and Structural Heart Disease
|The most common congenital heart disease at
one week of age and throughout the first three decades of life. 50% of all
patients with congenital heart disease have ventricular septal defects.
0.3-0.5/1000 Live births have significant left ventricular septal defects
requiring management. Premature infants have a much higher incidence (ten
times as high as full term babies).
Ventricular septation is a complex process
involving different septal structures from various origins and positioned
at various planes [3, 27, 28, 31]. These
structures eventually meet to complete the separation of the right and
During the fifth week, around day 30, a muscular fold
extending from the anterior wall of the ventricles to the floor
appear at the middle of the ventricle near the apex and grows
towards the AV valves with a concave ridge.
Most of the initial growth is achieved by growth of the two
ventricles on each side of the ventricular septum.
In addition trabeculations from the inlet region coalesce to
form a septum which grows into the ventricular cavity at slightly
different plane than the primary septum, this is the inlet
interventricular septum, which is at the same plane of that of the
atrial septum. The
point of contact between these two septa will cause the edge of the
primary septum to protrude slightly into the right ventricular
cavity forming the trabecular septomarginalis.
The fusion of these two septa forms the bulk of the muscular
interventricular septum. This
septum will then become in contact with the outflow septum.
interventricular foramen, which is bordered by the concave upper
ridge of the muscular interventricular septum and the fused AV canal
endocardial tissue, closes at the end of week 7.
This is achieved by growth of three structures: the right and
left bulbar ridges and the posterior endocardial cushion tissue.
This will close the interventricular foramen and connect the
ventricular septum to the outflow septum, thus connecting the right
ventricle to the pulmonary trunk and the left ventricle to the
tract septum: The
cardiac outflow tract include the ventricular outflow tract and the
aortopulmonary septum. There
has been much debate regarding this process, the following is a
summary of various theories.
(1942) suggested that there are
three embryological areas, the conus, the truncus and the pulmonary
arterial segments. Each
segment develop two opposing ridges of endocardial tissue, the opposing
pair of ridges and those from various segments meet to form the septum
separating the two outflow tracts and the aortopulmonary trunks.
The aortopulmonary septum is formed by ridges separating the fourth
(future aortic arch) and the sixth (future pulmonary arteries) aortic
arches. The truncus ridges
are formed at the area where the semilunar valves are destined to be
formed, therefore forming the septum between the ascending aorta and the
main pulmonary artery. The
conus ridges form just below the semilunar valves and from the septation
between the right and left ventricular outflow tracts.
Mierop (1979), agreed that there are
three pairs of ridges forming in the aortopulmonary, truncus and conus
regions, however, he stated that the pairs of ridges fuse independently
and later on fuse with each other to complete the septation. His theory indicate that the truncus ridges form
first, and as they fuse they form a truncal septum which then fuses
with the aortopulmonary septum which is formed by invagination of the
dorsal wall of the aortic sac between the fourth and the sixth aortic arch
Asami(1980), followed Van Mieropís theory, however, he stated that these
ridge fuse in the opposite direction of what Van Mierop has indicated,
i.e. from the outflow tract to the aortopulmonary region.
1984) and Orts Llorca et al (1982),
stated that there are only tow septa, a conotruncal (or bulbar) and an
et al (1989), introduced a new
theory. They stated that the
septation process of the ventricular outflow tracts, pulmonary and aortic
valves and the great vessels is mostly caused by a single septation
complex, which they termed aortopulmonary septum.
This septation complex develops at the junction of the muscular
ventricular outflow tract with the aortopulmonary vessel.
This junction has a saddle shape, i.e. not in one plane which would
allow the right ventricular outflow tract to be long with a short main
pulmonary artery, while the left ventricular outflow tract become short
with a long ascending aorta.
The ventricular outflow septation is formed by condensed mesenchyme,
embedded in the endocardial cushion tissue just proximal to the level of
the aorto-pulmonary valves. The
condensed mesenchyme will come in close contact with the outflow tract
myocardium, from the area just above the bulboventricular fold, and
participate in the septation of the outflow tract by providing an analogue
to muscle tissue. Myocardium
in contact with the mesenchymal arch grow rapidly and form the bulk of the
outflow septum and is continuous with the primary fold on the parietal
wall of the right ventricle and the myocardium on the right side of
the primary septum.
Membranous ventricular septal defect:
The membranous septum is very small,
therefore ventricular septal defects usually extend into the surrounding
muscle septum, this is called perimembranous ventricular septal defect.
This kind of ventricular septal defect is very close to the tricuspid
valve septal leaflets which may be damaged by shunting across the defect
whether it is involved , or not in forming an aneurysmal pouch leading
which may lead to ventricular septal defect closure. This type of
ventricular septal defect is most common accounting for 75% of all
ventricular septal defects. It is associated with malalignment of the
outflow septum as in tetralogy of Fallot.
Muscular ventricular septal defect:
This is the second most common type of
ventricular septal defects. It might be in the apical portion or mid
portion, either anteriorly or posteriorly. These ventricular septal
defects may be single but appear as multiple from the right ventricular
Outflow tract ventricular septal defect:
These affect the outflow tract septum, it has
the tendency to cause aortic valve cusp damage, which may lead to aortic
regurgitation, this is more common in the oriental population.
Endocardial cushion type:
This is the least common type of ventricular
septal defects, is located underneath the tricuspid valve. It may be
associated with superior axis deviation on electrocardiography.
|The larger the ventricular septal
defect the more pressure is transmitted to the right ventricle. Once
the right ventricular pressure equalizes with the left ventricular
pressure, this occurs when the defect is more than 50% of the area
of the aortic root. The determining factor for amount of
left-to-right shunting at that point becomes the systemic and
pulmonary vascular resistances. Muscular ventricular septal defects
become smaller during systole allowing less shunting. Symptoms with
ventricular septal defects usually start with a QP:QS ratio of 2.5:1
Large ventricular septal defects cause
hypertension of the right ventricle, pulmonary arteries and left atrium.
In case of patent ductus arteriosus and ventricular septal defect, the
pulmonary arterial and right ventricular pressures will become systemic if
these two defects are large enough and the amount of left-to-right
shunting will depend on the systemic and pulmonary vascular resistances
and not the size of the defects. In the association of a ventricular
septal defect and atrial septal defect, atrial shunting will further
increase the left-to-right shunting occurring at the ventricular level.
However, the shunting at the atrial septal defect will not affect the RV
Aortic stenosis, aortic insufficiency, mitral
stenosis and pulmonary stenosis are all factors that may influence the
amount of left-to-right shunting.
Hypoxemia causing elevated pulmonary vascular
resistance, as is encountered in high altitudes, will decrease
Mitral stenosis when present with ventricular
septal defect will elevate the pulmonary vascular resistance resulting in
less left to right shunting, if the mitral stenosis is relieved the LA and
consequently the PA pressure will drop allowing more left-to-right
Although only 15% of ventricular septal
defects are large enough to require hospitalization yet this is the most
common cause of hospitalization amongst congenital heart diseases.
Tachypnea is typically the first presenting symptom. Dyspnea results in
poor nursing and frequent rest during feedings. This will result in
failure to thrive. Hepatomegaly may be present.
The murmur of VSD is due to left-to-right
shunting at the ventricular level. Small ventricular septal defects are
typically louder than larger ones. The murmur of a VSD is heard best at
the left lower sternal border.
Right-to-left shunting at the VSD are not
audible due to a small amount of pressure difference between the right and
left ventricles. This is the reason why in tetralogy of Fallot a
ventricular septal defect murmur is not present, but rather a harsh
systolic ejection murmur due to right ventricular outflow tract
A loud third heart sound or diastolic rumble
is heard with large left-to-right shunting due to increased flow across
the mitral valve. A thrill is felt in many cases, particularly beyond
|The electrocardiogram is
typically normal or there is LVH due to volume overload exhibited by a
tall R in V5, V6 with a deep Q wave. There may also
be right ventricular hypertrophy and left atrial dilatation.
|The chest x-ray shows
cardiomegaly with increased pulmonary blood flow and Kerley B lines
may seen but rare.
2-D and color Doppler are valuable in
identifying ventricular septal defects. The number of defects can be
determined by using multiple planes.
ventricular septum is a complex curved structure. Not all parts of
the ventricular septum can be seen from a single echocardiographic
view. Most defects in the ventricular septum can bee seen from the
various sub-xiphoid views. In addition the muscular, apical and
perimenbrenous defects can be seen from the parastrernal long axis.
the parasternal short axis shows apical, muscular, perimembrenous and
outlet VSDs. The apical four chamber is a good view to visualize the
In addition to seeing the
VSD by 2-D, direction of blood shunting can be determined by color
Doppler. Shunting is typically left to right, unless the PVR is
The aortic valve may prolapse
with or without regurgitation in perimembrenous and outlet VSDs, this
should be interrogated by echocardiography.
Cardiac catheterization may be indicated to
further delineate the anatomy of the VSD although this is becoming
unnecessary nowadays due to echocardiography. Cardiac catheterization is
particularly important to determine the pulmonary vascular resistance in
older patients. The best views to visualize the ventricular septal defect
on a left ventricular angiogram are as follows:
- Perimembranous, mid muscular and apical
are best seen in the LAO views.
- Anterior muscular and subpulmonary
ventricular septal defects are best seen in the RAO views.
- Posterior muscular and inlet ventricular
septal defects are best seen in the hepatoclavicular (40 degrees LAO
and 40 degrees cranial angulation).
Cardiac catheterization is occasionally
performed to assess QP and QS as well as PVR.
Some VSDs such as muscular VSDs and some
perimembrenous VSDs are amenable to device closure in the cardiac
catheterization laboratory. VSD closure continue to be a surgical
procedure, however, as more experience is achieved with device closure,
this may become the method of choice in the near future.
Surgical repair of ventricular septal defects
is done in infants less than six months of age only when the child is not
gaining weight due to congestive heart failure. However, this is
associated with a high mortality rate which is about 20% in infants less
than one month of age versus 2% mortality rate in infants more than six
months of age. Uncontrolled congestive heart failure leading to surgery is
Pulmonary hypertension (more than 50% of
systemic blood pressure) in children six months to one year of age is
another indication for surgical repair.
Beyond the first year of life all ventricular
septal defects with a QP:QS ratio of more than or equal to 2:1 should be
In the past, devices were available for
closure of the ventricular septal defect. These were used with muscular
and apical ventricular septal defects but not with perimembranous
ventricular septal defects or subaortic ventricular septal defects since
these may cause damage to the aortic valve.
Perimembranous ventricular septal defects
which constitute the majority of ventricular septal defects have a
tendency to become smaller (about 50% of them do so). Therefore, it is
worthwhile allowing the child to grow since these ventricular septal
defects may close spontaneously. Closure of defects in most instances
involve tricuspid valve tissue. However, perimembranous defects with
malalignment as in the case of tetralogy of Fallot or without pulmonary
stenosis typically do not close or become smaller and almost always
require surgical intervention.
Muscular ventricular septal defects typically
become smaller and may close spontaneously. If they are large and do not
get smaller, surgical repair is typically more risky since it might
involve placement of a patch from the left ventricular side which would
necessitate surgical incision in the left ventricle which may cause left
ventricular dysfunction as well as future arrhythmias.
Outflow tract ventricular septal defects are
typically large and do not get smaller spontaneously. Therefore, they are
referred for surgical closure after six months of age or earlier if there
is failure to grow or if aortic insufficiency develops.
Inlet ventricular septal defects do not get
smaller spontaneously and they are best closed surgically early rather
- Residual ventricular septal defects 20%.
- Right bundle branch block or bifisicular
block 30-85% of the cases.
- Complete AV block 5%.
- Premature ventricular contractions 5%.
- Subacute bacterial endocarditis
41.4/10,000 person-years follow-up. The incidence of subacute
bacterial endocarditis occur equally in those who have been operated
and those who have not been operated.
|Course and Prognosis
Spontaneous diminution in size:
Perimembranous and muscular ventricular
septal defects typically get smaller. Inlet and infundibular ventricular
septal defects do not get smaller. Most changes in size occur within the
first six months of life.
Development of pulmonary vascular obstructive
This is rarely encountered nowadays. It would
occur after one year of age. If any of the
following are present then surgery is
- Pulmonary vascular resistance more than 8
- Pulmonary vascular resistance not
responsive to pulmonary vasodilators such as oxygen or nitrous oxide.
- No left-to-right shunting across the
ventricular septal defect.
- Predominantly right-to-left shunting
across the ventricular septal defect.
Mortality is very high with pulmonary
vascular obstructive disease during pregnancy and therefore should be
Aortic insufficiency, prolapse of the right
and noncoronary sinuses cups are noted in some cases of infundibular and
perimembranous ventricular septal defects. Closure of infundibular defects
will prevent occurrence of aortic insufficiency but closure of ventricular
septal defects after aortic insufficiency is noted does not necessarily
halt progression of insufficiency.
Aortic valvuloplasty may or may not halt
aortic insufficiency and sometimes aortic valve replacement is necessary.
Incidence of subacute bacterial endocarditis is high in patients with
ventricular septal defect and aortic insufficiency and occur in about 16%
of such population.
Subaortic stenosis is usually a discrete
membrane in the left ventricular outflow tract distal to the ventricular
septal defect and rarely proximal to the defect. This is more common in
patients with ventricular septal defect and coarctation of the aorta and
in patients S/P main pulmonary artery band. It is a progressive lesion
therefore surgery is indicated once pressure gradient is more than 30 mm
Hg. This could occur after closure of defect surgically. Surgical
resection is generally curative.
Ventricular Septal Defect
& Associated Defects:
Ventricular septal defect associated with
atrial septal defect:
7 % of all ventricular septal defects are
associated with atrial septal defects, some of which are only stretched
patent foramen ovales. Mortality for a pair of such lesions was higher in
the past but this does not appear to be the case nowadays.
Ventricular septal defect s associated with
patent ductus arteriosus:
After equalization of pressure through large
ventricular septal defect or patent ductus arteriosus the amount of
left-to-right shunting thereafter is dependent upon pulmonary vascular
resistance and systemic vascular resistance.
Ventricular septal defects and pulmonary
Acyanotic tetralogy of Fallot may present
clinically in early infancy just like a small ventricular septal defect.
Patients with ventricular septal defect and pulmonary stenosis without
malalignment of the outflow septum is different from tetralogy of Fallot
since they are not known to have right aortic arch.
Ventricular septal defects and double
chambered right ventricle:
The proximal portion of the right ventricular
outflow tract muscle bundle hypertrophy and divides the right ventricular
cavity into two chambers. The ventricular septal defect opens into the
infundibular or distal chamber. This may be associated with subaortic
In patients with ventricular septal defects
or mitral stenosis the pulmonary arterial pressures may be elevated
because of mitral stenosis and increased pulmonary blood flow, however,
their effects are not additive, i.e. elevated pulmonary vascular
resistance in these cases has better prognosis than elevated pulmonary
vascular resistance with ventricular septal defect alone.
Congenital aneurysm of the
sinus of Valsalva:
These are lesions affecting the coronary
sinuses. The right coronary sinus is most common and then noncoronary and
left coronary sinus is the rarest. The affected coronary sinus is thin and
protrudes and later on it may rupture into a cardiac chamber and in the
case of left coronary sinus may also rupture into the pericardium. The
right coronary sinus when ruptures it communicates the aorta or with the
right ventricular outflow tract and sometimes into the right ventricular
cavity in the area of the perimembranous ventricular septal defect. The
noncoronary sinus usually ruptures into the right atrium and less commonly
into the right ventricle and rarely into the right atrium and right
ventricle together. The left coronary sinus when ruptures communicates the
aorta to the left atrium with or without the connection to the
pericardium. Lesions associated with congenital aneurysm of the sinus of
Valsalva include ventricular septal defects, aortic valve abnormalities,
pulmonary stenosis and less commonly subaortic stenosis, coarctation of
the aorta, tetralogy of Fallot and atrial septal defect.