Complete atrioventricular canal

Complete atrioventricular canal (CAVC), also referred to as complete atrioventricular septal defect, is characterised by an ostium primum atrial septal defect, a common atrioventricular valve and a variable deficiency of the ventricular septum inflow. CAVC is an uncommon congenital heart disease, accounting for about 3% of cardiac malformations. Atrioventricular canal occurs in two out of every 10,000 live births. Both sexes are equally affected and a striking association with Down syndrome was found. Depending on the morphology of the superior leaflet of the common atrioventricular valve, 3 types of CAVC have been delineated (type A, B and C, according to Rastelli's classification). CAVC results in a significant interatrial and interventricular systemic-to-pulmonary shunt, thus inducing right ventricular pressure and volume overload and pulmonary hypertension. It becomes symptomatic in infancy due to congestive heart failure and failure to thrive. Diagnosis of CAVC might be suspected from electrocardiographic and chest X-ray findings. Echocardiography confirms it and gives anatomical details. Over time, pulmonary hypertension becomes irreversible, thus precluding the surgical therapy. This is the reason why cardiac catheterisation is not mandatory in infants (less than 6 months) but is indicated in older patients if irreversible pulmonary hypertension is suspected. Medical treatment (digitalis, diuretics, vasodilators) plays a role only as a bridge toward surgery, usually performed between the 3rd and 6th month of life.

[Morphological spectrum of atrioventricular septal defects]

Morphology of atrioventricular septal defect was studied on 73 heart specimens. All of them had a defect of atrioventricular septum and adjoining parts of atrial and ventricular septum, a shortening of inflow parts of both ventricles, a malformation of atrioventricular valves and changed position of aortic valve. There was a great variability of all the studied structures and nearly continuous spectrum of specimens was found as for the ventricles' size, localization and diameter of the defect, communication between atria and ventricles, anatomy of the left ventricle outflow tract as well as the whole atrioventricular valvular apparatus and occurrence of associated heart malformations. A common ostium was formed in 52 cases (71.2%), two separated ostia were found in 21 cases (28.8%) but a continuous transition between both groups was noticed. Both groups showed a great variety of single cusps of atrioventricular valves (in shape, number and anchoring), of papillary muscles and of the size of atrioventricular communication. The finding of frequently associated heart malformations was important from the clinical point of view, especially of the obstructive malformations of the left ventricle. A great morphological variability needs individual surgical solutions, namely reconstruction of valves, closure of septal defects and correction of associated heart malformations.

[Defects of the atrioventricular cardiac septum (persistent common atrioventricular canal)]

A new morphological-clinical classification was suggested for this type of heart malformations based on confrontation of authors' results with literature. The classification took into consideration appearance of the top of ventricular septum, form of atrioventricular valves, topography of the defect and its relation to the location of conducting system.

A communication from the left ventricle to the right atrium: a defect in the central fibrous body

An isolated defect in the membranous atrioventricular septum was found in a five-year-old girl who presented with a cystic lesion in the right atrium. This type of left ventricular-right atrial communication could result from a structural abnormality of the central fibrous body in combination with arrested maturation of the membranous ventricular septum.