Structural Heart Disease

A number of classification systems exist to categorize congenital structural heart disease. In this section, we have categorized lesions according to the age at which patients most commonly present with symptoms or require intervention (neonates [birth to 1 month], infants [1 month to 2 years], children [2 to 12 years], adolescents [12 to <16 years], and adults). Within each age group, lesions are described according to the pathophysiology of the defect. Please note that the number and variations of structural heart lesions are vast; thus, the following list is not meant to be exhaustive. We direct readers seeking more extensive knowledge of individual lesions to textbooks of pediatric cardiology.

Types of Structural Heart Disease Lesions

• Simple shunt lesions: These lesions involve defects in the atrial septum, ventricular septum, or both, and other abnormal vascular connections that lead to recirculation of blood (typically to pulmonary circulation). Patients with simple shunt lesions typically present with signs of pulmonary congestion due to increased flow to the pulmonary vasculature.

  • Examples include atrial septal defects, ventricular septal defects, and persistent patent ductus arteriosus.

• Obstructed pulmonary blood flow: These defects cause restriction to pulmonary blood flow. In many cases, these defects also involve a shunt lesion that allows deoxygenated (blue) blood from the systemic venous return to shunt directly to the systemic arterial system, thereby causing hypoxemia.

  • Examples include valvar pulmonary stenosis and tetralogy of Fallot.

• Obstructed systemic blood flow: These defects cause a restriction to systemic blood flow and are associated with signs of systemic hypoperfusion and cardiogenic shock.

  • Examples include coarctation of the aorta and valvar aortic stenosis.

• Complex lesions: These defects involve multiple lesions, often including complex, dynamic shunting between systemic and pulmonary circulations as well as multiple levels of obstruction to either pulmonary or systemic circulation and abnormal connections of systemic and pulmonary veins to the atria, atria to the ventricles, and ventricles to the great arteries. In some cases, these lesions require single-ventricle palliation (discussed below).

  • Examples include hypoplastic left heart syndrome, tricuspid atresia, and unbalanced atrioventricular (AV) septal defects, D-transposition of great arteries

In order to understand the pathophysiology of the various congenital heart defects, it is crucial to understand the cardiac circulation during fetal life and the natural transition to the neonatal circulation, which we describe next.

Neonates

Neonatal Circulation

Our understanding of the fetal circulation with relative distribution of blood flow through the various cardiac chambers and blood vessels stems from the early studies conducted by Rudolph and colleagues on fetal lambs. Later, using ultrasound techniques, similar findings were demonstrated in previable human fetuses. The data obtained from Rudolph’s early experiments form the basis of our understanding of the human fetal circulation; presently, newer technology such as cardiac MRI is in use to try to replicate these results in the human fetus.

The major difference between fetal circulation and postnatal circulation is that the fetus does not use the lungs to oxygenate its blood. Instead, the placenta receives deoxygenated blood from the fetus and returns oxygenated blood from maternal circulation to the fetus via the umbilical vein. Therefore, in the fetus, the systemic venous return from the inferior vena cava contains the oxygenated blood that needs to be delivered to the rest of the body of the fetus. The presence of the ductus venosus and the foramen ovale directs the majority of this oxygenated blood to the left atrium, left ventricle, and thus, the aorta. Another essential connection is the ductus arteriosus, which directs most of the blood from the pulmonary arteries to the descending aorta. . Consequently, only about 10% of the systemic venous return is pumped to the lungs.

After birth, the neonate will need to use its lungs to oxygenate the blood. Both the foramen ovale and ductus arteriosus close shortly after birth, directing the now deoxygenated systemic venous return to the pulmonary arteries to be oxygenated, returned to the left atrium via the pulmonary veins, and delivered to the body.

The distribution of blood flow in the heart and major vessels of the fetal sheep provided data relevant to other mammals, including humans. The following two diagrams show the normal percentages of cardiac output and normal oxygen saturation at different locations in the fetal circulation as determined by studies in fetal sheep.

The distribution of blood flow in the heart and major vessels of the fetal sheep. Abbreviations: RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle Numbers represent the percentage of combined ventricular output in various areas. (Adapted with permission from: Rudolph AM. Congenital Diseases of the Heart. Chicago, Year Book Medical Publishers, 1974.)

Fetal oxygen saturation in different regions of the heart and major vessels of the fetal sheep. Numbers represent oxygen saturations in each area of the heart. Abbreviations: RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle (Adapted with permission from: Rudolph AM. Congenital Diseases of the Heart. Chicago, Year Book Medical Publishers, 1974.)

Ductal-Dependent Heart Defects

Ductal-dependent structural heart disease refers to cardiac malformations in which adequate systemic or pulmonary blood flow is dependent on the flow through the ductus arteriosus. These lesions include:

Obstructed Pulmonary Blood-Flow Lesions:

• critical pulmonary stenosis

  • note that pulmonary stenosis is not always ductal dependent; “critical” pulmonary stenosis refers to severe pulmonary stenosis in which pulmonary blood flow is ductal dependent

• pulmonary atresia with intact ventricular septum

• pulmonary atresia with ventricular septal defect

Obstructed Systemic Blood-Flow Lesions:

• critical aortic stenosis

  • note that aortic stenosis is not always ductal dependent; “critical” aortic stenosis refers to severe aortic stenosis in which systemic blood flow is ductal dependent

• interrupted aortic arch

• critical coarctation of the aorta

  • note that coarctation of the aorta is not always ductal dependent; “critical” coarctation refers to severe narrowing of the aorta such that systemic blood flow is ductal dependent

• hypoplastic left heart syndrome (combination of mitral stenosis/atresia, aortic stenosis/atresia and aortic arch hypoplasia)

Complex Lesions:

• tricuspid atresia with obstruction to pulmonary or systemic blood flow

• double-inlet left ventricle with obstructed systemic blood flow

• unbalanced AV septal defects with obstruction to pulmonary or systemic blood flow

• transposition of the great arteries

Other complex lesions that present with extreme cyanosis but are not ductal dependent include total anomalous pulmonary venous return with obstructed pulmonary veins.

Delayed detection of ductal-dependent lesions: Newborns with structural heart disease that is not identified during fetal life and involves a ductal-dependent lesion will develop symptoms as the ductus arteriosus closes during the first week after birth. The nature of the symptoms that develop depends on the type of lesion (pulmonary or systemic blood flow), but both types of lesions will result in shock and death unless appropriate interventions are instituted promptly.

• Neonates with ductal-dependent pulmonary blood-flow lesions will develop progressive and profound cyanosis. This hypoxia will generally not improve with respiratory support measures such as oxygen or positive pressure ventilation.

• Neonates with ductal-dependent systemic blood-flow lesions will show signs of poor perfusion and cardiogenic shock

Given the risk of delayed detection of ductal-dependent congenital heart disease, many states in the U.S. have implemented newborn screening for congenital heart disease. Neonates with ductal-dependent lesions should be started on an infusion of prostaglandin to maintain ductal patency until they can undergo a surgical or catheter-based intervention to stabilize and ensure adequate pulmonary or systemic blood flow.

Note: Percentages refer to oxygen saturation as measured by pulse oximeter. (Source: Congenital Heart Defects Information for Healthcare Providers. Division of Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention 2018.)

Infants

The majority of cardiac malformations, including some complex lesions, are not ductal dependent. Infants with such lesions will have very few, if any, symptoms in the neonatal period. If the structural defect was not detected in utero, these newborns may be discharged home without any cardiac diagnosis.

Infants with known, non-ductal-dependent structural heart disease may be discharged to home from the nursery without any immediate intervention. They will need to be monitored at home to determine if and when an intervention is needed. Examples of lesions that often become symptomatic or require a surgical intervention during the first year of life include the following (see Cincinnati’s Children’s Heart Encyclopedia for more details about these heart defects and repairs):

Shunt Lesions:

• ventricular septal defects

• balanced atrioventricular septal defects (AVSD)

• symptomatic patent ductus arteriosus

Right Heart Lesions:

• tetralogy of Fallot

• pulmonary stenosis

• tricuspid atresia (with VSD and no pulmonary stenosis)

• Ebstein anomaly

Left Heart Lesions:

• aortic stenosis

• mitral stenosis

Complex Lesions:

• single ventricle with balanced pulmonary and systemic circulations including:

  • double-inlet left ventricle

  • unbalanced atrioventricular septal defects

Other:

• anomalous coronary artery from the left pulmonary artery

• total anomalous pulmonary veins that are unobstructed

• truncus arteriosus

• vascular rings

• Bicuspid aortic valve

Children

Some forms of structural heart disease may be recognized early in life but not cause clinically significant problems until later in life. These types are typically addressed during early childhood and include:

• moderate-to-large secundum atrial septal defects

• asymptomatic patent ductus arteriosus

• noncritical aortic or pulmonary stenosis

• bicuspid aortic valve

Acquired forms of structural heart disease may also develop in early childhood. Classic examples include:

• subaortic membrane

• double-chambered right ventricle from a perimembranous ventricular septal defect

Adolescents and Adults

Occasionally, patients with congenital structural heart disease remain asymptomatic throughout life or only develop symptoms during adulthood.

• Congenitally corrected transposition of the great arteries (CCTGA) is a classic example. The morphologic right and left ventricles are reversed, and the great arteries are transposed. In this rare instance, two wrongs do indeed make a right; the systemic venous return is directed to the pulmonary artery via a left ventricle and fully saturated pulmonary venous return is directed to the aorta via a right ventricle. Although patients with CCTGA rarely develop symptoms as children, the right ventricle is forced to pump to the systemic circulation — a job it was not designed to do. In approximately one-third of patients, the right ventricle will not be able to sustain this function and the patient will go on to develop heart failure.

Patients with repaired and palliated structural heart disease require lifetime follow-up by cardiologists trained in the management of adults with congenital heart disease (see Ambulatory Pediatric Cardiology). Adult congenital cardiologists are trained to recognize and manage these complications. Likewise, as the population of adults with congenital heart disease grows, the need for imaging, interventional, and surgical specialists trained to manage these patients will also grow.