A Complete Atrioventricular Canal Defect (CAV) is a congenital heart condition present from birth. It involves a significant structural failure in the center of the developing heart, creating a large communication between all four heart chambers. Understanding the specific nature of this defect is important for navigating the necessary medical and surgical journey.
Understanding Atrioventricular Canal Defects
The complete defect involves a failure of the heart’s central structure, the endocardial cushions, to properly divide the heart. This results in a single, large opening spanning the upper chambers (atria) and the lower chambers (ventricles). Instead of the separate mitral and tricuspid valves, a patient has a single, common atrioventricular valve.
This causes oxygen-rich blood from the left side to mix freely with oxygen-poor blood on the right side. Since the left side pressure is higher, blood is shunted left-to-right. This excessive flow is pumped into the lungs, creating volume overload that forces the heart and lungs to work harder.
The constant over-circulation causes lung blood vessels to stiffen and narrow, leading to pulmonary hypertension. CAV is distinct from a Partial Atrioventricular Canal Defect, which involves only a hole between the atria and an abnormal left-sided valve. The complete defect is significantly more complex and presents with severe symptoms earlier in infancy.
Genetic Factors and Associated Conditions
The specific cause of an Atrioventricular Canal Defect is often unknown, but it has a strong association with genetic syndromes. The most notable link is with Trisomy 21 (Down Syndrome). The complete defect occurs in approximately 40% to 50% of children born with Down Syndrome.
The incidence of this defect is estimated to be 2,000 times higher in infants with Trisomy 21 compared to the general population. This connection suggests the extra copy of chromosome 21 affects genes involved in the early formation of the endocardial cushions. Researchers have identified genes, such as CRELD1 and DSCAM, that may play a role in this developmental failure.
When the defect is not associated with a known syndrome, it is considered an isolated congenital heart defect. Less frequent risk factors may include certain maternal illnesses or environmental exposures during pregnancy. The defect forms very early, typically between the fourth and seventh weeks of gestation, when the heart is rapidly developing.
Recognizing Symptoms and Diagnostic Testing
The structural issues of CAV typically cause noticeable signs in the first weeks or months of an infant’s life. Symptoms relate to the heart’s difficulty handling volume overload and the resulting strain on the lungs. These include rapid or labored breathing, signaling lung congestion from excess blood flow.
Infants often exhibit difficulty feeding, tiring quickly, which leads to poor weight gain (“failure to thrive”). A bluish or gray tint to the skin or lips, known as cyanosis, may occur due to the mixing of oxygenated and deoxygenated blood. A pediatrician often detects a distinct heart murmur, an abnormal sound caused by turbulent blood flow, prompting further investigation.
Diagnosis relies on specialized imaging tests, primarily the echocardiogram. This non-invasive ultrasound creates detailed images of the heart, allowing cardiologists to visualize the defects, the common valve structure, and the extent of abnormal blood flow. If suspicion arises before birth, a fetal echocardiogram provides a prenatal diagnosis, enabling the care team to prepare for delivery.
Surgical Repair and Long-Term Management
Surgical intervention is mandatory for CAV, as the condition will not resolve on its own. The operation is typically performed within the first six months of life, often between three and six months, to prevent permanent damage to the lung blood vessels from prolonged pulmonary hypertension. This complex open-heart surgery has two primary goals: closing the holes and reconstructing the valves.
Surgeons use synthetic patches to close both the atrial septal defect and the ventricular septal defect, effectively restoring the separation between the left and right sides of the heart. The single common atrioventricular valve is then carefully divided and reconstructed into two separate, functioning valves, mimicking the normal mitral and tricuspid valves. The heart tissue eventually grows over the patches, making them a permanent part of the heart’s structure.
The long-term outlook for children who undergo successful surgical repair is generally positive, with high survival rates extending into adulthood. However, the repaired heart is not considered cured. Patients require lifelong, specialized follow-up care with a cardiologist experienced in congenital heart disease. Potential late complications requiring reintervention include the reconstructed valves becoming leaky (regurgitation) or narrowed, or the development of abnormal heart rhythms (arrhythmias).