In an atrial septal defect (ASD), an opening between the left and right atria allows shunting of blood between the chambers. Ostium secundum defect (most common) occurs in the region of the fossa ovalis and, occasionally, extends inferiorly, close to the vena cava; sinus venosus defect occurs in the superior-posterior portion of the atrial septum, sometimes extending into the vena cava, and is almost always associated with abnormal drainage of pulmonary veins into the right atrium; ostium primum defect occurs in the inferior portion of the septum primum and is usually associated with atrioventricular valve abnormalities (cleft mitral valve) and conduction defects.
ASD accounts for about 10% of congenital heart defects and appears almost twice as often in females as in males, with a strong familial tendency. Although ASD is usually a benign defect during infancy and childhood, delayed development of symptoms and complications makes it one of the most common congenital heart defects diagnosed in adults. The prognosis is excellent in asymptomatic patients but poor in those with cyanosis caused by large, untreated defects.
The cause of ASD is unknown. In this condition, blood shunts from left to right because left atrial pressure normally is slightly higher than right atrial pressure; this pressure difference forces large amounts of blood through a defect. The left-to-right shunt results in right heart volume overload, affecting the right atrium, right ventricle, and pulmonary arteries. Eventually, the right atrium enlarges, and the right ventricle dilates to accommodate the increased blood volume. If pulmonary artery hypertension develops because of the shunt (rare in children), increased pulmonary vascular resistance and right ventricular hypertrophy will follow. In some adult patients, irreversible (fixed) pulmonary artery hypertension causes reversal of the shunt direction, which results in unoxygenated blood entering the systemic circulation, causing cyanosis.
ASD is present in 4 of every 100,000 people. Symptoms usually develop before age 30. When no other congenital defect exists, the patient — especially children — may be asymptomatic.
ASD commonly goes undetected in preschoolers; such children may complain about feeling tired only after extreme exertion and may have frequent respiratory tract infections but otherwise appear normal and healthy. However, they may show growth retardation if they have large shunts. Children with ASD seldom develop heart failure, pulmonary hypertension, infective endocarditis, or other complications. However, as adults, they usually manifest pronounced symptoms, such as fatigability and dyspnea on exertion, frequently to the point of severe limitation of activity (especially after age 40).
In children, auscultation reveals an early to midsystolic murmur, superficial in quality, heard at the second or third left intercostal space. In patients with large shunts (resulting from increased tricuspid valve flow), a low-pitched diastolic murmur is heard at the lower left sternal border, which becomes more pronounced on inspiration. Although the murmur’s intensity is a rough indicator of the size of the left-to-right shunt, its low pitch sometimes makes it difficult to hear. Other signs include a fixed, widely split S 2, caused by delayed closure of the pulmonic valve, and a systolic click or late systolic murmur at the apex, resulting from mitral valve prolapse, which occasionally affects older children with ASD.
In older patients with large, uncorrected defects and fixed pulmonary artery hypertension, auscultation reveals an accentuated S2. A pulmonary ejection click and an audible S4 may also be present. Clubbing and cyanosis become evident; syncope and hemoptysis may occur with severe pulmonary vascular disease.
A history of increasing fatigue and characteristic physical features suggest ASD. The following findings confirm it:
❑ Chest X-ray shows an enlarged right atrium and right ventricle, a prominent pulmonary artery, and increased pulmonary vascular markings.
❑ Electrocardiography may be normal but usually shows right axis deviation, prolonged PR interval, varying degrees of right bundle-branch block, right ventricular hypertrophy, atrial fibrillation (particularly in severe cases after age 30) and, in ostium primum defect, left axis deviation.
❑ Echocardiography measures right ventricular enlargement, may locate the defect, and shows volume overload in the right side of the heart. (Other causes of right ventricular enlargement must be ruled out.)
Operative repair is advised for all patients with uncomplicated ASD with evidence of significant left-to-right shunting. Ideally, this is performed when the patient is between ages 2 and 4. Operative treatment shouldn’t be performed on patients with small defects and trivial left-to-right shunts. Because ASD seldom produces complications in infants and toddlers, surgery can be delayed until they reach preschool or early school age. A large defect may need immediate surgical closure with sutures or a patch graft.
Physicians have developed a new procedure, referred to as catheter closure or transcatheter closure of the atrial septal defect, that uses wires or catheters that can close ASD without surgery. In this procedure, the surgeon makes a tiny incision in the groin to introduce the catheters. Then, he advances the catheters into the heart and places the closure device across the ASD. This procedure may not be applicable to all patients.
❑ Before cardiac catheterization, explain pretest and posttest procedures to the child and her parents. If possible, use drawings or other visual aids to explain it to the child.
❑ As needed, teach the patient about prophylactic antibiotics to prevent infective endocarditis. (They may be administered before dental or other invasive procedures.)
❑ If surgery is scheduled, teach the child and her parents about the intensive care unit and introduce them to the staff. Show parents where they can wait during the operation. Explain postoperative procedures, tubes, dressings, and monitoring equipment.
❑ After surgery, closely monitor the patient’s vital signs, central venous and intra-arterial pressures, and intake and output. Watch for atrial arrhythmias, which may remain uncorrected.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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Title: Professional Guide to Diseases (Eighth Edition)
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2005
ISBN: 1-58255-370-X
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