What is an atrioventricular septal or AV canal defect?
Atrioventricular septal defect (AVSD), or AV canal, is a heart defect that involves the valves between the heart's upper and lower chambers and the walls between the chambers. Other terms used to describe this problem include endocardial cushion defect and AV canal defect. A similar but less serious form of atrioventricular septal defect is called primum atrial septal defect or incomplete or partial atrioventricular septal defect. The cause of atrioventricular septal defect is not known. Overall it is quite rare and accounts for 4% of heart defects diagnosed in children. However, it is quite common in children with Down syndrome and occurs in about 25% of these children. 
The heart's upper chambers are called the atria and the lower chambers are called the ventricles. The wall between the upper chambers is called the atrial septum and the wall between the lower chambers is called the ventricular septum. In the normal heart, the valve between the right atrium and right ventricle is called the tricuspid valve and the valve between the left atrium and the left ventricle is called the mitral valve. In children with AVSD, the tricuspid and mitral valves do not develop normally which then affects the growth of the atrial and ventricular septum. Most of the time, there is one "common" valve separating the hearts upper and lower chambers (1) instead of two separate valves. In addition, there is a hole in the atrial septum (2) called an atrial septal defect and a hole in the ventricular septum (3) called a ventricular septal defect. In primum atrial septal defect, there are two separate valves between the upper and lower heart chambers but they are not entirely normal and there is an atrial septal defect.
What are the effects of this defect on my child's health?
Atrioventricular septal defect is a serious heart problem that usually causes heart-related symptoms. Unlike some heart defects, the problem does not resolve with time and most children must undergo heart surgery. The good news is that this surgery is usually very successful and most children do very well. There are some patients with primum atrial septal defect who do not require surgery because the valves have little or no leakage and the atrial septal defect is small. The effects from AVSD are caused by the holes in the heart walls and leakage from the abnormal valve. The holes allow blood in the heart's left side (oxygenated or red blood that has returned from the lungs) to leak back to the heart's right side. This results in a large amount of blood that the right side of heart must pump again to the lungs. The heart has to work much harder than normal to pump enough blood out to the body because so much of it returns instead to the heart's right side. The workload is further increased by leakage of the heart valve. As a result of the extra workload, most babies with AVSD develop signs of congestive heart failure such as rapid breathing, feeding problems, slow weight gain, low energy, and cold, clammy sweating. These symptoms usually appear between 4 and 8 weeks of age but can occur earlier in some infants. Another possible health effect of AVSD is pulmonary artery hypertension. This problem develops more slowly and is caused by the extra pulmonary blood flow. The pulmonary arteries that take blood from the heart's right side to the lungs are not well suited to the increased pressure caused by the extra blood flow. Over time, if the problem is not corrected, the pulmonary arteries become thick and stiff which makes the heart have to work even harder. This is a very serious problem with no effective treatment. For unknown reasons, children with Down syndrome are very prone to this problem so heart surgery is often done when the child is 4-6 months old. Exercise recommendations: Exercise recommendations are best made by a patient's doctor so that all relevant factors can be included in the decision. In general, exercise restrictions for patients with repaired atrioventricular septal defects are not necessary and children can participate in competitive and vigorous athletic activities. Children with Down syndrome have an increased incidence of a spine abnormality that necessitates some restrictions in activity.
How is this problem diagnosed?
Clinical findings: Most newborns with AVSD do not have heart related symptoms, however, congestive heart failure usually develops during the first 1 to 2 months of life. Problems with slow growth and slow motor development are not uncommon. Some babies with AVSD look a little blue in the lips and/or under their fingernails, especially when they cry. This is called cyanosis and occurs when blood on the right side of heart flows to the left side of the heart (and out to the body) through one of the holes. Physical findings: A heart murmur is often the first clue that a child has an AVSD. In many children, the murmur is heard right after birth but it may not be heard until the child is 6 to 8 weeks of age. If the child is in congestive heart failure, there will be poor weight gain, the heart rate and breathing rate will be higher than normal, and the liver will be enlarged. Medical tests: The first tests often ordered by the doctor are an electrocardiogram, chest x-ray and oxygen saturation test. An AVSD alters the placement of the conduction or electrical system of the heart that often shows up as an abnormality on the electrocardiogram. The oxygen level in the blood is usually normal but can be a little low. The chest x-ray often shows a bigger than normal heart and extra blood flow to the lungs. The diagnosis of atrioventricular septal defect can be made with 100% accuracy by an echocardiogram. Cardiac catheterization is done if there are any questions not clearly answered by the echocardiogram or if there is concern about pulmonary hypertension.
How is the problem treated?
As described previously, surgery is almost always needed for children with AVSD. If possible, the surgery is delayed until the child is about 4 to 6 months of age to allow the child to grow. Before surgery, the goals of treatment are to control symptoms of congestive heart failure and to ensure adequate weight gain. Giving the child heart medicines such as digoxin (Lanoxin), and furosemide (Lasix) may do this. Sometimes a medicine that maintains potassium levels called spironolactone (Aldactone) is used. Medicines that lower blood pressure like captopril are also sometimes used to decrease the work of the heart. To promote weight gain, richer formula or breast milk supplements are helpful since infants with congestive heart failure need more calories than other babies. If the baby is still unable to gain weight, surgery may be done earlier. Open-heart surgery is the mainstay of treatment for children with AVSD. The repair involves placement of one or two patches to divide the common valve into right and left sides and close the holes. This is performed after beginning heart/lung bypass to support the circulation during the repair itself. Stitches are also placed in the valve to decrease valve leakage. The results for surgical repair are very good and 95% of patients do well without significant complications. Complications include abnormal heart rhythm and residual valve leakage.
Clinics
Care and services for patients with this problem are provided in the Congenital Heart and Cardiovascular Surgery clinics at the University of Michigan Medical Center in Ann Arbor.
What is the outlook for children with atrioventricular septal defect?
Surgical results have continued to improve and the outlook is good for the majority of children. Some children require reoperation for valve leakage, pacemaker implantation, or obstruction of blood flow within the heart. Later deaths from this problem are quite rare.
References
Merrill WH, Hoff SJ & Bender HW. The surgical treatment of atrioventricular septal defect. In C Mavroudis & C Backer (Eds) Pediatric Cardiac Surgery. St. Louis, MO: Mosby, 1994, 225-236. Written by: S. LeRoy RN, MSN Reviewed by: E.Bove, MD Reviewed January, 2010