What is Atrioventricular Canal Defects?
Atrioventricular canal defects, or AVCDs, are a variety of heart conditions that range from specific ventricle or atrium defects to septal defects, atrioventricular abnormalities, and endocardial cushion flaws. These defects are often linked with genetic abnormalities, especially trisomy 21, but they can also occur without any associated syndromes.
Among baby diseases, congenital heart diseases, or CHDs, are one of the most significant causes of death. They significantly impact the general health, everyday life, and medical costs of those affected. Ventricular and atrial septal defects, types of CHDs, are twice as common as some other heart diseases, like tetralogy of Fallot and transposition of great arteries.
Thanks to a technique called dynamic echocardiography, doctors have been able to detect early, symptomless, and even tiny atrioventricular canal defects. This could be a reason why the detection of CHDs has increased over the past few decades. The number of CHD cases in developing countries is still not certain, but it seems to be quite similar to that in developed countries.
What Causes Atrioventricular Canal Defects?
Most instances of AV canal defects, a type of heart issue, are usually tied to a certain medical syndrome. The medical syndromes often linked with AV canal defects include CHARGE, Down, Ellis-van-Creveld, Ivemark, Kaufman McKusick, Ritscher-Schinzel, Smith-Lemli-Opitz, and 3p. Out of all these, Down syndrome has a particularly strong link with AV canal defects.
Risk Factors and Frequency for Atrioventricular Canal Defects
AV canal defects, a type of congenital heart disease (CHD), occur in about 0.24 to 0.31 out of every 1000 live births. They also make up 3% to 5% of all the congenital heart diseases. Both boys and girls can have this condition, but some studies suggest that girls, especially those with Down syndrome, may be slightly more likely to have it.
- AV canal defects occur in about 0.24 to 0.31 out of every 1000 live births.
- They make up 3% to 5% of all congenital heart diseases.
- Both boys and girls can be affected by this condition.
- Some studies suggest that girls, especially those with Down Syndrome, may be slightly more likely to have AV canal defects.
- Factors like gestational diabetes (diabetes during pregnancy), pre-existing diabetes before pregnancy, and obesity are significantly linked to the development of AV canal defects without an associated syndrome.
Signs and Symptoms of Atrioventricular Canal Defects
Complete atrioventricular canal defects cause symptoms like an overactive pulmonary circulation typically before the child is 6 months old. The severity of these symptoms varies based on the type and size of the defects. Early symptoms include rapid breathing (tachypnea) and difficulty gaining weight. The presence and intensity of these symptoms can depend on factors like the level of AV valve leakage and presence of other congenital heart diseases, which can result in early onset congestive heart failure.
Children with a partial AV canal defect might not show symptoms until they are a bit older. Interestingly, ostium primum atrial septal defect, a type of hole in the heart that’s common in AV canal defects, tends to present earlier than another similar defect known as ostium secundum ASD. Children are often taken to a doctor for evaluation when a heart murmur is noticed. This murmur is a result of increased blood flow across the pulmonary valve, and it can be best heard at the upper left sternal border, which is the upper left side of the chest.
Telltale symptoms of congestive heart failure in children include heavy breathing, sweating during feeds, poor feeding, and increased sleepiness or lethargy. Signs that a healthcare professional might look for include rapid breathing, fast heart rate, failure to grow normally, abnormal lung sounds, irregular heartbeats, abnormal position of the heartbeat felt on the chest, enlarged liver, or increased pressure in the neck veins.
A thorough cardiac examination will seek:
- An unusually wide and persistent split between the two sounds of the heartbeat (S2), caused by a left-to-right shunt across the ASD that leads to too much blood in the right side of the heart.
- An S3 sound, caused by excessive blood flowing across the left ventricular walls, which are still flexible.
- Additional heart murmurs:
- A holosystolic murmur that arises due to leakage from the left AV valve, best heard at the apex of the heart.
- A mid-diastolic murmur if the shunt is large or there is significant AV valve leakage.
During a general physical examination, the presence of certain abnormal facial features or other physical signs common in children with Down syndrome will be checked. These include flat facial features, slanted eye openings, a single crease in the palm of the hand, and a particular shape of the toe. This examination especially applies to patients whose karyotype, or genetic type, is unknown; 40% to 45% of Down syndrome patients have an AV canal defect. Other congenital anomalies, such as cleft lip, cleft palate, or musculoskeletal abnormalities, should also be checked for.
Testing for Atrioventricular Canal Defects
An echocardiogram (a type of heart scan) is often used to screen unborn babies for heart-related abnormalities, such as septal defects. This early detection is key, though these cases often have a challenging outlook. If a potential problem is detected in general screening, a more thorough fetal echocardiogram takes place. This advanced scan gives a clear picture of the defect, the valve shape, whether there’s a hole (or shunt), and how blood is flowing.
After birth, a diagnosis is typically made if the newborn shows signs of congestive heart failure, or if a potential problem was detected or suspected during pregnancy. Nowadays, cardiac catheterization (a procedure to measure how the heart is working) isn’t the only way to diagnose defects in the heart’s atrioventricular (AV) canal. This is thanks to recent advancements in Doppler echocardiography, a tool that uses sound waves to visualize blood flow in the heart. However, cardiac catheterization is still routinely carried out before surgical treatment, to get a precise understanding of the heart’s structure.
A chest X-ray is another way doctors can detect AV canal defects. If the defect is partial, the X-ray usually shows enlargement of the right side of the heart and increased lung blood vessels. For more severe defects (intermediate and complete forms), the X-ray might show that all sections of the heart are enlarged. However, it might be hard to see enlargement of the left chambers of the heart because they are hidden behind the enlarged right chambers.
An electrocardiogram (ECG) is another useful diagnostic tool. Typical ECG findings in AV canal defects include a shift of the heart’s electrical axis more towards the left, and certain patterns in the right-sided leads due to increased volume or pressure. They might also indicate that the interval between the P wave and R wave on the ECG is longer than normal and signs of right ventricular enlargement.
Treatment Options for Atrioventricular Canal Defects
The best way to manage a complete atrioventricular canal defect (CAVCD) is through early surgical correction. However, overall care is usually divided into three stages: initial medication, definitive surgery, and long-term follow-up care.
It’s best to correct the defect before the child is six months old, in order to reduce the risk of developing lung-related diseases which can be worsened by the disease’s duration. Medical management aims to improve how the heart works by reducing the heart’s load and tension. This is done using water pills and medications such as angiotensin-converting enzyme inhibitors (ACEI) and angiotensin 2 receptor blockers (ARB). To strengthen the heart’s contractions, medicines like digoxin are used. Surgical management relies on various factors, such as the type of defect, the shape of the heart valves, and the presence of any other heart and blood vessel complications. The mortality rate during surgery stands at 3%, but there’s more than a 90% chance of surviving 10 years after the surgery.
The surgical approach for CAVCD changes based on the specifics of the defect. If the defect is balanced, the primary complete repair can be performed using a single-patch, double-patch or a modified single-patch.. However, if the defect is unbalanced, palliative interventions are conducted like single ventricle palliation, which is usually performed for conditions like HLHS and tricuspid atresia. For partial and intermediate AVCD, the primary surgical repair involves patch closure and mitral valvuloplasty (surgery to repair the heart’s mitral valve).
Long-term follow-up care is essential. It involves annual checkups with a cardiologist to prevent any potential complications due to the surgery. Children with AVCD are also at a higher risk for neurological problems, so regular screening for neurological and developmental disorders is recommended. In addition, measures should be taken to prevent heart infection, and pregnancy-related risks should be evaluated.
What else can Atrioventricular Canal Defects be?
When trying to identify a specific heart condition, doctors will consider at the possibility of several similar conditions, such as:
- A large hole in the wall separating the heart’s lower chambers (large ventricular septal defect)
- A hole in the wall between the heart’s two upper chambers (ASD)
- Needing surgery for a ventricular septal defect due to symptoms of congestive heart failure, which are common with a specific heart condition known as AVCD
While heart monitoring (ECG) and chest x-rays may show some common characteristics, using an ultrasound of the heart (echocardiography) can provide a more accurate diagnosis.
What to expect with Atrioventricular Canal Defects
The death rate for patients treated for atrioventricular canal defects is thought to be around 3%. Most of the patients treated for this condition, about 90%, are expected to live at least ten years after treatment. However, there’s a 10% to 20% chance the patient may need to undergo another operation.
Usually, the most common reason for having to do another operation, affecting 5-10% of the patients, is the worsening of mitral regurgitation, a condition where the heart’s mitral valve doesn’t close tightly, allowing blood to flow backward in the heart.
Possible Complications When Diagnosed with Atrioventricular Canal Defects
Regardless of the type of heart defect, patients will start to show blood flowing from the left side to the right side of their heart. The intensity of this blood flow, known as “shunting,” varies based on the kind of defect. In full AV canal defects – holes in the septum of the heart – the blood moves through the chambers and valves of the heart. For partial defects, blood flows through the ostium primum, a hole in the lower part of the heart.
If not corrected, these conditions can lead to heart failure symptoms in children before they even turn one. This increased blood flow to the right side of the heart can cause strain, leading to pulmonary hypertension, a condition where the blood vessels and arteries in the lungs face high blood pressure.
During the early stages of pulmonary hypertension, patients might see a slight improvement in symptoms which can be misleading, because this can lead to Eisenmenger syndrome – a more severe form of pulmonary hypertension that can be life-threatening.
Incompetent AV valves, or leaky heart valves, cause a significant amount of blood to regurgitate, or flow backward, into the heart chambers. Most of the backflow occurs on the same side of the heart, from the lower chamber to the upper chamber, but can happen from the left lower chamber to the right upper chamber due to a cleft in the left heart valve.
These conditions can enlarge the chambers of the heart or make the walls of the heart thicker, depending on the type of defect. This can speed up the onset of congestive heart failure, a condition that prevents the heart from pumping blood effectively, in children.
Preventing Atrioventricular Canal Defects
An atrioventricular canal defect is typically detected by a children’s heart specialist, known as a pediatric cardiologist. They might notice clear signs of heart failure or hear an abnormal sound, called a murmur, when examining the child’s heart. To confirm if the child has a heart disease, further tests may be performed. These may include:
Chest X-ray: This test uses radiations to capture images of the heart and lungs.
Electrocardiogram (ECG): This test records how the heart’s electrical activity functions.
Echocardiogram (echo): This test uses ultrasound (sound waves) to create a visual representation of the heart, allowing doctors to spot any structural problems.
Pulse Oximetry: This simple test checks the amount of oxygen present in the blood.
Cardiac Catheterization: With this test, a fine, long tube (catheter) is inserted into a blood vessel (often in the groin area) and guided to the heart. This allows doctors to measure the blood pressure and oxygen levels inside the heart and visualize its inner structure.
Cardiac MRI: This test provides three-dimensional images of the heart, which helps doctors identify any abnormalities.
When it comes to treatment, infants with an atrioventricular canal defect often have heart surgery within the first six months of their lives. In some cases, medications are used to manage symptoms until the surgery can be done. These medications may include:
Water Pills (diuretics): These pills lower the body’s water levels, reducing fluid in the lungs and potentially improving breathing abilities.
Digoxin: This medication boosts the strength of the heart’s pumping action and enhances overall heart function.
ACE Inhibitors: These medications relax blood vessels, making it easier for blood to flow out of the heart.
