OVERVIEW: What every practitioner needs to know

Are you sure your patient has atrioventricular septal defect? What are the typical findings for this disease?

Atrioventricular septal defects (AVSDs) comprise a spectrum of cardiac defects caused by a disruption in the development of the endocardial cushions, also known as the crux of the heart. There is a spectrum of severity with three main types of AVSD: complete AVSD, transitional AVSD, and partial AVSD.

The complete form of AVSD involves a common atrioventricular valve, a significant ventricular septal defect (VSD) component, and a primum atrial septal defect (ASD) (Figure 1). The transitional form of AVSD involves a common atrioventricular valve, a small or insignificant VSD component, and a primum ASD. Partial AVSD is primarily a primum ASD and a cleft in the mitral valve (Figure 2 and Figure 3).

AVSD has a significant association with chromosomal abnormalities and heterotaxy syndromes. Clinical presentation and timing of intervention is related to the significance of the intracardiac shunts, common atrioventricular valvar regurgitation, and presence of other associated congenital heart defects.

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Complete AVSD: The most common symptoms seen with complete AVSD are secondary to congestive heart failure resulting from the amount of shunting at the atrial and ventricular levels in the absence of pulmonary stenosis/right ventricular outflow tract obstruction. Typical symptoms include tachypnea, increased work of breathing, and failure to thrive. These symptoms may be seen in other forms of congenital heart disease. There are no symptoms specific to AVSD.

Partial AVSD: The symptoms associated with a partial AVSD are similar to those associated with an ASD which may include respiratory distress and poor growth associated with pulmonary overcirculation. The magnitude of left-to-right shunting through the primum ASD tends to increase with age in the first few months of life as the pulmonary vascular resistance decreases and right ventricular compliance improves. Patients are typically asymptomatic in infancy and early childhood but may become symptomatic with congestive heart failure symptoms in infancy in the setting of severe mitral regurgitation through the mitral valve cleft.

Transitional AVSD: The symptoms associated with transitional AVSD typically mimic those associated with a partial atrioventricular septal defect, as the VSD component is insignificant.

What other disease/condition shares some of these symptoms?

Other types of ASDs and VSDs can mimic symptoms associated with AVSD, depending on the magnitude of the shunt. Since AVSD can occur in conjunction with other forms of complex congenital heart disease such as tetralogy of Fallot, double-outlet right ventricle, and coarctation of the aorta, symptoms may also mimic these other forms of complex congenital heart disease.

What caused this disease to develop at this time?

Epidemiology: AVSD accounts for about 4%-5% of congenital heart disease and occurs in about 0.24-0.31 of 1000 live births. There is no particular sex or ethnic predilection.

Genetics: AVSD is highly associated with Down syndrome (trisomy 21). About 45% of children with Down syndrome will have congenital heart disease and of these, about 40% will have AVSD. Considering all children in whom AVSD develops, about 50% of these children will have Down syndrome. AVSD may also occur in conjunction with heterotaxy syndromes and other extracardiac anomalies. No gene has been definitively linked to the development of AVSD in nonsyndromic patients.

Embryology: There are no known teratogens that specifically cause AVSD. However, AVSD is caused by a disruption in the morphogenesis of the endocardial cushions, leading to failure of the adjacent portions of the atrial and ventricular septums to develop, along with failure of the primitive common atrioventricular valve to divide.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

There are no laboratory investigations that would specifically confirm the diagnosis of AVSD. Given the association with aneuploidy, chromosomal analysis performed either prenatally or postnatally is useful, especially if there are extracardiac anomalies.

Would imaging studies be helpful? If so, which ones?

Fetal echocardiography: Transabdominal fetal echocardiography can be performed as early as 16 weeks gestation but most commonly is performed between 18 and 22 weeks. Detection rates of AVSD vary depending on the center in which the procedure is performed.

Transthoracic echocardiography: Postnatal diagnosis with two-dimensional echocardiography is standard. Detailed morphologic characteristics of the common atrioventricular valve are essential, as are the severity of the common valvar regurgitation, intracardiac shunts, outflow tract obstruction, balance of right and left ventricular size, and the presence of associated cardiac abnormalities.

Cardiac catheterization: Catheterization is rarely needed to establish the diagnosis of AVSD. However, a cardiac catheterization study may be warranted in older children when there is a suspicion of pulmonary vascular occlusive disease (PVOD). Left ventricular angiography demonstrates a gooseneck deformity of the left ventricular outflow tract, which is pathognomonic for AVSD.

Electrocardiography: Left axis deviation with a counterclockwise vector loop is common (Figure 4). Prolongation of the PR and QRS intervals is also common.

Figure 4.

Electrocardiogram of a patient with complete AVSD demonstrating left axis deviation with a superior QRS axis.

Chest radiography: Cardiomegaly and increased pulmonary markings are typical with complete AVSD. The heart silhouette may be normal in size with partial or transitional AVSD.

Confirming the diagnosis

There are no specific clinical algorithms for suspicion or confirmation of the diagnosis.

If you are able to confirm that the patient has an atrioventricular septal defect, what treatment should be initiated?

Prenatal diagnosis by fetal echocardiography: Counseling regarding the diagnosis, prognosis, and treatment options are typically discussed at the time of the initial fetal echocardiogram and at subsequent follow-up visits.

Complete AVSD (without other associated congenital heart disease diagnoses): Immediate postnatal therapy is usually not necessary. However, as the pulmonary vascular resistance starts to fall during the first few months of life, pulmonary overcirulation and congestive heart failure may develop, requiring initiation of diuretics, afterload reduction, and digoxin (depending on the institution).

Provided that medical management can balance the congestive heart failure symptoms, infants are often discharged home with outpatient follow-up. Patients are typically referred for surgical repair within the first 6 months of life.

Partial/transitional AVSD: Patients are typically asymptomatic in infancy with rare exception. Therefore, these patients are typically referred for repair later in childhood compared with repair in the other forms of AVSD. Recent data have favored early childhood repair (younger than age 5 years) as opposed to repair in infancy in children with minor or no symptoms.

A significant ASD left-to-right shunt will result in right-sided heart enlargement. When there is insignificant shunting through the ASD and insignificant mitral regurgitation, surgical repair may be considerably delayed if performed at all. However, it is uncommon for patients not to become symptomatic at some point in life.

Complex AVSD: When AVSD is associated with other forms of congenital heart disease such as tetralogy of Fallot and double-outlet right ventricle, postnatal management and treatment options will vary depending on the primary physiologic disturbance.

What are the adverse effects associated with each treatment option?

AVSD repair performed very early in infancy may be associated with increased mortality and morbidity. Typically, infants referred for early surgical repair are severely compromised by congestive heart failure symptoms, despite maximized medical management, which may increase the risk of intraoperative or postoperative adverse events.

The definitive treatment for AVSD is surgical. In general, patients referred for surgical repair of complete AVSD tend to be younger than those referred for surgical repair of transitional or partial AVSD. Complications may be higher in younger patients and those with more complex atrioventricular anatomy.

With improvements in surgical technique over the past few decades, mortality and complications have decreased. The mortality rate for complete AVSD repair is less than 5% and the complication rate for postsurgical complete heart block is 1%-4%.

The most common reasons for reoperation after complete AVSD repair are left-sided valvular regurgitation or stenosis and left ventricular outflow tract obstruction (due to accessory mitral valve tissue in the left ventricular outflow tract). These complications occur in 5%-10% and 15%-20% of cases, respectively. Left ventricular outflow obstruction may develop as late as 20 years after the initial surgical repair.

What are the possible outcomes of atriovententricular septal defect?

Prognosis is generally excellent in children with AVSDs. Prenatal detection has improved in recent years, with most fetuses doing well in utero. Outcome may be worse if AVSD is associated with a marked imbalance of the ventricles or with complete atrioventricular heart block, either of which facilitate in utero recognition.

When not diagnosed prenatally, most cases of AVSD are detected by the presence of a heart murmur, findings such as cardiomegaly on a chest radiograph, or as part of screening in the presence of other congenital anomalies or suspected chromosomal abnormality. With improved early detection of AVSD, children are referred for surgical repair during childhood and, as previously mentioned, surgical outcomes are good in the current era.

Complete AVSD: Half of untreated children with AVSD typically die in the first year of life because of congestive heart failure. For those who survive beyond the first year of life, pulmonary hypertension due to PVOD tends to develop in children older than 2 years of age, although PVOD may rarely develop in children younger than 2 years. Long-term postoperative results are described above.

Partial and transitional AVSD: The natural history of partial AVSD and transitional AVSD is similar to that of secundum ASD, with the exception that shunting from the left ventricle to the right atrium may enhance the magnitude of the intracardiac shunt. Pulmonary hypertension tends to develop in untreated patients older than 20 years. Untreated patients may also experience exercise intolerance and atrial arrhythmias, such as atrial fibrillation, due to atrial enlargement, which may lead to significant disability.

Postoperative mortality and complication rates are typically similar or better than those with complete AVSD surgical repair. The incidence of the development of left ventricular outflow tract obstruction may be higher in patients with partial or transitional AVSD compared with patients with complete AVSD.

What causes this disease and how frequent is it?

Epidemiology: AVSD is relatively uncommon, occurring in about 4%-5% of all forms of congenital heart disease. However, AVSD is the most common heart defect detected by fetal echocardiography, with a detection rate of about 18% of all prenatally diagnosed fetal cardiac defects. There is no known seasonal or racial variation. There is also no widely accepted teratogen or environmental exposure implicated in the development of AVSD.

Although there is no specifically identified gene abnormality associated with AVSD, it has been linked with various chromosomal abnormalities and associations such as heterotaxy syndromes, particularly the asplenic type. In patients with AVSD without Down syndrome, about 20% have other genetic disorders such as Holt-Oram or Noonan syndrome.

Other clinical manifestations that might help with diagnosis and management

There are rare instances when closure of the primum septal defect in partial AVSD is contraindicated. The most common reason for not closing the ASD is when it functions as a pop-off for either the right or left ventricle in the setting of PVOD or ventricular dysfunction. Clinical symptoms may include cyanosis resulting from right-to-left shunting or symptoms related to left ventricular heart failure.

PVOD tends to develop in patients with Down syndrome earlier than in patients with non–Down syndrome AVSDs. Irreversbile PVOD may develop as early as 1 year of age in this patient population.

How can atrioventricular septal defects be prevented?

Given that AVSD is caused by a disruption in embryogensis without evidence of known teratogens, there are no measures that can be taken to prevent the development of this form of CHD. However, once the defect has been identified prenatally, amniocentesis along with genetic counseling should be offered given the high association of AVSD with other chromosomal abnormalities.

What is the evidence?

Backer, CL, Stewart, RD, Mavroudis, C. “Overview: History, anatomy, timing, and results of complete atrioventricular canal”. Semin Thorac Surg Pediatr. vol. 10. 2007. pp. 3-10. (The authors of this review article describe historical contributions to complete atrioventricular canal including anatomy and surgical techniques over the past 50 years.)

Boening, A, Scheewe, J, Heine, K. “Long-term results after surgical correction of atrioventricular septal defects”. Eur J Cardiothorac Surg. vol. 22. 2002. pp. 167-73. (Previous studies have shown that postsurgical outcomes after AVSD surgery depend on failure of the left atrioventricular valve. The authors of this retrospective cohort study reviewed surgical techniques used in biventricular repair of AVSD with a particular emphasis on closure of the cleft in the left-sided atrioventricular canal defect. Outcomes including death and need for reoperation were analyzed. Closure of the cleft in the left-sided atrioventricular valve improved postsurgical outcomes, whereas pulmonary hypertension increased risk of postoperative death.)

Craig, B. “Atrioventricular septal defect: from fetus to adult”. Heart. vol. 92. 2006. pp. 1879-85. (The author presents a comprehensive review article on AVSD, including embryology, anatomy, diagnostic modalities, clinical presentation, and treatment.)

Craig, R, Selzer, A. “Natural history and prognosis of atrial septal defect”. Circulation. vol. 37. 1968. pp. 805-15. (This is a retrospective cohort study of 128 consecutive cases of ASD in adults aged 18-67 years. Associated lesions, progression of symptoms, hemodynamic data including pulmonary vascular resistance, and cause of death were presented. The most severe risk factor of ASD was pulmonary hypertension between 20 and 40 years of age. Older individuals were more likely to have congestive heart failure associated with atrial arrhythmias.)

Freidberg, MK, Kim, N, Silverman, NH. “Atrioventricular septal defect recently diagnosed by fetal echocardiography: echocardiographic features, associated anomalies, and outcomes”. Congenital Heart Dis. vol. 2. 2007. pp. 110-4. (A small retrospective cohort study was performed at a single center with review of fetal echocardiograms from 2002-2004. Variables including incidence, detection of aneuploidy, asssociated cardiac/extracardiac lesions, and postnatal outcomes were analyzed. Diagnosis of AVSD including a comparison of fetuses with and without aneuploidy and postnatal outcomes. Isolated AVSD had a higher association with aneuploidy, whereas AVSD not associated with aneuploidy was more associated with other cardiac lesions. The outcome of AVSD was dependent on other associated lesions, with a high incidence of pregnancy termination and neonatal death.)

Jones, PN, Schowengerdt, KO. “Prenatal diagnosis of congenital heart disease”. Pediatr Clin North Am. vol. 56. 2009. pp. 709-15. (This article is an in-depth review of the goals, indications, and application, and limitations of fetal echocardiography in the prenatal diagnosis of congenital heart disease.)

Najm, HK, Williams, WG, Chuaratanaphong, S. “Primum atrial septal defect in children: early results, risk factors, and freedom from reoperation”. Ann Thorac Surg. vol. 66. 1998. pp. 829-35. (Previous studies have shown that the risk factors for postoperative morbidity and mortality are related to young age, congestive heart failure, and left atrioventricular morphologic type/regurgitation. The authors present a retrospective cohort study of surgical outcomes and risk for mortality and reoperation in children with primum ASDs. Early mortality was low and associated with congestive heart failure and young age at time of repair. Left atrioventricular valve regurgitation was the most common cause of late reoperation. Also, late subaortic stenosis had a higher incidence in children with partial AVSD compared with those with complete AVSD.)

Towbin, R, Schwartz, D. “Endocardial cushion defects: embryology, anatomy, and angiography”. AJR Am J Roentgenol. vol. 136. 1981. pp. 157-82. (The authors present a review article describing the embryology, anatomy, and angiography of endocardial cushion defects. The "gooseneck deformity" of the left ventricular outflow tract that is observed in the frontal projection is common to all forms of endocardial cushion defects. The lateral view of a left ventriculogram is hepful in identifying subtypes of endocardial cushion defects.)

Ongoing controversies regarding etiology, diagnosis, treatment

There is still controversy regarding timing of surgery for complete AVSD and even more so for transitional and partial AVSDs. Complete AVSD is a bit less controversial, as almost all children will undergo surgery within the first 6 months of life given the predisposition for severe congestive heart failure. However, patients with transitional and partial AVSDs tend to have mild or no congestive heart failure symptoms and a low risk of pulmonary vascular occlusive disease in the first 2 decades of life.