This document discusses the embryology, anatomy, classifications, and associated anomalies of atrioventricular septal defects (AVSDs). It describes the embryologic development of endocardial cushions and septum that can lead to partial or complete AVSD. Partial AVSD involves a cleft in the anterior mitral valve leaflet while complete AVSD lacks fusion of endocardial cushions, forming a common atrioventricular valve. Complete AVSD is further classified and associated anomalies are discussed, including conotruncal defects, coronary anomalies, and ventricular disproportion. Valve abnormalities like double orifice, papillary muscle anomalies, and their implications are also summarized.

1. Embryology and Surgical Anatomy of A V
Septal defects
Dr Gopi krishna

2. • Atrioventricular septal defects (AVSD) are a
group of anomalies that share a defect of the
atrioventricular septum and abnormalities of
the atrioventricular valves.
• The terms atrioventricular canal defects• or
endocardial cushion defects• also describe
these lesions.
• These lesions are divided into partial and
complete forms

3. Demographics
• AVSDs account for 4% to 5% of congenital
heart disease and an estimated occurrence of
0.19 in 1,000 live births .
• In a large fetal echocardiography experience,
AVSD was the most common anomaly
detected, constituting 18% of abnormal fetal
hearts .
• Gender distribution is approximately equal or
may show a slight female preponderance

4. • About 40% to 45% of children with Down
syndrome have congenital heart disease, and
among these, approximately 40% have an
AVSD, usually the complete form .
• Complete AVSDs also occur in patients with
heterotaxy syndromes (more common with
asplenia than with polysplenia).
• Common atrium has been associated with Ellis
van Creveld syndrome.

5. partial AVSD
• Primum atrial septal defect (ASD) is always
present
• There are two distinct mitral and tricuspid
valve annuli.
• The mitral valve invariably is cleft.

6. The complete AVSD
• This includes a primum ASD, but it is
contiguous with an inlet ventricular septal
defect (VSD).
• Common atrioventricular valve has a single
annulus.
• The clinical manifestations and management
of these patients depend on the extent and
severity of the lesions present.

10. The primitive cardiac tube has five zones:
the arterial trunk
the bulbus cordis )
} some would call these two together
the ventricle ) the primitive ventricle, with inlet
and outlet portions
the atrium
and the sinus venosus
The arterial trunk will divide to separate the pulmonary and systemic supply.
The bulbus and the ventricle will differentiate into the right and left ventricles.

20. Embryologic development of the the spectrum of AVSD

21. Anatomical Abnormalities
• Faulty development of the endocardial
cushions and of the atrioventricular septum is
thought to be responsible for the broad range
of AVSDs.
• In partial AVSDs, incomplete fusion of the
superior and inferior endocardial cushions
results in a cleft in the midportion of the
anterior mitral leaflet, often associated with
mitral regurgitation.

22. • The primum atrial septal component of this
defect is usually large.
• This results in downward displacement of the
anterior mitral leaflet to the level of the septal
tricuspid leaflet .
• In AVSDs, the atrioventricular valves have the
same septal insertion level in contrast to the
leaflet arrangement in the normal heart.

25. • The distance from the cardiac crux to the left
ventricular apex is foreshortened, and the
distance from the apex to the aortic valve is
increased in contrast to normal heart.
• In AVSDs the disproportion between the two
distances causes anterior displacement of the left
ventricular outflow tract (LVOT).
• As a result, the LVOT is longer and narrower than
normal and produces the gooseneck• deformity.
• After surgical repair of the defect, progressive
subaortic stenosis may develop .

27. • In the normal heart, the aortic valve is wedged
between the mitral and tricuspid annuli.
• In AVSD the aortic valve is displaced or sprung
anteriorly .
• This anterior displacement creates an elongate,
so-called gooseneck deformity of the LVOT.
• LVOT obstruction may occur in all forms of AVSD.
• It is more frequent when two atrioventricular
valve orifices are present than when there is a
common orifice.

30. Other causes that can exacerbate subaortic stenosis.
• The superior bridging leaflet attaches to the
crest of the ventricular septum, causing the
outflow tract to become elongated and
consequently narrowed.
• Discrete subaortic fibromuscular ridges.
• Septal hypertrophy,
• Abnormal left atrioventricular valve chordal
attachments.
• Abnormally oriented papillary muscles.
• can exacerbate subaortic stenosis.

31. • . LVOT obstruction may be subtle and
therefore not appreciated during preoperative
echocardiographic assessment.
• Obstruction may develop de novo after initial
repair of the AVSD and closure of the mitral
valve cleft .
• The LVOT obstruction often is progressive.

32. Mitral valve abnormalities
• Cleft.
• parachute mitral valve .
• Double-orifice mitral
valve al.

33. • In partial AVSD, the mitral and tricuspid annuli are
separate.
• The most frequent form of partial AVSD consists of a
primum ASD and a cleft anterior mitral valve leaflet .
• Most primum ASDs are large and located
anteroinferiorly to the fossa ovalis.
• The defect is bordered by a crescentic rim of atrial
septal tissue posterosuperiorly and by mitral-tricuspid
valvular continuity anteroinferiorly.
• These defects are not amenable to transcatheter
device closure because of their proximity to the
atrioventricular valves.

34. • The cleft in the anterior mitral leaflet is directed
toward the midportion of the ventricular septum,
along the anteroinferior rim of the septal defect .
• In contrast, isolated mitral clefts (not otherwise
associated with AVSD) are directed toward the
aortic valve annulus .
• The mitral orifice is triangular rather than
elliptical as in a normal heart and resembles a
mirror-image tricuspid orifice.
• The cleft mitral valve usually is regurgitant and,
with time, becomes thickened and exhibits
secondary hemodynamic alterations in
morphology that resemble mitral valve prolapse.

35. common associated anomalies
• secundum ASD and persistence of a left superior vena
cava connecting to the coronary sinus.
• Less frequently,
pulmonary stenosis,
tricuspid stenosis or atresia,
cor triatriatum,
coarctation of the aorta,
patent ductus arteriosus,
membranous VSD,
pulmonary venous anomalies,
hypoplastic left ventricle

36. Transitional form of partial AVSD
• There is aneurysmal
replacement of a
portion of the inlet
ventricular septum .
• Although small shunts
may occur, tricuspid
pouch usually obstructs
any shunting at the
ventricular level.

37. • The dextrodorsal conus cushion contributes to the
development of the right atrioventricular valve and
the outflow tracts lie adjacent to their respective
inflow tracts.
• So AVSDs may be associated with conotruncal
anomalies, such as tetralogy of Fallot and double-
outlet right ventricle.
• Shift of the atrioventricular valve orifice may
result in connection of the valve primarily to only
one ventricle, creating disproportionate or
unbalanced ventricles.

38. Complete AVSD
• complete AVSD is
associated with lack of
fusion between the
superior and inferior
cushions .
• consequently, with the
formation of separate
anterior and posterior
bridging leaflets along
the subjacent ventricular
septum .

39. Three types of straddling

40. Complete AVSD
• complete AVSD is
associated with lack of
fusion between the
superior and inferior
cushions .
• consequently, with the
formation of separate
anterior and posterior
bridging leaflets along
the subjacent ventricular
septum .

42. • The type of complete AVSD has some bearing
on the likelihood of associated lesions.
• Type A usually is an isolated defect and is
frequent in patients with Down syndrome.
• Type C is encountered with other complex
anomalies, such as tetralogy of Fallot, double-
outlet right ventricle, complete transposition
of the great arteries, and heterotaxy
syndromes.

43. • Coronary artery anomalies, when they occur,
tend to be associated with coexistent
conotruncal malformations rather than the
AVSD.
• The combination of type C complete AVSD
with tetralogy of Fallot is observed in patients
with Down's syndrome, whereas double-
outlet right ventricle is a feature of patients
with asplenia.

44. Orientation commissures and papillary muscles.
• Beneath the five commissures are five papillary
muscles.
• The two left-sided papillary muscles are oriented
closer together than in a normal heart, such that the
lateral leaflet is smaller than a normal posterior mitral
leaflet.
• The two papillary muscles often are rotated
counterclockwise, such that the posterior muscle is
farther from the septum than normal and the anterior
muscle is closer to the septum.
• This papillary muscle arrangement, in conjunction with
prominence of an anterolateral muscle bundle, may
contribute to progressive LVOT obstruction.

45. Double-orifice left A.V. valve
• Double-orifice left atrioventricular valve occurs
rarely in AVSDs.
• This abnormality is more common when two
distinct right and left atrioventricular valve
orifices are present.
• The combined effective valve area of a double-
orifice valve is always less than the valve area of a
single-orifice valve.
• This predisposes the valve to postoperative
stenosis.

47. single left ventricular papillary muscle
• Similar to the double-orifice valve, a single
papillary muscle will reduce the effective valve
area.
• In patients with a single left ventricular papillary
muscle, valve repair may be compromised owing
to relative leaflet hypoplasia

48. Unbalanced Defect
• One ventricle and its corresponding
atrioventricular valve are hypoplastic while
the other ventricle receives the larger portion
of the common atrioventricular valve.
• The most common arrangement is a dominant
right ventricle with a hypoplastic left ventricle.
• The left-sided component of the common
atrioventricular valve may be stenotic after
two-ventricle repair has been performed.

49. • When left ventricular hypoplasia and right
ventricular dominance occur ,the associated
malformations such as aortic arch hypoplasia
and coarctation are common.
• In contrast, if left ventricular dominance is
present, pulmonary valve stenosis or atresia is
a common associated defect.

50. • classification scheme from Bharati and Lev

51. • From van Son, JAM, Phoon CK, Silverman NH, et al. Predicting feasibility of
biventricular repair of right-dominant unbalanced atrioventricular canal. Ann
Thorac Surg 1997;63:1657
• )

52. Down Syndrome and Atrioventricular Septal Defect
• Children with Down syndrome are more likely to have
complete AVSD than children without Down syndrome.
• They are also more likely to have associated tetralogy
of Fallot .
• Sidedness (situs) and splenic anomalies are rare in
patients with Down syndrome.
• Patients with Down syndrome usually do not have
associated LVOT obstruction, left ventricular
hypoplasia, coarctation of the aorta, or additional
muscular VSDs .

53. • The extent and progression of pulmonary vascular
changes in children with Down syndrome and complete
AVSD remain controversial.
• Histologic studies have failed to reveal any differences
in the extent of pulmonary vascular changes when
patients with Down syndrome were compared with
normal children who also had AVSD.
• Other studies have suggested that children with Down
syndrome have relative pulmonary parenchyma
hypoplasia.
• Surgical results for patients with Down syndrome are
similar to those of the general population .

54. ?surgical anatomy importance
• Surgical repair of AVSD has been one of the great
successes of the last several decades of congenital
cardiac surgery.
• Studer et al. reported average operative mortality
<2%.
• Long-term survival has been excellent. A cumulative
20-year survival of 95% .
• However, at least 25% of patients await
reoperation, most commonly because of
progressive left atrioventricular valve regurgitation
or relief of left ventricular outflow tract obstruction.

55. Surgical Treatment of Partial Atrioventricular Septal Defect
• The objectives of surgical repair include closure of the
interatrial communication and restoration and
preservation of left atrioventricular valve competence.
• These objectives can be accomplished by careful
approximation of the edges of the valve cleft with
interrupted nonabsorbable sutures.
• On occasion, it is necessary to add eccentric
annuloplasty sutures to correct persistent central leaks.
• The repair is completed by closure of the interatrial
communication (usually with an autologous pericardial
patch), avoiding injury to the conduction tissue.
• This repair results in a two-leaflet valve .

56. • Danielson GK. Endocardial cushion defects. In: Ravitch MM, Welch KJ, Benson CD, et al., eds. Pediatric
Surgery. 3rd ed. Vol. 1. Chicago: Year Book Medical, 1979:720–726
• ,

57. • Alternatively, if the left atrioventricular valve is to
be considered a trileaflet valve, with the cleft
viewed as a commissure, surgical repair demands
that this commissure be left unsutured and that
various annuloplastic sutures be placed to
promote coaptation of the three leaflets.
• These morphologic concepts and surgical
methods, favored by Carpentier and Piccoli et
al, have not yet provided superior results.

58. The risk of hospital death for the surgical repair of partial AVSD is
approximately 3%.
• Determinants of hospital mortality include
• Congestive heart failure.
• Cyanosis.
• Failure to thrive.
• Age at operation of <4 years.
• Moderate to severe left atrioventricular valve
regurgitation.

59. • In a series of 334 patients from Mayo Clinic, 20-
and 40-year survivals after repair of partial AVSD
were 87% and 76%, respectively.
• Closure of the mitral cleft and age <20 years at
time of operation were associated with better
survival. Reoperation was performed for 11% of
these patients.
• Repair of residual/recurrent mitral valve
regurgitation or stenosis was the most common
reason for reoperation.

60. • A low frequency of postoperative arrhythmias
has been noted.
• Bradyarrhythmias, including severe sinus
node dysfunction, may occur.
• The finding of surgical complete heart block
has been rare.
• Permanent pacemaker implantation has been
required for these patients.
• Late onset of atrial flutter has been rare.

61. Surgical Treatment of Complete Atrioventricular Septal Defect
• Surgical repair of complete forms of AVSD is
indicated earlier in life than for the partial forms
of AVSD.
• Repair of complete AVSD must be done prior to
the development of irreversible pulmonary
vascular obstructive disease.
• Repair should be done electively before 6
months of age.
• Earlier repair should be considered for infants
with failure to thrive.

62. • For the symptomatic infant, surgical options include
palliative pulmonary artery banding and complete
repair of the anomaly.
• Although in the modern age complete repair appears
to be the procedure of choice for these infants,
proponents of pulmonary banding have alluded to the
relatively high risk of complete repair in infants <6
months of age.
• Silverman et al. reported excellent results of
pulmonary banding in 21 infants with complete AVSD
who were <1 year of age.
• In this series, there was one surgical death (5%), and
the remaining patients had excellent palliation.

63. • Williams et al. recommended pulmonary
artery banding for infants weighing <5 kg who
were unresponsive to medical treatment or
had significant associated anomalies.
• In the modern era, most centers perform
complete repair in small infants who fail to
thrive.
• This approach has largely obviated the need
for pulmonary artery band placement.

64. • The objectives of surgical repair include closure of
interatrial and interventricular communications,
construction of two separate and competent
atrioventricular valves from available leaflet tissue, and
repair of associated defects.
• Techniques for the surgical repair of complete AVSD have
been standardized and are based on the use of a single
patch or double patch (separate atrial and ventricular
patches) to close the ASD and VSD and then reconstruction
of the left atrioventricular valve as a bileaflet valve.
• Puga and McGoon (49) have described these techniques in
detail.

65. • Piccoli et al. and Studer et al. consider the cleft
of the left atrioventricular valve a true
commissure and envision this valve as a trileaflet
valve.
• On the basis of these concepts, Carpentier
prefers the two-patch technique.
• The left atrioventricular valve remains a trileaflet
structure .
• The two-patch technique has become the
method of choice.

66. • In a series of 310 patients reported by Studer
et al.
• The risk factors in the surgical repair of AVSDs
were,
1. age at operation,
2. severity of atrioventricular valve
regurgitation,
3. preoperative functional class.

67. • Chin et al, reported the results
obtained with complete repair in a group of patients
whose mean age at operation was 10 months.
• Hospital mortality ranged from 62% in their early
experience to 17% among 30 patients who underwent
operation during the period 1978 to 1980.
• Bender et al. reported 24 infants who had operation
between 3 and 38 weeks of age (mean 18 weeks) and
noted two operative deaths.
• Similar to repair of partial AVSD, postoperative sinus
node dysfunction occurs.
• Complete heart block requiring permanent pacemaker
placement is now rare.

68. • From Carpentier A. Surgical anatomy and management of the mitral component
of atrioventricular canal defects. In: Anderson RH, Shinebourne EA, eds. Paediatric
Cardiology. Edinburgh: Churchill Livingstone, 1978: 477 490
• ,

69. Special Problems in Complete Atrioventricular Septal Defect Surgery
• Parachute Deformity of the Mitral Valve.
• Double-Orifice Mitral Valve.
• Right or Left Ventricular Hypoplasia.
• Tetralogy of Fallot.
• Subaortic Stenosis.

70. Parachute Deformity of the Mitral Valve
• This problem has been addressed by David et
al.
• With such a deformity, closure of the mitral
cleft at the time of repair may result in an
obstructed mitral orifice.
• If the patient has significant atrioventricular
valve regurgitation, valve replacement may be
the only suitable option.

71. Double-Orifice Mitral Valve
• The surgeon must resist the temptation of
joining the two orifices by incising the
intervening leaflet tissue.
• The combined opening of both orifices is
satisfactory for adequate mitral valve function.

72. Right or Left Ventricular Hypoplasia
• These anomalies may be severe enough to
preclude septation.
• The only option for definitive surgical
treatment is the modified Fontan's procedure
preceded by adequate pulmonary artery
banding in infancy.

73. Tetralogy of Fallot
• In patients with this anomaly, all of whom have
the complete form, the infundibular septum is
displaced anteriorly, so that the typical inlet VSD
extends anteriorly and superiorly toward the
perimembranous area.
• Treat these cyanotic infants initially with a
systemic-to-pulmonary artery shunt and then by
complete repair at 2 to 4 years of age.
• The intracardiac repair of these hearts is best
accomplished through a combined right atrial and
right ventricular approach.

74. Subaortic Stenosis
• If discovered at the time of initial preoperative
evaluation, subaortic stenosis tends to be of the
fibromuscular membrane type and should be treated
by appropriate resection during surgical repair.
• However, subaortic stenosis usually appears late after
surgical repair of AVSD.
• The stenosis may be related to the uncorrected
deficiency in the inlet septum.
• The obstruction usually is due to the formation of
endocardial fibrous tags and fibromuscular ridges.
• Usually it can be treated by local resection, although in
some patients a modified Konno procedure may be
necessary.

75. Reoperation after Repair of partial Atrioventricular Septal Defects
 Regurgitation or stenosis of the left
atrioventricular valve [ 10% to 15%].
 Subaortic stenosis.
 Residual recurrent ASD.

76. • late reoperation following repair of complete
avsd occurs in approximately 17% of patients
during the first 20 years after surgical repair.
• Lesions requiring reoperation include left and
right atrioventricular valve regurgitation, left
atrioventricular valve stenosis (native and
prosthetic), and residual/recurrent ASDs or
VSDs.

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