and Structural Heart Disease
|A combination of lesions including primum ASD, inlet VSD and
a common atrioventriuclar valve resulting in significant
increase in left to right shunting across the ASD and VSD as
well as congestive heart failure due to the increase in
pulmonary blood flow as well as the AV valve regurgitation,
typically associated with this lesion.
|Sixty-nine per cent (69%) of all AV canal
have Down syndrome. Holosystolic murmur at the left lower sternal border
and apex is auscultated. In addition, the S2 is accentuated with an S3.
atrioventricular valves form during the fifth to eighth week of
endocardial cushion tissue forms bulges at the atrioventricular
junction. These bulges have the appearance of valves, and although such
tissue may play an important role in the eventual formation of the
atrioventricular valves, endocardial cushion tissues are
not the precursors of the mitral and tricuspid valves.
atrioventricular junction is guarded by two masses of endocardial
cushions, a superior and inferior cushion.
These two masses would meet in the middle, thus dividing the common
atrioventricular canal into a right and left atrioventricular orifices.
The process through which these two cushions fuse is not clear and
the role of apoptosis in this process is debatable.
The fusion of the two endocardial cushions resulting in the
formation of two atrioventricular orifices.
In addition, the atrioventricular cushion appear to play a role in
the closure of the inter-atrial communication at the edge of the primum
atrial septum. This septum
grows towards the atrioventricular endocardial cushion and fuse with it.
formation of the atrioventricular valve starts when the atria and inlet
portion of the ventricle enlarge, while the atrioventricular junction (or
canal) lags behind. Such a
process will cause the sulcus tissue to invaginate into the ventricular
cavity, forming a hanging flap. The
endocardial cushion tissue is located at the tip of this flap, which is
formed from three layers at this point:
The outer layer from atrial tissue, the inner layer formed by
ventricular tissue and the inner layer by invaginated sulcus tissue.
The inlet portion of the ventricles then become undermined forming
the tethering cords holding the newly formed valve leaflets.
The inner sulcus tissue will eventually come in contact with the
cushion tissue at the tip of valve leaflets, thus interrupting the
muscular continuity between the atria and ventricles.
The ventricular septal defect can be very
large extending beyond what endocardial cushion contributes to the
ventricular septum. It is rare for a ventricular septal defect to be
present with small primum atrial septal defect and even more rare
without an atrial septal defect. The atrial septal defect is very
variable in size. Primum atrial septal defect is seen with no VSD or a
tiny inlet VSD. Cleft mitral valves are seen with primum atrial septal
defect. A double inlet mitral valve is sometime noted with primum atrial
septal defects. Tricuspid valve may override the ventricular septum when chordea insert
into the left ventricle causing right atrial output to be directed into
the left ventricle which may lead to hypoplasia of the right ventricle.
The left ventricular papillary muscles may be single or close to each
other causing mitral stenosis. AV canal defect is present in 50% of all
children with Downs syndrome and congenital heart disease. It is rare to
have ventricular size discrepancy in children with AV canal and Down
syndrome in comparison to other children with AV canal defect. Tetralogy
of Fallot or pulmonary stenosis could also be present with AV canal
defect. Other types of congenital heart disease are common with AV canal
defects except in those with Down syndrome that tend to have either a
straight forward AV canal defect or AV canal defect with Tetralogy of
Fallot or pulmonary stenosis.
Types of AV canal:
- Type A: The anterior leaflet is divided
and attached to the crest of the VSD.
- Type B: Anterior leaflet is divided and
chordae from left sided leaflet crosses and inserts in the RV.
- Type C: Anterior leaflet is ridging
(single) with no chordal attachment (free floating).
|The atrial septal defect and
ventricular septal defects will cause left-to-right shunting
leading to congestive heart failure. The right ventricular
pressure will be systemic if the VSD is large enough.
Patients with AV canal defect develop elevated pulmonary
vascular resistance secondary to right ventricular
hypertension, increased pulmonary blood flow and upper
airway obstruction in patients with Downs syndrome. Children
with Downs syndrome tend to develop pulmonary vascular
resistance elevation earlier but not necessarily
|Left to right shunting at the
atrial and ventricular septal defects will cause increase
pulmonary blood flow (PBF). This will eventually lead
to congestive heart failure (CHF)
with dilation of all cardiac chambers, congested lungs as well as liver
and GI system due to elevated right atrial pressure.
In the neonatal period symptoms are not present due to the normally
elevated pulmonary vascular resistance (PVR) which would prohibit
excessive pulmonary blood flow. As this drops, PBF will increase
resulting in CHF.
CHF will cause tachypnea and failure to thrive.
On examination, CHF signs will be present, such as hepatomegaly, prominent
RV and LV impulses. In severe cases capillary refill becomes
sluggish and peripheral pulses are diminished due to decreased systemic
cardiac output. Lungs may exhibit wheezing on auscultation.
Cardiac auscultation reveals a holosystolic murmur at left lower sternal
border due to left to right shunting at the VSD, there may also be a
mid-diastolic murmur due to increase blood flow across the AVC. AVC
regurgitation is variable and will also present as holosystolic murmur,
heard best at cardiac apex.
|This shows a northwest axis as well as RVH
|Cardiomegaly is prominent
because of left and right ventricular dilatation and hypertrophy.
The pulmonary vascualture is prominent due to increased pulmonary
|AVC defect can be visualized
echocardiographically from many views.
The subxiphoid view shows the common AV valve as well as the primum ASD
and inlet VSD. The ventricles tend to be foreshortened in this view,
therefore, it may be difficult to assess the VSD size.
Apical 4-chamber view is an excellent view to assess the common AV valve,
the inlet VSD and primum ASD. The extent of AV valve regurgitation
is also well appreciated in this view. Any AV valve tissue
obstruction to the LVOT cold be assessed in the "5-Chamber"
modification of this view.
Additional defects should be sought, such as patent ductus arteriosus and
tetralogy of Fallot.
|Assessment of the PVR may be
needed in children older than one year of age with AVC defect,
particularly if CHF symptoms and signs are not present despite large
Surgical repair will be necessary. This is
performed at 6-12 months of age, because the likelihood of developing
irreversible pulmonary vascular obstructive disease is higher after one
year of age. When repairing AVC defect, one or two patches are used to
close the ASD and VSD, then the common AV valve is fashioned to make two
functional AV valves.
Pulmonary artery banding may be associated
with increased AV valve insufficiency and should be avoided if possible.
Univentricular repair is considered when one
of the ventricles is hypoplastic due to mal-alignment of the AV valve
orifice and the ventricles.
|Course and Prognosis
Factors influencing mortality:
AV canal anatomy
Mal alignment of AV valves and ventricles.
Single papillary muscle
Double orifice mitral valve
Down syndrome patients do not have a higher
mortality than the rest of the population with AV canal defect.
Infants are usually asymptomatic. Symptoms
when develop are due to left-to-right shunting at the atrial level causing
increased pulmonary blood flow. There may or may not be mitral
regurgitation due to the mitral valve cleft which will further cause
pulmonary venous congestion and increase in pulmonary arterial pressure.
The signs are those of increased pulmonary blood flow where there is a
hyperactive precordium, a systolic murmur due to pulmonary blood flow or
MR could be auscultated. There is wide splitting of S2 . Also,
if MR is present there will be a holosystolic murmur at the apex.
Superior axis deviation with or without
incomplete right bundle branch.
Cardiomegaly with increased pulmonary blood
flow. Cardiomegaly may be out of proportion to left-to-right shunting
secondary to mitral insufficiency.
Echocardiography shows the primum ASD as well
as a cleft mitral valve and mitral insufficiency. Mitral regurgitation may
be directly to the RA through the atrial septal defect. The mitral
regurgitation when its directed to the right atrium may explain why the
left atrium may not be dilated in these circumstances. The attachment of
valve leaflets to the septum and the number and spacing of papillary
muscles could also evaluated by echocardiography.
Cardiac catheterization is not necessary in
This is best delayed if possible since AV
valve replacement may be necessary and therefore the older the child the
better unless symptoms are excessive secondary to large left-to-right
shunting with or without mitral insufficiency. Mitral insufficiency may
worsen even after surgery but generally postop results are very good