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KEY POINTS
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Key Points

  • Hypoplastic left heart syndrome (HLHS) is a spectrum of disorders involving aortic atresia with or without mitral atresia or stenosis.

  • The condition may be diagnosed as severe ventricular hypoplasia before 20 weeks’ gestation, or it may evolve from aortic stenosis to HLHS during the second half of pregnancy.

  • Prenatal diagnosis of classic HLHS is straightforward as the ventricular disproportion is obvious, leading to prenatal detection rates as high as 85%.

  • Delivery needs to be carefully planned to optimize the availability of pediatric specialists, and will include immediate prostaglandin infusion and referral to cardiothoracic surgeons for initial palliation.

  • Surgical management includes a choice between traditional three-stage Norwood procedure leading ultimately to a single ventricle repair, versus hybrid palliation involving open surgical and interventional catheterization until cardiac transplantation is available.

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CONDITION
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Hypoplastic left heart syndrome (HLHS) represents a spectrum of abnormalities in which there is underdevelopment of the left-sided cardiac structures, such as the left ventricle, the mitral valve, and aortic valve, such that the systemic circulation cannot be adequately supported (Rychik, 2005). Classic HLHS involves both aortic valve atresia, and either atresia or stenosis of the mitral valve (Simpson, 2000).

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The spectrum of malformations can include congenital hypoplasia of the left ventricular wall, atresia of the aortic and/or mitral valves, and coarctation or hypoplasia of the aortic arch. Critical aortic stenosis can evolve into HLHS (see Chapter 50), and unbalanced atrioventricular canal defects (see Chapter 45) in which the left ventricle is quite underdeveloped and can also behave similar to HLHS (Simpson, 2000). Each of the components of HLHS may occur with varying degrees of severity, ranging from aortic stenosis with a small left ventricle to complete aortic and mitral atresia with a slit-like left ventricular remnant. Hypoplastic left ventricle and mitral atresia may also occur without aortic atresia, but such an anomaly is rare (Kiel, 1990). The cause of HLHS is unknown, but it may be due to abnormal intracardiac streaming during weeks 5 to 8 of embryonic life (Harh et al., 1973). HLHS may also evolve during prenatal life from isolated severe aortic stenosis (see Chapter 50), which may result in decreased right-to-left shunting between the atria, and subsequent hypoplasia of the left ventricle (Sharland et al., 1991).

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Postnatally, left-to-right shunting occurs in the newborn, returning oxygenated blood from the pulmonary veins through a patent foramen ovale into the right atrium. The right ventricle provides both pulmonary and systemic circulations, the latter through a patent ductus arteriosus with retrograde flow to the aortic arch and coronary vessels. The mitral valve is hypoplastic; the tricuspid valve is often large and regurgitant. The aortic outflow tract may end blindly below the coronary arteries, and the aortic valve and arch may be hypoplastic. Associated cardiac anomalies are common with HLHS. Other associated cardiac ...

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