Patients with an AVSD have typically had at least 1 prior attempt to repair the AVSD, have different risks of arrhythmia, and may have other anatomic lesions (eg, sub- aortic stenosis [subAS]). In 1 meta-analysis of studies of adult left atrioventricular valve sur- gery in patients with AVSD, the risk of needing a pacemaker was higher in those who under- went valve replacement than in those who un- In another single-center study, one third of repaired patients required Recommendations for Atrioventricular Septal Defect (Continued) COR LOE Recommendations CLINICAL STATEMENTS AND GUIDELINES an additional reoperation.S4.1.4-3 When replace- ment is required, the choice to use mechanical versus bioprosthetic valve is individualized, but a mechanical valve is usually necessary because of the potential for LVOT obstruction from the struts of the bioprosthetic valve. Nevertheless, valve repair is preferred to valve replacement when it is technically feasible. 3. There are no large studies on residual shunts in patients with AVSD, but extrapolating from in- formation on residual isolated ASD or isolated VSD, a moderate or large residual shunt is likely to result in worsening clinical status over time and thus merits consideration of repair.S4.1.4-11 S4.1.4-13 See Sections 4.1.1 and 4.1.3 for related consider- ations regarding ASD and/or VSD. Pulse oximetry at rest and with ambulation may identify patients with increased pulmonary resistance and shunt reversal. There is a subset of patients with rest- ing systemic oxygen saturation >90% who will have a decrease in oxygen saturation with activity to <90%, emphasizing the importance of per- forming resting and ambulatory pulse oximetry assessment. 4. Patients with AVSD are at risk of LVOT obstruc- tion because of the abnormal anatomy of the LVOT. 