It might come as a surprise to many that congenital heart disease (CHD) is far more common than Down syndrome.
According to consultant paediatrician and paediatric cardiologist Dr Ang Hak Lee, CHD occurs in one of every 125 babies, while Down syndrome occurs in one of every 600 to 700 babies.
“So, CHD is more common than Down syndrome,” he says, adding that CHD is not an uncommon disease in general.
About one quarter of CHD cases are critical, meaning that the baby must be treated, either via surgery or a catheter-based procedure, before they are one year old, or they may not survive.
The problem is that “a lot of them may not be symptomatic at birth” and many cannot be picked up during the regular ultrasounds pregnant women go through, he adds.
Among the common symptoms of CHD are sudden collapse, blue skin (due to a lack of oxygen) and a heart murmur, which is an abnormal heart sound picked up by a stethoscope.
These symptoms may not be apparent immediately after birth because the baby’s heart is adjusting from being in their mother’s womb to being out in the world on their own.
In the womb, the baby or foetus receives oxygen from their mother via the umbilical cord.
This oxygenated blood enters the foetus through what will become their belly button and proceeds to the right atrium (upper chamber) of the heart, where it passes to the left atrium via a hole in the wall between these two compartments known as the foramen ovale.
This hole is suppose to close about six to 12 months after birth, but when it doesn’t, it becomes known as a patent foramen ovale.
This condition is not considered a CHD, and does not usually cause a problem as it can exist in many people unknown.
The reason why the oxygenated blood passes from the right atrium to the left atrium, rather than to the right ventricle (lower chamber of the heart) after birth, is because the foetus’ lungs cannot work while in the womb.
After birth, the right atrium receives deoxygenated blood from the body and sends it to the right ventricle, which will then pump it to the lungs to receive oxygen.
In the foetus, the right atrium also receives deoxygenated blood from the body – which mixes with the oxygenated blood – but sends it to the right ventricle instead of the left atrium.
This deoxygenated blood will be shunted to the aorta (which exits from the left ventricle) from the pulmonary artery (which exits the right ventricle) via a connecting blood vessel called the ductus arteriosus.
The aorta will then send the deoxygenated blood back to the umbilical cord to be reoxygenated at the placenta.
The ductus arteriosus usually closes a few days after birth as the baby uses its lungs. If it doesn’t, the now-patent ductus arteriosus (PDA) becomes a CHD itself.
However, if the PDA is coupled with another heart defect, it may actually help the baby to survive a bit longer after birth by diverting some blood from the pulmonary artery to the aorta, and vice versa.
Too much or too little
Dr Ang shares that CHDs can be classified into three types depending on the blood flow. These are:
• Too much blood to the lungs
An example of this would be a ventricular septal defect (VSD), which is a hole between the two ventricles of the heart.
Because the pressure in the left ventricle is higher than the right after birth, oxygenated blood entering the left ventricle will be pushed to the right via the VSD.
The pressure in the left ventricle is higher as it needs to pump blood to the entire body, versus the right ventricle, which only needs to pump blood to the lungs.
Because of this, too much blood will be pumped to the lungs, and not enough to the body.
This will cause difficulty in breathing, including breathlessness; increased effort in breathing, including marked withdrawal of the baby’s intercostal muscles (the muscles in between the rib bones) during respiration; an increased respiratory or breathing rate; enlargement of the heart as it strives to pump more blood to the rest of the body; and an increased heart rate.
“For newborn babies, both sides of the heart have equal pressure,” says Dr Ang.
“It takes two to six weeks for the right side of the lung to drop its pressure, which is when the blood will start flowing from the high pressure system to the low pressure system (i.e. left ventricle to the right ventricle via the VSD).”
That is why a baby with VSD might only show symptoms of heart failure (as listed above) two to six weeks after being born.
• Too little blood to the lungs
In this situation, Dr Ang explains that: “The blood vessel pumping to the lungs is either blocked or narrowed.
“Too little blood going to the lungs has an obvious presentation – less blood going to the lungs means less oxygen coming back to go to the body, and the baby will be blue.”
The baby will go into shock and collapse as the body does not receive enough oxygen, which is why CHDs that cause this are considered critical.
However, this may not happen immediately as the PDA will initially help the baby by diverting some of the blood from the aorta to the pulmonary artery so that it can be reoxygenated.
“This PDA actually saves the baby and puts the baby into an asymptomatic state.
“But this vessel will close in five to seven days – in normal babies, it usually closes in 24 hours – and the baby will become blue,” he says.
An example of this CHD is the tetralogy of Fallot, which is the most common CHD that causes a baby to go blue (cyanotic).
Babies with this condition have four defects in their heart:
> Pulmonary valve stenosis
This is the narrowing of the valve between the right ventricle and the pulmonary artery.
> Overriding aorta
This means that the aorta, which usually exits from the left ventricle, is placed directly above the VSD, meaning that it receives both oxygenated and deoxygenated blood to send to the rest of the body.
> Right ventricular hypertrophy
This is where the right side of the heart becomes overly muscular as it is required to pump more and more blood to the body as the body does not receive enough oxygen,
Over time, this will cause the heart to stiffen, and eventually fail more quickly.
• Too little blood to the body
This situation is also caused by a blockage or narrowing of the blood vessels, but of those that supply the body.
Babies with these conditions will experience the same symptoms as those who have too little blood going to the lungs, as essentially, they do not have enough oxygen to supply the body and will go into shock.
An example of this condition is hypoplastic left heart syndrome.
Says Dr Ang: “This condition is where the whole left side of the heart is hypoplastic, i.e. small.
“So the heart on the left side is small and the vessel coming out of the left side is small, so it is not pumping blood well to the whole body.”
Plug or ligate
There are basically two ways to fix CHDs: “plug it or ligate it”, as Dr Ang says.
Defects that are holes are “plugged” or closed, either via a device, usually inserted through catheter-based intervention, or stitched up via open surgery.
Defects that are in a vessel are “ligated”, i.e. closed by tying it off.
“But if it’s a major structural problem, then it is difficult.
“For example, if you are born with no blood vessel going to the lung – called pulmonary atresia – how do you create a blood vessel? You have to put in an artificial one.
“But for a growing child, you have one more problem: they are growing. How big of an artificial vessel do you want to put?
“Too big a vessel means they will have too much blood going to the lungs. Besides, you can’t put too big a vessel in a small baby.
“A small one means that it will become too small when the baby grows up and you will have to replace the vessel more frequently,” he explains.
Dr Ang adds that the baby will need to undergo regular surgeries as he or she grows up anyway, as the artificial blood vessel will not grow with them and will need to be replaced.
Fortunately, he says that about 30% of CHDs are VSDs, while about another 12%-15% are atrial septal defects (ASDs), both of which can be easily “plugged”.