Atypical atrial septal defects in children: noninvasive evaluation by cardiac MRI

Background  Atypical left-to-right shunts at the level of the atrium in children such as sinus venosus atrial septal defects (ASDs) and partial anomalous pulmonary venous return (PAPVR) may be difficult to assess by transthoracic or transoesophageal echocardiography. Free-breathing cardiac MRI may be a powerful alternative. Objective  To assess the value of free-breathing cardiac MRI in the delineation of atypical ASDs in children. Materials and methods  A total of 82 children (mean age 5.9 years, range 1.1–15.7 years) with suspected ASD and inconclusive transthoracic echocardiography underwent cardiac MRI under free-breathing, mostly sedated conditions. Phase-contrast MRI was used for defect visualization and shunt quantification, and multiphase inflow MR angiography for delineation of pulmonary/systemic venous connections. Results  Of the 82 patients, 34 (41%) were diagnosed with atypical shunt lesions at the level of the atrium and 48 (59%) with simple secundum ASDs. No false-negative or false-positive findings were reported by MRI compared to cardiac catheterization and intraoperative findings. Superior sinus venosus ASD with partial anomalous PAPVR was present in 10 of the 82 children (12.2%), whereas 2 (2.4%) had a large posterior-inferior defect, 5 (6.1%) had isolated PAPVR, and 17 (20.7%) had multiple ASDs and/or associated vascular anomalies. Q_p/Q_s by phase-contrast MRI agreed well with oximetry values (mean difference 3%, limits of agreement ±21–25%; Bland/Altman analysis). Conclusion  Free-breathing cardiac MRI under sedation allows reliable identification of atypical left-to-right shunt defects at the level of the atrium in children in whom transcatheter ASD closure is unsuitable, including delineation of pulmonary or systemic venous anomalies and shunt quantification.