VSD, EMBRYOLOGY

1. Ventricular septal defect
Embryogenesis
&
Classification

2. Introduction
 Firstdescribed by Roger in 1879
 Most common congenital heart disease
 1.5 – 2.5/1000 live births
 20% of CHD
 Most common disorder in various chromosomal
disorders
 Has Multifactorial etiology

3. Ventricular septum
 Complex non – planar structure; 4 components
 Inlet septum – lightly trabeculated; extends from
tricuspid annulus to attachments of tricuspid
valve
 Trabecular septum – heavily trabeculated;
trabecular septum extends from inlet out to apex
and up to smooth-walled outlet
 Outlet septum – non trabeculated; extends up to
pulmonary valve
 3 diverge from small membranous septum

5. Ventricular septation
 Ventricles derived from 2 imporatant
components of primitive heart – inlet & outlet
 Three septal components are necessary for
septation
 Expansion of inlet & outlet components leads to
formation of partial septum between two –
primary interventricular septum
 Two intrinsic septum in two segments called
inlet & outlet septum
 mainly formed by inlet and primary septa

6. Ventricular septation
 growth of two ventricles on either side causes
primary septum to be more prominent
 inlet septum result from muscular
trabeculations in inlet region of ventricles
 in same plane as that of atrial septum
 third component comes from endocardial
cushion tissue – membranous portion of
ventricular septum
 septation starts at about 37 days of gestation &
complete by 49th day of gestation

7. Muscular septum
 During 5th week(day 30), muscular fold extends from
anterior wall of ventricles to floor
 appear at middle of ventricle near apex and grows
towards AV valves with concave ridge
 Most of initial growth achieved by growth of two
ventricles on each side of ventricular septum
 In addition trabeculations from inlet region coalesce
 grows into ventricular cavity at slightly different plane
than primary septum
 inlet interventricular septum is at same plane as that of
atrial septum

8. Ventricular Outflow septation
 from horse-shoe shaped condensed mesenchyme
embedded in endocardial cushion tissue
 Just proximal to level of development of aorto-
pulmonary valves
 Condensed mesenchyme will come in close
contact with outflow tract myocardium
 Area just above bulboventricular fold appears to
reach out to condensed mesenchyme
 Participate in septation of outflow tract by
providing an analogue to muscle tissue

9. Primary foramen
 Communication between inlet & outlet
components
 Exists because primary septum is incomplete
 Divided into R & L by growing septation
 L component forms LVO
 Due to differential growth, LV apex formed by
inlet component
 RV apex formed by outflow component

10. Interventricular Foramen
 Bordered by concave upper ridge of muscular
interventricular septum and fused AV canal
endocardial tissue, closes at end of week 7
 Achieved by growth of three structures: right and
left bulbar ridges and posterior endocardial
cushion tissue
 Closes interventricular foramen and connect
ventricular septum to outflow septum
 Connecting right ventricle to pulmonary trunk and
left ventricle to aortic trunk

11. Outflow Tract
 Includes ventricular outflow tract and
aortopulmonary septum
 Three embryological areas, conus, truncus and
pulmonary arterial segments
 Each segment develop two opposing ridges of
endocardial tissue
 Opposing pair of ridges and those from various
segments meet to form septum separating two
outflow tracts and aortopulmonary trunks

14. VSD CLASSIFICATION
Anatomic classification
Physiological classification
Perimembranous
Outlet
Inlet
muscular

15. Perimembranous
 most common defect
 80% of surgical and autopsy series
 usually extends into muscular, inlet, or outlet areas
 synonyms: infracristal, membranous

16. Outlet
 5%-7% of autopsy and surgical series (29% in Far
East)
 situated just beneath the pulmonary valve
 synonyms: supracristal, conal, infundibular,
subpulmonary,doubly committed subarterial

17. Inlet
 5%-8%
 posterior and inferior to perimembranous defect

18. Muscular
 5%-20%
 Central: mid-muscular, may have multiple
apparent channels on RV side and coalesce to
single defect on LV side
 Apical: multiple apparent channels on RV side
may be single defect on LV side as with central
defect
 Marginal: along RV septal junction
 "Swiss cheese" septum: large number of
muscular defects

19. a, outlet defect; b, papillary muscle of the conus; c, perimembranous defect
d, marginal muscular defects; e, central muscular defects; f, inlet defect; g, apical
muscular defects

20. Physiological classification
Determines effect of VSD on patient
Depends on size of defect
Resistance of flow through lungs (PVR)

21. Small defect with low PVR
Moderate defect with variable
PVR
Large defect with mild to
moderate ⇑ PVR
Large defect with high PVR

22. Size Also classified as…
Restrictive
Nonrestrictive

24. Association
 Partof many complex structural heart diseases
 Secondary AR
 RVOTO
 Subaortic obstruction

25. P-LAX
VS
P-SAX
AP-4C AP-5C P-SAX b

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