Functionally Univentricular Heart (Single Ventricle)
"Single ventricle anomalies" are also known as "functionally univentricular hearts" and include a variety of congenital heart defects that present challenges to the congenital heart surgeon.
The name "Single Ventricle" is a misnomer, as almost always, a second, rudimentary ventricle can be identified. Consequently, hearts classified as “single ventricles” are also classified as “functionally univentricular hearts”. These defects are unique in that at birth, the pulmonary and systemic circulations are in parallel. As such, decisions concerning initial palliation involve determining the status of the following:
- pulmonary blood flow (too much, too little, just the right amount);
- systemic outflow obstruction (present or absent); and
- the status of pulmonary venous return (obstructed, restrictive, unobstructed).
Hypoplastic left heart syndrome (HLHS) is the most common functionally univentricular (single ventricle) anomaly. HLHS is discussed in detail in a separate chapter of this Pediatric and Congenital Cardiac Section of this STS E-Book (Chapter 42) entitled: “Hypoplastic left heart syndrome (HLHS)”.
For the other varieties, The Society of Thoracic Surgeons International Congenital Heart Surgery Nomenclature and Database Project  categorizes the lesions in the following large groups:
- Double-inlet atrioventricular connection (double-inlet left ventricle [DILV] and double-inlet right ventricle [DIRV]);
- Absence of one atrioventricular connection (includes tricuspid atresia and mitral atresia);
- Common atrioventricular valve with one well developed ventricle (unbalanced atrioventricular canal);
- Heterotaxy syndrome with one developed ventricle; and, finally
- Other (i.e., those that do not fit into any of the aforementioned categories).
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