Atrioventricular Canal Defect: Symptoms, Types, Causes and Treatment

Atrioventricular canal defect (AVCD), also known as atrioventricular septal defect (AVSD), is a complex congenital heart condition. It disrupts the normal separation between the heart’s chambers and affects the function of the heart valves, resulting in inefficient blood flow and a range of symptoms. Understanding AVCD is essential for timely diagnosis and effective management, particularly as it often presents early in life and can be associated with other syndromes or anomalies.

Symptoms of Atrioventricular Canal Defect

Atrioventricular canal defect can manifest in infancy or early childhood, but its presentation can vary widely depending on the defect's size and severity. Early recognition of symptoms is crucial for prompt intervention and better outcomes.

Symptom	Description	Age Group Most Affected	Source(s)
Heart Failure	Rapid breathing, feeding problems, poor weight gain	Infants	3 9
Cyanosis	Bluish tint to skin or lips	Infants, Children	3 9 12
Murmur	Heart murmur due to abnormal blood flow	All ages	3 4
Recurrent Respiratory Infections	Frequent lung infections or pneumonia	Infants, Young Children	9

Table 1: Key Symptoms

Heart Failure and Growth Issues

Infants with AVCD often present with signs of heart failure, such as rapid breathing, poor feeding, and failure to thrive. These symptoms occur because the oxygen-rich and oxygen-poor blood mix within the heart, reducing the efficiency of circulation. As the lungs become congested, infants may develop difficulty breathing and recurrent respiratory infections 3 9.

Cyanosis

Cyanosis, or a bluish tint to the lips and skin, can be seen in more severe or unbalanced forms of AVCD. This occurs when oxygen-poor blood is circulated to the body due to abnormal connections between the heart chambers 3 12.

Heart Murmur

A heart murmur, typically detected during a routine examination, is a common finding in AVCD. This is caused by turbulent blood flow across the abnormal valves and septal defects 3 4.

Respiratory Infections

Because of increased blood flow to the lungs and congestion, children with AVCD are prone to recurrent respiratory infections and pneumonia, further complicating their overall health 9.

Types of Atrioventricular Canal Defect

Not all AVCDs are the same. They are classified based on the location and extent of the septal defects and the involvement of the heart valves. Understanding the different types helps guide treatment and prognosis.

Type	Main Features	Valve Involvement	Source(s)
Complete	Defects in both atrial and ventricular septa, single common AV valve	Both mitral and tricuspid	3 4 5
Partial	Primum atrial septal defect, separate AV valves, cleft mitral valve	Mostly mitral	3 4 10
Intermediate	Features between partial and complete, small bridging valvular tissue	Variable	3 4
Unbalanced	AV valve aligned more toward one ventricle; one ventricle is hypoplastic	Variable	12

Table 2: Types of AVCD

Complete AV Canal Defect

This is the most severe form, involving a large hole where the atrial and ventricular septa meet. There is a single common atrioventricular valve instead of separate mitral and tricuspid valves. This type allows mixing of blood from all four heart chambers and is often associated with additional cardiac anomalies. It is more frequently seen in patients with chromosomal abnormalities, such as Down syndrome 3 4 5.

Partial AV Canal Defect

Partial AVCD, or ostium primum defect, involves a hole in the lower part of the atrial septum (ostium primum type) with two separate AV valves. However, the mitral valve often has a cleft, leading to valve leakage (regurgitation). This form generally has less severe symptoms and a better prognosis 3 4 10.

Intermediate (Transitional) AV Canal Defect

This type falls between complete and partial forms. There are features of both, such as a primum atrial septal defect, a small ventricular septal defect, and partially fused AV valves with some bridging tissue. Severity and symptoms can vary 3 4.

Unbalanced AV Canal Defect

In about 10% of cases, the AV valve is shifted to one side, favoring one ventricle over the other. This results in one ventricle being underdeveloped (hypoplastic), making surgical management more complex and outcomes less certain 12.

Causes of Atrioventricular Canal Defect

The causes of AVCD are complex and multifactorial, involving both genetic and developmental factors. Understanding these underlying causes is important for counseling families and identifying associated conditions.

Cause Type	Example/Mechanism	Associated Conditions	Source(s)
Genetic	Chromosomal abnormalities (e.g., Down syndrome, Deletion 8p)	Down syndrome, syndromic anomalies	5 7
Developmental	Failure of endocardial cushion fusion	Other congenital heart defects	3 7
Syndromic	Noonan, Ellis-van Creveld, Smith-Lemli-Opitz, VACTERL	Multiple organ involvement	5
Unknown	Idiopathic in some cases	-	5 7

Table 3: Causes of AVCD

Genetic Factors

AVCD is commonly associated with genetic syndromes, most notably Down syndrome (trisomy 21). Other chromosomal imbalances, such as deletion 8p, have also been linked to AVCD. The presence of additional cardiac and extracardiac anomalies is more frequent in syndromic cases 5 7.

Developmental Mechanisms

During normal heart development, the endocardial cushions are essential for forming the septa that separate the heart chambers and for the proper development of the AV valves. Failure of these cushions to fuse leads to persistent openings between chambers and malformation of the AV valves. This mechanism underlies both complete and partial forms of AVCD 3 7.

Syndromic Associations

Aside from Down syndrome, AVCD can be seen in other genetic syndromes such as Noonan, Ellis-van Creveld, Smith-Lemli-Opitz, and VACTERL association. These conditions often involve multiple systems, so careful evaluation for other anomalies is warranted 5.

Idiopathic Cases

In a significant number of cases, especially in those without recognized syndromes or genetic abnormalities, the cause of AVCD remains unknown. Ongoing research into transcription factors and signaling molecules involved in heart development may uncover additional causes in the future 7.

Treatment of Atrioventricular Canal Defect

Timely and appropriate treatment is vital to prevent complications and improve quality of life in children born with AVCD. Treatment strategies are tailored to the defect type, associated anomalies, and overall health of the patient.

Approach	Description	Outcome/Notes	Source(s)
Surgical Repair	Closure of septal defects, reconstruction of AV valves	High success, low mortality	8 9 10 11
Medical Management	Diuretics, inotropes, nutrition support	Temporizing, not curative	9
Early Intervention	Surgery in infancy if severe heart failure is present	Improves growth, prognosis	9
Complex Repair	Single or biventricular repair for unbalanced defect	Higher risk, individualized	12 11

Table 4: Treatment Strategies

Surgical Repair

Definitive treatment for AVCD is surgical correction. Procedures involve closing the atrial and ventricular septal defects and reconstructing or repairing the AV valves. Techniques such as the modified single patch or two-patch repair are commonly used. Surgical mortality has decreased significantly, with survival rates exceeding 90% in many centers. Valve function is generally preserved, though some patients may require reoperation, especially for valve regurgitation 8 9 10 11.

• Complete AVCD: Surgery is typically performed in infancy, particularly in those with signs of heart failure or pulmonary hypertension. Early correction is associated with improved growth and developmental outcomes 9.
• Partial AVCD: Repair is also surgical, focusing on closing the atrial septal defect and correcting the mitral valve cleft. Outcomes are excellent, with low mortality and good long-term valve function 10.

Medical Management

Before surgery, medical therapy may be used to control symptoms of heart failure. This includes diuretics to reduce fluid overload, inotropes to improve heart function, and nutritional support to address growth failure. However, medication does not correct the underlying defect, and surgery is ultimately required 9.

Treatment of Unbalanced AV Canal

Unbalanced AV canal defects require a more individualized approach. If one ventricle is too small to support normal circulation, single-ventricle repair strategies or staged surgical procedures may be necessary. These cases carry a higher risk of complications and require careful preoperative evaluation 12.

Management of Associated Anomalies

AVCD often coexists with other heart defects (e.g., double-orifice mitral valve, tetralogy of Fallot, anomalous pulmonary veins), which may need simultaneous surgical correction. Advanced surgical techniques allow for repair of these complex presentations with good outcomes 10 11.

Conclusion

Atrioventricular canal defect is a complex congenital heart condition with diverse presentations, underlying causes, and management strategies. Early recognition and intervention are crucial for optimal outcomes.

Key takeaways:

• AVCD presents with symptoms like heart failure, cyanosis, and recurrent infections, especially in infants 3 9 12.
• There are several types—complete, partial, intermediate, and unbalanced—each with distinct anatomical features and implications for treatment 3 4 12.
• The causes are multifactorial, including genetic syndromes (notably Down syndrome), developmental errors in heart formation, and unknown factors in some cases 5 7.
• Surgical repair is the mainstay of treatment, offering excellent survival and functional outcomes when performed early and tailored to the defect type 8 9 10 11 12.

With continued advances in diagnosis, genetics, and surgical techniques, the outlook for children born with AVCD continues to improve. Comprehensive care and early intervention remain the pillars of successful management.