CLINICAL STATEMENTS AND GUIDELINES Therapeutic (Continued) IIb C-EO Surgery for primary repair of atrioventricular septal defect or closure of residual shunts in adults with repaired atrioventricular septal defect may be considered in the presence of a net left-to-right shunt (Qp:Qs 1.5:1), if PA systolic pressure is 50% or more systemic, and/or pulmonary vascular resistance is greater than one third systemic. III: Harm C-LD Surgery for primary repair of atrioventricular septal defect or closure of residual shunts in adults with repaired atrioventricular septal defect should not be performed with PA systolic pressure greater than two thirds systemic, pulmonary vascular resistance greater than two thirds systemic, or a net Synopsis AVSDs represent about 4% to 5% of congenital heart defects and include a primum ASD, inlet VSD, and com- mon atrioventricular valve. They can occur in several anatomic variations including partial AVSD with only a primum ASD component and typically a cleft left atri- oventricular valve, complete AVSD with both ASD and VSD and a common atrioventricular valve, and transi- tional and intermediate AVSD with incomplete atrial and VSDs and/or incomplete abnormalities of the com- mon atrioventricular valve. AVSD anatomy is also com- monly described by the Rastelli classification.S4.1.4-7,S4.1.4-8 The Rastelli classification describes anatomic variations of the superior bridging leaflet of the atrioventricular valve. In addition to the Rastelli classification or other similar descriptors, the relative sizes of the ventricles as balanced or unbalanced guide the type of repair (eg, bi- ventricular or single ventricle repair). This section refers to patients with balanced AVSD and biventricular repair. AVSD also occurs in association with other congenital lesions including TOF, CoA, and heterotaxy. There is also a strong association with syndromes, most com- monly trisomy 21 (Down syndrome). From a management perspective, most adults with AVSD will have had surgical repair as children. 