Congenital Heart Defects

Objectives - Differentiate congenital cardiovascular disease from congenital cardiovascular malformation, understand fetal circulation concepts, differentiate cyanotic and acyanotic defects, and identify common congenital heart diseases.

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Core Definitions

Congenital heart disease is an abnormality in cardiocirculatory structure or function that is present at birth, even if it is discovered much later.

Congenital heart malformations usually result from altered embryonic development of a normal structure or failure of a structure to progress beyond an early stage of embryonic or fetal development.

Congenital malformations and congenital diseases are both types of congenital heart defects. They can significantly affect heart function throughout life and may require surgical correction or heart transplant to ensure survival.

Causes and Detection

Congenital heart defects can occur through:

• Genetic disorders or abnormalities at birth, such as trisomy or Down syndrome
• Environmental toxins
• Maternal diabetes
• Alcohol or drug use
• Viral infections during pregnancy

Specific cardiac defects in neonates and infants may be associated with:

• Scalp edema
• Ascites
• Pericardial effusion
• Decreased fetal movements
• Low birth weight

Preterm infants under 1500 g, or about 3 lb, have the highest incidence of patent ductus arteriosus.

Diagnostics

Diagnosing congenital heart defects requires a fetal echocardiogram. Fetal echocardiography is ultrasound of the fetal heart and is described in the source as the new standard of care for mothers with increased risk for fetal cardiac anomalies.

Common diagnostic tools include:

Acyanotic Heart Diseases

Acyanotic defects generally involve left-to-right shunting at first.

ASD and PFO

ASD pathophysiology includes:

• Left-to-right shunt
• Right-sided heart failure
• Supraventricular arrhythmias
• Possible transient right-to-left shunt, which may decrease oxygen saturation, cause dyspnea, and allow blood clots to cause strokes or heart attacks

ASD types include:

• Ostium secundum: most common, in the middle of the atrial septum
• Ostium primum: lower atrial septum and may occur with other congenital heart problems
• Sinus venosus: rare, upper atrial septum, often associated with other congenital heart problems
• Coronary sinus ASD: rare, involving failed development between the coronary sinus and left atrium

PFO has the same pathology as ASD. It is primarily a left-to-right shunt, but a transient right-to-left shunt can cause decreased oxygen saturation and paradoxical embolism, including stroke or heart attacks.

VSD and AV Septal Defect

A VSD allows blood to pass from the left side to the right side of the heart. Oxygenated blood is pumped back to the lungs instead of out to the body, causing the heart to work harder.

Clinical manifestations include:

• Pulmonary hypertension
• Increased right ventricular workload
• Right ventricular hypertrophy
• Cyanosis and clubbing in adults with chronic low PaO2
• Decreased oxygen saturation and pulmonary hypertension in infants

An atrioventricular septal defect can include defects between the atria, defects between the ventricles, and malformation of the mitral and tricuspid valves. Clinical manifestations include decreased oxygen saturation from left-to-right shunting, pulmonary hypertension, right ventricular dilation, and heart failure.

PDA

The ductus arteriosus is part of normal fetal circulation. In utero, right-to-left shunting bypasses the lungs. After birth, the ductus arteriosus normally closes within two or three days.

Closure occurs because of:

• Pressure changes within the heart and lungs
• Pulmonary vascular resistance becoming less than systemic vascular resistance
• Increased oxygen levels in the blood
• Decreased prostaglandin levels

Risk factors for PDA include premature birth, family history of heart defects or genetic conditions such as Down syndrome, infections during pregnancy, and high-altitude births.

Clinical manifestations and pathophysiology include:

Some PDAs are duct dependent and necessary for survivability. PDA or ASD may prevent complete cyanosis in defects such as pulmonary atresia or stenosis, atrioventricular defect, tetralogy of Fallot, coarctation of the aorta, and hypoplastic left heart syndrome.

Treatment or correction may include closure device by cardiac catheterization, coil placement, surgical closure in severe cases, and non-steroidal anti-inflammatory drugs that block prostaglandin effects.

Cyanotic Heart Diseases

Cyanotic defects involve significant right-to-left shunting, mixed circulation, or decreased pulmonary blood flow.

TOF

TOF begins with narrowing of the right ventricular outflow tract into the pulmonary artery. This impedes blood flow to the pulmonary arteries and lungs.

The RVOT obstruction causes right ventricular hypertrophy. The VSD may initially produce a left-to-right shunt, but severe RVOT obstruction can force blood from the right ventricle into the left ventricle, creating a right-to-left shunt and cyanosis. The overriding aorta straddles the VSD and allows mixed blood to be pumped to the body.

Symptoms include:

• Cyanosis from low blood oxygen
• Shortness of breath and rapid breathing during feeding or exercise
• Poor weight gain
• Fatigue during play or exercise
• Irritability and prolonged crying
• Heart murmur
• Fainting
• Digital clubbing from chronic hypoxemia

Diagnosis includes echocardiography and chest x-ray with enlarged right ventricle, described as a "boot sign." Treatment includes prostaglandins and surgical correction, usually during the first year of life.

HLHS

HLHS means all structures on the left side of the heart are severely underdeveloped. It is characterized by:

• Severely underdeveloped left ventricle
• Atresia or stenosis of the aortic or mitral orifices
• Hypoplasia of the aorta
• ASD
• PDA

HLHS has duct-dependent systemic blood flow and severe symptoms during the first week of life. PDA and ASD prevent infant death. Correction includes prostaglandin to prevent PDA closure, staged surgeries, and possible heart transplant.

The source lists staged correction as:

Coarctation of the Aorta

Coarctation is narrowing or constriction in the aorta, most often near the ductus arteriosus. It may occur with other heart defects, bicuspid aortic valves, or genetic disorders.

Diagnosis may include echocardiography, cardiac catheterization, differences between upper and lower body blood pressures, delayed or weak femoral pulses, differences between upper and lower extremity SpO2, heart murmur, and chest x-ray.

Correction may be surgical, balloon dilation, or balloon dilation with stent to help prevent re-coarctation.

Tricuspid Atresia, Truncus Arteriosus, Pulmonary Atresia, and TGA

In tricuspid atresia, the right ventricle usually has hypoplasia and the tricuspid valve is generally absent. Blood circulates through an ASD or VSD. Constant mixing causes cyanosis and low blood oxygen.

In truncus arteriosus, one vessel forms the outlet of both ventricles and gives rise to the systemic, pulmonary, and coronary arteries. It is always accompanied by a VSD. Correction includes a VSD patch, creating a new aorta using the truncus, and placing a shunt and artificial valve to create a new pulmonary artery and valve.

In pulmonary atresia, reduced flow through the pulmonary outflow tract decreases blood flow to the lungs and causes persistent pulmonary artery hypertension. Clinical manifestations include persistent right-to-left shunt, persistent fetal circulation, cyanosis, low saturations, and low PaO2.

In TGA, the aorta and pulmonary artery are transposed. The source describes two closed circuits: blood returning from the body is pumped back to the body, and blood returning from the lungs is pumped back to the lungs. VSD or ASD usually allows some oxygenation. Severity depends on the size of the VSD or ASD and shunting within the heart.

Eisenmenger Syndrome

Eisenmenger syndrome is a group of symptoms caused by congenital heart defects with large septal defects. Persistent left-to-right shunting leads to severe pulmonary arterial hypertension and elevated vascular resistance. Over time, increased pulmonary vascular resistance causes the shunt to become right-to-left, resulting in hypoxemia and cyanosis.

Uncorrected defects can cause:

• Increased right ventricular pressure
• Increased pulmonary artery pressure
• Right-to-left shunt

Possible causes include atrioventricular canal defect, ASD, VSD, and PDA. VSD is listed as the most common cause.

Symptoms include:

• Cyanosis
• Digital clubbing
• Polycythemia
• Arrhythmias
• Fatigue and dyspnea
• Shortness of breath at rest

Treatment includes antiarrhythmics, blood thinners, and drugs to reduce pulmonary hypertension, including bosentan, nitric oxide, and sildenafil.