The term “atrioventricular septal defect” (atrioventricular canal – AVSD) refers to a group of conditions characterized by anatomical abnormalities of the atrioventricular septum and the atrioventricular valves. The anatomical defect may involve both the atrial and ventricular septa (complete form) or only the atrial septum (partial form).
The incidence of the condition is estimated at 4–5% of congenital heart diseases (CHD), while the overall prevalence is estimated at 0.3–0.4 per 1,000 live births. There is a strong association between atrioventricular septal defects and trisomy 21 (Down syndrome), and it has been estimated that the risk of trisomy 21 reaches 40–50% when a prenatal diagnosis of AVSD is established during pregnancy. AVSD may also occur as an isolated condition without the presence of an associated syndrome, and in such cases it has been associated with maternal diabetes or obesity.
Anatomy
As with most congenital heart diseases, many terms have been used to describe the various anatomical forms of the condition. The term “complete atrioventricular septal defect” refers to the presence of a primum atrial septal defect in continuity with a posteriorly located ventricular septal defect (inlet portion of the ventricles).
In this form, a common atrioventricular valve is present. The term “partial atrioventricular septal defect” describes the presence of a primum atrial septal defect with a common atrioventricular valve annulus; however, the valves have two separate orifices.
Anatomical illustration of the atrioventricular septum (reversed for correspondence with the above description) (MV: mitral valve, TV: tricuspid valve, AOV: aortic valve, PV: pulmonary valve).
A cleft (split) of the anterior leaflet of the mitral valve is also present. In cases where a ventricular septal defect coexists but is covered by multiple chordae tendineae, resulting in a hemodynamically insignificant communication, the canal is described as transitional. The term “intermediate canal” describes a complete canal in which the common atrioventricular valve is divided by tissue into two separate orifices, eliminating the need for surgical separation of the valves during repair.
Classification according to Rastelli, based on the anatomy of the leaflets of the common atrioventricular valve, is also frequently used. Functionally, the canal may preferentially direct blood flow toward either the left or the right ventricle, resulting in ventricles of unequal size (unbalanced canal), which is often associated with a corresponding size discrepancy of the great vessels (atrioventricular septal defect with Tetralogy of Fallot).
AVSD may also be associated with abnormalities of visceral symmetry (heterotaxy syndromes), including right isomerism (asplenia) and left isomerism (polysplenia).
Clinical Presentation – Diagnosis – Management
Complete Atrioventricular Septal Defect (Complete AVSD)
The clinical presentation during the neonatal period in cases of complete atrioventricular septal defect is that of heart failure. Specifically, tachypnea, tachycardia, hepatomegaly, feeding difficulties, and failure to gain weight are observed. The clinical picture becomes more evident after the first days of life due to the progressive decrease in pulmonary vascular resistance and the accompanying increase in pulmonary blood flow.
Partial Atrioventricular Septal Defect (Partial AVSD)
Neonates are usually asymptomatic. In the rare case of heart failure, careful evaluation is required for the presence of significant mitral regurgitation, subaortic stenosis, coarctation of the aorta, or hypoplasia of the left ventricle (unbalanced canal).