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Atrial Septal Defect (ASD)

By

Lee B. Beerman

, MD, Children's Hospital of Pittsburgh of the University of Pittsburgh School of Medicine

Last full review/revision Dec 2020| Content last modified Dec 2020
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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 years 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 wide and fixed splitting of the 2nd heart sound (S2) is common. Diagnosis is by echocardiography. Treatment is transcatheter device closure or surgical repair.

Atrial septal defects 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). The combination of an atrial septal defect and atrioventricular conduction disturbance Atrioventricular Block Atrioventricular (AV) block is partial or complete interruption of impulse transmission from the atria to the ventricles. The most common cause is idiopathic fibrosis and sclerosis of the conduction... read more Atrioventricular Block may be associated with a mutation in the NKX2-5 homeobox gene.

Classification

ASDs can be classified by location:

Pathophysiology of ASD

Normal circulation with representative right and left cardiac pressures (in mm Hg)

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.

Normal circulation with representative right and left cardiac pressures (in mm Hg)

In atrial septal defect, shunting is left to right initially (see figure Atrial septal defect Atrial septal defect 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... read more ). 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. If unrepaired, these large shunts may lead to pulmonary artery hypertension, elevated pulmonary vascular resistance, and right ventricular hypertrophy by the time people are in their 30s or 40s. Atrial arrhythmias, such as supraventricular tachycardia Reentrant Supraventricular Tachycardias (SVT) including Wolff-Parkinson-White Syndrome Reentrant supraventricular tachycardias (SVT) involve reentrant pathways with a component above the bifurcation of the His bundle. Patients have sudden episodes of palpitations that begin and... read more (SVT), atrial flutter Atrial Flutter Atrial flutter is a rapid regular atrial rhythm due to an atrial macroreentrant circuit. Symptoms include palpitations and sometimes weakness, effort intolerance, dyspnea, and presyncope. Atrial... read more , or atrial fibrillation Atrial Fibrillation Atrial fibrillation is a rapid, irregularly irregular atrial rhythm. Symptoms include palpitations and sometimes weakness, effort intolerance, dyspnea, and presyncope. Atrial thrombi may form... read more may also occur. The presence of an atrial shunt, even if predominantly left-to-right, may be associated with a paradoxical embolus due to a transient right-to-left shunt. Ultimately, the increase in the pulmonary artery pressure and vascular resistance may result in a bidirectional atrial shunt with cyanosis (Eisenmenger syndrome Eisenmenger Syndrome Eisenmenger syndrome is a complication of uncorrected large intracardiac or aortic to pulmonary artery left-to-right shunts. Increased pulmonary resistance may develop over time, eventually... read more ) during mid to late adulthood (most commonly over the age of 40).

Atrial septal defect

Pulmonary blood flow and RA and RV volume are increased. (Note: Intracardiac pressures generally remain in the normal range throughout childhood.) With a large defect, RA and LA pressures are equal. 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.

Atrial septal defect

Symptoms and Signs of ASD

Most patients with small or moderate-sized atrial septal defects are asymptomatic. Even large ASDs may not cause symptoms in young children. Larger shunts may cause slow weight gain in early childhood and exercise intolerance, dyspnea during exertion, fatigue, and/or palpitations in older patients. Passage of microemboli from the venous circulation across the ASD (paradoxical embolization), often associated with arrhythmias, may lead to cerebral or systemic thromboembolic events, such as stroke. Rarely, when an ASD is undiagnosed or untreated for decades, Eisenmenger syndrome Eisenmenger Syndrome Eisenmenger syndrome is a complication of uncorrected large intracardiac or aortic to pulmonary artery left-to-right shunts. Increased pulmonary resistance may develop over time, eventually... read more develops.

Auscultation typically reveals a grade 2 to 3/6 midsystolic (ejection systolic) murmur (see table Heart Murmur Intensity Heart Murmur Intensity Auscultation of the heart requires excellent hearing and the ability to distinguish subtle differences in pitch and timing. Hearing-impaired health care practitioners can use amplified stethoscopes... read more ) 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 lower sternal borders. 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 of ASD

  • Chest x-ray and ECG

  • Echocardiography

Diagnosis of an atrial septal defect is suggested by cardiac examination, chest x-ray, and ECG and is confirmed by 2-dimensional echocardiography with color flow and Doppler studies.

If a significant shunt is present, ECG may show right axis deviation, right ventricular hypertrophy, or right ventricular conduction delay (an rSR pattern in V1with a tall R). 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.

Echocardiography will confirm the presence of an ASD, define the anatomic location and size of the defect, and assess the degree of right atrial and right ventricular volume overload.

Cardiac catheterization is rarely necessary unless transcatheter closure of the defect is planned.

Treatment of ASD

  • Observation, transcatheter closure, or surgical repair

Most small (< 3 mm), centrally located atrial septal defects close spontaneously; many defects between 3 mm and 8 mm close spontaneously by age 3 years. These defects probably represent a stretched patent foramen ovale rather than true secundum ASDs. Ostium primum ASDs and sinus venosus ASDs do not close spontaneously.

Asymptomatic children with a small shunt require only observation and occasional echocardiography (typically about every 3 to 5 years). Although these children are theoretically at risk of paradoxical systemic embolization, this event is rare in childhood. Thus, it is not standard practice to close a small, hemodynamically insignificant defect.

Moderate to large ASDs (evidence of right ventricular volume overload on echocardiography) should be closed, typically between ages 2 years and 6 years. Repair may be considered earlier in children with chronic lung disease. Transcatheter closure with various commercial devices (eg, Amplatzer® or Gore HELEX®septal occluder) is possible in 85 to 90% of defects and 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 (1 Treatment reference 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... read more ). 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.

Treatment reference

  • 1. Faccini A, Butera G: Atrial septal defect (ASD) device trans-catheter closure: limitations. J Thorac Dis 10 (Suppl 24):S2923–S2930, 2018.

Key Points

  • An atrial septal defect (ASD) is an opening in one of several parts of the interatrial septum, causing a left-to-right shunt.

  • Small atrial communications often close spontaneously, but larger ones do not, causing right atrial and ventricular overload and ultimately pulmonary artery hypertension, elevated pulmonary vascular resistance, and right ventricular hypertrophy; supraventricular tachycardia, atrial flutter, or atrial fibrillation may also occur.

  • ASDs can allow emboli from the veins to enter the systemic circulation (paradoxical embolization), causing arterial occlusion (eg, stroke).

  • Auscultation typically reveals a grade 2 to 3/6 midsystolic murmur and a widely split, fixed S2; these findings may be absent in infants.

  • Moderate to large ASDs should be closed, typically between ages 2 years and 6 years, using a transcatheter device when possible.

More Information

The following are some English-language resources that may be useful. Please note that The Manual is not responsible for the content of these resources.

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