What is Hypoplastic Left Heart Syndrome?

What is Hypoplastic Left Heart Syndrome (HLHS)? It is the most deadly type of cardiac congenital anomaly an infant can have.  It wasn't more than 60 years ago when nothing could be done for these babies. It has a 100% mortality rate without intervention. Even as recently as the 90s the mortality was 40-50%. Now, over 90% of children are living and one year survival rates are around 68%.

The easiest way to think of HLHS is that the infant's left ventricle is severely underdeveloped and blood isn't oxygenated the normal way it should be. The left ventricle is the portion of your heart that is most responsible for propelling blood forward to the rest of your body. If that isn't working well-- you can see how this can prove difficult for the infant. 

Now, there are only two options for treatment of this rare but fatal heart condition and that is a three staged surgical repair (A BT shunt, a bi-directional Glenn, and a Fontan repair) done over the first couple of years of life or a heart transplant. Even if the infant goes to transplant they will likely need one lifesaving surgery after birth because their life depends on certain holes in the heart staying open. This is where the term "ductal dependant" lesion comes from. The obvious difficulty with offering transplant for these patients is the scarce number of infant hearts available for transplant.

What's interesting and new in medicine is that they're trying to predict, based on some blood testing, which infants will do better getting surgery and which will do better going to transplant. What they're looking at is a micro RNA marker which is a biomarker that could predict the success of surgery for these patients. 

What might be some signs of a congenital heart defect (not necessarily this one) in an infant? Even with today's ultrasound technologies-- not ALL cardiac anomalies are detected prior to birth though a large majority are.

Look for:

1. Increased breathing rate above what would be normal for that age. A normal respiratory rate for an infant is between 40-60. Anything consistently over 60 breaths/minute is concerning. 

2. Increased heart rate.

3. Hepatomegaly. This means the liver is large. The liver sits on the right side of your abdomen housed just under the right rib cage. You should be able to feel the lower edge (maybe 1/2-1 finger breadth) but anything over that should be checked. The reason the liver will become palpable is due to blood congestion from a poor functioning heart.

4. Difference in blood pressure between the upper and lower extremities. As a screening test, blood pressure may be done on all extremities.

5. Difference in oxygen level between upper and lower extremities. 

Another way to pick up on a heart defect in a child is to give them oxygen and see if it changes their oxygen levels. If an infant's heart is "shunting" where oxygen may not go directly to the lungs then giving oxygen will not change the patient's oxygen levels or it will change them very little. 

Below are some steps we would use to stabilize the infant in the ED setting for a "ductal dependant" heart lesion: 

1. Give medication to keep the holes in the heart open. This would be a prostaglandin drip.

2. Prevent shock but don't overload the heart. This is typically done through fluid boluses but we would give half the normal dose over a longer time period.

3. Use a vasopressor (this is a medication to keep the BP up) like Dopamine if needed.

4. If continued blood pressure support is required then add a medication like Milrinone which will decrease SVR (the resistance in the body the heart has to beat against) and increase circulation.
 

So, if you need a tough diagnosis for your fictional pregnant family to deal with--Hypoplastic Left Heart Syndrome might be the choice for you.