Ventricular Septal Defects, by Doctor David Bailey.
Hello, my name is David Bailey.
I'm a pediatric cardiologist and pediatric cardiac intensivist.
And today, we're going to be talking about ventricular septal defects.
We're going to start by outlining the anatomy and physiology of this cardiac lesion, followed
by typical and atypical presentations.
And then we'll talk about the imaging and diagnostic workup.
Finally, we'll talk about the initial management and pre-operative considerations for patients
with ventricular septal defects.
Anatomy and Physiology.
So to begin with, a ventricular septal defect is a defect that can occur anywhere along
the ventricular septum.
There can be one or many, and it can occur in one location or even multiple locations.
The nomenclature of ventricular septal defects is known to be quite convoluted.
Here we use five typical subcategories, the first being muscular ventricular septal defects.
This is the most common, it presents about 60% of the time.
And it's important to know these different nomenclatures in as much as that we now understand
a little bit more about the natural history of each of these different types of lesions.
Muscular defects, again, as I said, is the most common.
They're also the most likely type to close spontaneously.
30% of them, in fact, close spontaneously.
They also often present with multiple defects, which are sometimes hard to see by echocardiography.
The next most common type is membranous, also known as peri- or peramembranous defects.
And these account for about 30% percent of the total of ventrical septal defects that
we see.
These lesions are less likely to close on their own.
However, sometimes tissue from the tricuspid valve will occlude the defect.
And so they will close in that circumstance.
The last three types rarely, if ever, close on their own.
There's the malalignment defect, as is usually seen with Tetralogy of Fallot.
And again, that really closes on its own.
And it's often seen in addition to other cardiac lesions.
There's the subpulmonary or conal type of ventricular septal defects.
These ones will rarely close on their own, if ever at all.
Some people would say the diagnosis is an indication for surgical repair because they
close so rarely.
And they're more common in the Asian population.
This is important because they're also more commonly associated with aortic regurgitation,
which is more commonly associated with bacterial endocarditis, before and even after repair.
So for those of you practicing in those countries, this is a lesion you may see more frequently.
So keep in mind the increased instance of endocarditis in that subcategory.
And then finally, there's the endocardial cushion defects.
This is classically seen in patients with atrioventricular canals and obviously, the
incidence of Trisomy 21 that is correlated with that specific lesion.
We often talk about the size of ventricular septal defects.
We call them large, medium, and small.
Large defects are simply those which are greater than 50% the size of the diameter of the aorta.
Small defects are typically restrictive.
And medium sized defect lie somewhere in between.
Now the physiology ventricular septal defects is very interesting.
It's a defect that shunts predominantly during systole, and then imparts both a volume and
a pressure load to the pulmonary circulation, and then to the left side of the heart.
So during systole, the heart squeezes, the LV contracts and ejects blood if there's an
unrestricted defect into the right ventricle at systemic pressures.
The bulk of the blood is actually injected into the pulmonary artery because the right
ventricle is also undergoing systole at that same time.
That pressure and that volume is imparted to the pulmonary circulation, which returns
to the left side of the heart.
The increased volume burden to the left side of the heart is evidenced by a left atrial
and left ventricular enlargement if the volume burden is significant.
It is this volume burden and pressure burden that causes the usual presentation that we
see.
Presentation.
So how do these patients present?
As you would imagine, they present in congestive heart failure and pulmonary artery hypertension
if it's longstanding and unchecked.
The congestive heart failure is due to a few things.
The main determinants of the degree of congestive heart failure and failure to thrive is the
degree of shunt and the degree of work of breathing that's imparted by that shunt.
So the cardiac output needed to maintain a normal systemic circulation in the setting
of increased pulmonary blood flow must be increased.
Therefore, the total cardiac output in the setting of a VSD is a significant contribution
to the metabolic demands needed by these patients.
In addition to the increased pulmonary blood flow, there's an increased pulmonary metabolic
demand from that work of breathing.
Those two things are the main determinants of congestive heart failure and failure to
thrive in these patients.
Again, if the pulmonary circulation is left unchecked, if the defect is not closed, or
the P.A.
Is not banded as it was in the past, the contribution of a combined volume and pressure load to
the pulmonary circulation can lead to the development of early onset pulmonary hypertension.
Sometimes even in the neonatal period if there's concomitant lesions.
So what will these patients look like and sound like when they walk into your office
or when you see them in your hospital?
They'll be maybe cachectic, have some increased work of breathing, easy tachypnea, they'll
be very prone to respiratory infections due to the increased pulmonary blood flow.
They'll be particularly vulnerable when they're anemic.
So, right around two months when they reach their physiologic nadir, the anemia combined
with the increased cardiac demands can cause them to have more profound failure to thrive
then you might expect.
On physical exam, you'll hear a pansystolic murmur as blood is shunted across the ventricular
septum
[SOUND OF HEART BEATING]
The murmur will begin right after the S1.
It may be slightly delayed if it's a muscular defect with some constriction.
The S2 is very important to listen to and to characterize.
If the S2 is accentuated, if it is palpable, if it is singular, all those things denote
an increase in degree of pulmonary hypertension.
And it's important to understand the progression of pulmonary hypertension, especially in patients
with VSDs.
If the pulmonary hypertension progresses to a point that the pulmonary vascular resistance
is higher than the systemic vascular resistance, the shunt murmur will no longer be appreciated,
and those patients are then categorized as having Eisenmenger Complex.
Other lesions that also present with VSDs determine how they present.
We talked a little about aortic regurgitation and the increased incidence of bacterial endocarditis.
The murmur from aortic regurgitation is rarely heard before the age of five, even though
the incidence of aortic regurgitation-- we're finding out it's more common now that we have
better imaging modalities.
Aortic Stenosis, some arch hypoplasia and coarcation is also commonly seen with ventricular
septal defects.
And these patients may have a click.
They also may develop more pulmonary vascular congestion, due to L.A. Hypertension, than
some of your other patients.
If you find an ASD with the patient, look for extra cardiac defects, as they're more
common in patients who have both an ASD and a VSD.
And then there's the double chamber right ventricle that can often occur, most commonly
in those with membranous ventricular septal defects, due to hypertrophy of the muscle
or the muscles around the moderator band itself.
The EKG and the chest x-ray, in combination with your physical exam finding, often are
not conclusive enough to diagnose a VSD with double chamber right ventricle, and it is
in this setting especially that echocardiogram is important.
Imaging and diagnostic work-up.
As far as imaging and diagnostic modalities go, the work-up is pretty intuitive.
The echo should donate the size of the lesion, the location of the lesion, and the physiologic
burden, the shunt, and the pressure of the lesion.
The EKG-- you would look for signs of right ventricular elevated pressure or left ventricular
enlargements.
And it's the classic EKG findings of RVH and LVH that you would see.
If you see either one of those things, consider PS or a significant shunt burden.
The chest x-ray usually will show increased pulmonary blood flow and congestion.
However, you may see some hyperexpansion on the chest x-ray, particularly, in those infants
with left atrial enlargement from a large shunt burden and often those who have a VSD
and a ductus.
The atrial enlargement can cause bronchial compression and hyperexpansion by chest x-ray.
The echo is a definitive tool to make the diagnosis.
And if there's any question about the pulmonary artery pressures or the characterization of
the defect, then cath would be indicated.
If pulmonary vascular resistance is markedly elevated above normal limits of three woods
units, closure may not be possible.
If pulmonary vascular resistance is within normal limits closure or continued medical
management is appropriate.
Initial Management Strategies.
The management of these patients centers around treating the congestive heart failure, the
failure to thrive, and in close follow up again to understand the pulmonary vascular
changes that will be ongoing in these patients.
In neonates and infants it is recommended that if the defect is large or unrestrictive
and there is any evidence of heart failure, failure to thrive, or ongoing pulmonary hypertension
to close the lesion at that time.
If the infant is able to get out to the six month period, and there's no overt signs of
heart failure or pulmonary hypertension, medical management is very reasonable in this patient
population.
Continued use of lasix and increasing caloric density of their formula are two of the mainstays
that we use here to allow them to grow.
Particularly, if it is a muscular septal defect, which was known to often close spontaneously
over time.
Again it's important to consider endocarditis to these patients.
20% of them will have a residual lesion and puts them at increased risk for endocarditis.
So in summary, ventricular septal defects are very common.
They're common in isolation and they're common with other lesions.
They present with increased blood flow to the left side of the heart with LV enlargement
and over time they can progress to pulmonary hypertension.
The other summary points of VSDs are it's the size of the defect that determines the
amount of increase left to right shunt.
Defects that are restrictive, it's the size of the defect that determines it.
Those that are unrestrictive, it is the relative resistance of the two circulations that determines
the degree of shunt.
They present with heart failure and failure to thrive, any signs of pulmonary hypertension
including accentuated S2 or cyanosis is very concerning and should warrant immediate evaluation
and consideration for surgical repair.
Finally, imaging is best achieved via the echo modality, x-ray, and EKG can be helpful
in understanding pulmonary blood flow, and the management of these patients centers around
failure to thrive, therapies, and congestive heart failure therapies, namely lasix and
increased caloric density.
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