EA: But, what is it exactly?

A NORMAL HEART:

Before we discuss how the heart develops incorrectly in Ebstein's Anomaly (EA), we need to understand how the heart normally functions in a newborn and child.

Before birth, a hole called the ductus arteriosis, is present between the upper rooms of the heart so that blood can flow through the heart without getting to the lungs. After a baby is born and using their lungs, that hole closes to form a wall called the atrial septum which separates the right and left sides.  

Oxygen-poor blood from the body flows from the right atrium through the tricuspid valve (a door which prevents the blood from flowing backwards) to the right ventricle. From the right ventricle, the heart squeezes blood into the lungs so that it can get oxygen. Then the oxygen rich blood flows back into the left side of the heart at the left atrium where it passes to the left ventricle, and is eventually squeezed out of the heart and carried to all the cells of the body. The cells of the body need oxygen in order to function properly. 

Click here to watch how blood flows through a normal heart.

Figure 1. A normal heart. The tricuspid valve

closes properly, preventing blood from flowing

backwards into the right atrium, and the

atrial septum is fully formed. [1]

A HEART WITH EBSTEIN'S ANOMALY:

 Ebstein's Anomaly (EA) is a defect of the right side of the child's heart that develops while the child is in the womb; this is also known as a congenital heart defect. 

In EA, the door that separates the right atrium and right ventricle, the tricuspid valve, is pushed downward.[2]

As a result, the right atrium is much larger than normal and the the right ventricle much smaller than normal. This results in less blood flowing to the lungs to get oxygen. Tricuspid valve door also does not close properly, and the oxygen poor blood is allowed to flow backwards into the right atrium.[2] 

The backward flow of blood keeps the hole (ductus arteriosis) in the wall between the left and right atria open, so the atrial septum does not fully form (this is also known as an atrial septal defect),  to allow blood to flow into the left atrium from both the lungs and the right atrium.[2]

The result is a mix of oxygen-rich blood from the lungs and oxygen-poor blood from the right side of the heart being pushed to the body from the left ventricle. 

As a result, the cells of the body do not receive all of the oxygen they need to work properly. The child may have a characteristic blue appearance to the skin, known as cyanosis, due to a lack of oxygen to the cells of the body. 

Click here to watch blood flow through the heart in EA. 

Figure 2. This is a heart with EA. The tricuspid valve 

is pushed into the left atrium and the atrial septal 

defect is shown. Blood can flow backwards

 from the left ventricle and into the left atrium 

through the tricuspid valve and hole between the 

right and left atria. [1]

What Causes EA?

Although the exact causes of EA are not well understood, EA has been linked to the following [2,3]:

• Inherited genetic defects.
• Infants born to women over the age of 35.
• Marijuana use during pregnancy.
• Exposure to "organic solvents" (paint, varnish, cleaning agents) during pregnancy.
• Use of lithium during pregnancy.

Lithium is considered the major factor in development of EA in newborns. Lithium is commonly used to treat bipolar mania and other manic disorders. Lithium is very toxic when not used properly and these toxic effects can be transferred to the fetus if the woman uses Lithium during pregnancy. If a woman is pregnant or planning to become pregnant and taking Lithium to treat mania, she should discuss the safety of Lithium in pregnancy and other treatment options with her health care provider. 

References:

1. Ebstein's Anomaly. The Mayo Clinic Web site. Available from: http://www.mayoclinic.org/diseases-conditions/ebsteins-anomaly/multimedia/ebsteins-anomaly/img-20007245. Accessed January 21, 2015. 
2. Osiro S, Tiwari KJ, Mathenge N, et al. When Lithium Hurts: A Look at Ebstein Anomaly. Cardio in Rev.           October 2013: 21(2): 257-263. doi: 10.1097/CRD.0b013e318280c966
3. Galea J, Ellul S, Schembri A, et al. Ebstein Anomaly: A Review. Neonat Network.  September 2014: 33(5): 268-274.