Atrial Septal Defects, by Dr. David Bailly.
My name is David Bailly.
I'm a fellow here at Boston Children's Hospital in the Department of Anesthesia and Critical
Care I am also a boarded pediatrician and a boarded pediatric cardiologist.
And I am going to speak with you today about atrial septal defects.
Atrial septal defects are very common overall, and they're commonly seen in other cardiac
lesions.
Up to 50% of all cardiac constellations include an atrial septal defect.
We're going to talk initially about the anatomy and the physiology of the different types
of atrial septal defects, followed by the usual presentation, including some of the
unusual presentations, followed by the imaging and diagnostic modalities used to help us
treat and diagnose atrial septal defects, followed by initial management strategies
for patients with atrial septal defects and the sequelae of that lesion.
Anatomy and Physiology.
So, to start out with the anatomy and physiology, atrial septal defects are simply any defect
in the atrial septum.
They can be large, they can be small, they can be single, there can be multiple defects
anywhere within the atrial septum.
The three broad categories that we typically divide them out into are secundum atrial septal
defects, which account for about 70% of the defects that we see-- and those are actually
a defect in the primum portion of the septum from an embryologic standpoint.
The second most common type is primum defects, which are defects in the atrial septum that
occur in the inferior level of the atrial septum.
They're often associated with AV canal defects, but they don't always have to be.
The last type are the sinus venosus atrial septal defects, and they broadly fan out into
two categories-- those involving the superior vena cava, which are the most common type,
and those involving the inferior vena cava, which are the least common type.
Those are essentially a defect in the lumen of the SVC and the lumen of a pulmonary vein
such that there's a communication.
The entrance to the pulmonary veins is actually normal back into the left atrium.
But because there's a communication between the wall of the pulmonary vein and the wall
of the superior vena cava, a left-to-right shunt occurs.
So the physiology of all atrial septal defects is essentially a left-to-right shunt at the
atrial level that evokes a volume burden on the right side of the heart.
And we can use box diagrams to illustrate this quite clearly.
Box diagram here shows that we have the right atrium, the right ventricle into the pulmonary
arteries, the blood will return to the left side of the heart into the left atrium, the
left ventricle, and into the aorta.
So if we draw blood flowing through the heart in a usual pathway, you'll see denoted here
as simply an arrow, blood going to the RA, the RV, the PAs, and then back to the left
side of the heart.
This is the usual course of blood flow, as you all know.
Now, if there's an atrial septal defect, once the blood returns to the left atrium, it essentially
has a decision to make.
Is it going to shunt to the right side of the heart, or continue on to the left side
of the heart?
The definitive point of that - where the blood shunts, is determined by the relative compliance
of the two ventricles.
Now, at birth, the right ventricle is less compliant, because it has essentially been
behaving as a left ventricle in utero by providing systemic circulation through the ductus arteriosis.
However, after birth, the placenta is detached, the lungs are inflated, the pulmonary vascular
resistance drops, and the systemic vascular resistance rises over time as the LV supports
a systemic circulation and as we go through life and have coronary artery disease and
other reasons to have hypertension, the LV becomes less compliant; the RV becomes more
compliant.
So initially, at birth, there's very little shunting at the atrial level.
But over time, as the RV relaxes and the LV becomes more stiff, there's increased flow
across the atrial septum and to the right side of the heart.
And with this flow, obviously, it evokes a volume burden on the right side of the heart.
So more blood's going to the right atrium, the right ventricle, to the pulmonary arteries.
And it's this physiology that describes the presentation and the ECHO findings that we
describe.
And this is the reason to go for surgical repair.
Presentation.
So how do these patients typically present?
Usually, it's a perfectly well asymptomatic child that shows up for a well child check.
They're about 3 years old, parents have no complaints, no concerns, but during their
check, someone actually hears a murmur.
It's not a murmur that anyone's heard on prior occasions due to these compliance issues that
we just talked about.
The RV has finally relaxed to the point where there's enough flow through the right side
of the heart that there's what we call a relative stenosis of the pulmonary valve.
So you hear a 2 over 6 systolic ejection murmur as blood flows across the pulmonary valve.
Pulmonary valve itself is normal.
It's just there's extra blood flow from the atrial level shunt.
So you hear a 2 over 6 ejection murmur at the pulmonary valve position, which is the
left upper sternal border.
[HEART BEATING] Now, the heart sounds in atrial septal defect are very important to note.
They're fixed, and they're wide.
They're fixed because in the setting of a nonrestrictive atrial septal defect, there's
equalization of the respiratory influence on the right- and left-sided cardiac outputs
which gives you a fixed S1 and S2.
And it's wide because the delayed emptying of the right ventricle causes delayed closure
of the pulmonary valve, giving you a wide and fixed split S2.
In addition to the murmur of pulmonary stenosis, which we already talked about, they can also
have a murmur of relative tricuspid stenosis.
And over time, if the RV continues to enlarge, the tricuspid valve apparatus will stretch,
and then you can have tricuspid regurgitation and a murmur that is coincident with that
as well.
The main thing that we worry about in patients with atrial septal defects is the development
of pulmonary vascular obstructive disease.
This is a rare presentation in this day and age, when most of these murmurs are picked
up by routine exams and through echocardiography.
And it typically presents in the second decade of life and in less than 10% of the population.
Other presentations include atrial arrhythmias, again, we believe due to the right atrial
enlargement that causes arrhythmias.
Now, there's a small subset of patients with atrial septal defects that actually present
with Failure to Thrive or cyanosis.
These are outliers.
Any patient who has Failure to Thrive or cyanosis with an isolated atrial septal defect should
undergo a very thorough evaluation for other causes for Failure to Thrive and cyanosis--
including, but not limited to, reflux, obstructive sleep apnea.
And there's also been case series that have found that many of these patients with Failure
to Thrive and atrial septal defects often have spontaneous closure of their atrial septal
defects, implying that perhaps, for whatever reason, there was some degree of left atrial
hypertension, whether it was from a coarct or something else that caused, over time,
spontaneous closure of the atrial septal defect, when in fact, originally it may have been
more of a stretched foramen from the high left atrial pressures.
Imaging and Diagnostic Work-Up.
Imaging is a key component of identifying and diagnosing atrial septal defects.
Echocardiography is the benchmark for diagnosing these lesions, as we're usually able to get
adequate windows to diagnose the lesion itself, its location, as well as the size.
An important concept to remember, regardless of the imaging modality used, is that all
key neighboring structures need to be identified, particularly the pulmonary veins.
10% of patients with secundum atrial defects can have an anomalous pulmonary venous return.
So it's important that all the pulmonary veins are seen prior to surgical repair.
EKG findings are usually significant for some right axis deviation, positive 90 to a positive
180 degrees, some right ventricular hypertrophy, and/or right heart enlargement.
The chest x-ray also shows right heart enlargement.
Perhaps a prominent main pulmonary artery, some cephalisation, or increased pulmonary
blood flow can also be appreciated if the ASD has been long standing and is large.
MRI can be helpful if there is not an ability to clearly see all the key neighboring structures
by ECHO.
And cath is rarely needed except in the circumstances where there is already pulmonary vascular
obstructive disease that has developed.
Or if there is an inability to adequately quantify the degree of pulmonary blood flow
pre-operatively.
Cath is obviously used when devices are used to close the atrial septal defect, but is
rarely used as a diagnostic tool in and of itself.
Point of Clarification: catheter intervention can only be done for secundum ASDs where there
are sufficient rims.
Secundum ASDs can also be closed surgically.
Primum ASDs and Sinus Venosus defects are not amenable to closure in the catheterization
lab, and must be closed surgically.
Initial Management Strategies.
Now, the management of patients with atrial septal defects is very limited because they
often present asymptomatically.
The management really revolves around deciding on how best to repair the lesion.
The two main options available to most people are either a catheter intervention if there's
sufficient rims to occlude the defect or a surgical intervention, which is the traditional
mainstay repair that has been around the longest.
The morbidity and mortality of both of these options are extremely low with less than 1%
mortality reported overall.
It's important to remember, however, that patients who've had closure of the atrial
septal defect via surgical repair are at risk for postpericardiotomy syndrome, which is
an immune-modulated effusive response that leads to a pericardial effusion 1 to 6 weeks
after repair.
This syndrome can be life-threatening and it presents with the usual symptoms of pericardial
effusion, such as hypotension, muffled heart sounds, or an exaggerated JVD impulse.
Deciding who to repair is center-specific, but there are a few things that we have seen
that carries over to all centers.
If the defect is greater than 8 millimeters, they rarely, if ever, close on their own.
And that will require repair, and it's worth considering an earlier repair in those patients.
Typically, they're closed around 3 to 4 years of age prior to going to school but before
the development of pulmonary vascular obstructive disease.
Defects that are less than 3 millimeters, however, often close spontaneously, and those
can usually be watched for a few years.
However, if you have a defect that's 5 millimeters with still significant shunt seen by echocardiography,
it's worth considering closure of that.
Again, around the age of 3 to 4 years.
So in summary, atrial septal defects are very common overall, and they're commonly seen
in other cardiac lesions.
Up to 50% of all cardiac constellations include an atrial septal defect.
They usually present as an asymptomatic patient during a well child check with a 2 over 6
systolic ejection murmur at the left upper sternal border.
So early detection of these lesions is very important to overcome the effects of pulmonary
vascular obstructive disease that can develop if they're not caught early on.
Imaging can be very straightforward usually with echocardiography, and there's the x-ray
and EKG findings of right heart enlargements and increased pulmonary blood flow.
And finally, the management is by closure either in the cath lab or surgically.
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