Unbalanced Atrioventricular (AV) Canal Defects

Aditya Suryakumar, MD, Viktoria H. Weixler, MD, Sitaram M. Emani, MD

Key Points

  1. Definition and Classification
    Unbalanced AV canal defects are a subset of atrioventricular septal defects characterized by an abnormal distribution of the common AV valve over the ventricles, resulting in hypoplasia of the non-dominant ventricle. These defects are classified based on the degree of ventricular imbalance and the morphology of the dominant ventricle (right or left), with further anatomical subtypes described by the Rastelli classification (Types A, B, and C).
  2. Embryology and Anatomy
    The embryological basis involves abnormal development and fusion of the endocardial cushions, leading to a common AV junction and variable defects in the atrial and ventricular septa. The anatomy is further complicated by the unequal distribution of the AV valve, which influences the size and development of the ventricles and associated structures such as the outflow tracts and papillary muscles.
  3. Clinical Presentation and Diagnosis
    Patients typically present in infancy with symptoms ranging from congestive heart failure (especially in right-dominant defects) to cyanosis (more common in left-dominant defects with pulmonary outflow obstruction). Diagnosis relies on echocardiography for anatomical assessment, with advanced imaging (MRI, CT) and cardiac catheterization reserved for complex cases or when further anatomical or hemodynamic clarification is needed.
  4. Surgical Management
    Surgical strategies are tailored to the degree of ventricular imbalance and associated lesions. Options include biventricular repair (using single-patch, two-patch, or modified single-patch techniques) or univentricular palliation. Early intervention is emphasized to prevent irreversible pulmonary vascular disease, with timing and approach influenced by the patient’s clinical status and detailed anatomical findings.
  5. Outcomes and Future Directions
    Outcomes after repair are closely linked to the adequacy of the hypoplastic ventricle and the distribution of the AV valve. Mortality varies widely (5–50%), and long-term complications include AV valve regurgitation and ventricular dysfunction. Advances in imaging, surgical techniques, and tissue engineering are shaping future management, with ongoing efforts to improve prediction of successful biventricular repair and optimize long-term ventricular growth and function.

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