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Duke-NUS Graduate Medical School | Ventricular_Septal_Defects
Hi. Today we'll be talking about ventricular septal defects.
By the end of this lecture you should be able to describe the pathophysiology, identify the clinical presentation,
and understand the management of Ventricular Septal Defects, or VSD for short.
Let's start off with a general overview of congenital heart defects, categorizing them into acyanotic versus cyanotic
conditions.
Acyanotic conditions have left to right shunting, causing blood to recirculate through the lungs. Cyanotic
conditions, on the other hand, have right to left shunting. This causes de-oxygenated blood in the right side of the
heart to bypass the lungs and go straight back into the body without picking up oxygen.
VSDs fall under the acyanotic category. They are the most common congenital heart defect.
VSDs can be sporadic, part of congenital symptoms, or a component of more complex defects, such as the
tetralogy of fallot. They usually occur in the membranous portion of the septum.
The direction of blood flow through the VSD depends on the differential pressures between the ventricles. It also
depends on the resistance and the outflow tracks from each ventricle, especially in the case where the VSD is
large enough for the pressures in the right and left ventricles to equalize.
In the absence of other defects, systemic resistance is much higher than pulmonary vascular resistance. This
causes the left to right shunt that we see in isolated VSDs. The lungs become over circulated, which leads to the
symptoms seen with VSDs as the disease progresses.
During the first few weeks of life pulmonary vascular resistance remains high. This keeps shunting from the left to
a minimum, and allows patients with large VSDs to be asymptomatic.
However, as pulmonary resistance decreases over the first six to eight week of life, shunting increases, and
causes symptoms to develop.
The presentation of a VSD is highly variable, and depends on both the size of the defect and the state of
pulmonary vascular resistance. Patients with small defects tend to be asymptomatic, and may present later as
adults.
In this day and age VSDs are largely picked up in neo-nates by a murmer noted on examination. Larger defects,
however, may lead to pulmonary over circulation, and eventually congestive heart failure.
These patients present in early childhood with tachypnea, dyspnea, fatigue, diaphoresis during feeding, and
failure to thrive. On examination a holosystolic murmur at the left lower sternal border its classic for VSD.
Additionally a mid-diastolic murmur may be heard at the apex, due to the increased volume of blood flowing
across a now relatively small mitral valve.
If pulmonary arterial pressures have begun to increase, a loud P2 and narrow splitting of S2 may be present.
Bibasal crepitations in the lungs and hepatomegaly may also be observed due to fluid over circulation.
Large VSDs may lead to changes on chest X-ray and ECG. With a large amount of shunting, ECG may reflect less
atrial and ventricular enlargement and hypertrophy. If shunting is severe right ventricular hypertrophy may also
occur.
Chest X-rays show cardiomegaly, with enlargement of the pulmonary artery, and increased pulmonary vascular
markings. 2D echo with doppler is diagnostic of VSD.
VSDs can lead to several cardiac complications, including right ventricle outflow tract obstruction, aortic
regurgitation, and subaortic stenosis. However, the important complication to learn at this point is the development
of Eisenmenger Syndrome.
The increased volume of blood received by the lungs causes increased pulmonary pressure, and increased
pulmonary vascular resistance.
Eventually the resistance in the lungs overcome the resistance in the aorta, leading to a reversal in the direction of
the shunt. Blood now flows from the right heart to the left, leading to late cyanosis. This pulmonary hypertension in
the setting of a congenital heart defect is what we call Eisenmenger Syndrome.
Up until recently treatment for this was limited to heart-lung transplants and palliative care. Recently however,
vasodilators approved for idiopathic pulmonary hypertension have been shown to improve symptoms in
Eisenmenger Syndrome as well, and have been recommended as part of patient management.
Let's now turn to the management of VSDs. Note that most VSDs will close spontaneously. However, there are
options for symptomatic treatment. The goal for this would be addressing the congestive heart failure and failure
to thrive in these children.
Target caloric intake should be increased to meet the children's increased metabolic demand. These children also
tend to have poor intake due to tiring while feeding.
Nasogastric boluses or continuous feeding may be necessary in severe cases. Diuretics can be given to address
fluid overload from heart failure. And ACE inhibitors can be given to decrease after load, thereby decreasing the
volume of the shunt to the right heart.
The use of Digoxin, presumably to help with heart contractility in the setting of large defects is debatable.
In patients with small shunts, and normal pulmonary arterial pressures, surgery is not recommended. However,
large defects can lead to changes in the pulmonary and vascular systems.
The proper management for these patients is early surgical correction of the VSD before too much damage, and
especially Eisenmenger Syndrome set in.
Some indications with surgery are listed here.
However, how much benefit a patient will get from surgical intervention depends on the pre-operative pulmonary
vascular resistance. If the elevation in the pulmonary resistance has already reached moderate to severe levels,
pulmonary vascular disease is likely not to change after the operation, and may even continue to progress.
Patients with normal or mildly elevated pulmonary vascular resistance have much better prognosis following
surgery.
The last component in the management of the VSD is considering antibiotic prophylaxis against bacterial
endocarditis. This is indicated for all children with congenital heart defects. It is needed if the defect is unrepaired,
if palliative shunts are in place, or if there are residual defects at or near prosthetic patches in the patient.
For patients undergoing complete surgical repair, antibiotic coverage should be given for six months following the
procedure.
So in summary, VSD is the most common congenital heart defect. It leads to left to right shunting, causing over
circulation of the lungs, and elevation in pulmonary and vascular resistance over time.
Eisenmenger Syndrome is an important complication due to changes in pulmonary resistance that lead to the
reversal of a shunt and late cyanosis.
While small asymptomatic VSDs do not require much treatment, large VSDs should undergo early surgical
intervention to avoid pulmonary vasculary disease.