Hypoplastic Left Heart Syndrome

Disease Overview

Hypoplastic left heart syndrome is a term used to describe a group of closely related rare heart defects that are present at birth (congenital). The normal heart has four chambers. The two upper chambers, known as atria, are separated from each other by a fibrous partition known as the atrial septum. The two lower chambers are known as ventricles and are separated from each other by the ventricular septum. Valves connect the atria (left and right) to their respective ventricles. The valves allow for blood to be pumped through the chambers. Blood travels from the right ventricle through the pulmonary artery to the lungs where it receives oxygen. The blood returns to the heart through pulmonary veins and enters the left ventricle. The left ventricle sends the now oxygen-filled blood into the main artery of the body (aorta). The aorta sends the blood throughout the body.

Hypoplastic left heart syndrome is characterized by the underdevelopment (hypoplasia) of the chambers on the left side of the heart (i.e., left atrium and ventricle). In addition, the mitral valve, which connects these chambers to each other, is usually abnormally narrow (stenosis) or closed (atresia) and the aortic valve, which connects the heart to the major vessels that lead from the lungs (ascending aorta), may also be narrow or closed. Infants with hypoplastic left heart syndrome also have an abnormally narrow ascending aorta.

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Synonyms

• Aortic and Mitral Atresia with Hypoplasic Left Heart Syndrome
• HLHS

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Signs & Symptoms

The symptoms of hypoplastic left heart syndrome are directly related to the underdevelopment of the left side of the heart and associated structures. In all cases, infants have impaired blood flow from the lungs, through the heart, and on to other parts of the body (systemic circulation). Symptoms may include difficulty breathing (dyspnea), a high-pitched noise while inhaling (rales), and grayish-blue discoloration of the skin (cyanosis) during the first 48 hours of life, which occurs because of low levels of circulating oxygen in the blood. Impaired blood flow characteristic of hypoplastic left heart syndrome results in fluid buildup in the heart, lung and various body tissues (congestive heart failure).

Infants with hypoplastic left heart syndrome may accumulate excessive acids in their blood and other body tissues (metabolic acidosis). Symptoms may include poor feeding habits, frequent vomiting, lethargy, and/or shock. When shock occurs, the symptoms may include abnormally high pulse (tachycardia) and respiration rate, respiratory distress, abnormally enlarged liver (hepatomegaly), cool moist skin, abnormally low blood pressure, and/or paleness. In most cases, if left untreated, life-threatening complications usually occur.

The progression and severity of hypoplastic left heart syndrome depend upon a structure called the ductus arteriosus, which is present in all newborns. The ductus arteriosus is a passageway that allows blood to travel from the right ventricle to the aorta and then throughout the body, bypassing the left side of the heart and the lungs. However, the ductus arteriosus closes shortly after birth forcing blood to travel through the malformed left ventricle resulting in impaired blood flow throughout the body.

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Causes

The exact cause of most cases of hypoplastic left heart syndrome is not known. It occurs for no apparent reason (sporadically) in the majority of cases. Research suggests that the interaction of many genes and other environmental factors (multifactorial inheritance) may be responsible for hypoplastic left heart syndrome. In some cases, autosomal dominant and recessive inheritance has been suggested.

In most cases, the malformations associated with hypoplastic left heart syndrome occur as a result of a developmental failure during early fetal (embryonic) growth. The reason that this occurs is not fully understood. Conditions that limit blood flow from the right to left atrium during fetal development may result in underdevelopment of the left heart. Such conditions may include premature closure of the foramen ovale and fetal heart muscle disease (cardiomyopathy).

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Affected populations

Hypoplastic left heart syndrome is a rare disorder that affects males (67 percent) more often than females. The estimated prevalence of the disorder is 1 in 100,000 live births. Hypoplastic left heart syndrome accounts for 7-9 percent of all congenital heart defects. The symptoms of this disorder are present at birth (congenital).

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Disorders with Similar Symptoms

Symptoms of the following disorders can be similar to those of Hypoplastic Left Heart Syndrome. Comparisons may be useful for a differential diagnosis:

Atrioventricular Septal Defect is a rare heart defect that is present at birth (congenital) and is characterized by the improper development of the septa and valves (atrial and ventricular septa and atrioventricular valves). Infants with the complete form of Atrioventricular Septal Defect usually develop congestive heart failure. Excessive fluid also accumulates in other areas of the body, especially the lungs. Pulmonary congestion may lead to difficulty breathing (dyspnea). Other symptoms may include a bluish discoloration of the skin and mucous membranes (cyanosis), poor feeding, abnormally rapid breathing (tachypnea), excessive sweating, and/or an abnormally rapid heartbeat (tachycardia). (For more information on this disorder, choose “Atrioventricular Septal Defect” as your search term in the Rare Disease Database.)

Atrial Septal Defects are common congenital heart defects characterized by the presence of a small opening between the two atria of the heart. This defect leads to an increase in the workload on the right heart, and excessive blood flow to the lungs. The symptoms, which may become apparent during infancy, childhood, or adulthood, can vary greatly and depend on the severity of the defect. The symptoms tend to be mild at first and may include difficulty breathing (dyspnea), increased susceptibility to respiratory infections, and/or an abnormal bluish discoloration of the skin and mucous membranes (cyanosis). Some people with Atrial Septal Defects may be at increased risk for the formation of blood clots that can travel to the major arteries (embolism), possibly blocking blood circulation. (For more information on this disorder, choose “Atrial Septal Defects” as your search term in the Rare Disease Database.)

Ventricular Septal Defects (Cor Triloculare Biventricularis) are a group of common congenital heart defects characterized by the absence of one atrium. Infants with this defect have 2 ventricles and 1 large atrium. Symptoms of these defects may include an abnormally rapid rate of breathing (tachypnea), wheezing, a rapid heartbeat (tachycardia), and/or an abnormally enlarged liver (hepatomegaly). Ventricular Septal Defects can also cause the excessive accumulation of fluid around the heart leading to congestive heart failure. (For more information on this disorder, choose “Ventricular Septal Defects” as your search term in the Rare Disease Database.)

Cor Triatriatum is an extremely rare congenital heart defect characterized by the presence of an extra chamber above the left atrium of the heart. The pulmonary veins, returning blood from the lungs, drain into this extra “third atrium.” The symptoms of Cor Triatriatum vary greatly and depend on the size of the opening between the chambers. Symptoms may include abnormally rapid breathing (tachypnea), wheezing, coughing, and/or abnormal accumulation of fluid in the lungs (pulmonary congestion). (For more information on this disorder, choose “Cor Triatriatum” as your search term in the Rare Disease Database.)

Cor Triloculare Biatriatum is an extremely rare congenital heart defect characterized by the absence of one ventricle. Infants with this defect have two atria and one large ventricle. The symptoms are similar to those of Hypoplastic Left Heart Syndrome and may include breathing difficulties (dyspnea), excessive accumulation of fluid in the lungs and around the heart (pulmonary edema), and/or a bluish discoloration of the skin and mucous membranes (cyanosis). Other symptoms may include poor feeding habits, abnormally rapid breathing (tachypnea), and/or an abnormally rapid heartbeat (tachycardia).

Mitral Valve Stenosis is a rare heart defect that may be present at birth (congenital) or acquired. In the congenital form, the symptoms vary greatly and may include coughing, difficulty breathing, heart palpitations, and/or frequent respiratory infections. In acquired Mitral Valve Stenosis, the symptoms may also include weakness, abdominal discomfort, chest pain angina), and/or periodic loss of consciousness.

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Diagnosis

The diagnosis of hypoplastic left heart syndrome is made based upon a thorough clinical evaluation, identification of characteristic findings and a variety of specialized tests. Such tests used to confirm hypoplastic left heart syndrome in newborns include x-ray examination and a special ultrasound test to study the structure and function of the heart (echocardiography).

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Standard Therapies

Treatment

Treatment of hypoplastic left heart syndrome is directed toward the maintenance of adequate oxygen levels in the blood. The intravenous administration of prostaglandin E-1 (PGE-1) may help to keep the ductus arteriosus open allowing blood flow to bypass the malformed left side of the heart.

Eventually, infants with hypoplastic left heart syndrome require surgical intervention. In most cases, affected infants undergo a process that involves three separate surgical procedures (i.e., Norwood, hemi-Fontan, and Fontan procedures). The goal of this three-stage process is to separate systemic and pulmonary circulation. In some cases, affected infants have been treated by heart (cardiac) transplantation. A neonatal cardiologist is best qualified to give parents an opinion as to the type of treatment which best suits their child.

Other medications to prevent and control congestive heart failure may also be administered including digoxin and various diuretics. Antibodies, such as amoxicillin, may be used to treat infection of the valves of the heart (endocarditis) that may occur after heart surgery. Genetic counseling may be of benefit for families with a child who has hypoplastic left heart syndrome. Other treatment is symptomatic and supportive.

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Clinical Trials and Studies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010

Email: [email protected]

For information about clinical trials sponsored by private sources, contact:

www.centerwatch.com

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References

TEXTBOOKS

Mulreany M, Donner RM. Hypoplastic Left Heart Syndrome. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:50-1.

Behrman RE, ed. Nelson Textbook of Pediatrics, 15th ed. Philadelphia, PA: W.B. Saunders Company; 1996: 1325-28.

Buyce ML., ed. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications; For: The Center for Birth Defects Information Services Inc; 1990:166-69.

Braunwald E, ed. Heart Disease. A Textbook of Cardiovascular Medicine. 3rd ed. Philadelphia, PA: W. B. Saunders Company; 1988:938-9.

JOURNAL ARTICLES

Norwood Jr. WI, et al. Fontan procedure for hypoplastic left heart syndrome. Ann Thorac Surg. 1992;54:1025-9; Discussion 1029-30.

Farrell Jr. PE, et al. Outcome and assessment after the modified Fontan procedure for hypoplastic left heart syndrome. Circulation. 1992;85:116-22.

Starnes VA, et al. Current approach to hypoplastic left heart syndrome. Palliation, transplantation, or both? J Thorac Cardiovasc Surg. 1992;104:189-94; Discussion 194-95.

Jobes DR, et al. Carbon dioxide prevents pulmonary overcirculation in hypoplastic left heart syndrome. Ann Thorac Surg. 1992;54:150-51.

Jackson GM, et al. Intrapartum course of fetuses with isolated hypoplastic left heart syndrome. Am J Obstet Gynecol. 1991;165:1068-72.

Blake DM, et al. Hypoplastic left heart syndrome: prenatal diagnosis, clinical profile, and management. Am J Obstet Gynecol. 1991;165:529-34.

Bove EL. Transplantation after first-stage reconstruction for hypoplastic left heart syndrome. Ann Thorac Surg. 1991;52:701-4; Discussion 704-07.

Norwood Jr. WI. Hypoplastic left heart syndrome. Ann Thorac Surg. 1991;52:688-95.

Bailey LL, et al. Hypoplastic left heart syndrome. Pediatr Clin North Am. 1990;37:137-50.

Brenner JI, et al. Cardiac malformations in relatives of infants with hypoplastic left-heart syndrome. Am J Dis Child. 1989;143:1492-94.

FROM THE INTERNET

McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Entry No:241550; Last Update:2/19/94.

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