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In general, the most complex forms of congenital heart disease (CHD) fall into the category of single-ventricle defects. Only in recent decades has survival beyond the neonatal period become the norm in the developed world, owing to a number of factors, namely the introduction of prostaglandin infusion, innovative surgical strategies such as the Norwood procedure, accurate postnatal noninvasive assessment through echocardiography, and improvements in prenatal diagnosis. Today, surgical palliation of single-ventricle CHD is expected to result in favorable short- and long-term outcomes into early adulthood for most patients. With the improvement in survival in recent decades, attention is now being turned toward optimizing long-term outcomes and addressing the many functional limitations still experienced by survivors of single-ventricle CHD.
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Broadly speaking, single-ventricle CHD can be defined as any congenital heart defect in which there is admixture of systemic and pulmonary venous return in association with atresia (absence of a normally patent structure) or significant hypoplasia (smaller size than normal) of a cardiac valve or chamber.1 Depending on the defect, admixture can occur at 1 or multiple anatomic locations within the heart. Single-ventricle CHD results from atresia or hypoplasia of either an atrioventricular valve or semilunar valve; atresia or hypoplasia of the ventricle associated with the affected atrioventricular or semilunar valve typically exists in conjunction with the valve abnormality. For example, a common form of single-ventricle CHD affecting the right side of the heart is tricuspid atresia, wherein a hypoplastic or imperforate tricuspid valve is associated with underdevelopment of the right ventricle and right ventricular outflow tract. Pulmonary blood flow is provided by antegrade flow from the left ventricle (via a ventricular septal defect) or, in the absence of a ventricular septal defect, via the ductus arteriosus. In either situation, admixture of systemic and pulmonary venous return occurs via obligatory right-to-left shunting at the atrial level. The prototypic form of single ventricle affecting the left side of the heart is hypoplastic left heart syndrome (HLHS).2 In HLHS, atresia or hypoplasia of the mitral valve and/or aortic valves is associated with atresia or hypoplasia of the entire ensemble of left heart structures. Systemic output is provided by the right ventricle and ductus arteriosus, with admixture of systemic and pulmonary venous return occurring via left-to-right shunting at the atrial level. From an anatomic standpoint, it is important to recognize that abnormalities of the systemic and pulmonary veins with respect to their number, size, and site of drainage are frequently associated with single-ventricle CHD and that these additional defects can increase the complexity of surgical approaches and affect outcomes.3,4,
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It should be noted that “true” single ventricle (ie, the situation in which there is only 1 ventricle) is quite rare.5 In most cases of single-ventricle CHD, there is a dominant ventricle of either left or right ventricular morphology, and the secondary ventricle is typically hypoplastic or rudimentary. Due to the relative rarity ...