Wednesday, February 1, 2017

A neonate with cyanotic heart disease (Case #1)

A 24-hour-old newborn, born to a diabetic mother, appears blue in all extremities. He is found to have a single, loud S2 murmur. He is given NICU support. CXR hows cardiomegaly with, an apparent narrowing of the superior mediastinum and increased pulmonary vasculature markings.

Diagnosis? Treatment till surgery is performed?

It's Transposition of great arteries (TGA).

How did I narrow down my differential?

First, congenital cyanotic heart diseases are few:
1. Tetralogy of Fallot
2. Transposition of the great arteries
3. Truncus arteriosus
4. Pulmonary atresia
5. Total anomalous pulmonary venous return
6. Tricuspid atresia
7. Hypoplastic left heart

Alright. So we still have a huge differential. What else do we know about the kid?

Murmur: Doesn't tell us much.
Cardiomegaly: Doesn't tell us much.

The pulmonary vasculature markings! It helps in the differentiation!

The increase or decrease in pulmonary vascular markings is indicative of pulmonary blood

Increased pulmonary markings (increased pulmonary blood flow):
1. Transposition of great arteries
2. Total anomalous pulmonary venous return
3. Truncus arteriosus

Decreased pulmonary markings (diminished pulmonary blood flow):
1. Pulmonary atresia or severe stenosis
2. Tetralogy of Fallot
3. Tricuspid atresia
4. Ebstein anomaly

So we have narrowed our differential to 3 conditions. Radiology of the heart helps us next:

"Narrowing of the superior mediastinum"
Classic for TGA. Cardiac contours in TGA are classically described as appearing like an egg on string.

Why not TA (Truncus arteriosus)?
It usually shows a widened mediastinum (Only sometimes, the main pulmonary artery, arising from common trunk, may be small/unusual in position which may result in a narrow mediastinum.)
Also, the physical examination in TA would show a systolic ejection murmur, a wide pulse pressure and a hyperdynamic precordium.

Why not TAPVR (Total anomalous pulmonary venous return)?
The radiology again! TAPVR will show a large supracardiac shadow (A snowman appearance, figure of 8 heart or cottage loaf heart). The dilated vertical vein on the left, brachiocephalic vein on top, and the superior vena cava on the right form the head of the snowman; the body of the snowman is formed by the enlarged right atrium.

Some notes on TGA:
- Transposition of the great arteries (TGA) is the most common cyanotic congenital cardiac anomaly with cyanosis in the first 24 hours of life.
- It is most common in infants of diabetic mothers.
- TGA is dependent on embryological shunts like VSD, ASD and PDA for survival. Therefore, PGE1 is used to keep the PDA open till surgery is performed. (Mnemonic: E1 kEEps PDA open)

Someone asked on the study group why the loud S2... Here's the explanation:
Single S2 is seen in:
- Presence of only one semilunar valve: Aortic or pulmonary atresia, truncus arteriosus
- P2 not audible: Tetralogy of Fallot, transposition of great arteries
- A2 delayed: Severe aortic stenosis
- May be normal in a newborn

Someone asked why P2 isn't audible in TGA... Here's what I found out:
In TGA, the aorta remains anterior to the pulmonary artery. Consequently the aortic component of the second sound can be exceptionally loud, and the pulmonary component may be virtually inaudible.

That's all!

Sooooo... I am a question maker now :P

I am working on this project where I revise and edit questions. Inspired, I wrote a cardiology question today :D

I admit my explanation stinks. But hey, it was a good question, wasn't it? (I'll get better, someday...)



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