Common Atrioventricular Canal Defects

Atrioventricular canal defects are characterized by deficiency of atrioventricular septum and a common atrioventricular annulus. They are considered an abnormality in the formation of the endocardial cushions. They are highly associated with Down syndrome. Spectrum of disease is dependent on the location of the atrioventricular valve within the atrioventricular septal defect. Complete form of the defect has a large ventricular septal defect component (atrioventricular valve has minimal attachments to the ventricular septum) whereas incomplete (partial) form has no ventricular septal defect component (because of adherent attachments of the atrioventricular valve to the ventricular septum). In the incomplete form, the common annulus is divided at the ventricular septum into two atrioventricular orifices. The aorta sits more anterior than normal in these defects resulting in elongation of the left ventricular outflow tract. Echocardiography is the primary imaging modality required to make this diagnosis and to assess the spectrum and variation of the disease. Surgery is required to treat atrioventricular canal defects. Since the atrioventricular valve(s) are by definition abnormal, regurgitation before and after surgery is common.