Classification of Ventricular Septal Defects (VSDs): A Landmark-Based, Surgery-Ready Framework

A VSD description becomes truly actionable when it is anatomy-first:

(1) define the defect by what forms its rims (fibrous vs muscular) and

(2) localize where it opens on the RV septal surface using consistent right-ventricular landmarks.

This “rim + RV-compartment” method is the most transferable language across echo, operative exposure, and risk prediction—particularly for conduction injury and semilunar valve distortion. [1, 2]

1) Orientation: RV landmarks that organize VSD morphology

Before “naming” the defect, identify these structures from the RV perspective:

• Membranous septum (fibrous area near AV–arterial continuity)
• Tricuspid valve (TV) plane (inlet boundary)
• Aortic valve (AoV) and pulmonary valve (PV) planes (outlet boundary)
• RV outflow tract (RVOT) / outlet septal region
• Septomarginal trabeculation (septal band) and moderator band (trabecular framework)

Decision rule → classification becomes straightforward once you answer:

1. Is any part of the rim membranous/fibrous? → Perimembranous
2. Is the rim entirely myocardium? → Muscular
3. Is the superior rim formed by both semilunar valves (AoV + PV) due to outlet septal deficiency? → Doubly committed juxtaarterial

This logic mirrors the classic morphologic framework proposed by Soto et al. and refined in later anatomy-focused reviews. [1, 2]

2) Category A — Perimembranous VSDs: “anchored” at the membranous septum

Core definition

A perimembranous VSD (pmVSD) borders the membranous septum, typically within the zone of tricuspid-to-aortic fibrous continuity. [1, 2]

Why it matters (surgical/clinical implications)

• The conduction axis courses close to the posteroinferior rim → closure must respect this border to minimize complete heart block risk. [2, 4]
• The lesion frequently interfaces with valve tissue (TV and/or AoV) → the report should explicitly describe valve attachments and cusp support.

Subtypes (by dominant RV opening / extension)

1. Outlet-type pmVSD
• pm “anchor” with extension toward the RVOT/outlet septum beneath the AoV.
• Reporting focus: AoV cusp support/prolapse, RVOT muscle relationships.
2. Central-type pmVSD (confluent / trabecular extension)
• pm “anchor” with broader extension into the trabecular septum.
• Reporting focus: effective orifice(s) (single vs fenestrated), shunt geometry.
3. Inlet-type pmVSD
• pm “anchor” with extension toward the TV inlet.
• Reporting focus: TV chordal/leaflet attachments and the posteroinferior rim (conduction-risk zone).

Reusable echo/OR phrasing

“Perimembranous VSD with membranous septal involvement and dominant extension toward the RV [outlet / central(trabecular) / inlet] compartment.” [1, 2]

3) Category B — Muscular VSDs: “fully rimmed by myocardium”

Core definition

A muscular VSD has a circumference formed entirely by myocardium—with no membranous/fibrous border. [1, 2]

Natural history and practical implications

• In a large pediatric follow-up cohort (n=799), muscular VSDs showed higher spontaneous closure than perimembranous defects (overall spontaneous closure ~42.7% for muscular vs ~13.1% for perimembranous), with many closures occurring early in life. [3]
• The main challenges are often multiplicity and exposure (apical/trabecular defects), rather than conduction proximity.

Subtypes (by RV compartment)

1. Outlet muscular VSD
2. Apical trabecular muscular VSD
• Often multiple (“Swiss-cheese” spectrum); describe number, dominant defect, and whether there is a true principal orifice.
3. Inlet muscular VSD
• Inlet location without membranous involvement (the rim statement prevents mislabeling as inlet-type pmVSD).

Anti-confusion habit (high yield)

Always pair the label with the rim statement:

“Muscular (fully rimmed) VSD, apical trabecular type …” rather than “apical VSD.” [1, 2]

4) Category C — Doubly committed juxtaarterial VSDs: “subarterial under both valves”

Core definition

A doubly committed juxtaarterial VSD has its superior rim formed by both semilunar valves (AoV and PV) because the muscular outlet septum is deficient/absent, producing aortopulmonary fibrous continuity above the defect. [1, 2]

What the report must include

Treat this as a VSD + semilunar valve problem, not “just a hole”:

• Relationship to AoV/PV commissures and cusps
• Presence/absence of cusp prolapse and aortic regurgitation
• Patch strategy concept (aim: minimize hinge-line distortion and tension)

5) A surgery-ready checklist for imaging review and operative planning

When reading an echo/CT/3D dataset, run this sequence:

1. Rim identity: perimembranous vs muscular vs doubly committed juxtaarterial [1, 2]
2. RV opening compartment: outlet vs central(trabecular) vs inlet vs apical trabecular [1, 2]
3. Valve relationships: AoV cusp support/prolapse, PV proximity, TV chordal attachments [2]
4. Conduction-risk border: define the posteroinferior rim (especially in pmVSD) [2, 4]
5. Multiplicity: single vs fenestrated vs “Swiss-cheese” [3]

6) A concise documentation template (echo note / op note style)

“VSD is [perimembranous / muscular / doubly committed juxtaarterial], with dominant RV opening in the [outlet / central(trabecular) / inlet / apical trabecular] compartment. Valve relationships: AoV [normal support / cusp prolapse / AR], PV [adjacent/not adjacent], TV [chordal/leaflet attachments described]. Conduction-risk margin: posteroinferior rim characterized. Morphology: [single / fenestrated / multiple].” [1, 2, 4]

References (PubMed-verified)

[1] Soto B, Becker AE, Moulaert AJ, Lie JT, Anderson RH. Classification of ventricular septal defects. Br Heart J. 1980;43(3):332-343.

[2] McCarthy KP, Ho SY, Anderson RH. Ventricular septal defects: morphology of the doubly committed juxtaarterial and muscular variants. Images Paediatr Cardiol. 2000;2(4):5-23.

[3] Erdem S, Ozbarlas N, Küçükosmanoğlu O, Poyrazoğlu H, Salih OK. [Long term follow-up of 799 children with isolated ventricular septal defects]. Turk Kardiyol Dern Ars. 2012;40(1):22-25.

[4] Manning PB. Ventricular Septal Defect Closure: How I Teach It. Ann Thorac Surg. 2018;106(2):324-326.

[5] Ammash NM, Warnes CA. Ventricular septal defects in adults. Ann Intern Med. 2001;135(9):812-824.