Unbalanced Atrioventricular Canal Defects

Unbalanced atrioventricular septal(or canal) defect is a variation of the more usual pattern, where in the common atrioventricular junction is shared unequally between the ventricles. Unequal sharing can result in right or left ventricular dominance, with the frequent association of obstruction of the outflow from the complementary hypoplastic ventricle, and the precise degree of imbalance, contributing to the appropriate surgical repair. Those with severely unbalanced defects undergo functionally single-ventricle pathway palliation, while those with only mild unbalance and no significant associated lesions may undergo two-ventricle repair similar to that used for those with balanced defects. Complex decision-making is required for those with moderately unbalanced lesions to determine if functionally single-ventricle, two-ventricle, 1.5-ventricle, or staged left ventricular rehabilitation toward two-ventricle repair is appropriate. We review the several methods that have been proposed to assess the extent of imbalance as a guide in surgical decision-making.