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Functionally single ventricle


Functionally single ventricle is an umbrella term for a group of severe congenital heart defects that are not suitable for the creation of a biventricular circulation and that can only be palliated using a univentricular approach. This is mainly due to the hypoplasia of one of the ventricles and the inability to generate adequate cardiac output, as in hypoplastic left heart syndrome, pulmonary atresia with intact ventricular septum, or unbalanced defect of the atrio-ventricular septum. In other cases, there is a univentricular atrio-ventricular connection, as in atrio-ventricular valve atresia ( mitral or tricuspid atresia ) or in double inlet ventricle. Finally, some patients with large or multiple ventricular septal defects may also require univentricular palliation.

These defects are becoming increasingly rare because of the progress in prenatal screening and account for approximately 5% of the congenital heart defects. Surgical palliation in patients with functionally single ventricle is a multistep process aiming to create a total cavo-pulmonary connection (Fontan circulation). The univentricular pathway is burdened with significant morbidity and mortality due to the number of differences from normal biventricular circulation.

Hypoplastic left heart syndrome

Hypoplastic left heart (HLH) syndrome is a common term for a group of cardiac defects characterized by underdevelopment of the left-sided heart structures. In extreme cases, there is mitral and aortic atresia and the left ventricular cavity is not detectable. At the other end of the spectrum, the mitral and aortic valves are stenotic, and the left ventricle has borderline dimensions, but is unable to sustain the systemic circulation.

It is important to mention that a small but functionally adequate left ventricle may be present in other malformations such as coarctation of the aorta (see Chapter 17 , Figure 10 ). The presence of ventricular imbalance is usually the result of altered fetal hemodynamics caused by changes in preload or afterload and does not determine the intrinsic ventricular hypoplasia. In some patients with a borderline left ventricle, the decision between univentricular or biventricular repair is particularly challenging.

In hypoplastic left heart syndrome, the left ventricle is typically very dysfunctional. Another hallmark of the disease is the presence of endocardial fibroelastosis, which affects the growth and the function of the left ventricle. The aortic arch is always hypoplastic and coarctation of the aorta is often present. There is the retrograde filling of the ascending aorta from the duct due to negligible or no blood flow across the aortic valve and the circulation is thus duct dependant.

Figure 1, Apical four-chamber view in a neonate with hypoplastic left heart syndrome and severe mitral and aortic stenosis. The left ventricle is diminutive, nonapex forming, and dysfunctional. Note the presence of endocardial fibroelastosis ( arrows ). LA , left atrium; LV , left ventricle; RA , right atrium; RV , right ventricle.

Figure 2, Parasternal short-axis view in a patient with hypoplastic left heart syndrome demonstrating a severely reduced mitral valve orifice area ( arrowheads ) and endocardial fibroelastosis ( arrows ). LV , left ventricle; MV , mitral valve; RV , right ventricle.

Figure 3, Apical four-chamber view in a child with severe hypoplasia of the left ventricle. There is detectable flow across the very stenotic mitral valve ( arrow ) on color flow mapping. Note the right atrial and ventricular dilatation. LA , left atrium; LV , left ventricle; RA , right atrium; RV , right ventricle.

Figure 4, (A) Apical four-chamber view in a newborn with hypoplastic left heart syndrome and a very diminutive left ventricle. Note the incomplete coaptation between the anterior and septal leaflets of the tricuspid valve caused by the reduced motion of the fixed septal leaflet. Dotted arrow indicates the tip of the antero-superior tricuspid valve leaflet, plain arrow the tip of the septal tricuspid valve leaflet. (B) As a consequence, there is severe tricuspid regurgitation contributing to the dilatation of the right-sided chambers. LA , left atrium; LV , left ventricle; RA , right atrium; RV , right ventricle.

Figure 5, Apical four-chamber view in a neonate with hypoplastic left heart syndrome and mitral and aortic atresia. The mitral valve is absent and no left ventricular cavity is visible. The right atrium and ventricle are dilated. LA , left atrium; RA , right atrium; RV , right ventricle.

Figure 6, Parasternal long-axis view demonstrating hypoplasia of the left ventricle. The aortic and mitral valves are small and severely stenotic. There is hyperechogenicity of the endocardium consistent with endocardial fibroelastosis ( arrows ). AoV , aortic valve; LA , left atrium; LV , left ventricle; MV , mitral valve; RV , right ventricle.

Figure 7, Modified suprasternal notch view in a neonate with hypoplastic left heart syndrome and mitral and aortic atresia. Arrowheads indicate the very hypoplastic ascending aorta, the size of which is much smaller than the diameter of the right pulmonary artery. LA , left atrium; RA , right atrium; RPA , right pulmonary artery; RV , right ventricle.

Figure 8, Suprasternal notch view in a patient with hypoplastic left heart syndrome and aortic atresia showing a severely hypoplastic ascending aorta ( arrowheads ). Color flow mapping demonstrating retrograde filling of the aortic arch from the duct. BCT , brachiocephalic trunk; LA , left atrium; LCCA , left common carotid artery; LSCA , left subclavian artery; RPA , right pulmonary artery.

Figure 9, (A) High parasternal short-axis view in a newborn with hypoplastic left heart syndrome. Note the severe hypoplasia of the ascending aorta. Due to an infusion of prostaglandins, the arterial duct, which is continuous with the descending aorta, is very large. (B) Corresponding color flow mapping showing a right-to-left shunt across the duct. Retrograde filling of the aortic arch from the duct is not shown in this figure. Ao , aorta; DAo , descending aorta; LA , left atrium; LPA , left pulmonary artery; PA , pulmonary artery; PDA , patent ductus arteriosus; RA , right atrium; RPA , right pulmonary artery.

Figure 10, Patients with hypoplastic left heart syndrome are usually born with a restrictive interatrial communication, as illustrated in this figure. It is thought that intrauterine restriction at the atrial level decreases blood flow to the left side of the heart, thus contributes to its underdevelopment. Subcostal view with color flow mapping showing restrictive left-to-right shunt across a small patent foramen ovale ( arrow ). LA , left atrium; RA , right atrium; RV , right ventricle; TV , tricuspid valve.

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