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Atrioventricular Canal Defect (AVCD)

ATRIOVENTRICULAR CANAL DEFECT


Overview


Atrioventricular canal defect is a combination of heart problems causing a defect in the centre of the heart. The condition happens when there's a hole between the heart's chambers and problems with the valves that regulate blood flow in the heart.

Sometimes referred to as endocardial cushion defect or atrioventricular septal defect, atrioventricular canal defect is present at birth (congenital). The situation is often related to Down syndrome.

Atrioventricular canal defect allows more blood to go to the lungs. The extra blood pressures the heart to overwork, making the heart muscle enlarge.

If not treated, atrioventricular canal defects can lead to heart failure and high blood pressure in the lungs. Doctors usually recommend surgery during the first year of life to cover the hole in the heart and to reconstruct the valves.





What are the types of Atrioventricular canal defect?


This condition presents a spectrum of anatomical variations, ranging from partial defects to complete defects, each with its own unique features and implications for treatment and prognosis. In a normal heart, there is a septum (wall) that separates the right and left sides, as well as valves that control blood flow between the atria and ventricles. In individuals with AV canal defect, these structures are malformed or incomplete, leading to abnormal communication between the chambers. Understanding the types of AV canal defect is crucial for healthcare professionals and families affected by this condition.

  1. Complete Atrioventricular Canal Defect: Complete AV canal defect is the most severe form of the condition, involving a large opening in the center of the heart that affects both the atrial and ventricular septa, as well as the mitral and tricuspid valves. This results in a single, common atrioventricular valve and abnormal communication between all four chambers of the heart. The features of complete AV canal defect include:

  • A large atrial septal defect (ASD) allowing blood to flow freely between the atria.

  • A large ventricular septal defect (VSD) allowing blood to mix between the ventricles.

  • A common atrioventricular valve, often referred to as the "atrioventricular valve" or "AV valve," which may be malformed or incompetent.

  • Abnormal blood flow patterns leading to volume overload of the heart chambers and pulmonary hypertension.

  1. Partial Atrioventricular Canal Defect: Partial AV canal defect is a less severe form of the condition, characterized by a smaller opening in the center of the heart that typically affects only the atrial septum and the mitral valve. The ventricular septum remains intact, although the mitral valve may be malformed or incompetent. The features of partial AV canal defect include:

  • A smaller ASD allowing blood to flow between the atria, but with less significant mixing compared to complete AV canal defect.

  • A variable degree of involvement of the mitral valve, ranging from minor abnormalities to complete absence of the valve's leaflets.

  • The presence of two separate atrioventricular valves (mitral and tricuspid), although the mitral valve may be abnormal.

  1. Intermediate Forms: In addition to complete and partial AV canal defects, there are intermediate forms that exhibit characteristics of both types. These intermediate forms may involve variations in the size and location of the septal defects, as well as the degree of involvement of the atrioventricular valves. The classification of AV canal defects into complete, partial, and intermediate forms allows for a better understanding of the spectrum of anatomical variations and helps guide treatment decisions.


What are the symptoms of Atrioventricular canal defect?


Atrioventricular canal defect (AV canal defect) is a congenital heart condition characterized by abnormalities in the structures that separate the heart's chambers. While some infants born with AV canal defect may exhibit obvious symptoms shortly after birth, others may not show signs until later in infancy or childhood. Common symptoms may include:

  1. Respiratory Symptoms: Infants with AV canal defect may experience respiratory symptoms due to the heart's inability to pump oxygen-rich blood efficiently to the body. These symptoms may include:

  • Rapid or labored breathing, especially during feeding or physical activity.

  • Difficulty breathing, leading to shortness of breath or wheezing.

  • Cyanosis, characterized by a bluish discoloration of the skin, lips, or nail beds, indicating inadequate oxygenation of the blood.

  • Frequent respiratory infections, such as pneumonia or bronchiolitis, due to impaired immune function and fluid buildup in the lungs.

  1. Poor Feeding and Growth: Children with AV canal defect may have difficulty feeding and gaining weight appropriately due to the increased workload on the heart and inadequate oxygen delivery to the body's tissues. Common feeding-related symptoms may include:

  • Poor sucking or feeding efficiency, leading to fatigue and frustration during feedings.

  • Failure to thrive, characterized by inadequate weight gain or growth compared to age-appropriate standards.

  • Increased calorie requirements to support the heart's increased energy needs and compensate for poor growth.

  1. Heart-related Symptoms: AV canal defect can cause various symptoms related to heart function and circulation. These symptoms may include:

  • Heart murmur, a characteristic sound heard during a physical examination due to turbulent blood flow through the abnormal openings in the heart's septa and valves.

  • Rapid or irregular heartbeat (arrhythmia), which may manifest as palpitations, dizziness, fainting, or chest discomfort.

  • Enlargement of the heart (cardiomegaly) on imaging studies, indicating increased workload and volume overload of the heart chambers.

  • Congestive heart failure, a serious condition characterized by fluid buildup in the lungs (pulmonary edema) and other tissues due to the heart's inability to pump blood effectively.

  1. Other Symptoms: In addition to respiratory and heart-related symptoms, children with AV canal defect may experience a range of other symptoms, including:

  • Fatigue or lethargy, due to decreased oxygen delivery to the body's tissues and increased energy expenditure by the heart.

  • Difficulty with physical activity or exercise intolerance, leading to reduced stamina and endurance compared to peers.

  • Developmental delays or cognitive impairments, resulting from inadequate oxygen supply to the brain during critical periods of growth and development.


The normal-functioning heart


The right side of your heart moves blood into vessels that go to the lungs. There, oxygen enriches the blood. The oxygen-rich blood flows back to your heart's left side and is pumped into a large vessel (aorta) that circulates blood to every part of the body of your body.

Valves manage the flow of blood in and out of the chambers of your heart. These valves give way to allow blood to move to the other chamber or to one of the arteries, and close to keep blood from flowing backwards.


What causes Atrioventricular canal defect?


While the exact cause of AV canal defect remains elusive, researchers have made significant strides in understanding the potential factors that contribute to its development. Some factors that may increase the risk of AV canal defect include:

  1. Genetic Factors: Genetic predisposition is believed to play a significant role in the development of atrioventricular canal defect. Several genetic syndromes are strongly associated with AV canal defect, including:

  • Down syndrome (Trisomy 21): Individuals with Down syndrome have an increased risk of AV canal defect, with approximately 40-50% of affected individuals exhibiting this cardiac anomaly. The presence of an extra copy of chromosome 21 disrupts normal cardiac development, leading to structural abnormalities in the heart, including AV canal defect.

  • Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome): These chromosomal abnormalities are also linked to an elevated risk of AV canal defect, although less frequently than Down syndrome.

  • 22q11.2 deletion syndrome (DiGeorge syndrome): This genetic disorder, characterized by the deletion of a small piece of chromosome 22, is associated with a variety of congenital anomalies, including AV canal defect.

Mutations in specific genes involved in cardiac development and function may also contribute to the development of AV canal defect. These genes play critical roles in regulating processes such as cardiomyocyte proliferation, chamber septation, and valve formation. While research in this area is ongoing, identifying the precise genetic variants associated with AV canal defect could enhance our understanding of its pathogenesis and inform targeted therapeutic approaches in the future.

  1. Environmental Influences: In addition to genetic factors, environmental exposures during pregnancy may influence the risk of atrioventricular canal defect. Certain maternal health conditions, lifestyle factors, and exposures to toxins or medications have been implicated as potential environmental risk factors for AV canal defect. These include:

  • Maternal diabetes: Women with pre-existing diabetes or gestational diabetes may have an increased risk of having a child with AV canal defect. Hyperglycemia during pregnancy can disrupt normal embryonic development, leading to structural abnormalities in the developing heart.

  • Maternal obesity: Obesity during pregnancy has been associated with an elevated risk of congenital heart defects, including AV canal defect. The underlying mechanisms linking maternal obesity to cardiac malformations are complex and may involve factors such as inflammation, oxidative stress, and alterations in fetal cardiac gene expression.

  • Exposure to teratogenic agents: Certain medications, chemicals, or environmental toxins have been implicated as potential teratogens that could disrupt normal cardiac development and increase the risk of AV canal defect. These may include retinoic acid derivatives, alcohol, tobacco smoke, and certain industrial chemicals.


Risk factors


Factors that may enlarge a baby's risk of developing atrioventricular canal defect prior to birth include:

Down syndrome

Smoking when pregnant

German measles (rubella) or every other viral illness during a mother's early pregnancy

Alcohol intake during pregnancy

Poorly controlled diabetes throughout pregnancy

Certain medications taken when pregnant — discuss with your doctor before taking any drugs while you're pregnant or trying to become pregnant

Someone whose parent had a congenital heart defect.

 


How is an Atrioventricular canal defect detected?


AV canal defect is typically diagnosed during infancy or early childhood, often during routine prenatal ultrasound or newborn screening tests. The diagnosis of atrioventricular canal defect requires a meticulous and comprehensive approach, encompassing clinical evaluation, non-invasive imaging, electrocardiography, and consideration of differential diagnoses. Early detection and accurate diagnosis are paramount for initiating timely interventions and optimizing outcomes for individuals affected by this complex congenital heart condition. Additional diagnostic tests may include:

  1. - Clinical Assessment: The diagnosis of AV canal defect often begins with a thorough clinical evaluation by a pediatrician or pediatric cardiologist. Key components of the clinical assessment may include:

  • Detailed medical history, including prenatal history, family history of congenital heart disease, and symptoms suggestive of cardiac abnormalities.

  • Physical examination to assess signs such as abnormal heart sounds (murmurs), cyanosis, respiratory distress, poor growth, or other features suggestive of congenital heart defects.

  1. Non-Invasive Imaging: Non-invasive imaging techniques play a pivotal role in diagnosing AV canal defect and evaluating its anatomical features and hemodynamic consequences. Common imaging modalities utilized in the diagnostic process include:

  • Echocardiography: Transthoracic echocardiography (TTE) is the primary imaging modality for diagnosing AV canal defect. It allows for detailed visualization of cardiac structures, including septal defects, valve morphology, and abnormal blood flow patterns.

  • Fetal Echocardiography: Prenatal diagnosis of AV canal defect is possible through fetal echocardiography, which enables early detection and prenatal counseling for affected pregnancies.

  • Cardiac MRI: In cases where additional imaging is required to assess complex anatomy or provide detailed functional information, cardiac MRI may be employed as a complementary diagnostic tool.

  1. Electrocardiography (ECG): Electrocardiography (ECG or EKG) is a valuable adjunctive tool in the diagnosis of AV canal defect, providing information about the heart's electrical activity and identifying abnormalities such as atrial or ventricular hypertrophy, conduction abnormalities, or arrhythmias. While ECG findings may be nonspecific in isolation, they contribute to the overall diagnostic assessment in conjunction with clinical and imaging data.

  2. Differential Diagnosis: Due to the diverse clinical presentations of AV canal defect and its overlapping features with other congenital heart conditions, differential diagnosis is essential to distinguish it from similar entities. Conditions that may mimic AV canal defect include ventricular septal defect (VSD), atrial septal defect (ASD), tetralogy of Fallot, and other complex congenital heart defects. A comprehensive evaluation, including clinical assessment, imaging studies, and sometimes genetic testing, helps differentiate AV canal defect from other cardiac anomalies.

  3. Multidisciplinary Approach: Diagnosing AV canal defect often necessitates a multidisciplinary approach involving pediatric cardiologists, cardiac imaging specialists, pediatric cardiac surgeons, genetic counselors, and other healthcare professionals. Collaboration among these specialists facilitates comprehensive evaluation, accurate diagnosis, and coordinated management plans tailored to the individual needs of patients and their families.


Complications


Complications of atrioventricular canal defect may include:

Enlargement of the heart. Increased blood goes with the flow through the heart pressuring it to work harder than normal, making it enlarge.

Pulmonary hypertension. When there is a hole (defect) that allows the mixing of oxygenated (red) and deoxygenated (blue) blood, the amount of blood that flows to the lungs is increased. This results in pressure buildup in the lungs, resulting in high blood pressure in the lungs.

Respiratory tract infections. Atrioventricular canal defects can cause intermittent bouts of lung infections.

Heart failure. -->

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