Tuesday, March 7, 2017

Study group discussion: PGE and congenital heart diseases

We had a discussion on this question on our study group today :)

PGE causes clinical worsening in an infant with?
A. PS without VSD
B. Hypoplastic left heart syndrome
C. Obstructive TAPVC
D. Obstruction in Aorta

Let's work this out - choice by choice!

A. PS without VSD
Pulmonary stenosis causes fixed obstruction of flow from the right ventricle of the heart to the pulmonary artery. So you'll need a patent ductus arteriosus to have some blood flow to the pulmonary system, so PGE will help since it keeps the ductus arteriosus open.

B. Hypoplastic left heart syndrome
Because the mitral valve, left ventricle, and aortic valve are hypoplastic (often with aortic atresia), oxygenated blood coming into the left atrium from the lungs is diverted across the atrial communication into the right heart, where it mixes with desaturated systemic venous return. This relatively desaturated blood exits the right ventricle through the pulmonary artery to the lungs and through the ductus arteriosus to the systemic circulation. Systemic blood flow is maintained only through the right-to-left ductal shunt; thus immediate survival depends on patency of the ductus arteriosus.

D. Obstruction in Aorta
If the narrowing is proximal to the ductus arteriosus (Preductal coarctation), blood flow to the aorta distal to the narrowing is dependent on a patent ductus arteriosus, and hence its closure can be life-threatening.

C. Obstructive TAPVC
In TAPVR, you'll require a right to left shunt! So having a left to right shunt (Like a PDA) will make the already loaded pulmonary circulation worse.

Because all systemic and pulmonary venous blood enters the right atrium and nothing drains into the left atrium... A right-to-left shunt is required for survival and is usually via a large patent foramen ovale (PFO)

Doubt by an awesomite: What if there is no patent foramen ovale?
Pressure will be high in the right atrium. So it'll keep the foramen open. For the foramen to close the left atrium pressure should be higher than the right, which isn't happening.


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