17.4 Complications of Congenital Heart Defects

Heart Failure

Heart failure occurs when the heart cannot pump enough blood to supply the body with sufficient oxygen-rich blood. Heart failure can be caused by weakening of the heart muscle or lack of proper filling of the ventricles with blood due to stiffening. Congenital heart defects are a common cause of heart failure in infants, such as atrial and ventricular septal defects, abnormal formation of heart chambers or major arteries, or valve stenosis that interrupts normal blood flow through the heart. As a result of these defects, blood backs up in the heart or lungs, resulting in fluid overload. As the heart works harder to pump blood, the heart muscle hypertrophies (enlarges) and then weakens in its ability to pump, causing heart failure.^[1]

Symptoms of heart failure depend on the severity of pump failure and whether it is left- or right-sided heart failure, although in infants the distinction between left- and right-sided heart failure is often difficult to determine on assessment. Right-sided heart failure causes ineffective pumping of blood to the lungs, resulting in a back up of blood to the rest of the body. This commonly manifests as abdominal distension as blood engorges the liver and ascites (fluid) seeps into the abdominal cavity. It may also include edema in the feet and lower legs.

Left-sided heart failure causes ineffective pumping of blood through the aorta to the rest of the body. This causes blood to back up into the lungs, causing pulmonary congestion, fine crackles on lung auscultation, and dyspnea. Because the left side of the heart is not effectively pumping blood to the rest of the body, signs and symptoms of low cardiac output also occur, such as poor feeding and growth (due to the energy required during feeding), excessive sweating (especially during feeding and crying), decreased peripheral pulses, and possibly cyanosis of the hands and feet. Additionally, the infant or child may experience tachycardia and dysrhythmias as the heart rate increases to try to compensate for decreased cardiac output. An extra S3 heart sound known as a gallop may also occur, which indicates fluid volume overload. Severe heart failure presents with pallor, lethargy, bradycardia, apnea, and minimal spontaneous movements, all of which indicate death may be imminent.^[2]

Heart failure is diagnosed through various diagnostic tests, including a chest X-ray and an echocardiogram. An echocardiogram shows how blood is being pumped through the heart, as well as the ejection fraction, or percentage of blood ejected from the left ventricle with each heartbeat. It can also show if there is regurgitation of blood back through a valve or if heart defects are present. A cardiac catheterization may also be performed to determine pressures within the heart and lungs, as well as blood flow and oxygen levels throughout the heart.^[3]

Treatment of heart failure in children includes close monitoring with frequent follow-up visits to prevent acute decompensated heart failure with decreased cardiac output. Medication therapy may include several classes of medications. Loop diuretics, such as furosemide, or thiazide diuretics, such as hydrochlorothiazide, are prescribed for clients with fluid overload. Because heart failure leads to activation of the renin-angiotensin-aldosterone system (RAAS), ACE inhibitors such as enalapril are typically prescribed to reduce afterload and prevent ventricular hypertrophy. An aldosterone antagonist, such as spironolactone, may be added as a potassium-sparing diuretic to reduce fluid overload. Beta-blockers, such as metoprolol or carvedilol, are often prescribed to reduce chronic sympathetic nervous system stimulation of the myocardium. Inotropes such as digoxin may be prescribed to increase cardiac output. Antiarrhythmics may be prescribed to stabilize abnormal or fast heart rhythms. Surgeries may be performed to correct underlying causes, such as valve stenosis, or heart transplantation may be performed for severe, end-stage heart failure.^[4]

Pulmonary Hypertension

Recall that during fetal circulation, pulmonary artery pressures are high because the lungs are collapsed. This elevated pressure facilitates oxygenated blood flow from the placenta through fetal shunts that bypasses the fetal lungs. At birth when the neonate takes its first breaths, pulmonary pressures rapidly decrease as the lungs expand. This pressure change facilitates closure of the fetal shunts and transition to neonatal circulation as blood is transported to the expanded lungs for oxygenation. It takes up to six to eight weeks for pulmonary vascular resistance to decrease to normal pressure.^[5]

However, in approximately 2 out of 1,000 term live births, this decrease in pulmonary artery pressures does not occur, resulting in persistent pulmonary hypertension of the newborn (PPHN). Congenital heart defects, such as a patent foramen ovale and patent ductus arteriosus, can contribute to PPHN. Mortality rates of PPHN are approximately 5-10% with treatment, and about 25% of infants with PPHN develop significant neurodevelopmental impairments due to restricted oxygen delivery.^[6]

Pulmonary hypertension associated with congenital heart disease is not classified as PPHN, but the symptoms and treatment are similar. Pulmonary hypertension (increased pressure in the arteries of the lungs) can develop as a result of certain congenital heart disorders and from heart failure:

• Pulmonary hypertension can be caused by an obstruction limiting blood flow out of the left side of the heart. With left-sided heart obstructions, such as coarctation of the aorta and mitral valve stenosis, blood is not pumped out of the left side of the heart as it should and backs up into the pulmonary vessels, causing increased pressure.
• Congenital heart defects that allow left to right shunting of blood through the heart, such as ventricular septal defects, atrial septal defects, and patent ductus arteriosus, cause excess fluid to enter the pulmonary circulation, resulting in fluid overload and increased pulmonary pressures.
• If left-sided heart failure develops because of congenital defects and the heart cannot effectively pump blood forward, the backward pressure forces blood to back into the lungs, leading to elevated pulmonary artery pressure and ultimately pulmonary hypertension.^[7]

Common symptoms of pulmonary hypertension include dyspnea, tachypnea, fatigue, anemia, syncope, cyanosis, and hypotension. Over time, right-sided heart failure may develop due to blood and associated pressure backing up into the right ventricle. Pulmonary hypertension is diagnosed by echocardiogram that evaluates blood flow through the heart and lungs. Additionally, cardiac catheterization may be performed to determine specific heart and lung pressures.^{[8],[9],[10],[11]}

Treatment depends on severity of the pulmonary hypertension and may include supplemental oxygen administration, pulmonary artery dilators such as inhaled nitrous oxide and oral/intravenous sildenafil, or diuretics to reduce excess fluid volume in the heart and lungs. If pulmonary hypertension worsens, surgery to correct congenital heart defects may be required, and extracorporeal membrane oxygenation (ECMO) may be performed. During ECMO, blood is routed from the body through special intravenous and intra-arterial cannulas, to a machine where it is oxygenated and carbon dioxide is removed, and back to the body, bypassing the lungs. In severe cases of pulmonary hypertension, especially with associated heart failure, heart-lung transplantation may be necessary.^{[12],[13],[14],[15]}