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Hypoplastic Left Heart Syndrome

© Kristine Raymond

This week's article will focus on a particularly devastating form of congential heart disease called hypoplastic left heart syndrome (HLHS), a cardiac anomaly that is unconditionally fatal by the sixth week of life if it is left untreated. Before the advent of the first heart successful heart transplant in 1967, parents whose babies received this grim diagnosis had to face the inevitable death-sentence it implied. Their only recourse was to provide a comfortable level of care for the short duration of their child's life. Short of a miracle, this diagnosis was metaphorically and literally lethal.

Today, the outlook for such patients has never been brighter. Although some families opt to forgo surgical intervention or transplant because the long-term outlook remains highly uncertain, the medical advances that are being continuously refined in this field are helping to ensure that no parent ever has to experience the heart-wrenching grief that accompanies a diagnosis that leaves no room for hope. In this article, I will provide an explanation of this condition, and an overview of the surgical options that are now available to treat HLHS.

Hypoplastic left heart syndrome is a congenital defect that occurs when the left side of the heart (responsible for pumping blood throughout the the body) fails to develop normally in-utero. This is the thirteenth most common form of congenital heart disease, occurring in 0.05-0.25 out of every 1000 live births. A baby's heart begins to develop at about the third week of pregnancy and starts to beat on the 22nd day. This organ is said to have reached "maturity" at 8 weeks gestation, corresponding to the beginning of the fetal stage. For a fascinating, detailed look at cardiac embryology, please visit http://www.meddean.luc.edu/lumen/MedEd/G...

The left ventricle receives oxygenated blood from the left atrium, and is responsible for pumping oxygen-rich blood throughout the entire body. As such, it is a very powerful pumping mechanism. In HLHS, the left ventricle is very small (hypoplastic), and therefore unable pump with sufficient power to meet the circulatory demands of this task. In addition, the mitral and aortic valves are tiny; in some cases, they are altogether absent. The first part of the aorta itself (ascending aorta) is also underdeveloped and functionally insufficient. This prevents blood coming back from the pulmonary veins to be distributed throughout the body. The only source of oxygen for the neonate with HLHS is the patent ductus arteriosis, a passage that allows oxygenated blood to be distrubuted throughout the body, albeit insufficiently. This ductus closes shortly after birth without medication to keep it open. This will be discussed shortly. Pictures are always worth a thousand words. Here is a view of a normal heart contrasted with a diagram of HLHS.

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