Atrioventricular septal defect (ASVD) is a general term for a group of rare heart defects that are present at birth (congenital). Infants with ASVDs have improperly developed atrial and ventricular septa and adjoining valves.
The normal heart has four chambers. The two upper chambers, known as atria, are separated from each other by a fibrous partition called the atrial septum. The two lower chambers, known as ventricles, are separated from each other by the ventricular septum. Valves (e.g., mitral and tricuspid) connect the atria (left and right) to their respective ventricles. The valves allow for blood to be pumped through the chambers. Blood travels from the right ventricle through the pulmonary artery to the lungs where it receives oxygen. The blood returns to the heart through pulmonary veins and enters the left ventricle. The left ventricle sends the now oxygen-filled blood into the main artery of the body (aorta). The aorta sends the blood throughout the body.
The parts of the heart described above are formed from an embryonic structure called the endocardial cushions. In individuals with ASVD there is some combination of malformation of these parts of the heart. They may include a hole in the atrial septum, a hole in the ventricular septum, and/or abnormalities of the mitral and triscupid valves. ASVD may be classified as one of three forms: an incomplete (or partial) ASVD (atrial septal defect primum); a transitional form (atrial septal defect and small ventricular septal defect); or a more severe or complete form (large atrial and ventricular defects).
The symptoms of ASVD vary greatly and depend on the severity of the malformations (e.g., valve leakage between ventricles and ventricular size). About half the cases of ASVD occur in children with Down syndrome.
Infants with the complete form of atrioventricular septal defect usually develop a limited ability to circulate blood to the lungs and the rest of the body resulting in fluid buildup in the heart, lung and various body tissues (congestive heart failure). Pulmonary congestion may lead to difficulty breathing (dyspnea) and fatigue. Infants with complete atrioventricular septal defect often have a bluish discoloration of the skin and mucous membranes (cyanosis) due to insufficient oxygen supply to these tissues.
Other symptoms that may occur in all forms of ASVD include poor feeding, abnormally rapid breathing (tachypnea), excessive sweating, and/or an abnormally rapid heartbeat (tachycardia).
Frequent episodes of acute inflammation of the lungs (pneumonia) and bronchial tubes (bronchitis) are common in children with all forms of ASVD. Abnormally high pressure within the artery that leads to the heart from the lungs (pulmonary artery) may impair lung function and result in permanent pulmonary vascular disease before the age of 1 year. Some more severely affected infants may have congestive heart failure as a direct result of these serious complications.
Older children with untreated ASVD may be at risk for brain abscesses, the development of blood clots (thrombosis) that may travel and lodge in the arteries (embolism), and/or acute inflammation of the inner membranes that line the heart (bacterial endocarditis).
Adults with ASVD who have not had surgery to correct this heart defect may develop Eisenmenger syndrome. This is a rare disorder characterized by restricted blood flow between the lungs and the heart that occurs because of a ventricular septal defect. Symptoms of this condition may include abnormally low blood pressure, irregular heartbeats, and/or rapid heart rate. (For more information on this disorder, choose “Eisenmenger” as your search term in the Rare Disease Database.)
The exact cause of atrioventricular septal defect is not known (idiopathic). This birth defect can occur alone with no apparent cause (sporadically), or it can occur in association with other disorders such as Down syndrome.
Researchers believe that, in cases of isolated ASVD, environmental, genetic, and/or other factors (multifactorial) may be involved in some way.
Atrioventricular septal defect affects males and females in equal numbers. Approximately 50 percent of cases occur in association with other disorders, especially Down syndrome. ASVD may also occur with other congenital heart defects, in 10 percent of cases it occurs in association with patent ductus arteriosus or tetralogy of Fallot. (For more information on these disorders, choose the exact disorder name as your search term in the Rare Disease Database.)
The exact incidence of ASVD in the general population is unknown. The complete form of ASVD occurs more often than the partial or transitional forms. Approximately 75 percent of cases of complete ASVD occur in individuals with Down syndrome. Most cases of partial ASVD do not occur in individuals with Down syndrome.
The diagnosis of atrioventricular septal defect can be made by imaging techniques of the heart such as magnetic resonance imaging (MRI) and echocardiogram (EC). In another procedure known as a cardiac catheterization, a long fine tube (catheter) is inserted into a large vein and then channeled directly into the heart. This allows the physician to determine the extent of the defect (i.e., complete, transitional, or incomplete) and to determine the rate of blood flow through the heart. Angiography is another useful diagnostic procedure and allows the physician to view an enhanced x-ray of the heart. Children with ASVD typically have an abnormal EKG reading.
Infants with ASVD should be referred to a hospital that can perform sophisticated diagnostic procedures and cardiovascular surgery. Infants with ASVD generally require surgery at a young age, usually before the age of 6 to 12 months.
Prior to surgery, congestive heart failure associated with ASVD may be managed by reducing fluid volume with diuretic drugs and, if necessary, the dietary restriction of fluids and salt. The drug digoxin may also be administered to decrease the heart rate and increase the strength of the heart's contractions. Oxygen therapy and adequate nutrition may also prove beneficial.
Because children with ASVD are susceptible to bacterial infection of the membranes that surround the heart (endocarditis), any respiratory infection should be treated vigorously and early. Affected individuals should also be given antibiotics before invasive dental procedures (e.g., root canal or extractions) or other surgical procedures to help prevent potentially life-threatening infections.
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