Atrioventricular septal defect (ASVD) is a general term for a group of rare heart defects that are present at birth (congenital). Infants with ASVDs have improperly developed atrial and ventricular septa and adjoining valves.
The normal heart has four chambers. The two upper chambers, known as atria, are separated from each other by a fibrous partition called the atrial septum. The two lower chambers, known as ventricles, are separated from each other by the ventricular septum. Valves (e.g., mitral and tricuspid) connect the atria (left and right) to their respective ventricles. The valves allow for blood to be pumped through the chambers. Blood travels from the right ventricle through the pulmonary artery to the lungs where it receives oxygen. The blood returns to the heart through pulmonary veins and enters the left ventricle. The left ventricle sends the now oxygen-filled blood into the main artery of the body (aorta). The aorta sends blood throughout the body.
The parts of the heart described above are formed from an embryonic structure called the endocardial cushions. In individuals with ASVD, there is some combination of malformation of these parts of the heart. They may include a hole in the atrial septum, a hole in the ventricular septum, and/or abnormalities of the mitral and triscupid valves. ASVD may be classified as one of three forms: an incomplete (or partial) ASVD (atrial septal defect primum); a transitional form (atrial septal defect and small ventricular septal defect); or a more severe or complete form (large atrial and ventricular defects).
The symptoms of ASVD vary greatly and depend on the severity of the malformations (e.g., valve leakage between ventricles and ventricular size). About half the cases of ASVD occur in children with Down syndrome.
Types
Based on atrioventricular valve morphology and its development, atrioventricular septal defects are classified into complete and partial.
- A complete atrioventricular septal defect – is characterized by a common atrioventricular valve, ostium primum atrial septal defect and ventricular septal defect of inlet type. It is caused by the complete failure of the endocardial cushions to fuse.[rx]
- A partial atrioventricular septal defect – is characterized by separate atrioventricular valves, an ostium primum atrial septal defect, a ventricular septal defect of inlet type, and cleft mitral valve. It is caused by incomplete fusion of endocardial cushions.[rx]
- In the complete form of the atrioventricular septal defect – it is a common atrioventricular valve has five leaflets, including superior bridging, interior bridging, left mural, right mural, and anterosuperior. Rastelli divided the complete atrioventricular septal defect into three anatomical subgroups.[rx]
- In type A – the superior bridging leaflet of the common atrioventricular valve is attached to the left ventricular surface of the interventricular septum with the help of chordae.
- In type B – the superior bridging leaflet of the common atrioventricular valve overhangs the interventricular septum and is attached to the right ventricle with the help of chordae.
- In type C – the superior bridging leaflet does not have an attachment to the interventricular septum and floats freely, thus providing a large unrestricted ventricular septal defect.
Rastelli type A is associated with left-sided obstruction, type C is associated with tetralogy of Fallot and other complex congenital heart diseases, and type B is the least common form of the complete atrioventricular septal defect
Symptoms
Infants with the complete form of atrioventricular septal defect usually develop a limited ability to circulate blood to the lungs and the rest of the body resulting in fluid buildup in the heart, lung and various body tissues (congestive heart failure). Pulmonary congestion may lead to difficulty breathing (dyspnea) and fatigue. Infants with complete atrioventricular septal defect often have a bluish discoloration of the skin and mucous membranes (cyanosis) due to insufficient oxygen supply to these tissues.
Other symptoms that may occur in all forms of ASVD include poor feeding, abnormally rapid breathing (tachypnea), excessive sweating, and/or an abnormally rapid heartbeat (tachycardia).
Frequent episodes of acute inflammation of the lungs (pneumonia) and bronchial tubes (bronchitis) are common in children with all forms of ASVD. Abnormally high pressure within the artery that leads to the heart from the lungs (pulmonary artery) may impair lung function and result in permanent pulmonary vascular disease before the age of 1 year. Some more severely affected infants may have congestive heart failure as a direct result of these serious complications.
Older children with untreated ASVD may be at risk for brain abscesses, the development of blood clots (thrombosis) that may travel and lodge in the arteries (embolism), and/or acute inflammation of the inner membranes that line the heart (bacterial endocarditis).
Adults with ASVD who have not had surgery to correct this heart defect may develop Eisenmenger syndrome. This is a rare disorder characterized by restricted blood flow between the lungs and the heart that occurs because of a ventricular septal defect. Symptoms of this condition may include abnormally low blood pressure, irregular heartbeats, and/or rapid heart rate. (For more information on this disorder, choose “Eisenmenger” as your search term in the Rare Disease Database.)
Causes
The exact cause of atrioventricular septal defect is not known (idiopathic). This birth defect can occur alone with no apparent cause (sporadically), or it can occur in association with other disorders such as Down syndrome.
Researchers believe that, in cases of isolated ASVD, environmental, genetic, and/or other factors (multifactorial) may be involved in some way.
Related Disorders
Diagnosis
The diagnosis of atrioventricular septal defect can be made by imaging techniques of the heart such as magnetic resonance imaging (MRI) and echocardiogram (EC). In another procedure known as a cardiac catheterization, a long fine tube (catheter) is inserted into a large vein and then channeled directly into the heart. This allows the physician to determine the extent of the defect (i.e., complete, transitional, or incomplete) and to determine the rate of blood flow through the heart. Angiography is another useful diagnostic procedure and allows the physician to view an enhanced x-ray of the heart. Children with ASVD typically have an abnormal EKG reading.
During cardiac catheterization, a small hollow tube (catheter) is inserted into a large vein and threaded through the blood vessels leading to the heart. This procedure allows physicians to determine the rate of blood flow through the heart, measure the pressure within the heart, and/or thoroughly identify anatomical abnormalities.
- Chest X-ray – In partial defect, chest X-ray shows right heart enlargement with increased pulmonary vasculature. While intermediate and complete forms show more of the diffuse enlargement of all chambers, although left atrial involvement is unusual and left ventricular enlargement is not very obvious due to the masking by the enlarged right ventricles.[rx]
- Echocardiography – In transthoracic echocardiography, an atrial septal defect may be seen on color flow imaging as a jet of blood from the left atrium to the right atrium. If agitated saline is injected into a peripheral vein during echocardiography, small air bubbles can be seen on echocardiographic imaging. Bubbles traveling across an ASD may be seen either at rest or during a cough. (Bubbles only flow from right atrium to left atrium if the right atrial pressure is greater than left atrial). Because better visualization of the atria is achieved with transesophageal echocardiography, this test may be performed in individuals with a suspected ASD which is not visualized on transthoracic imaging.
- Transcranial doppler bubble study – A less invasive method for detecting a PFO or other ASDs than transesophageal ultrasound is transcranial Doppler with bubble contrast.[rx] This method reveals the cerebral impact of the ASD or PFO.
- Electrocardiogram – The ECG findings in atrial septal defect vary with the type of defect the individual has. Individuals with atrial septal defects may have a prolonged PR interval (a first-degree heart block). The prolongation of the PR interval is probably due to the enlargement of the atria common in ASDs and the increased distance due to the defect itself. Both of these can cause an increased distance of internodal conduction from the SA node to the AV node.
- Transthoracic echocardiography/Doppler examination – an ultrasound image of the heart combined with measurements of blood flow to check the heart’s structure and see how well it is working.
- Transesophageal echocardiography (TEE) Doppler examination – an ultrasound took through the esophagus is used to get a better picture of the atria and more details about the size and shape of the ASD. A TEE helps the doctor and can also be used to check the heart valves.
- Intracardiac echocardiography (ICE)/Doppler examination – an ultrasound taken inside the heart. A tiny camera (echo probe) is sent to the heart through a peripheral vein. The test shows the size and shape of the defect and the direction of the blood flow across it. This study is often used during the percutaneous (nonsurgical) repair of the defect.
- Right heart catheterization – a small, thin tube (catheter) is inserted into the heart through a peripheral vein. Pressures and the amount of oxygen in the blood (oxygen saturation) are measured in each chamber of the heart. The oxygen levels determine how much blood is flowing across the ASD. Your doctor may also use a tiny balloon at the end of the catheter or a special dye to check the size of the defect (atrial angiogram).
- Left heart catheterization – during this procedure, a special dye is sent into the blood vessels of the heart through a catheter (angiography). The test can check for coronary artery disease (hard, narrow arteries).
- Pulse Oximetry – The test looks at how much oxygen is in the blood
- Cardiac Catheterization – The test measures blood pressure and oxygen inside the heart. It also lets the doctor look at the inside of the heart. The test is done with a long thin tube (catheter) that is put in through a blood vessel in the groin or other area and moved to the heart.
- Cardiac MRI – This test gives 3-D images of the heart. It can show any defects. They are usually treated early in infancy with heart surgery (the first 6 months of life). Sometimes, medications can help control the symptoms until the surgery is scheduled. They can include:
- Water Pills (diuretics) – These help rid the body of excess water. This reduces fluid in the lungs and may improve breathing.
- Digoxin – This helps the heart pump blood with more force and improves how the heart works.
- ACE Inhibitors – These make blood vessels relax and allow blood to flow more easily from the heart.
Treatment
Infants with ASVD should be referred to a hospital that can perform sophisticated diagnostic procedures and cardiovascular surgery. Infants with ASVD generally require surgery at a young age, usually before the age of 6 to 12 months.
Prior to surgery, congestive heart failure associated with ASVD may be managed by reducing fluid volume with diuretic drugs and, if necessary, the dietary restriction of fluids and salt. The drug digoxin may also be administered to decrease the heart rate and increase the strength of the heart’s contractions. Oxygen therapy and adequate nutrition may also prove beneficial.
Because children with ASVD are susceptible to bacterial infection of the membranes that surround the heart (endocarditis), any respiratory infection should be treated vigorously and early. Affected individuals should also be given antibiotics before invasive dental procedures (e.g., root canal or extractions) or other surgical procedures to help prevent potentially life-threatening infections.
Complete AVCD
1. Balanced lesion
Primary complete repair
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Single-patch
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Double-patch
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Modified single-patch
2. Unbalanced lesion
Palliative intervention: Single ventricle palliation (usually done for HLHS and tricuspid atresia)
Partial and Intermediate AVCD
Primary surgical repair
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Patch closure
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Mitral valvuloplasty
Surgical Treatment
Surgical correction is the ultimate treatment of atrioventricular septal defect. Atrioventricular septal repair is a complex surgical procedure and carries operative mortality of more than 3% even in the contemporary era of advanced surgical techniques.[rx] It also carries significant postoperative mortality and morbidity due to residual intracardiac shunts, atrioventricular valve regurgitation, left ventricular outflow tract obstruction, and arrhythmias.[rx]
Assessment of pre-operative imaging and hemodynamic data is essential for the optimal selection of surgical procedures to reduce the requirement of recurrent surgery and postoperative complications.[rx] In previous studies, the requirement of the recurrent procedure is reported as high as 18.2% at 15 years after surgical correction and left atrioventricular valve dysplasia, absence of cleft closure and associated cardiac malformations are found to increase the rate of recurrent procedures.[rx]
In complete AVSD, surgical closure should be performed in early infancy to reduce the pulmonary vascular disease, whereas, in incomplete atrioventricular septal defect, a repair can be slightly delayed if the patient is not symptomatic.
For partial AVSD, the primary repair is preferred with patch closure and atrioventricular valvuloplasty.
For balanced complete AVSD, early primary repair with two patch closure techniques is preferred over one patch closure, as one patch closure is associated with an increased rate of recurrent procedures due to patch dehiscence and residual shunt. Pulmonary artery banding is no longer used as a routine procedure in complete AVSD repair.[rx]
For unbalanced complete AVSD, repair techniques may include single ventricle palliation with the staged biventricular repair or primary biventricular repair.[rx]
Long-term Follow-up Care
Annual cardiologist evaluation is recommended to check for and prevent complications in uncorrected individuals and due to surgery. Children with AVCD are at risk for neurological impairment; hence routine screening for neurological and developmental disorders is advised. The other general measures that have to be taken care of are infective endocarditis prophylaxis and risk assessment during pregnancy.
References
