Ventricular septal defect

Video summary

Ventricular septal defect (VSD) is a type of congenital heart defect that affects the septum, the wall that separates the two ventricles of the heart. In VSD, there is an abnormal opening in the septum that allows blood to flow between the two ventricles. This results in increased blood flow to the lungs, causing pulmonary hypertension and, in severe cases, heart failure. VSD is typically diagnosed during infancy or childhood, and imaging tests such as echocardiography or cardiac catheterization may be used to confirm the diagnosis. Treatment options for VSD depend on the size and location of the defect, and can include medications, surgery, or catheter-based procedures to close the hole and restore normal blood flow in the heart.

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I With ventricular septal defects, ventricular refers to the heart's two lower chambers called the ventricles. Septal refers to the septum, which is the wall that separates them, while defect means there's an opening that shouldn't be there.
So a ventricular septal defect is a congenital heart defect characterized by an abnormal gap in the wall separating the ventricles.
To understand how this opening forms, we need to review how the ventricular septum develops during fetal life. Early during heart development, the left ventricle starts as a primitive ventricle, while the right ventricle develops from the bulbous cortex.
Around the 4th week of development, a muscular ridge begins growing upward from the heart's apex, eventually fusing with a membranous wall coming down from the endocardial cushions.
This fusion divides the lower half of the heart into the left and right ventricles. If these walls don't fuse correctly, a gap is left between the two chambers.
This opening is what we call a ventricular septal defect or VSD. VSDs are actually one of the most common congenital heart defects in babies, and they tend to show up even more often in fetal alcohol syndrome and Down syndrome.
Now we classify VSDs based on the location of this opening. Most VSDs occur in the upper membranous portion of the septum, which happens to be the last part to close during fetal development.
On the flip side, muscular VSDs are less common but more likely to close on their own. In some cases, the defect might arise in the inlet portion of the septum near the tricuspid and mitral valves, or in the outlet portion close to where the blood exits the ventricles toward the great vessels.
During fetal life, VSDs usually don't cause problems because the pressure in the right and left ventricles is pretty much the same, and that's all thanks to how fetal circulation works in the fetus.
The lungs are collapsed and filled with fluid, so the pulmonary vessels are squeezed tight. Because of this high resistance in the pulmonary vessels, the right ventricle is unable to pump blood into the lungs.
Instead, the blood takes a detour to through fetal shunts. First, there's the foramen ovale, a small opening that allows blood to flow directly from the right atrium to the left atrium.
Then there's the ductus arteriosis, a vessel that connects the pulmonary artery to the aorta. These shunts allow the blood from the right ventricle to bypass pulmonary circulation and flow directly into systemic circulation.
At the same time, the placenta provides a low resistance pathway for blood leaving the left side of the heart, so the left ventricle doesn't need to generate much more pressure than the right.
In this setup, pressures on both sides of the heart remain similar, so there's little to no blood flow across the VSD before birth.
However, everything changes with the baby's first breaths as the lungs expand. The pulmonary vessels open, causing pulmonary resistance to drop.
At the same time, clamping the umbilical cord takes the placenta out of the circulation, removing its low resistance pathway and raising systemic resistance.
On top of that, the two fetal shunts, the foramen ovale and the ductus arteriosis, begin to close, so the two sides of the heart are no longer directly connected.
Because of these changes, the left ventricle starts pumping against a much higher pressure than the right ventricle, making the pressure in the left ventricle greater than in the right ventricle.
And since the left ventricle is now stronger, it pushes the oxygen-rich blood through the VSD into the right ventricle, creating a left to right shunt.
The extra blood sent to the right ventricle gets pumped back to the lungs, essentially taking an extra trip through the pulmonary circulation.
Because of that, you'll see a higher oxygen saturation in the right ventricle and pulmonary artery, but not the right atrium.
If the defect is small, a child can usually tolerate this extra flow just fine. But if it's large, this extra blood puts significant strain on the right side of the heart and the lungs.
Over the years, this increased workload causes the lungs to adapt, but in the wrong way. The pulmonary arteries thicken and stiffen, thereby increasing the pressure in the pulmonary circulation and causing pulmonary hypertension.
At the same time this means that the right ventricle has to work overtime like a muscle forced to lift heavier weights every day to keep up it grows stronger and thicker, which is known as right ventricular hypertrophy.
All these changes eventually cause the pressure in the right ventricle to overcome the pressure of the left ventricle, flipping the direction of the shunt from left to right to right to left.
When this happens, deoxygenated blood from the right ventricle flows through the VSD into the left ventricle, entering systemic circulation.
Low oxygen levels in the systemic circulation result in cyanosis, which is a bluish tint of the skin, fingers, and toes.
This late complication, known as Eisenmanger syndrome, turns what started as a harmless defect into a condition that severely deprives tissues of oxygen.
Now small VSDs are often asymptomatic and might go unnoticed. However, when the defect is larger, symptoms usually appear a few weeks after birth when the pulmonary resistance drops enough to allow significant left to right shunting.
In infants, this shows up as rapid breathing, poor feeding, and failure to thrive. In older children and adults, large VSDs cause non-specific symptoms such as fatigue, shortness of breath, and frequent respiratory infections due to increased pulmonary blood flow.
On auscultation, a small VSD produces a loud, harsh, holosystolic murmur best heard at the lower left sternal border. Interestingly, the smaller the defect, the louder the murmur because the blood is being forced through a narrow opening at a higher velocity.
On the flip side, larger VSDs can produce a softer murmur and even a mid-diastolic rumble at the apex. Due to increased flow across the mitral valve.
In cases where pulmonary hypertension sets in, the murmur might start to fade. This is not because things are getting better, but because the pressure on both sides of the heart is evening out, so less blood is flowing through the defect.
Ironically, this fading murmur can signal trouble ahead, as it may be the first sign of a shunt reversal. Once you suspect of ESD, be sure to order an echocardiogram, which can help determine the size and exact location of the defect.
Infants with small VSDs often get a wait and watch approach, since many of these tiny holes close on their own as the heart muscle grows and expands, gradually sealing off the defect.
But when the defect is larger, it usually calls for action and surgical closure. This can mean traditional open heart surgery or a less invasive catheter procedure, which is a bit like patching a hole in a wall without tearing down the whole room.
Timing is crucial, repairs must happen before pulmonary hypertension sets in and flips the shunt direction, because once that switch flips, closing the defect can actually make heart failure worse instead of better.
All right, as a quick recap, a ventricular septal defect is a congenital heart defect where there's an abnormal opening in the septum separating the left and right ventricles.
After birth, as pulmonary resistance drops and systemic resistance increases, blood begins to shunt from the left ventricle to the right, increasing blood flow to the lungs.
Small VSDs often cause no symptoms and might close on their own, but larger ones over time can lead to pulmonary hypertension and right ventricular hypertrophy.
If left untreated, the right ventricle can overcome the pressure in the left ventricle, eventually reversing the shunt, causing the blood to flow from the right ventricle to the left one.
This condition is known as Eisenmeger syndrome.