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An atrial septal defect (ASD) is an opening in the interatrial septum, causing a left-to-right shunt and volume overload of the right atrium and right ventricle. Children are rarely symptomatic, but long-term complications after age 20 yr include pulmonary hypertension, heart failure, and atrial arrhythmias. Adults and, rarely, adolescents may present with exercise intolerance, dyspnea, fatigue, and atrial arrhythmias. A soft midsystolic murmur at the upper left sternal border with a prominently split 2nd heart sound (S2) is common. Diagnosis is by echocardiography. Treatment is transcatheter or surgical repair.
ASDs account for about 6 to 10% of cases of congenital heart disease. Most cases are isolated and sporadic, but some are part of a genetic syndrome (eg, mutations of chromosome 5, Holt-Oram syndrome).
Classification:
ASDs can be classified by location:
Pathophysiology
To understand hemodynamic changes seen in ASD (and other anomalies), see Fig. 1: Congenital Cardiovascular Anomalies: Normal circulation with representative right and left cardiac pressures (in mm Hg). for normal hemodynamic data.
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Fig. 1
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| Normal circulation with representative right and left cardiac pressures (in mm Hg). |
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Representative right heart O2 saturation = 75%; representative left heart O2 saturation = 95%. Atrial pressures are mean pressures.
AO = aorta; IVC = inferior vena cava; LA = left atrium; LV = left ventricle; PA = pulmonary artery; PV = pulmonary veins; RA = right atrium; RV = right ventricle; SVC = superior vena cava.
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In ASD, shunting is left to right initially (see Fig. 2: Congenital Cardiovascular Anomalies: Atrial septal defect.). Some small ASDs, often just a stretched patent foramen ovale, close spontaneously during the first few years of life. Persistent moderate-to-large ASDs result in large shunts, leading to right atrial and right ventricular volume overload and, over a number of years, pulmonary artery hypertension, elevated pulmonary vascular resistance, and right ventricular hypertrophy. Atrial fibrillation may also occur later. Ultimately, the increase in the pulmonary artery pressure and vascular resistance may result in a bidirectional atrial shunt with cyanosis during adulthood (Eisenmenger's reaction).
Symptoms and Signs
Most small ASDs are asymptomatic. Larger shunts may cause exercise intolerance, dyspnea during exertion, fatigue, and atrial arrhythmias with palpitations. Passage of microemboli from the venous circulation across the ASD (paradoxical embolization), often associated with arrhythmias, may lead to cerebral or systemic thromboembolic disorders. Rarely, when an ASD is undiagnosed or untreated, Eisenmenger's syndrome develops.
Auscultation typically reveals a grade 2 to 3/6 midsystolic (ejection systolic) murmur and a widely split, fixed S2 at the upper left sternal border in children. A large left-to-right atrial shunt may produce a low-pitched diastolic murmur (due to increased tricuspid flow) at the left lower sternal border. These findings may be absent in infants, even those who have a large defect. A prominent right ventricular cardiac impulse, manifested as a parasternal heave or lift, may be present.
Diagnosis
Diagnosis is suggested by cardiac examination, chest x-ray, and ECG and is confirmed by 2-dimensional echocardiography with color flow and Doppler studies.
With a significant shunt, ECG may show right axis deviation, right ventricular hypertrophy, or right bundle branch block (with rSR′ pattern in V1). Chest x-ray shows cardiomegaly with dilation of the right atrium and right ventricle, a prominent main pulmonary artery segment, and increased pulmonary vascular markings.
Cardiac catheterization is not usually necessary unless a transcatheter intervention is planned.
Treatment
Most small ostium secundum ASDs (< 3 mm) close spontaneously; many defects between 3 mm and 8 mm close spontaneously by age 18 mo. However, ostium primum and sinus venosus ASDs do not close spontaneously.
Asymptomatic children with a small shunt require only observation and periodic echocardiography. Although these children are theoretically at risk of paradoxical systemic embolization, it is not standard practice to close a small, hemodynamically insignificant defect.
Children with moderate to large defects (eg, pulmonary flow:systemic flow ratio > 1.5:1, or definite evidence of right ventricular volume overload on echocardiography) should have the ASD closed, typically between ages 2 to 6 yr. Transcatheter closure with various devices (eg, Amplatzer® or Gore HELEX® septal occluder) is preferred when appropriate anatomic characteristics, such as adequate rims of septal tissue and distance from vital structures (eg, aortic root, pulmonary veins, tricuspid annulus), are present. Otherwise, surgical repair is indicated. Sinus venosus and ostium primum (atrioventricular septal type) defects are not amenable to device closure. If ASDs are repaired during childhood, perioperative mortality rate approaches 0, and long-term survival rates approach those of the general population. Before repair, children with large shunts and heart failure should be treated with diuretics, digoxin, and ACE inhibitors.
Endocarditis prophylaxis is not needed preoperatively and is required only for the first 6 mo after repair or if there is a residual defect adjacent to a surgical patch.
Last full review/revision March 2010 by Lee B. Beerman, MD
Content last modified March 2010
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