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Hypoplastic left heart syndrome

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Cardiovascular system

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Hypoplastic left heart syndrome

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High Yield Notes
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Hypoplastic left heart syndrome

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USMLE® Step 1 style questions USMLE

1 questions

USMLE® Step 2 style questions USMLE

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Preview

A 4500-g (9.9-lb) male newborn is delivered at term to a gravida 2, para 2, mother. Maternal medical history includes poorly controlled type I diabetes mellitus. Prenatal ultrasound shows that the baby has hypoplastic left heart syndrome (HLHS). Which of the following findings must the patient also have to ensure initial survival?

Transcript

Content Reviewers:

Rishi Desai, MD, MPH

Hypo means “beneath” or “under,” and plasia means “molding” or “formation,” so hypoplastic means “under form” or in this case, “underdeveloped.” Therefore, hypoplastic left heart syndrome means that the left side of the heart doesn’t fully develop.

Hypoplastic left heart syndrome, or HLHS, is a congenital heart defect that affects the left side of the heart; it specifically affects the left ventricle and ascending aorta. Also, the aortic valve and mitral valve might be either too small to allow enough blood to flow through, or they might be absent altogether, which is called atresia. The exact mechanism that causes HLHS isn’t known, but one popular theory is that there might be some other primary congenital heart defect that reduces the blood flow through the LV and outflow tract during fetal development, so that part of the heart does not grow and develop normally. This said, HLHS is also often associated with other congenital heart defects, and in particular, with an atrial septal defect, which is an opening between the left and right atria. In fact, not only do these babies usually have this defect, they essentially need it to survive after birth. This is in addition to a patent ductus arteriosus, or PDA, a blood vessel that connects the aorta to the pulmonary artery, which usually closes within a few days after birth.

Let’s switch to a more simplified version of the heart to see what happens with blood flow. So, right here you have the atrial septal defect connecting the left and right atria, and the ductus arteriosus, which connects the aorta to the pulmonary artery. This is a really underdeveloped left ventricle and a smallish aortic and mitral valve.

Summary
Hypoplastic left heart syndrome is a rare congenital heart defect in which the left heart is severely underdeveloped. It is the most common cause of death from cardiac defects in the first month of life. It occurs due to failure of the left ventricle to develop, with a tiny left ventricular chamber and a left-to-right shunt at the level of the atria. A patent ductus arteriosus is necessary for life. Diagnosis is with echocardiography. Prostaglandin E1 is given till surgical repair (usually the Norwood procedure) can be arranged. 
Sources
  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "Hypoplastic left heart syndrome: from comfort care to long-term survival" Pediatric Research (2016)
  5. "Current Therapy for Hypoplastic Left Heart Syndrome and Related Single Ventricle Lesions" Circulation (2016)
  6. "Opciones quirúrgicas actuales y sus resultados en neonatos con síndrome de corazón izquierdo hipoplásico" Anales de Pediatría (2019)