Atrioventricular septal defects (AVSD), also known as common atrioventricular canal, are a group of congenital heart diseases characterized by abnormal development of the endocardial cushions. This defect leads to pathological communication between the atria and ventricles and malformation of the atrioventricular valve complex. The result is a variable combination of atrial and ventricular septal defects and abnormalities of the mitral and tricuspid valves.
AVSDs account for approximately 4–5% of all congenital heart defects, with an estimated prevalence of 0.3–0.5 per 1,000 live births. They are frequently associated with genetic syndromes, especially Down syndrome, in which they represent the most common cardiac lesion.
The anatomo-clinical spectrum of atrioventricular septal defects is highly variable, ranging from complete forms with a large atrial and ventricular shunt and a common atrioventricular valve, to partial or intermediate forms with more localized defects and a divided but malformed valve apparatus.
Early recognition and timely surgical correction are essential to prevent the development of irreversible pulmonary hypertension, congestive heart failure, and permanent structural and functional cardiac damage.
Atrioventricular septal defects arise from an abnormal development of the endocardial cushions, embryonic structures that are essential for the formation of the atrioventricular septum and the cardiac valves. This developmental anomaly occurs early, between the fifth and eighth weeks of gestation, impairing the normal formation of the atrial septum, the ventricular septum, and the atrioventricular valves.
Definite etiological causes include well-established chromosomal anomalies, especially trisomy 21 (Down syndrome), where AVSD is found in up to 40–50% of cases. The defect is attributed to early dysfunction of cell migration and fusion mechanisms in the central endocardial cushions. Other genetic abnormalities, such as 8p23 deletion and Ellis-van Creveld syndrome, have been described as less common causes.
Among modifiable risk factors, although less well defined, potential contributors include uncontrolled maternal diabetes, exposure to teratogens during pregnancy (such as lithium, isotretinoin, alcohol), and certain congenital infections (e.g., rubella). However, the role of these factors is probabilistic and insufficient to cause the defect in the absence of an underlying genetic predisposition.
From a pathogenic perspective, the failure of fusion of the endocardial cushions results in the presence of an ostium primum atrial septal defect and a ventricular septal defect located in the inlet portion of the septum, often associated with a single atrioventricular valve, undivided into the distinct mitral and tricuspid leaflets.
The pathophysiology varies according to the extent of the defect. In complete forms, a significant left-to-right shunt occurs at both atrial and ventricular levels, leading to volume overload of the pulmonary circulation, dilation of both right and left heart chambers, valvular insufficiency, and progressive development of pulmonary hypertension. Over time, rising pulmonary vascular resistance may reverse or equalize the shunt (Eisenmenger syndrome), causing severe clinical deterioration and a poor prognosis if not surgically corrected.
In partial forms, the defect may be limited to the atrial septum, with partially divided but dysplastic valves. This leads mainly to an atrial-level shunt and mitral regurgitation, resulting in a more subtle clinical picture that may still progress over time.
The progressive atrial and ventricular dilation, together with myocardial wall hypertrophy due to chronic volume overload, predisposes to the development of atrial arrhythmias, supraventricular tachycardias, and, in advanced stages, systolic dysfunction and refractory heart failure.
The clinical presentation of atrioventricular septal defects depends on the extent of the defect, the anatomical type (complete, partial, or intermediate), valve function, and the magnitude of the left-to-right blood shunt. Complete forms tend to manifest early in postnatal life, whereas partial forms may remain asymptomatic for years and be diagnosed later in life due to the onset of progressive symptoms.
In neonatal history, patients with complete AVSD often exhibit feeding difficulties, poor weight gain, tachypnea, and sweating during feeding, which are early signs of congestive heart failure.
In infants and young children, the most common symptoms include:
On physical examination, findings may include:
In partial forms, the clinical presentation may occur later, with exertional dyspnea, palpitations, or the incidental detection of a cardiac murmur during auscultation. Mitral regurgitation may worsen over time, leading to atrial enlargement and a higher risk of supraventricular arrhythmias.
The diagnosis of atrioventricular septal defects is based on integrating clinical findings with instrumental investigations, starting from the suspicion of a cardiac shunt or a persistent murmur in newborns and children.
Transthoracic echocardiography is the gold standard for diagnosis. It allows direct visualization of the atrial and ventricular septal defects, as well as the morphology and function of the atrioventricular valves. Color Doppler imaging is essential to document the direction and extent of the shunt, the presence of valvular regurgitation, and any pulmonary hypertension.
In cases of limited acoustic window or when a more precise definition of valvular anatomy is needed, a transesophageal echocardiogram may be indicated.
The electrocardiogram (ECG) often shows biventricular hypertrophy and a junctional rhythm or right bundle branch block. In complete forms, an atypical leftward QRS axis is frequently observed. ECG is also useful in follow-up to detect early signs of arrhythmia.
Chest radiography may reveal global cardiomegaly and signs of pulmonary congestion in cases with a hemodynamically significant shunt. It is commonly performed in symptomatic patients during initial evaluation.
Cardiac catheterization is reserved for selected cases requiring precise hemodynamic assessment, particularly when planning surgical repair in patients with significant pulmonary hypertension. It allows direct measurement of pulmonary vascular resistance and quantification of the shunt (Qp/Qs ratio).
Other imaging modalities, such as cardiac magnetic resonance imaging or cardiac computed tomography, can be helpful in specialized centers for preoperative assessment of complex forms or in cases where echocardiography yields inconclusive anatomical data.
The treatment of AVSD is surgical and represents the definitive therapy. Ideally, it should be performed within the first year of life in complete forms, before the onset of irreversible pulmonary hypertension. Early correction significantly improves long-term survival and quality of life.
In symptomatic complete forms, early surgical correction is indicated, preferably between 3 and 6 months of age. The procedure consists of patch closure of the atrial and ventricular septal defects and reconstruction of the atrioventricular valve into two distinct leaflets (functionally separate mitral and tricuspid valves).
In partial forms, the indication for surgery is based on the presence of significant mitral regurgitation or progressive chamber dilation. In such cases, surgery may be performed later, but it must still be planned to prevent structural damage and arrhythmias.
In patients with severe pulmonary hypertension, a thorough hemodynamic evaluation is essential to rule out Eisenmenger syndrome. In these cases, surgery may be contraindicated, and management becomes palliative, with medical therapy and close monitoring.
In the preoperative period or in patients who are not immediately eligible for surgery, supportive medical therapy may be used, including:
Long-term management includes regular cardiology follow-up, with echocardiographic monitoring, valve function assessment, and screening for arrhythmias, especially in patients with complex valve reconstructions or prosthetic replacements.
The prognosis of patients with atrioventricular septal defects is closely related to the anatomical type of the defect, the timing of diagnosis, and the quality of surgical intervention. In untreated complete forms, the natural course leads to progressive cardiac dysfunction, development of irreversible pulmonary hypertension, and risk of death within the first few years of life.
With early surgical correction, performed within the first year of life, long-term survival improves dramatically, with 10-year survival rates exceeding 90%. Most children who undergo surgery lead normal lives, with adequate growth and development. However, regular follow-up is necessary to monitor valve function and prevent late complications.
Partial forms generally have a more favorable prognosis, but if left untreated they may slowly progress to worsening mitral regurgitation and atrial dilation with a risk of arrhythmias. Even in these cases, surgery is curative in the majority of patients, with excellent functional outcomes when performed before the onset of irreversible damage.
Complications related to atrioventricular septal defects may be early or late, and can affect both untreated patients and those who have undergone surgical correction.
The main complications in untreated forms include:
Postoperative complications may include:
Finally, operative mortality is now very low (<2–3%) in centers with expertise in pediatric cardiac surgery, but remains higher in cases with delayed diagnosis, advanced pulmonary hypertension, or complex anatomical anomalies.