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
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
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
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
[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
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
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
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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