Hypoplastic left heart syndrome

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S.[2], Cafer Zorkun, M.D., Ph.D. [3], Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S.[5]

Hypoplasia can affect the heart, which typically results in the failure of either the right ventricle or the left ventricle to develop adequately, leaving only one side of the heart capable of pumping blood to the body and lungs. Hypoplasia of the heart is rare but is the most serious form of congenital heart defect; it is called hypoplastic left heart syndrome when it affects the left side of the heart and hypoplastic right heart syndrome when it affects the right side of the heart. In both conditions, the presence of a patent ductus arteriosus (and, when hypoplasia affects the right side of the heart, a patent foramen ovale) is vital to the infant’s ability to survive until emergency heart surgery can be performed, since without these pathways blood cannot circulate to the body (or lungs, depending on which side of the heart is defective). Hypoplasia of the heart is generally a cyanotic heart defect.

Hypoplastic left heart syndrome is a rare congenital heart defect in which the left side of the heart is severely underdeveloped. In babies with HLHS, the aorta and left ventricle are very small, and the aortic and mitral valves are either too small to allow sufficient blood flow or are atretic (closed) altogether. As blood returns from the lungs to the left atrium, it must pass through an atrial septal defect to the right side of the heart. ^{[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]}

In patients with hypoplastic left heart syndrome, the left side of the heart is unable to send enough blood to the body. As a result, the right side of the heart must maintain the circulation for both the lungs and the body. The right ventricle can support the circulation to both the lungs and the body for a while, but this extra workload eventually causes the right side of the heart to fail.

As with most congenital heart defects, there is no known cause. Approximately 10% of patients with hypoplastic left heart syndrome also have other birth defects.

Signs and symptoms of hypoplastic left heart syndrome may be similar to other conditions. A differential diagnosis is essential to definitively diagnose hypoplastic left heart syndrome from associated conditions.

Hypoplastic left heart is more common in males than in females.

Failure to treat hypoplastic left heart syndrome can be fatal for the infant. However, with treatment, infants have a good chance at survival well into late adulthood. Potential complications may develop such as heart failure, arrhythmias, and even neurological complications.

At first, a newborn with hypoplastic left heart may appear normal. Symptoms usually occur in the first few hours of life, although it may take up to a few days to develop symptoms. Common symptoms include cyanosis, dyspnea, and poor circulation.

A physical examination is an integral part of diagnosing hypoplastic left heart syndrome. During a routine visit, a doctor may find signs of right ventricle enlargement, presence of additional birth defects, and hemodynamic imbalances.

Laboratory studies that should be ordered include a complete blood count, and an arterial blood gas.

An electrocardiogram should be ordered if hypoplastic left heart syndrome is suspected. Findings that may be depicted are right axis deviation, right ventricular hypertrophy, and prominent p waves.

Findings on chest x ray include increased markings of pulmonary vasculature, and cardiomegaly.

The echocardiogram is of high diagnostic value in the assessment of hypoplastic left heart syndrome. Doppler echocardiography will also help in visualizing the flow in the ventricles.

Failure to treat hypoplastic left heart syndrome can be fatal for the infant. Medical therapy can be used prior to surgical intervention to allow the ductus to open and promote bloodflow. It is only a temporary solution, surgical intervention is needed to ultimately repair hypoplastic left heart syndrome.

Failure to treat hypoplastic left heart syndrome can be fatal for the infant. Surgical therapy is the only true way to treat and permanently fix hypoplastic left heart syndrome. Two main methods exist for treatment: transplantation and a three-stage surgical procedure.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S.[2], Cafer Zorkun, M.D., Ph.D. [3], Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S.[5]

In patients with hypoplastic left heart syndrome, the left side of the heart is unable to send enough blood to the body. As a result, the right side of the heart must maintain the circulation for both the lungs and the body. The right ventricle can support the circulation to both the lungs and the body for a while, but this extra workload eventually causes the right side of the heart to fail.

The only possibility of survival is a connection between the right and the left side of the heart, or between the arteries and pulmonary arteries (the blood vessels that carry blood to the lungs).In babies with HLHS, the aorta and left ventricle are very small, and the aortic and mitral valves are either too small to allow sufficient blood flow or are atretic (closed) altogether. As blood returns from the lungs to the left atrium, it must pass through an atrial septal defect to the right side of the heart. In a healthy human, the left side of the heart receives oxygen-rich blood from the lungs and pumps it out to the rest of the body; with these structures underdeveloped, they cannot circulate blood to other organs, and the right ventricle must pump blood to both the lungs, as it would normally, and to the rest of the body, a situation which cannot be sustained for long.

In cases of HLHS, the right side of the heart often must pump blood to the body through a patent ductus arteriosus. As the ductus arteriosus usually closes within eleven days after birth, blood flow is severely restricted and eventually cut off, leading to dangerously low circulation and eventually to shock.

HLHS appears to be genetically sporadic and multiple loci have been implicated.

Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology

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  Hypoplastic left ventricle
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  Hypoplastic left ventricle

• HLHS is seen in patients Turner syndrome, Trisomy 18, Trisomy 13 and Jacobsen syndrome
• Anomalous pulmonary venous connection
• Coarctation of the aorta
• Complete atrioventricular canal
• Coronary artery abnormalities (especially in patients with aortic atresia and mitral stenosis)
• Persistent left superior vena cava
• Endocardial fibroelastosis (especially in patients with aortic atresia and mitral stenosis)

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