Atrioventricular septal defect - AbsoluteAstronomy.com

Atrioventricular septal defect (AVSD) or atrioventricular canal defect (AVCD), previously known as "common atrioventricular canal" (CAVC) or "endocardial cushion defect", is characterized by a deficiency of the atrioventricular septum

Atrioventricular septum

The atrioventricular septum is a septum of the heart between the right atrium and the left ventricle .Although the name "atrioventricular septum" implies any septum between an atrium and a ventricle, in practice the divisions from RA to RV and from LA to LV are mediated by valves, not by septa...

of the heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

. It is caused by an abnormal or inadequate fusion of the superior and inferior endocardial cushions

Endocardial cushions

Atrioventricular cushions or endocardial cushions refers to a subset of cells in the primordial heart that play a vital role in proper heart septation.They develop on the atrioventricular canal.During development the heart starts out as a tube...

with the mid portion of the atrial septum and the muscular portion of the ventricular septum.

Classification

A variety of different classifications have been used, but the defects are usefully divided into "partial" and "complete" forms.

In the partial AVSD, there is a defect in the primum or inferior part of the atrial septum but no direct intraventricular communication (ostium primum defect).
In the complete AVSD (CAVSD), there is a large ventricular component beneath either or both the superior or inferior bridging leaflets of the AV valve. The defect involves the whole area of the junction of the upper and lower chambers of the heart, i.e. where the atria join the ventricles. There is a large hole between the lower portion of the atria and the upper or `inlet' portion of the ventricles and this is associated with a significant abnormality of the valves separating the atria from the ventricles. The valves in effect become a common atrio-ventricular valve, and the severity of the defect depends largely on the supporting attachments of the valve to the ventricles and whether the valve allows dominant flow from the right atrium to right ventricle and from left atrium to left ventricle ("unbalanced" flow). The overall problems are similar to those of VSD but are more complicated. There is an increased flow of blood to the lungs through both the ventricular and atrial components of the defect. In addition, the abnormal atrio-ventricular valve invariably leaks, so that when the ventricles contract, blood flows not only forwards to the body and the lungs, but also backwards into the atria. The back-pressure effect on the atria causes congestion of blood in the left atrium in particular, and this in turn causes congestion in the veins draining the lungs. The effect on the baby is to worsen the heart failure that is associated with an isolated VSD and to hasten the onset of pulmonary hypertension. It should be mentioned that CAVSD is found in approximately one-third of babies who have Down syndrome, but it also occurs as an isolated abnormality.

Pathophysiology

If there is a defect in the septum, it is possible for blood to travel from the left side of the heart to the right side of the heart, or the other way around. Since the right side of the heart contains venous blood with a low oxygen content, and the left side of the heart contains arterial blood with a high oxygen content, it is beneficial to prevent any communication between the two sides of the heart and prevent the blood from the two sides of the heart from mixing with each other.

Associated conditions

This type of congenital heart defect is associated with patients with Down syndrome

Down syndrome

Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...

(trisomy 21) or heterotaxy syndromes. Forty-five percent of children with Down syndrome have congenital heart disease. Of these, 35–40% have AV septal defects. Similarly, one-third of all children born with AVSDs also have Down syndrome.

Diagnosis

AVSDs can be detected by cardiac auscultation

Auscultation

Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...

; they cause atypical murmurs and loud heart tones. Confirmation of findings from cardiac auscultation can be obtained with a cardiac ultrasound

Medical ultrasonography

Diagnostic sonography is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions...

(echocardiography

Echocardiography

An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart . Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart...

- less invasive) and cardiac catheterization

Cardiac catheterization

Cardiac catheterization is the insertion of a catheter into a chamber or vessel of the heart. This is done for both investigational and interventional purposes...

(more invasive).

Tentative diagnosis can also be made in utero via fetal echocardiogram. An AVSD diagnosis made before birth is a marker for Down syndrome, although other signs and further testing are required before any definitive confirmation of either can be made.

Treatment

Treatment is surgical and involves closure of the atrial and ventricular septal defects and restoration of a competent left AV valve as far as is possible. Open surgical procedures require a heart-lung machine

Heart-lung machine

Cardiopulmonary bypass is a technique that temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and the oxygen content of the body. The CPB pump itself is often referred to as a heart–lung machine or "the pump"...

and are done with a median sternotomy

Median sternotomy

Median sternotomy is a type of surgical procedure in which a vertical inline incision is made along the sternum, after which the sternum itself is divided, or "cracked"...

. Surgical mortality for uncomplicated ostium primum defects in experienced centers is 2%; for uncomplicated cases of complete atrioventricular canal, 4% or less. Certain complications such as tetralogy of Fallot

Tetralogy of Fallot

Tetralogy of Fallot is a congenital heart defect which is classically understood to involve four anatomical abnormalities...

or highly unbalanced flow across the common AV valve can increase risk significantly.

Infants born with AVSD are generally in sufficient health to not require immediate corrective surgery. If surgery is not required immediately after birth, the newborn will be closely monitored for the next several months, and the operation held-off until the first signs of lung distress or heart failure. This gives the infant time to grow, increasing the size of, and thereby the ease of operation on, the heart, as well as the ease of recovery. Infants will generally require surgery within three to six months, however, they may be able to go up to two years before the operation becomes necessary, depending on the severity of the defect.

External links

Atrioventricular Septal Defect information from Seattle Children's Hospital Heart Center
AVSD information, diagram and flash animation from Cincinnati Children's Hospital Medical Center
Overview and diagram at umich.edu
Diagram at fairview.org
Explanation and simple diagram from Down's Heart Group, a UK based charity offering support and information relating to heart problems associated with Down's Syndrome.
Animation of atrioventricular septal defect at AboutKidsHealth.ca