“Atrial Septal Defects” by Dr. David Bailly for OPENPediatrics


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. Please help us improve the content by providing
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