Atrioventricular Septal Defects (AVSD)

Facts about Atrioventricular Septal Defects (AVSD)

What is Atrioventricular Septal Defect?

As with many things in medicine, the name is somewhat self explanatory. An Atrioventricular Septal Defect (AVSD) affects the valves between a patient’s Atrium and Ventricles (also know as Atrioventricular Valves, or AV valves). Essentially AVSD is a heart defect in which there are holes between the chambers of the right and left sides of the heart, and the valves that control the flow of blood between these chambers may be malformed.  You may also find this condition referred to as an atrioventricular canal defect or endocardial cushion defect.

What’s important to remember is that in AVSD, blood flows where it normally shouldn’t go. Because of this atypical blood flow the patient often has lower than normal Pa02 levels as well as extra blood flow into the lungs. This extra blood flow to the lungs forces the heart and lungs to work harder than normal as the heart attempts to increase its cardiac output through increased heart rate and increased force of contractility. In some patients this may lead to congestive heart failure (CHF).

AVSD can be categorized as either complete or partial/incomplete:

  1. Complete AVSD
    This is when there’s a large hole in the center of the heart that allows blood to flow between the four heart chambers. This hole appears in the septal wall that separates the left and right atrium and in the septal wall that separates the left and right ventricles (it usually occurs in the middle, where the atrial septum meets the ventricular septum). To make things even stranger, there’s only one common atrioventricular valve in the center of the heart instead of two separate valves – The AV valve on the right is called the tricuspid valve and the AV valve on the left side of the heart is called the mitral valve. This singular common valve usually has flaps that may not have been formed correctly or do not close properly. This type of AVSD occurs first in utero  when the common valve fails to separate into the two distinct valves (tricuspid and mitral valves) and when the septal walls that split the atriums and ventricles of the heart during gestation fail to grow to meet in the center of the heart.
  2. Partial or Incomplete AVSD
    A partial or incomplete AVSD occurs when the heart has some, but not all of the defects of a complete AVSD. Typically there’s a hole in either the atrial wall or in the ventricular wall near the center of the heart. A partial AVSD usually has two AV valves (the mitral and tricuspid valves), but one of the valves (usually mitral) may not close completely, allowing blood back-flow from the left ventricle into the left atrium.

So how common is AVSD?

Approximately 1 in 2000

Causes and Risk Factors

The causes are mostly unknown. We do know some babies have heart defects because of DNA changes in their genesor chromosomes and AVSD is more common in babies with Down Syndrome. Another hypothesis is congenital heart defects in general may be caused by a combination of genes and other factors that might increase the risk of having a baby with a congenital heart defect, such as things the mother comes in contact with in her environment such as the food she eats and types of medications used throughout the pregnancy. It’s usually diagnosed during pregnancy with ultrasound or soon after the baby is born. It’s important to note not all AVSD are easily seen on ultrasound. If there’s a high index of suspicion, a fetal EKG should be used to confirm or deny the same since it has a higher sensitivity and specificity than ultrasound imaging.

What do I do after the baby is born?

During the initial physical exam, use your stethoscope to listen for a heart murmur, listening for a whooshing sound caused by blood flow through the hole in the septal wall. Remember though, not all heart murmurs are present at birth. Babies with a complete AVSD often don’t show any signs of problems within the first few weeks after birth. When symptoms do occur, they may include things like

  • Breathing problems
  • Pounding heart
  • Weak pulse
  • Ashen or bluish skin color
  • Poor feeding, slow weight gain
  • Tiring easily
  • Swelling of the legs or belly

When it comes to partial AVSDs, and especially if the holes in the septal wall are not large, signs and symptoms may not even occur during infancy, sometimes delaying diagnosis for years.  Symptoms which might indicate that a child’s complete AVSD or partial AVSD is getting worse include

  • Arrhythmia, an abnormal heart rhythm. An arrhythmia can cause the heart to beat too fast, too slow, or erratically. When the heart does not beat properly, it can’t pump blood effectively.
  • Congestive heart failure, when the heart cannot pump enough blood and oxygen to meet the needs of the body.
  • Pulmonary hypertension, a type of high blood pressure that affects the arteries in the lungs and the right side of the heart.

Treatments

The definitive treatment for AVSD is a surgery where holes in the chambers are closed using patches. If the mitral valve does not close completely, it is repaired or replaced. For a complete AVSD, the common valve is separated into two distinct valves – one on the right side and one on the left side.

When the surgery happens depends on the health of the child and the structure of the AVSD in question. The goal is to complete surgery before there’s permanent damage to the pulmonary system from excessive blood flow to the lungs. Medication can be used to treat CHF but this is only a short term solution /to buy time until a child is strong enough to undergo a surgery. Even after surgical repair, patients fan expect to have continued complications throughout their lives, one of the most common being a leaky mitral valve which can cause the heart to have to work harder in order to effectively perfuse the rest of the body. Any patient with AVSD should seek regular follow-ups throughout their lives.

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