Background: In right-dominant unbalanced atrioventricular (AV) canal, there are no criteria to judge adequacy of the left ventricle for biventricular repair. The purpose of this study was to test the hypothesis that right ventricular volume overload in this condition results in right-to-left septal bowing and contributes to the appearance of a small left ventricle.
Methods: Five consecutive neonates and young infants (age range, 23 days to 5 months; median age, 3 months) with right-dominant unbalanced complete AV canal underwent biventricular repair. Preoperative and postoperative echocardiographic measurements of left (LV) and right ventricular size and AV valve component size were made. Potential LV volume was assessed preoperatively using a theoretic model that assumed a normalization of septal bowing.
Results: There was no perioperative mortality; 1 patient died 71 days postoperatively of problems related to the left AV valve. Preoperatively, all patients had severe LV hypoplasia, with a mean end-diastolic indexed true LV volume of 14.8 +/- 9.1 mL/m2, indexed potential LV volume of 32.0 +/- 18.8 mL/m2, left AV valve to total AV valve ratio of 0.30 +/- 0.06, and LV to right ventricular long-dimension ratio of 0.65 +/- 0.1. Postoperatively, all patients had indexed true LV volumes greater than 30 mL/m2 (mean volume, 35.6 +/- 3.9 mL/m2), and the left AV valve to total AV valve ratio and the LV to right ventricular long-dimension ratio increased to 0.42 +/- 0.03 and 0.88 +/- 0.11, respectively. Both preoperative potential and true LV volumes correlated well with postoperative true LV volumes: r = 0.90 (p = 0.040) and r = 0.93 (p = 0.023), respectively. Increases in LV length and left AV annulus size indicated contributions of volume loading and surgical patching to the right of the ventricular crest to the increase in LV size.
Conclusions: In our small series, preoperative indexed potential LV volume of 15 mL/m2 or greater (present in all patients) allowed biventricular repair of right-dominant unbalanced AV canal. Any previous criteria for LV hypoplasia in this condition need to be reconsidered. This study also has implications for other right-sided volume-loaded lesions in which the left ventricle initially is judged to be hypoplastic but in which biventricular repair may be feasible.