Morphological Features of AVSD on the Short-Axis View
Atrioventricular septal defect (AVSD) is best approached as a malformation of the atrioventricular (AV) junction, not simply “ASD + VSD.” The defining substrate is a common AV junction guarded by a characteristic 5-leaflet valve, with secondary re-organization of the LVOT geometry, papillary–chordal apparatus, and conduction system [1]. Modern management emphasizes that these morphologic relationships—visible on the basal short-axis plane—are the best predictors of (i) LVOT obstruction, (ii) left AV valve (LAVV) competence, and (iii) AV block risk [1, 2].
1) What the basal short-axis plane is really showing
In the short-axis slice through the AV junction, the goal is to convert “labels” into a functional map.
Landmarks to identify first
- Aortic valve (AoV) position relative to the AV junction (wedged vs unwedged) [1]
- Septal crest / ventricular septum (the “bridge” the valve spans) [1]
- Common AV valve components
- Superior bridging leaflet (SBL)
- Inferior bridging leaflet (IBL)
- Right and left mural leaflets (plus the right-sided anterior component depending on schema) [1]
- LV papillary muscles (their spacing/angulation is often abnormal) [3, 4]
- The conduction “danger zone” (AV node/His axis is displaced) [1]
Interpretation principle
➡ In AVSD, valve competence and LVOT patency are coupled systems: leaflet geometry cannot be interpreted without the subvalvar apparatus and LVOT configuration [2].
2) Aortic valve: the “unwedged” (anteriorly displaced) aorta
Core morphologic concept
- In the normal heart, the AoV is relatively “wedged” between the mitral and tricuspid annuli.
- In AVSD, loss of normal AV septation produces an “unwedged” aorta with inlet–outlet disproportion and an elongated LV outlet length [1].
Why this matters (LVOT vulnerability)
- The elongated LVOT (“gooseneck” configuration) predisposes to baseline narrowing and later LVOT obstruction, often as a multifactorial process rather than a single discrete lesion [3, 4].
- Morphometric analyses highlight that LVOT risk is not simply “diameter,” but the 3D relationship between the outflow tunnel and the AV valve/subvalvar apparatus [3, 4].
Practical echo implication
➡ LVOT assessment should include: subaortic geometry, tunnel length, and any chordal/leaflet tissue encroaching on the outflow, not diameter alone [3, 4].
3) Common AV valve: a 5-leaflet valve in a single junction
AVSD is characterized by a common AV junction guarded by a valve with a 5-leaflet architecture, with the bridging leaflets spanning the septal crest [1]. This is why “two valves + a hole” language is misleading.
Surgical–echo translation
- The bridging leaflets (SBL/IBL) determine:
- where coaptation will (or will not) occur,
- how much tissue/chordae may drift toward the LVOT,
- and what “cleft/zone of apposition” closure can realistically achieve.
Durability principle
➡ Even after an excellent repair, the LAVV is not a normal mitral valve. Persistent vulnerability reflects intrinsic abnormalities in leaflet geometry and—critically—the subvalvar apparatus [5].
4) LV papillary muscles: malalignment that predicts LVOT and LAVV behavior
The short-axis view is ideal for appreciating papillary muscle geometry. A classic AVSD pattern (as in your schematic) is:
- Anterior papillary muscle (APM) deviates rightward
- Posterior papillary muscle (PPM) deviates leftward
This can be reframed as abnormal spacing, angulation, and chordal vector alignment, which can:
- narrow the LVOT directly (muscle within/near the tunnel), and/or
- tether bridging/anterior valve tissue toward the LVOT, coupling LVOT narrowing with LAVV mechanics [3, 4].
Echo predictors of post-repair LVOT obstruction
- Contemporary echo-derived predictors emphasize small LVOT dimension and chordae crossing/encroaching on the LVOT as high-yield markers for later LVOTO risk [6].
- These variables can be combined into practical prediction tools (reported model performance in the mid–high accuracy range in single-center series), reinforcing the concept that LVOTO is often “preloaded” by pre-repair morphology rather than created purely by the patch [6].
5) Conduction system: the displaced AV node and “no-go” suture territory
A defining surgical hazard in AVSD is posteroinferior displacement of the AV node/His axis, altering where conduction tissue lies relative to the septal crest and inferior bridging leaflet attachments [1].
Operative implication
- The safe repair strategy is not only about closing the septal components, but about respecting the displaced conduction axis when placing sutures along the inferior/posterior margins of the defect complex [1].
➡ In other words: the anatomy tells you where AV block lives.
6) “Recent” imaging emphasis: why 3D echo changes planning
Modern echo practice increasingly uses 3D imaging (TEE or transthoracic 3D where feasible) to define:
- bridging leaflet geometry,
- commissural relationships,
- chordal insertions and crossings,
- and the true mechanism of LAVV regurgitation in a way that 2D imaging may under-represent [7].
Practical upgrade
- Use 2D short-axis for landmark orientation and LVOT screening.
- Add 3D datasets to confirm the repair-relevant mechanism (coaptation line, cleft/zone of apposition configuration, and chordal constraints) [7].
7) A concise short-axis checklist (morphology → consequence → planning)
- AoV unwedged / inlet–outlet disproportion? → anticipate elongated LVOT and track LVOTO risk [1, 3]
- Any bridging leaflet/chordae near the LVOT? → LVOTO risk increases, especially post-repair [4, 6]
- Papillary muscle malalignment (spacing/angles)? → LVOT–LAVV coupling; consider subvalvar contribution to obstruction/regurgitation [3, 4]
- Conduction danger zone mapped? → suture strategy must respect displaced AV node/His axis [1]
- 3D confirmation obtained? → refine mechanism-based LAVV and LVOT planning [7]
References
[1] Adachi I, Uemura H, McCarthy KP, Ho SY. Surgical anatomy of atrioventricular septal defect. Asian Cardiovasc Thorac Ann. 2008;16(6):497-502.
[2] Shuhaiber JH, Ho SY, Rigby M, Sethia B. Current options and outcomes for the management of atrioventricular septal defect. Eur J Cardiothorac Surg. 2009;35(5):891-900.
[3] Suzuki K, Ho SY, Anderson RH, Becker AE, Neches WH, Devine WA, Tatsuno K, Mimori S. Morphometric analysis of atrioventricular septal defect with common valve orifice. J Am Coll Cardiol. 1998;31(1):217-223.
[4] Gallo P, Marino B, Calcagni G, Marcelletti C. Left ventricular outflow tract obstruction in atrioventricular septal defects: a pathologic and morphometric evaluation. Clin Cardiol. 1991;14(6):513-521.
[5] Kanani M, Elliott M, Cook A, Juraszek A, Devine W, Anderson RH. Late incompetence of the left atrioventricular valve after repair of atrioventricular septal defects: the morphologic perspective. J Thorac Cardiovasc Surg. 2006;132(3):640-646.e1-3.
[6] Abarbanell GL, Morrow G, Kelleman MS, Kanter KR, Border WL, Sachdeva R. Echocardiographic Predictors of Left Ventricular Outflow Tract Obstruction following Repair of Atrioventricular Septal Defect. Congenit Heart Dis. 2016;11(6):554-561.
[7] Faletra FF, Nucifora G, Ho SY. Real-time 3-dimensional transesophageal echocardiography of the atrioventricular septal defect. Circ Cardiovasc Imaging. 2011;4(3):e7-9.