): septum flattens in diastole.
  • LBBB: early downward septal motion in pre-ejection, then upward during ejection ("septal bounce").
  • Post-cardiac surgery: paradoxical septal motion toward RV in systole with normal thickening - from translational motion, not true dysfunction.

Cards

  • basicIII.H-001
    Which echocardiographic view is most sensitive for interatrial septum evaluation?
    → Subcostal 4-chamber view — the beam is perpendicular to the septum, minimizing drop-out.
  • basicIII.H-002
    Describe lipomatous hypertrophy of the atrial septum.
    → Non-encapsulated fatty infiltration of the interatrial septum with a characteristic 'dumbbell' shape that SPARES the fossa ovalis. Benign; can be very echogenic.
  • basicIII.H-003
    On agitated saline contrast study, within how many cardiac cycles must bubbles appear in the LA to suggest an intracardiac (PFO) shunt?
    → Within 3 cardiac cycles of RA opacification. Later appearance (> 3–5 beats) suggests an intrapulmonary shunt (e.g., pulmonary AVM in HHT).
  • basicIII.H-004
    State four types of ASD in order of frequency.
    → 1) Secundum (~75%, fossa ovalis). 2) Primum (inferior AV septum, associated with cleft AMVL). 3) Sinus venosus (SVC or IVC type, often with anomalous right PV drainage). 4) Coronary sinus (unroofed CS).
  • basicIII.H-005
    Define an atrial septal aneurysm.
    → Excursion of the atrial septum > 10 mm into either atrium from the mid-septal plane, or 15 mm total excursion. Associated with PFO and cryptogenic stroke.
  • basicIII.H-006
    Which type of VSD is most likely to lead to progressive aortic regurgitation, and why?
    → Supracristal (outlet / subpulmonary / infundibular) VSD — the defect sits below the pulmonic valve near the aortic annulus. Right coronary cusp of the AV prolapses into the defect over time, leading to AR.
  • basicIII.H-007
    What is a Gerbode defect?
    → A congenital or acquired shunt from the LV to the RA through the membranous IVS, above the septal leaflet of the tricuspid valve. Rare complication of endocarditis, MI, or congenital heart disease.
  • basicIII.H-008
    Describe septal motion after cardiac surgery.
    → Paradoxical septal motion toward the RV in systole, with PRESERVED normal thickening. From translational motion of the heart (post-op adhesions/altered geometry), not true dysfunction.
  • basicIII.H-009
    Sinus venosus ASD is most commonly associated with what pulmonary vein anomaly?
    → Anomalous drainage of the right upper pulmonary vein (partial anomalous pulmonary venous return — PAPVR), typically into the SVC.
  • basicIII.H-010
    Most common type of VSD overall and its typical closure tendency?
    → Perimembranous VSD is most common overall. Muscular VSDs (particularly small ones) close spontaneously most often. Perimembranous defects may partially close by TV septal leaflet coverage ('windsock' or aneurysm formation).