The Society of Thoracic Surgeons (2026) Expert Consensus Document on Management of Borderline Left Heart Excluding Unbalanced Atrioventricular Septal Defect and Strategies for Biventricular Conversion.

BACKGROUND

Strategies to recruit the left ventricle in borderline left heart (BLH), whether utilizing primary or staged recruitment strategy, are challenged by lack of consensus regarding optimal substrate, timing, and technique.

METHODS

A panel of experienced congenital cardiac surgeons, cardiologists and imaging experts were convened to develop key questions related to BLH management, excluding unbalanced atrioventricular septal defect, from neonatal period through 1 year, using the PICO (Patients/Population, Intervention, Comparison/Control, Outcome) framework. Literature searches were performed for each question. Using a modified Delphi method, consensus statements were developed.

RESULTS

For neonates with BLH, primary biventricular repair should be adopted cautiously, and only with favorable anatomic and physiologic criteria determined by echocardiography and/or magnetic resonance imaging. Neonates in the 'grey-zone', with smaller mitral and aortic valve sizes, endocardial fibroelastosis, indexed left ventricular diastolic volume < 25 ml/m2 and ascending aortic flow < 2.0 L/min/m2, should undergo staged recruitment to potentially facilitate growth of left-sided structures and more durable surgical rehabilitation of left ventricular inflow and outflow. Timing and type of subsequent procedures should be guided by interval cardiac catheterization and magnetic resonance imaging data. Initial palliation of grey-zone neonates can be accomplished with either surgical Norwood or hybrid stage 1 with possible atrial level restriction, and subsequent endocardial fibroelastosis resection along with aortic and mitral valve repair as components of successful complete biventricular conversion.

CONCLUSIONS

Biventricular approaches in BLH should be guided by integration of anatomic and physiologic criteria, with most neonates recommended for staged recruitment rather than primary repair.