Pediatric Atrial Septal Defects

Congenital heart defects (CHD) are common in children, with an incidence of approximately 8 cases per 1000 live births. These defects can cause an array of problems in the primary care of children. Atrial septal defects (ASDs) are a prevalent form of CHD. An understanding of human embryology is essential for diagnosing these abnormalities, and an understanding of the pathophysiology is helpful in planning long-term treatment.

Cardiac tissues are first detectable on the 18th or 19th day of fetal life. Cardiac development continues for the next several weeks. The atrial septum begins to form during the fourth week of gestation and is complete by the end of 5 weeks' gestation.

Classic model of cardiac development

According to the classic model of cardiac development, the process begins when a thin crescent-shaped membrane (septum primum) begins to form along the dorsal and cranial walls of the atrium. The space between the septum primum and the endocardial cushions (ostium primum) becomes progressively smaller as the septum primum grows toward the endocardial cushions. Before the ostium primum completely closes, small perforations develop in the anterosuperior wall of septum primum and ultimately coalesce to form a second interatrial communication, the ostium secundum. Meanwhile, the leading edge of the septum primum fuses with the endocardial cushions, and the ostium primum disappears.

Near the end of 5 weeks' gestation, the second phase of the process begins when a second crescent-shaped membrane (septum secundum) begins to form within the atrium to the right of the first septum. This membrane also begins to grow toward the endocardial cushions, covering the ostium secundum. However, the septum secundum remains incomplete. The foramen ovale is the opening remaining after the septum secundum completely forms.

The final phase of the process begins when the upper portion of the septum secundum proceeds to degenerate and finally disappears. The fully formed atria now have two overlapping but incomplete septae. The upper portion of the septum secundum covers the ostium secundum and creates a one-way valve allowing right-to-left shunting of blood in the fetus.

Van Praagh and Corsini model of cardiac development

Van Praagh and Corsini proposed another model of cardiac development.[1] According to their model, the septum primum (also known as the flap valve of the foramen ovale) grows from the portion of the left venous valve of the sinus venosus that is furthest left. As it extends from the most dorsal aspect of the atrium, the septum primum begins to meet the septum secundum, which is an invagination of the most rostral portion of the primitive atrium. The marginal edges of the septum primum eventually meet the left aspect of the septum secundum.

During embryonic and fetal life, the central portion of the septum primum billows into the left atrium due to the normal right to left shunting at the atrial level. After birth, the remainder of the septum primum adheres to the left aspect of the septum secundum.

Recent identification of an anomaly called deviated superior attachments of septum primum provides evidence in favor of the Van Praagh and Corsini model. Additional detailed morphologic analysis of murine cardiac development is needed to determine which model is correct.

Types of atrial septal defects

Four basic types of atrial septal defects are known. Patients who simultaneously have the first three types of atrial septal defect, as described below, are said to have common atrium.

The first type is an ostium secundum defect. The most common yet least serious type of atrial septal defect is an ostium secundum defect. This defect occurs in the area of the fossa ovalis and presumably results from excessive fenestration or resorption of septum primum, underdevelopment of septum secundum, or some combination of the two conditions (see images below).

In approximately one half of patients with left atrioventricular (AV) valve underdevelopment (ie, hypoplastic left heart syndrome or Shone complex), the superior attachments of the flap valve of the foramen ovale lie on the left atrial roof, well to the left of the septum secundum. Weinberg et al (1986) called this anomaly "(leftward and posterior) deviation of the superior attachments of septum primum."[2] This deviation is observed extremely rarely in patients with a normal-sized left AV valve. Of importance, the classic model does not explain its existence well. This type can be regarded as a variation of an ostium secundum defect, although it is most rigorously designated as a malalignment-type atrial septal defect.

A second variant of the ostium secundum defect is its association with an aneurysm of the atrial septum. This is thought to be due to redundancy of the valve of the fossa ovalis. It may be associated with mitral valve prolapse or atrial arrhythmias. There is debate regarding its association with thrombus formation and an increased risk for stroke.

The second type is an ostium primum defect. This atrial septal defect presumably results from failure of the endocardial cushions to close the ostium primum. Because endocardial cushions also form the mitral and tricuspid valves, ostium primum defects are virtually always associated with a cleft in the anterior mitral valve leaflet (see the images below).

The third type is a sinus venosus defect. This atrial septal defect is found in the posterior aspect of the septum near the superior vena cava (where it may coexist with partial anomalous pulmonary venous connection of the right upper pulmonary vein) or the inferior vena cava (where it may coexist with partial anomalous pulmonary venous defect of the right lower pulmonary vein). See the image below.

The sinus venosus defects may also be located in the inferior-posterior part of the atrial septum, overriding the inferior vena caval orifice, but these are extremely rare.[3]

The fourth type is a coronary sinus septal defect. This least common type of atrial septal defect is called an unroofed coronary sinus or coronary sinus septal defect. A portion of the roof of the coronary sinus is missing; therefore, blood can be shunted from the left atrium into the coronary sinus and subsequently into the right atrium. This type is often associated with a left superior vena cava.

To complete the discussion of the atrial septal defects, one might add patent foramen ovale (PFO) to the list of atrial septal defects. The PFO is present in nearly one third of healthy infant populations and is likely to be a normal variant.[3] However, the PFO may become important in the presence of structural abnormalities of the heart in that it facilitates intracardiac shunts to permit egress and/or mixing of blood flows. The PFO is also deemed be the seat of paradoxical embolism resulting in stroke/transient ischemic attacks, or in other conditions such as migraine, Caisson disease and platypnea-orthodexia syndrome, particularly in adult subjects.[3]

Left-to-right shunting

Clinical effects of isolated atrial septal defects are usually related to left-to-right shunting. The magnitude of shunt is related to the size of the defect in the septum, to the relative compliance of the left-sided and right-sided cardiac chambers, and indirectly related to the resistance of the pulmonary and systemic circulations. At birth, the right and left ventricles are of equal thickness and similar compliance. In the first few days to weeks after birth, the pulmonary vascular resistance (PVR) remains mildly elevated and has not reached its nadir.

As impedance to pulmonary blood flow decreases and the right ventricle becomes more compliant, blood is able to flow to the pulmonary vascular bed more easily, and the atrial level left-to-right shunt increases.

On occasion, the septal defect is small, with little left-to-right shunting. However, most defects that cause murmurs or symptoms are moderate to large, and the size of the defect does little to limit left-to-right shunting. Approximately 15% of ostium secundum atrial septal defects spontaneously close by age 4 years, and others may decrease in size as to not be hemodynamically significant.

Although many cases of atrial septal defect are sporadic, atrial septal defect clearly has a genetic component and may be associated with genetic syndromes.[4, 5]

Ostium secundum atrial septal defect is typically a part of the Holt-Oram syndrome, which is caused by mutations in the T-box transcription factor TBX5 on chromosome 12q. Most of the mutations are deletions, frameshifts, or premature stop codons. This autosomal dominant and highly penetrant disease also includes absent or hypoplastic radii and first-degree heart block.[6]

Ostium secundum atrial septal defect can also be associated with the following genetic abnormalities: Ellis-van Creveld syndrome, Noonan syndrome, Rubinstein-Taybi syndrome, Kabuki syndrome, Williams syndrome, Goldenhar syndrome, and thrombocytopenia-absent radius syndrome, as well as chromosomal abnormalities (eg, deletions in 1, 4, 4p, 5p, 6, 10p 11, 13, 17, 18, 22) or in trisomy 18 and Klinefelter syndrome.[7] Ellis-van Creveld syndrome can be associated with a common atrium.

Ostium secundum, ostium primum atrial septal defect, or both may occur in trisomy 21 (Down syndrome). For unknown reasons, sinus venosus defects are rare in Down syndrome, making common atrium similarly rare in this population.

An autosomal dominant form of familial atrial septal defects with incomplete penetrance has been detected.

Mutations in NKX2.5, a homeodomain-containing transcription factor, have been associated with atrial septal defects with and without atrioventricular (AV) block and was the first gene identified leading to nonsyndromic atrial septal defect. To date, more than 40 NKX2.5 mutations have been detected.[8] Interestingly, the type and location of the mutation predicts the phenotype, with nonsense mutations, frameshift mutations, and all mutations located in the homeodomain causing AV conduction disease, and missense mutations outside the homeodomain show no AV conduction disease.

Mutations in GATA4, an important regulator of cardiac development, have been associated with atrial septal defects. Interactions between GATA4and NKX2.5 and interactions between GATA4 and TBX5 may be the root of the cardiac defects seen with GATA4 mutations, which establishes a link among these genes.[7, 9]

TBX20, a member of the TBX transcription factor family, is very highly expressed in the embryonic heart and also interacts extensively with NKX2.5, GATA4 and TBX5 during cardiac embryogenesis. It has been speculated that it may have a role in defects of the atrial septum.[7]

Interestingly, a missense mutation in myosin heavy chain 6 (MHY6) has also been identified with an autosomal dominant form of atrial septal defect. MHY6 was previously described in late-onset hypertrophic cardiomyopathy. This gene is highly expressed in the developing atria and appears to be influenced by TBX5 and GATA4 mutations, again establishing a link between several genes. In a recent study by Posch et al, 3 novel missense mutations were found in MYH6 and no other mutations were identified in 11 other sarcomeric genes analyzed, leading the authors to conclude that MYH6 was the predominant sarcomeric disease gene for familial atrial septal defect.[7, 10]

The prognostic implications of the involvement of a sarcomeric protein with atrial septal defects has yet to be fully elucidated but suggest that sarcomeric filaments play a role in cardiac morphogenesis and atrial septal development. Further genetic analysis will likely yield other mutations and genetic links associated with familial atrial septal defects.

Atrial septal defects have been linked to maternal disease and exposure to environmental risk factors during pregnancy. Maternal diseases include phenylketonuria, pregestational diabetes, methylenetetrahydrofolate reductase deficiency (MTHFR deficiency), febrile illnesses, and influenza. Environmental risk factors include medications such as anticonvulsants and nonsteroidal anti-inflammatory drugs (NSAIDs) or exposure to organic solvents. Atrial septal defects are also found in children with fetal alcohol syndrome.

United States data

Research indicates that congenital heart disease is diagnosed in 0.8% of children in the first year of life. Atrial septal defect is the second most common congenital heart defect in children and adults and occurs in anywhere from 0.67-2.1 per 1000 live births. Secundum atrial septal defects comprise just over 90% of all atrial septal defects, whereas sinus venosus and primum atrial septal defects comprise between 3-4% each. About 15-30% of healthy adults have an unfused foramen ovale in which the valve functions normally but has failed to fuse. In these individuals, a cardiac catheter passed into the right atrium can pass into the left atrium through the foramen ovale (ie, probe-patent foramen ovale).

Sex- and age-related demographics

The female-to-male ratio is approximately 2:1.

Atrial septal defect, a congenital abnormality, is present at birth. However, in most cases, a murmur is not audible until the child is a few months old. Symptoms usually do not occur in individuals with atrial septal defect until late childhood, adolescence, or adulthood.

Secundum type (ie, ostium secundum), sinus venosus, and unroofed coronary sinus defects are sometimes not diagnosed until the third decade of life.

Ostium primum atrial septal defects are usually diagnosed in the first few years of life because of mitral regurgitation murmur or an abnormal ECG.

A common atrium (ie, a combination of sinus venosus, ostium secundum, and ostium primum defects) is usually diagnosed in the first few years of life because systemic venous blood and pulmonary venous blood often partially mix before entering each ventricle; this condition manifests as cyanosis. In addition, a common atrium may be associated with complex CHD, and patients may present relatively early because of other intracardiac abnormalities.

The prognosis for a child with an atrial septal defect (ASD) is good; the rate of surgical mortality is less than 1%. Many children are candidates for catheter-based device implantation, which also carries a very low procedural morbidity and mortality and avoids the risks associated with a median sternotomy and cardiopulmonary bypass.

Ostium secundum defects may spontaneously close. A wide range of spontaneous closure rates have been reported among different studies, ranging from 4-87%. The likelihood of spontaneous closure appears to be closely related to the initial size of the defect. One study demonstrated a 56% spontaneous closure rate and 30% regression to a diameter of less than 3 mm for defects 4-5 mm in diameter. Conversely, none of the defects more than 10 mm in diameter closed spontaneously, and 77% of those required intervention. The general thought is that spontaneous closure does not occur with ostium primum, sinus venosus, or coronary sinus defects.[11, 12]

Infants weighing less than 10 kg with ostium secundum defects may undergo interventional closure with favorable outcomes and without any additional major risks.[13] Favorable outcomes are likely even in select infants with significant noncardiac comorbid conditions.[13]

Certain patients with ostium primum atrial septal defects and an abnormal mitral valves may require a second operation for mitral valve dysfunction later in their lives.

The repair of sinus venosus atrial septal defects can be more complex and often involves baffling of the right upper pulmonary vein to the left atrium and anastomosis of the superior vena cava to the right atrial appendage. Stenosis of the right upper pulmonary vein baffle or superior vena cava/atrial appendage anastomotic site may require further catheter-based or surgical intervention.[14]

Endocarditis of catheter-placed devices has been reported (but rare) and may necessitate removal of the hardware and surgical repair.

Surgical or catheter-based intervention of atrial septal defects in individuals outside of childhood is generally feasible, even in the face of pulmonary vascular changes and evidence of pulmonary hypertension. This is distinctly different from similar aged individuals with moderate-to-large post-tricuspid shunts (ventricular septal defect, aortopulmonary window, patent ductus arteriosus, or major aortopulmonary collateral vessels), who often have markedly elevated pulmonary vascular resistance and Eisenmenger physiology. However, when compared with earlier timing of intervention, some evidence suggests that patients repaired later in life have higher longer-term morbidity.[15]

Morbidity/mortality

In developed countries, mortality rate of atrial septal defect is low (< 1%). Morbidity secondary to atrial septal defect is unusual and typically limited to three groups of patients.

Approximately 1% of infants with moderate or large (ie, nonrestrictive) atrial septal defects, but no other left to right shunting lesion (eg, patent ductus arteriosus, ventricular septal defect), have tachypnea and failure to thrive. In these individuals, the pulmonary artery pressure, when measured during catheterization or Doppler echocardiography, is at or near systemic level. In most instances, this is a flow-related phenomena (high flow/low resistance), but in infants predisposed to abnormal pulmonary vasculature, there may be a combination of both elevated flow and resistance. Attempts to exclude mitral or left ventricular diastolic abnormalities as a cause of these hemodynamics must be undertaken, as well as a thorough assessment of pulmonary anatomy and mechanics, as both left-sided cardiac disease and primary pulmonary disease can mimic symptoms of pretricuspid shunting.

Patients in whom atrial septal defects go unrecognized until late childhood may develop arrhythmias (eg, atrial fibrillation, atrial tachycardia) or pulmonary hypertension. Atrial septal defects that initially appear in middle-aged or elderly adults can indicate congestive heart failure (CHF). Symptoms of CHF can also appear in pregnant women with undiagnosed atrial septal defect due to the increased circulating blood volume normally seen in pregnancy.

Patients with atrial septal defects may have an embolic stroke as the initial presentation.

Complications

Atrial septal defect is usually an asymptomatic disease. However, children with atrial septal defects are at increased risk for several complications, such as endocarditis (if associated mitral valve insufficiency is present) and respiratory tract infections, which are less well tolerated in children with atrial septal defects than in children without atrial septal defects. Any individual with an atrial level shunt is at risk for a paradoxical embolus from a venous thrombus, but in children, this is exceedingly rare, unless there is an underlying hypercoagulable state.

Children with clinically significant and untreated atrial septal defects are at risk for various cardiac complications, including congestive heart failure, pulmonary hypertension, and arrhythmias. However, these cardiac complications generally manifest in adulthood.

Focus patient education on ensuring that the family and caregivers understand potentially serious symptoms so that they seek prompt medical attention when necessary. However, parents also require consistent education regarding long-term prognosis, which is generally quite good, as well as the expected signs and symptoms that can be seen with the defect, which are usually minimal.

Reassurance is often needed due to the stigmata associated with the diagnosis of congenital heart disease (CHD). Some children may be unnecessarily restricted from activity by well-meaning medical personnel or by over-cautious parents.

Education regarding care of an atrial septal defect and its complications should also include input from the cardiologist and cardiac surgeon.

Infants and young children with atrial septal defects (ASDs) are typically asymptomatic. Most atrial septal defects are diagnosed after a suspicious murmur is detected during a routine health-maintenance examination.

Even in symptomatic children with atrial septal defects, clinical manifestations are often subtle and nonspecific. Some children with atrial septal defects have poor weight gain, they remain somewhat small, and they may have exertional dyspnea or frequent upper respiratory tract infections.

Relatively severe symptoms, such as arrhythmia, pulmonary artery hypertension, and pulmonary vascular obstructive disease (PVOD), are rare in children with atrial septal defects. Some infants and young children with large defects may present with symptoms of congestive heart failure (CHF), especially if they have an associated lesion (eg, patent ductus arteriosus) or lung disease (eg, bronchopulmonary dysplasia and/or chronic lung disease).

Most children with atrial septal defects (ASDs) are asymptomatic. In developed countries, the diagnosis is usually made during an evaluation of a suspicious murmur or during an evaluation of fatigue and exercise intolerance. Atrial septal defects that are not diagnosed in childhood can result in problems in adulthood.

Upon initial evaluation, many children with atrial septal defects appear completely healthy; however, careful physical examination often yields clues to the diagnosis.

Patients with atrial septal defects may have a precordial bulge, a prominent right ventricular cardiac impulse, and palpable pulmonary artery pulsations. All of these are signs of increased blood flow through the right side of the heart and pulmonary vascular bed.

Upon auscultation of the individual with atrial septal defect, the first heart sound may be normal or split. The sound associated with closure of the tricuspid valve may be accentuated if blood flow across the pulmonic valve is increased and leads to a midsystolic pulmonary ejection murmur. This sound is best appreciated at the upper left sternal border and may be transmitted to the lung fields.

Although the second heart sound may be normal in newborns with atrial septal defects, it becomes widely split and fixed over time as pressures on the right side of the heart decrease. This fixed splitting occurs as the result of increased capacitance in the pulmonary vascular bed, leading to low pulmonary impedance and, therefore, a long hangout interval after the end of right ventricular systole. Fixed splitting of S2 is an important diagnostic finding in atrial-level shunting.

A large shunt increases flow across the tricuspid valve, and the patient with atrial septal defect is likely to have a mid-diastolic rumble at the left sternal border.

Mitral valve prolapse occurs with increased frequency in the presence of atrial septal defect and may be caused by compression of the left side of the heart secondary to enlargement of the right side. In patients with mitral valve prolapse, an apical holosystolic or late systolic murmur often is heard radiating to the axilla. A midsystolic click may be present, but this murmur can be difficult to detect in some patients with atrial septal defects.

Pulmonary vascular resistance (PVR) may increase through childhood, adolescence, and adulthood, resulting in PVOD. The rise in PVR and pulmonary artery pressure results in right ventricular hypertrophy, which, in turn, reduces right ventricular compliance and may subsequently reduce the degree of left-to-right shunting.

Upon physical examination, patients may have a prominent right ventricular impulse, but the previously noted diastolic tricuspid flow rumble and the systolic ejection murmur in the pulmonic area may be diminished. The wide splitting of the second heart sound may narrow, and the pulmonic component of the second heart sound may become loud, with intensity equal to that of the aortic component.

In all patients with common atrium, right-to-left shunting occurs, resulting in cyanosis, although this may be mild due to preferential streaming of blood across the respective atrioventricular (AV) valves.

In adults with an unrecognized atrial septal defect, the left-to-right shunt may worsen if systemic arterial hypertension develops. The result may be left ventricular hypertrophy, reduced left ventricular compliance, and increased left-to-right shunt.

In general, no specific laboratory studies are available to aid in the diagnosis of an atrial septal defect (ASD). Determinations of brain natriuretic peptide (BNP) or pro-BNP levels may be helpful in infants and in some children with large atrial septal defects and congestive heart failure (CHF) when their clinical symptoms are equivocal. BNP levels are elevated in patients with ventricular volume overload and CHF.

Radiography

Plain radiographic findings in atrial septal defect (ASD) are nonspecific but include right atrial and right ventricular dilatation, pulmonary artery dilatation, and increased pulmonary vascular markings. In general, an enlarged right atrium leads to overall cardiomegaly on the anteroposterior (AP) radiograph. Pulmonary artery dilatation results in a prominent hump between the aortic knob and the left ventricular contour on the AP radiograph. Although pulmonary vascular obstructive disease (PVOD) is rare, if it develops, the main pulmonary artery becomes large and the lung fields become oligemic.

Echocardiography

Two-dimensional and Doppler echocardiography revolutionized the diagnosis of atrial septal defects. These studies can effectively reveal both the extent of the defect and provide clues to the degree of left-to-right shunting. In small patients, the anatomy is observed especially well on subcostal views. The anomaly called deviated superior attachments of septum primum is reliably observed with only the modified subcostal left oblique view.[16]  The size and location of the ASD can be determined in most young patients and right ventricular volume overloading (dilatation of the right ventricle with flat to paradoxical septal motion) can be assessed.

In older children, large adolescents, or adults, transesophageal echocardiography (TEE) may be required to document an atrial septal defect because of limited transthoracic echocardiographic windows. This is particularly true if sinus venosus and unroofed coronary sinus type atrial septal defects are present.

TEE is useful in recognizing and further elucidating pulmonary venous abnormalities associated with sinus venosus defects and ruling out partial anomalous pulmonary venous return in general. TEE may also be useful in small children with poor echocardiographic windows, but the procedure requires sedation and specific expertise. TEE is very useful in further characterizing the size and location of the defect at the time of attempted catheter-based device closure, as well as assisting the interventional cardiologist with balloon-sizing of the defect and device placement.[17]   Intracardiac echocardiography (ICE) is used by some interventional cardiologists to assist in defining the defect and in device closure.

Cardiac MRI

Cardiac magnetic resonance imaging (MRI) has the advantage of not being limited by acoustic windows and offering imaging in essentially any plane. It may be useful in the diagnosis of sinus venosus or coronary sinus defects in both children and older individuals. In experienced hands, cardiac MRI can easily depict anomalous pulmonary venous drainage associated with sinus venosus defects and a left superior vena cava, which is often associated with coronary sinus defects.[18] In general, older children do not require sedation for cardiac MRI (this is generally not the case with transesophageal echocardiography). Cardiac MRI can also be used to calculate the effective left to right shunt (Qp:Qs) and quantitate right ventricular function and volumes.[19, 20]

It generally should not be used in attempts to further define atrial septal anatomy when entertaining the possibility of percutaneous device closure because transesophageal echocardiography defines the margins of the atrial septal defect much more effectively. Additionally, cardiac MRI is not readily available at all centers and requires a considerable amount of technical expertise, especially when imaging pediatric patients.

CT angiography

Computed tomography (CT) angiography is a quick and effective means to identify pulmonary venous abnormalities associated with sinus venosus defects or to rule out suspected anomalous pulmonary venous return identified on echocardiography prior device closure. It has the advantage of providing a comprehensive assessment of the pulmonary arteries and the lung parenchyma in patients in whom interstitial/chronic lung disease or pulmonary artery hypertension is an added concern.[19] In children, similar to cardiac MRI, it is not an adequate modality to evaluate the atrial septal anatomy when assessing for the possibility of percutaneous closure. However, electrocardiographic (ECG)-gated cardiac CT scanning has been demonstrated as an accurate method to determine intraatrial shunting in adults.[21]

Some data support a stronger correlation between TEE-derived atrial septal defect dimensions and CT-derived dimensions, when compared with transthoracic echocardiographic dimensions, especially for larger atrial septal defects in the pediatric population.[22] This has potential relevance if there is concern regarding the success of a catheter-based approach, in the face of a large atrial septal defect. However, CT angiography comes with the added adverse effect of radiation, and care must be taken to find the best imaging modality at the lowest possible risk. Newer version CT scanners can be adjusted to provide lower radiation doses for children, while not sacrificing very short scanning times.

In some instances, cardiac catheterization is needed to provide further hemodynamic information prior to intervention (see Procedures). Pulmonary-to-systemic flow can be accurately determined when symptoms and results of other imaging modalities do not correlate. Additionally, calculations of pulmonary vascular resistance can be performed if pulmonary hypertension is a concern, and measurements of pulmonary vein saturations can aid in the evaluation of primary pulmonary diseases that might be confounding the clinical picture. Ideally, a mechanism should be in place to perform percutaneous device placement if the defect is suitable for closure at the time of the hemodynamic catheterization.

Electrocardiography (ECG) most commonly demonstrates right-axis deviation, right ventricular hypertrophy, and an rSR' or rsR' pattern in the right precordial leads. The QRS duration is usually normal. However, the ECG may be normal, especially in infants and in young children with small defects (see the image below).

Left-axis deviation with a superiorly oriented counterclockwise frontal-plane loop suggests an ostium primum atrial septal defect (ASD) (see the image below).

All types of atrial septal defect can result in prolonged PR intervals. This prolongation of internodal conduction may be related to the increased size of the atrium and a long internodal distance (which is a result of the defect).

Cardiac catheterization is rarely necessary in the preoperative evaluation of a child with atrial septal defect (ASD), but it is an integral part of transcatheter occlusion of the defect. Cardiac catheterization may be necessary if pulmonary hypertension is suggested to document PVR and to assess the response of PVR to vasodilator substances. It may also be necessary to evaluate associated lesions, especially in patients with more than one left-to-right shunt.

Findings on catheterization include a step-up in oxygen saturation from the superior vena cava to the right atrium (usually >10%), slightly increased right ventricular pressures, a small pressure gradient across the pulmonary valve (due to increased flow across a fixed valve orifice) and normal to mildly increased pulmonary artery pressures. If a large defect is present, the mean pressures in the right and left atria are identical.

The above being said, catheter-based interventions for the closure of selected secundum ASDs have become most common in pediatric patients. Although catheterization is rarely needed for diagnosis, it may be useful from a treatment standpoint. See Treatment for further details.

Provide routine medical care with special attention to signs of congestive heart failure (CHF) or increased pulmonary vascular resistance (PVR). Most patients with an atrial septal defect (ASD) are asymptomatic and require only routine well-child care until they undergo elective surgical repair or transcatheter device placement for their defects.

Most children with uncomplicated atrial septal defects are followed up by their primary care provider and receive follow-up with a pediatric cardiologist every year or every other year. Children who require medical intervention or who have other comorbidities are seen by a cardiologist more frequently.

Transfer

An isolated atrial septal defect almost never causes clinically significant problems in the neonatal period or in infancy. Refer a child who is to have elective atrial septal defect surgical repair or transcatheter intervention to a pediatric center with experience in performing cardiopulmonary bypass and surgical atrial septal defect closure or catheter based procedures in young children.

A patient with an ostium primum atrial septal defect may have associated clinically significant AV valve insufficiency and may require earlier surgical intervention. Refer this patient to a center with experience in the evaluation and repair of this problem.

Any attempt at closure with a transcatheter device should be performed at a center with experience in pediatric interventional cardiology with surgical support. Additionally, since some atrial septal defects are detected outside of childhood, transcatheter interventions in adults are often performed by adult interventionalists with the assistance of a pediatric interventionalist. Adult interventionalists may be very comfortable with transcatheter patent foramen ovale closure, but not as familiar with the nuances of true atrial septal defect device closure, especially larger defects.

Medical therapy is of no benefit in children with asymptomatic atrial septal defects (ASDs). With the exception of ostium secundum types, atrial septal defects are structural defects that do not spontaneously close. Surgical closure is ultimately required for most atrial septal defects, other than ostium secundum atrial septal defects. Occasionally, small primum ASDs may not require closure, but due to their association with mitral valve abnormalities, they may be closed at the time of mitral valve repair, if such a repair is indicated. An ostium secundum atrial septal defect that measures 6 mm in diameter or smaller in the patient's first year of life is likely to spontaneously close; however, such closure is substantially slower than that of a typical small, muscular ventricular septal defect.

Infants who are severely affected with an atrial septal defect and who develop congestive heart failure (CHF) may be treated as any other child with CHF from a left-to-right shunt. This treatment, which includes diuretics, afterload reduction, and less commonly, digoxin, is covered in other articles. As noted previously, it is of particular importance to rule out other etiologies of symptoms in these infants, especially those with secundum ASDs, due to the typical paucity of symptoms associated with this lesion in infancy and early childhood.

Arrhythmias associated with atrial septal defect are similarly uncommon in childhood become increasingly common with age. In fact, the development of atrial fibrillation may trigger CHF in adults with atrial septal defect who are younger than 40 years. Arrhythmias may result from atrial distention, and these individuals may require antiarrhythmic therapy until the atrial septal defect is repaired. In some cases, arrhythmias may persist after repair due to the chronicity of the right atrial dilation.

Some children with an atrial septal defect present with recurrent respiratory tract infections, which may be poorly tolerated. If immunologically normal, these children are not at a higher risk for infection in general, but the chronically increased pulmonary blood flow, when combined with the inflammatory changes associated with lower respiratory tract infections, can lead to prolonged symptoms and altered cardiopulmonary interactions.

Bacterial endocarditis prophylaxis is not necessary for the typical patient with an isolated atrial septal defect, although the ostium primum type of atrial septal defect may need subacute bacterial endocarditis prophylaxis because of the associated mitral valve abnormality. Prophylaxis is recommended prior to surgical repair if the atrial septal defect is part of complex cyanotic congenital heart disease (CCHD). Endocarditis prophylaxis is recommended for 6 months following either surgical or percutaneous repair of atrial septal defects and, in some instances, may be recommended for longer in patients with residual mitral valve abnormalities after surgical repair of primum atrial septal defects. Additionally, endocarditis prophylaxis is recommended indefinitely for any persistent residual shunting detected by echocardiography after surgical or device closure. For more information see Antibiotic Prophylactic Regimens for Endocarditis.

Definitive therapy for an atrial septal defect (ASD) has historically been limited to surgical closure. However, with the advent of transcatheter techniques,[23, 24, 25] many children undergo successful treatment in the cardiac catheterization laboratory.[26]

The most common surgical approach to the defect is primary repair with suture closure or with patch repair (generally with glutaraldehyde treated autologous pericardium, Gore Tex patch or fabric made of polyester fiber [Dacron]).

Not all children with an atrial septal defect are candidates for surgery, which is only indicated for those children with clinically significant left-to-right shunting. In general, a pulmonary-to-systemic flow ratio of 1.5:1 or more is considered the principal indication for surgical repair. Shunting less than this in children with small defects and in those with existing pulmonary hypertension may be observed. Because cardiac catheterization is rarely necessary, echocardiographic evidence of right atrial and right ventricular enlargement is usually considered evidence of a clinically significant left-to-right shunt and an indication for surgical closure of the atrial septal defect.

Surgery is ideally performed in children aged 2-4 years and has a very low mortality rate. However, surgery may be performed earlier than this if the child has evidence of CHF. Surgery can be deferred until later in childhood if there is a specific family preference without adding any substantial risk by delaying intervention.

Newer, minimally invasive surgical techniques have been developed. These improve cosmetic appearances and decrease hospital stays. These techniques are ideally suited for simple closure of a secundum atrial septal defect.[27]

The surgical mortality rate is low in patients with uncomplicated atrial septal defects. In an experienced pediatric center, the mortality rate should be less than 1%.

Postoperative morbidity in individuals with atrial septal defects is almost exclusively due to accumulation of pericardial fluid (postpericardiotomy syndrome), which occurs in approximately one third of patients. On occasion, tamponade occurs and requires pericardiocentesis. Pericardial effusion should be suspected in any pediatric patient who undergoes postsurgical repair of an atrial septal defect and who presents with chest pain, fever, shortness of breath, or general malaise. In young children, symptoms may be nonspecific and include irritability and decreased appetite.

Transcatheter approaches to atrial septal defect closure are well accepted in the pediatric population. Secundum atrial septal defects are currently the only subtype of atrial septal defect that are amenable to this approach. The preference for timing of catheter-based closure is institution/interventionalist specific, but generally around age 4-6 years with a known, hemodyanmically significant defect. Catheter-based intervention has been successful in smaller children.[28]

Such techniques require individuals with considerable expertise in the field of interventional pediatric cardiology and cooperation between the interventionalist and the noninvasive imaging specialists. For a detailed description of the procedure and results in children[3, 29, 30] and adults,[31] the reader is referred to these publications in the References section.

Benefits of the transcatheter approach include its minimal invasiveness, the lack of median sternotomy, the avoidance of cardiopulmonary bypass, and the relatively quick recovery time. Potential drawbacks and concerns include residual shunting around the device, embolization during placement requiring surgical intervention, lack of adequate septal rims to properly seat the device and the need for specific technical expertise and equipment.

Long-term safety concerns are noted because device placement in smaller children is still relatively new. There has been some recent concern regarding device erosion of surrounding tissue, which is not limited to the pediatric population.[32] Further follow-up should provide additional information regarding optimal patient selection, as well as longer-term prognosis of the catheter-based approach. Overall however, the medium- to long-term outcomes of atrial septal defect closure, either surgically or percutaneously, appear very good.[33]

For patients with ostium primum atrial septal defects and sinus venosus atrial septal defects, surgical closure is necessary owing to the need to address mitral valve cleft and anomalous pulmonary venous return, respectively. Surgery is also the procedure of choice for most coronary sinus atrial septal defects, although very small defects may be addressed by transcatheter methods.[34]

Diagnosis of an atrial septal defect (ASD) in a newborn or an older child should prompt consultation with a pediatric cardiologist.

Almost all newborns have a small left-to-right shunt at the foramen ovale, as detected during echocardiography in the neonatal period. In the absence of a murmur or other signs of a true atrial septal defect on subsequent well-child care visits, consultation with a cardiologist is probably not necessary, although review of the initial echocardiogram report is prudent to verify the description of the defect.

When closure of the atrial septal defect is considered, an interventional pediatric cardiologist should be consulted.

Children with atrial septal defects (ASDs) generally have no restrictions on their activity. Children with compensated congestive heart failure with an atrial septal defect are candidates for surgical or catheter-based intervention and should be able to resume normal activity after the defect is corrected. Following transcatheter occlusion, restriction of physical activity for several months after occlusion is suggested.