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