Atrioventricular Septal Defect
Atrioventricular septal defects (AVSD) result from abnormal development of the membranous
and muscular atrioventricular septum. Depending on severity, the defect can be classified
as complete or partial. The ventricular septal defect is located at the 'inlet' portion of
the ventricle and the atrial septal defect occurs as an ostium primum type (a deficiency of
the septum primum in its inferior and anterior aspect). AVSD can accompany other complex
congenital heart disorders.
Clinical:
A thorough history and physical examination is critical when evaluating the patient with
an AVSD, as this cardiac pathology, perhaps more than any other, is associated with a
variety of other pathologies and syndromes. For example, perhaps as many as 80% of patients
with AVSD have Trisomy 21 (Down's Syndrome). Conversely, when diagnosis of Trisomy 21 is
made, it can be expected that 20-35% will have some type of AVSD. In addition, an AVSD is
frequently seen in patients with abnormalities of situs and heterotaxy syndromes. These
AVSD defects tend to be complex (unbalanced) and/or associated with complications of
ventricular outflow and the great arteries. Other rare syndromes and genetic disorders are
known to be associated with atrioventricular septal defects.
Presentation of the patient with an AVSD depends to some degree on the size and extent of
the defect. Patients with a partial AVSD will likely have a different presentation than the
patient with a complete atrioventricular septal defect.
Clinical Presentation of Partial AVSD:
These patients are usually asymptomatic during infancy and early childhood. When signs and
symptoms do exist they are most commonly minimal and likely to be due to mitral
regurgitation and its effect on the atrial shunting. Infants and young children with
partial AVSD and moderate or severe mitral regurgitation may present with increased
incidence of respiratory symptoms and more difficulty with routine upper respiratory
illnesses common to this age group. They may demonstrate slower growth than age matched
peers and when the mitral regurgitation is severe, they may present with the signs and
symptoms of congestive heart failure.
Through childhood and into adolescence, patients with partial AVSD defects are likely to
present with a history similar to those patients with a large secundum ASD. Often these
patients have an increasing, changing or new murmur. These patients may also complain of
relative fatigue compared to their peers, particularly with exercise or activity. Later in
childhood or adolescence, patients may complain of dyspnea on exertion, palpitations and
even tachyarrhythmias.
On examination, the patient with a partial atrioventricular septal defect usually reveals a
right ventricular lift with palpation. On auscultation, the first heart sound is normal and
the second heart sound is often widely split and fixed. There is usually a pulmonary
systolic ejection murmur at the upper left sternal boarder. This murmur is rarely
accompanied by a thrill, and usually a grade 3/6 or less. If the atrial shunt is large,
there may be a mid-diastolic rumble along the mid-sternal boarder. There may be a second
murmur that is high pitched in quality and pansystolic, located at the cardiac apex with
radiation to the axilla. This murmur results from the mitral regurgitation through the
cleft in the left atrioventricular valve.
Clinical Presentation of Complete AVSD:
In contrast to the patient with a partial AVSD, the infant with a complete AVSD almost
universally presents early in infancy, often in the first few weeks of life. Patients who
do not present in the neonatal period, will likely present in early infancy with signs and
symptoms of congestive heart failure. This commonly occurs by 3-6 weeks of age when the
pulmonary vascular resistance approaches its nadir and when the blood viscosity decreases
as a result of the normal physiologic anemia of the infant.
Whether patients present in the first two weeks or in the first two months, these patients
most often present to the primary care provider with a history of poor feeding, frequent
respiratory problems, failure to gain weight, and congestive cardiac failure. These
symptoms result from the large volume atrial and ventricular shunt, the left-sided
atrioventricular valve regurgitation and the concomitant fall in pulmonary vascular
resistance. In fact, if the patient with a complete atrioventricular septal defect does not
develop these signs and symptoms, one must be concerned about complicating obstruction to
pulmonary blood flow or pulmonary vascular disease.
Physical examination of the infant with a complete AVSD will reveal a hyperactive
precordium on palpation. The second heart sound may be palpable. On auscultation, the first
heart sound will be single, and the second sound will narrowly split with a loud P2 sound.
There may be an S3 gallop in some patients. There is often a murmur heard at the cardiac
apex that is holosystolic in nature and may be prominent. It may radiate to the axilla and
up the sternal boarder, and results from regurgitation of the atrioventricular valve. Some
patients will also demonstrate a mid-diastolic murmur at the lower left sternal boarder
resulting from the increased volume of ventricular inflow.
Natural history:
Fetal survival is poor with as many as 50% succumbing before birth, likely the result of
the frequent association of AVSD with chromosomal and structural pathologies.
The eventual clinical course depends on many factors. For example: the extent of the canal
defect, the relative ventricular sizes, the degree of atrioventricular valve regurgitation,
the obstruction of the ventricular outflows and the associated structural heart disease,
non-cardiac pathologies and genetic syndromes.
Patients with a partial atrioventricular septal defect that goes untreated will likely
survive into adulthood, but some early studies suggested that survival beyond 40 years
occurred in less than half of all patients. These patients are likely to have morbidity and
mortality from atrial fibrillation and complete heart block as well as other arrhythmias.
Pulmonary overcirculation also leads to symptoms, and while pulmonary artery pressure may
be somewhat increased in these adults, pulmonary hypertension is relatively uncommon.
In those with a complete atrioventricular septal defect, the vast majority will have
complications resulting from congestive cardiac failure beginning in infancy. If untreated,
most of these patients will die in the first or second year. However, some patients develop
pulmonary hypertension without significant early CHF and survive infancy. These patients
will develop obstructive pulmonary vascular disease later in childhood. Shunting across the
atrial and ventricular components becomes minimal as pressures, compliance and distal
vascular resistance equalize. While they may survive into their third and fourth decade,
these patients will suffer from complications resulting from pulmonary vascular disease in
the face of intracardiac shunting including cyanosis, resultant polycythemia, clubbing, and
other debilitating symptoms.
Patients with AVSD complicated by other cardiac pathology will follow a natural history
typically related to the associated anatomy. For example, unbalanced atrioventricular
septal defects follow the course of a single ventricle, while tetralogy of Fallot may have
recurrent issues of pulmonary artery obstruction.
Hemodynamics:
The pathophysiology of an uncomplicated, complete balanced AVSD is that of a large volume
shunt lesion. The large VSD allows equalization of left and right ventricular pressure. If
there is no significant left or right ventricular outflow obstruction, then the pulmonary
artery pressure is at systemic levels, producing pulmonary hypertension. The pulmonary
vascular resistance falls progressively from the first breath through the first month or
so, resulting in further left to right shunting at the ventricular level. This is coupled
with the increasing volume of atrial shunting that typically follows birth as the right
ventricle becomes more compliant and the volume of pulmonary venous return and left atrial
volume increases. Volume loading of the left atrium and left ventricle can be further
complicated by regurgitation of the leftward component of the atrioventricular valve. This
in turn further decreases the compliance of the left ventricle, leading to increased left
to right shunting at the atrial level.
The combination of the large volume of pulmonary blood flow along with the high pressure
resulting from the unrestricted ventricular level shunt leads to significant pulmonary
vascular congestion. Complicating this process, is the normally occurring physiologic nadir
of the infant hematocrit. With the physiologic anemia that occurs in the first 30-60 days
of life, there is a further decrease in the pulmonary vascular resistance, additional left
to right shunting and the resulting pulmonary overcirculation. This inevitably leads to
congestive heart failure.
In contrast, patients with a partial AVSD and ostium primum atrial septal defect present
with congestive heart failure much less frequently. In these patients, the primary shunt is
at the atrial level. In the fetal state, the shunt is right to left with blood returning
from the umbilical vein (via the inferior vena cava) directed to the atrial septum and left
atrium. After birth, the direction of shunting becomes predominantly left to right in the
otherwise well neonate. The volume of the shunt leads to enlargement of the right atrium,
right ventricle and pulmonary vasculature. Like the complete atrioventricular septal
defect, there is a high incidence of left atrioventricular valve regurgitation that leads
to a volume load on the left atrium and ventricle and typically decreases the compliance of
the left ventricle. As atrial shunting is a reflection of the compliance of the ventricular
chambers, there is further left to right atrial shunting as LV compliance decreases.
AVSD defects may coexist with other congenital heart disease. Among these are the
complicated heterotaxy syndromes, unbalanced ventricular mass, varying degrees of right
ventricular outflow obstruction, tetralogy of Fallot, coarctation and other left heart
obstruction involving either the inflow or outflow portion of the left ventricle.
DIAGNOSIS NOTES:
Echocardiography is most useful for diagnosis and management of AVSD and is usually best
achieved from the apical four-chamber view and subcostal view. Together, these two views
provide excellent visualization of the atrial septum, ventricular septum, the
atrioventricular valve structure, the degree of atrioventricular valve regurgitation, left
sided component of the atrioventricular valve, chordal insertions of the valve, patency of
the outflow tracts and the relative ventricular sizes. With the addition of color flow
Doppler, the assessment of atrial level and ventricular level shunting can be made.
Transesophageal echocardiography (TEE) provides outstanding imaging of the posterior
cardiac structures such as the atrial and ventricular septa and the atrioventricular
valves. However, because of its relative semi-invasive nature, it is utility in the young
patient with an atrioventricular septal defect is greatest in the operating room. When
performed prior to the operative repair, TEE can provide important information about
insertion of the atrioventricular valve apparatus, how the components of the valve are
distributed to the ventricles and the degree of AV valve regurgitation and the nature of
the cleft. Off cardiopulmonary bypass, the TEE can provide useful information to surgical
and medical teams regarding the status of the repair and identify residual pathology.
Prenatally, fetal echo can accurately diagnose the presence of an atrioventricular septal
defect. Characteristic findings can be seen as early as 12-16 weeks of gestation. The
typical four-chamber view is distinctly abnormal in these cases as there is a deficiency in
the central portion or ÒcruxÓ of the heart. In addition, an assessment of ventricular size,
AV valve regurgitation and associated defects can be ascertained. Because of the
association of atrioventricular septal defects with genetic abnormalities and syndromes, a
thorough fetal examination should be performed when such cardiac abnormalities are
identified.
Chest Xray (CXR) will vary depending on the extent of the AVSD. In those with a partial
AVSD defect, CXR may resemble a secundum atrial septal defect. There will be cardiomegaly
and increased pulmonary vascularity, both of which become more prominent with increasing
mitral regurgitation. In patients with a complete AVSD defect, the CXR will reveal
cardiomegaly in most cases and there will be pulmonary vasculature congestion. This may
include prominent shunt vascularity markings toward the lung apices. On lateral film, the
posterior aspect of the heart may be enlarged, projecting into the airways and esophagus.
ECG: As a result of the location of the AVSD defect the ÒnormalÓ course of the conduction
system is affected. The AV node is displaced inferiorly and the bundle branches are also
abnormal. This results in a typical pattern of the electrocardiogram seen in almost all
patients with an atrioventricular septal defect. The ECG typically reveals a leftward and
superior frontal QRS axis as the ventricles are depolarized from a right inferior position
to a left superior position. In some, a superior rightward axis may also be seen. There is
usually sinus rhythm, but an associated first-degree heart block may be present. There is
often an rSrÕ pattern seen in the anterior precordial leads. There may be evidence of right
ventricular - or combined ventricular - hypertrophy present.
Management:
Patients with balanced atrioventricular septal defects have two surgical option
Complete repair of the defect at newborn or early infancy stage, or
Protection of the pulmonary vascularity with a pulmonary artery banding procedure in early
infancy, followed by a complete repair in later infancy with a takedown of the pulmonary
artery band at that time.
Most pediatric cardiovascular centers recommend surgical repair in early infancy. Pulmonary
artery banding is often reserved for complicated cases of AVSD - such as unbalanced
ventricles with single ventricle physiology and pulmonary overcirculation, and AVSD in the
premature infant in CHF.
Complete repair is accomplished by placing a patch that extends from the inferior aspect of
the ventricular component of the defect all the way to the superior aspect of the atrial
component of the defect. Importantly, the conduction system generally courses in the
anterior and superior ridge of the ventricular defect, and thus is at risk for damage
during the placement of the patch. At the time of repair, assessment of the left-sided
component of the atrioventricular valve is made and issues of repair or replacement are
addressed since cleft mitral valve may accompany these defects.
Apical 4 chamber view of an atrio-ventricular septal defect
predominantly demonstrates a primum atrial septal defect. At surgery multiple atrial septal
defects were found as well as a cleft mitral valve which was repaired. No VSD was found at
surgery.
Echo
Apical color doppler imaging 4 chamber view of an atrio-ventricular
septal defect demonstrates the left - to - right shunting across the primum atrial septal
defect.
Echo
Long axis view in an atrio-ventricular septal defect demonstrates
enlargement of the right ventricle due to left - to - right shunting across the primum
atrial septal defect and slight doming during mitral opening indicating a cleft valve.
Echo
Short axis view of the left ventricle in an atrio-ventricular septal
defect demonstrates segmentation of the mitral valve orifice typical of a cleft mitral
valve.
Echo
Tilted apical 4 chamber view of an atrio-ventricular septal
defect demonstrates a primum atrial septal defect but also shows a large coronary sinus
which indicates the presence of a persistent left superior vena cava (LSVC).
survival
Echo
Subcostal view of the atrio-ventricular septal defect. Cleft mitral
valves are common in this entity.
Echo
Subcostal view of the atrio-ventricular septal defect showing the
flow across the defect.Cleft mitral valves are common in this entity and may give rise to
mitral regurgitation.
Echo
Survival
