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Single ventricle or univentricular heart refers to a limited number of congenital heart lesions from a strict anatomic perspective. Anatomically, single ventricle lesions can be either a single left ventricle, due to agenesis of the right ventricular inlet (there is often a small component of the right ventricular outlet present), or a single right ventricle, secondary to agenesis of the left ventricle.1,2 In both, the atria drain through one or two atrioventricular valves into the only ventricular chamber (Fig. 498-1). These lesions are rare, and do not include common lesions such as tricuspid atresia and hypoplastic left-heart syndrome.

Figure 498-1.

Diagram illustrates anatomy of double inlet single ventricle (A) and common inlet single ventricle (B).

(Source: Modified from Schultz AH, Kreutzer J. Cyanotic heart disease. In: Vetter VL, ed. Pediatric Cardiology. The Requisites in Pediatrics. Philadelphia, PA: Mosby Elsevier; 2006:51-78.)

In practice the concept of “single ventricle” expands beyond the strict anatomic definition, and refers to all congenital heart lesions that share a single ventricle physiology, regardless of the underlying structural variant.3,4 This expanded functional definition includes all those lesions in which the patient lacks a second ventricle that can independently support the pulmonary circulation. In most such lesions, components of a second ventricle exist.

In single ventricle physiology the circulations mix at the atrial and/or ventricular level. The surgical approach typically consists of various staging procedures which result in a complete separation, or “bypass,” of the pulmonary circulation from the heart. The final surgical stage that fully separates the pulmonary circulation is known as the modified Fontan operation. The “single ventricle” then becomes the systemic pumping chamber, and the systemic venous return flows passively through the pulmonary circulation without interposition of a ventricular pump.3

Thus, the single ventricle from a physiologic perspective includes patients with

  • single right ventricle
  • single left ventricle
  • unbalanced complete atrioventricular (AV) canal (a common AV valve is more aligned to one ventricle than the other, typically associated with asymmetry in the development of the two ventricular chambers)
  • tricuspid atresia (eFig. 498.1)
  • hypoplastic tricsupid valve and right ventricle, frequently with intact ventricular septum and pulmonary atresia
  • mitral atresia
  • hypoplastic left heart syndrome and its variants (eFig. 498.2)

In addition, single ventricle physiology also exists in patients with complex intracardiac anatomy such that surgical septation of the ventricles cannot be performed, thus, they are managed in the same pathway as those with more traditional forms of single ventricle physiology. Examples are double outlet right ventricle and straddling atrioventricular valves, noncommitted ventricular septal defects, and complex multiple ventricular septal defects, for which surgical septation is not feasible. In such patients, following a Fontan procedure, two ventricles function together as the systemic ventricle.

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