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INTRODUCTION

In clinical practice, the term single ventricle has become a functional categorization, applied to all congenital heart 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.

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

  • 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 2 ventricular chambers)

  • Tricuspid atresia

  • Hypoplastic tricuspid valve and right ventricle, frequently with intact ventricular septum and pulmonary atresia

  • Mitral atresia

  • Hypoplastic left heart syndrome and its variants (Fig. 492-1)

Figure 492-1

The anatomic features of hypoplastic left heart syndrome. In this case, there is mitral atresia (arrow), a diminutive left ventricle, and a small ascending aorta, fed by a patent ductus (*) from the main pulmonary artery (MP). The pulmonary venous return enters the left atrium (LA) and, through the interatrial communication, flows to the right atrium (RA) and right ventricle (RV) Reproduced with permission from Chang AC, Hanley FL, Wernovsky G, et al: Pediatric Cardiac Intensive Care. Baltimore: William & Wilkins;1998.

In addition, single-ventricle physiology also exists in patients with complex intracardiac anatomy such that surgical septation of the ventricles cannot be performed, so that 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 AV 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, the 2 ventricles function together as the systemic ventricle.

Within the group of patients with heterotaxy (variable and often discordant situs of the viscera and cardiac segments), single-ventricle variants are frequent, especially in the asplenia group (right atrial isomerism), in which a common AV valve drains into a main ventricle, with hypoplasia of a secondary ventricle. D-malposition of the aorta, severe stenosis or atresia of the pulmonary outflow tract, and anomalous pulmonary venous connections are frequent associated findings.

PATHOLOGY

The comprehensive diagnosis in these complex patients is optimally described using the segmental approach, first considering the atrial arrangement, ...

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