eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology

Hypoplastic Left Heart Syndrome

Author: P Syamasundar Rao, MD, Professor of Pediatrics and Medicine, University of Texas-Houston Medical School; Director, Division of Pediatric Cardiology, Children's Memorial Hermann Hospital; Professor of Pediatrics, MD Anderson Cancer Center, University of Texas
Coauthor(s): Daniel R Turner, MD, Consulting Staff, Department of Pediatric Cardiology, Detroit Medical Center, Children's Hospital of Michigan, Wayne State University; Thomas J Forbes, MD, Assistant Professor, Department of Pediatrics, Division of Cardiology, Children's Hospital of Michigan, Wayne State University
Contributor Information and Disclosures

Updated: Aug 15, 2006

Introduction

Background

Hypoplastic left heart syndrome (HLHS) describes a spectrum of cardiac abnormalities characterized by marked hypoplasia of the left ventricle and ascending aorta. The aortic and mitral valves are atretic, hypoplastic, or stenotic. The ventricular septum is usually intact. A large patent ductus arteriosus supplies blood to the systemic circulation. Systemic desaturation may be present because of complete mixing of pulmonary and systemic venous blood in the right atrium via an atrial septal defect or patent foramen ovale. Coarctation of the aorta commonly coexists.

Hypoplastic left heart syndrome is a uniformly lethal cardiac abnormality if not surgically corrected. In 1979, Norwood performed the first successful surgical palliation on a neonate. Currently, this approach consists of a series of 3 operations: the Norwood procedure (stage I), the hemi-Fontan or bidirectional Glenn procedure (stage II), and the Fontan procedure (stage III). Orthotopic heart transplantation provides an alternative therapy, with results similar to those of the staged surgical palliation. Currently, the survival rate of infants treated with these surgical approaches is similar to that of infants with other complex forms of congenital heart disease in which a 2-ventricle repair is not possible.

Pathophysiology

The newborn infant with hypoplastic left heart syndrome has a complex cardiovascular physiology. Fully saturated pulmonary venous blood returning to the left atrium cannot flow into the left ventricle because of atresia, hypoplasia, or stenosis of the mitral valve. Therefore, pulmonary venous blood must cross the atrial septum and mix with desaturated systemic venous blood in the right atrium. The right ventricle then must pump this mixed blood to both the pulmonary and the systemic circulations that are connected in parallel, rather than in series, by the ductus arteriosus. Blood exiting the right ventricle may flow (1) to the lungs via the branch pulmonary arteries or (2) to the body via the ductus arteriosus and descending aorta. The amount of blood that flows into each circulation is based on the resistance in each circuit.

Blood flow is inversely proportional to resistance (Ohm law); that is, when resistance in blood vessels decreases, blood flow through these vessels increases. Following birth, pulmonary vascular resistance decreases, which allows a higher percentage of the fixed right ventricular output to go to the lungs instead of the body. Although increased pulmonary blood flow results in higher oxygen saturation, systemic blood flow is decreased. Perfusion becomes poor, and metabolic acidosis and oliguria may develop. Coronary artery and cerebral perfusion also are dependent on systemic blood flow through the ductus arteriosus. Therefore, increased pulmonary blood flow results in decreased flow to the coronary arteries and brain, with a risk of myocardial or cerebral ischemia.

Alternatively, if pulmonary vascular resistance is significantly higher than systemic vascular resistance, systemic blood flow is increased at the expense of pulmonary blood flow. This may result in profound hypoxemia. A careful delicate balance between pulmonary and systemic vascular resistance ensures adequate oxygenation and tissue perfusion.

Most patients with hypoplastic left heart syndrome also demonstrate coarctation of the aorta. This can be significant enough to interfere with retrograde flow to the proximal aorta.

Frequency

United States

Incidence of hypoplastic left heart syndrome is 0.16-0.36 per 1000 live births. Hypoplastic left heart syndrome accounts for 7-9% of all congenital heart disease diagnosed in the first year of life. Before surgical treatment was available, hypoplastic left heart syndrome was responsible for 25% of cardiac deaths in the neonatal period. The rate of occurrence is increased in patients with Turner, Noonan, Smith-Lemli-Opitz, or Holt-Oram syndrome. Certain chromosomal duplications, translocations, and deletions also are associated with hypoplastic left heart syndrome.

International

Frequency is similar to that in the United States.

Mortality/Morbidity

• Without surgery, hypoplastic left heart syndrome is uniformly fatal usually within the first 2 weeks of life. Survival for a longer period occurs rarely and only with persistence of the ductus arteriosus.
• Following the Norwood procedure (stage I), overall success (survival to hospital discharge) is approximately 75%. Success rates are higher (85%) in patients with low preoperative risk and lower (45%) in patients with important risk factors. Some centers have reported stage I survival rates in excess of 90%. This appears to be related, in part, to institutional surgical volume. The overall success following the hemi-Fontan procedure (stage II) approaches 95%. Success after completing the Fontan procedure (stage III) approaches 90%. Orthotopic heart transplantation results in early and long-term success similar to that of staged reconstruction. Among low-risk patients who undergo staged reconstruction or transplantation, actuarial survival at 5 years is approximately 70%.
• Most studies report neurodevelopmental disabilities in a significant number of patients who survive either staged surgical reconstruction or cardiac transplantation.

Sex

Hypoplastic left heart syndrome is more common in males than in females, with a 55-70% male predominance.

Age

Hypoplastic left heart syndrome typically presents within the first 24-48 hours of life. Presentation occurs as soon as the ductus arteriosus constricts, thereby decreasing systemic blood flow, producing shock, and, without intervention, causing death. Infants with pulmonary venous obstruction (absent or restrictive patent foramen ovale) may present sooner. Very rarely, an infant with persistence of high pulmonary vascular resistance and the ductus arteriosus may present later because of balanced pulmonary and systemic blood flow.

Clinical

History

• Although hypoplastic left heart syndrome can easily be detected on fetal echocardiography, many infants are not identified prenatally because routine obstetric ultrasound examination may not concentrate on cardiac anatomy. Pregnancies are typically uncomplicated, and fetal echocardiography is not indicated routinely. The fetus grows and develops normally because the fetal circulation is not altered significantly. Most neonates are born at term and initially appear normal.
• Occasionally, respiratory symptoms and profound systemic cyanosis are apparent at birth (2-5% of cases). In these infants, significant obstruction to pulmonary venous return (a congenitally small or absent patent foramen ovale) is usually present.
• As the ductus arteriosus begins to close normally over the first 24-48 hours of life, symptoms of cyanosis, tachypnea, respiratory distress, pallor, lethargy, metabolic acidosis, and oliguria develop. Without intervention to reopen the ductus arteriosus, death rapidly ensues.

Physical

• Before the initiation of prostaglandin E1 infusion to reestablish patency of the ductus arteriosus, infants exhibit signs of cardiogenic shock, including the following:
  • Hypothermia
  • Tachycardia
  • Respiratory distress
  • Central cyanosis and pallor
  • Poor peripheral perfusion with weak pulses in all extremities and in the neck
  • Hepatomegaly
• After reestablishment of systemic blood flow via the ductus arteriosus, signs of shock resolve, leaving the stable infant with tachycardia, tachypnea, and mild central cyanosis. If a coarctation of the aorta is present, arterial pulses in the legs may be more prominent than those in the arms, particularly the right arm.
• Cardiac examination
  • Palpable right ventricular impulse
  • Normal first heart sound
  • Loud single second heart sound
  • Nonspecific, soft, systolic ejection murmur at the left sternal border (not always present)
  • High-pitched holosystolic murmur at the lower left sternal border, indicating tricuspid regurgitation (not always present)
  • Diastolic flow rumble over the precordium, indicating increased right ventricular diastolic filling (not always present)

Causes

• The exact cause of hypoplastic left heart syndrome is unknown. Most likely, the primary abnormality occurs during aortic and mitral valve development. During cardiac development, adequate flow of blood through a structure is largely responsible for the growth of that structure. With little or no blood flow because of aortic and mitral valve atresia, growth of the left ventricle does not occur.
• Similarly, growth of the ascending aorta does not occur because of lack of left ventricular output. The ascending aorta is perfused in retrograde manner from the ductus arteriosus functioning only as a common coronary artery.
• Premature closure or absence of the foramen ovale represents another theoretical cause of hypoplastic left heart syndrome, as it eliminates fetal blood flow from the inferior vena cava to the left atrium. Fetal pulmonary blood flow is not sufficient for normal development of the left atrium, left ventricle, and ascending aorta.

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