Medica

Surgical Management of
Unbalanced Atrioventricular Canal Defect
Meryl S. Cohen and Thomas L. Spray
Approximately 10% of endocardial cushion defects exhibit unbalance at the atrioventricular
inlet. When the atrioventricular valve sits more over one ventricle than the other, the
contralateral ventricle is typically hypoplastic. Surgical intervention for unbalanced atrioventricular canal has amuch higher morbidity and mortality than for the balanced form of
the defect. With unbalanced atrioventricular canal to the right, no universal criteria are in
place to choose single versus biventricular repair. In many cases, risk factors have been
extrapolated from other lesions with left ventricular hypoplasia. Even if biventricular repair
is successful, the reoperation rate is high forthis lesion. Little data exist in the literature
regarding left unbalanced atrioventricular canal. In general, right ventricular hypoplasia is
better tolerated than left ventricular hypoplasia, and biventricular repair is usually possible.
If cyanosis or high systemic venous pressure results, the one and one half ventricle repair
(biventricular repair with bidirectional Glenn anastomosis) is anoption. This article reviews
the present understanding of unbalanced atrioventricular canal and discusses diagnostic
and surgical strategies for this complex lesion.
Semin Thorac Cardiovasc Surg Pediatr Card Surg Ann 8:135-144 © 2005 Elsevier Inc. All
rights reserved.
KEYWORDS: Unbalanced atrioventricular canal, endocardial cushion defect, ventricular hypoplasia, biventricular repair, one andone half ventricle repair

A

trioventricular canal defect (AVC) represents a spectrum
of lesions where the endocardial cushion portion of the
embryonic heart, derived from mesenchymal tissue, does not
develop and the superior and inferior cushions fail to fuse.
This deficit results in an ostium primum atrial septal defect, a
ventricular septal defect (VSD) component in some cases,
and acommon atrioventricular valve with leaflets that bridge
over both ventricular inlets. In approximately 10% of cases,
the common atrioventricular valve sits more over one ventricle than the other, often with significant hypoplasia of the
contralateral ventricle.1,2
Reparative strategies for unbalanced AVC pose a unique
challenge for the cardiothoracic surgeon, and outcome remains poor incomparison to balanced forms of the defect.3 In
general, the surgical approach may include biventricular repair if the hypoplastic ventricle is deemed “adequate” or sinFrom The Cardiac Center at The Children’s Hospital of Philadelphia, Divisions of Cardiology and Cardiothoracic Surgery, Departments of Pediatrics and Surgery, University of Pennsylvania School of Medicine, Philadelphia, PA.
Addressreprint requests to Thomas L. Spray, MD, The Children’s Hospital of
Philadelphia, Division of Cardiothoracic Surgery, 34th and Civic Center
Blvd., Philadelphia, PA 19104.

1092-9126/05/$-see front matter © 2005 Elsevier Inc. All rights reserved.
doi:10.1053/j.pcsu.2005.02.006

gle-ventricle palliation if the ventricle cannot support the
systemic (left ventricular hypoplasia) or pulmonary (rightventricular hypoplasia) circulation. With right ventricular
hypoplasia, a biventricular repair with an additional pulmonary blood flow source from a Glenn anastomosis (“one and
one-half ventricle repair”) may be used. The goal is to choose
the surgical pathway with the most optimal outcome. There
are no universally accepted diagnostic criteria to help determine which surgical approach totake. The minimal required
ventricular volume and associated valvar structures have remained uncertain for unbalanced AVC. Moreover, changing
surgical strategies after one pathway has “failed” is associated
with a high morbidity and mortality. In this article, the current literature addressing unbalanced AVC and surgical options for right and left-sided unbalance are discussed.

Unbalanced...