Endocardial cushion tissue defects (atrioventricular septal defects)
- Endocardial cushion defects are those anomalies that arise from defects in the endocardial cushions that participate in formation of the atrioventricular canal, atrial and ventricular septa, as well as leaflets of the adjacent mitral and tricuspid valves.
- Defects are primarily due to the total absence of the membranous atrioventricular septum and commonly associated with deficiencies in both atrial and ventricular musculature and valves.
- Atrioventricular septal defects can be considered to exist as a continuum with severity ranging from simple defects in the atrial septum, to the complete absence of central structures within the heart.
- Partial (incomplete) AV canal defects, are characterized by the presence of an ostium primum atrial septal defect and clefts in the anterior leaflets of the left atrioventricular valves. Importantly, there are typically two distinct atrioventricular valves with separate annuli.
- Transitional canal defects consist of two distinct atrioventricular annuli with defects in the atrial and ventricular septa.
- Complete AV canal defects are characterized by a defect in the atrial and ventricular septum leaving a complete, common, atrioventricular annulus with an inferior and superior bridging leaflet.
- Physiologically, atrioventricular canal defects typically present with atrioventricular valvular regurgitation, as well as consequences similar to those expected from atrial or ventricular septal defects. In addition, an overriding tricuspid valve allows for mixing of pulmonary and systemic venous return. Finally, a large ventricular opening allows for equilibration between the right and left ventricular pressures, which then results in pulmonary hypertension and this eventually leading to pulmonary vascular disease.
- Endocardial cushion defects are commonly secondary diagnoses and associated with almost any other type of congenital heart defects except in children with Down syndrome.
- It is recommended that all three types of atrioventricular septal defects be surgically repaired between six and twelve months of age; preferably by age two to three, to avoid post-operative complications. The specific procedures and repairs performed for a patient is dependent on the severities of the defects and presence of associated congenital heart malformalities.