Oxygenated blood from the left heart (left atrium or left ventricle) or the aorta shunts to the right heart (right atrium or right ventricle) or the pulmonary artery through an opening or communication between the 2 sides. Immediately after birth, pulmonary vascular resistance is high and flow through this communication may be minimal or bidirectional. Within the first 24 to 48 h of life, however, the pulmonary vascular resistance progressively falls, at which point blood will increasingly flow from left to right. The additional blood flow to the right side increases pulmonary blood flow and pulmonary artery pressure to a varying degree. The greater the increase, the more severe the symptoms; a small left-to-right shunt typically does not cause symptoms or signs.

High-pressure shunts (those at the ventricular or great artery level) become apparent several days to a few weeks after birth; low-pressure shunts (atrial septal defects) become apparent considerably later. If untreated, elevated pulmonary blood flow and pulmonary artery pressure may lead to pulmonary vascular disease and eventually Eisenmenger syndrome. Large left-to-right shunts (eg, large ventricular septal defect [VSD], patent ductus arteriosus [PDA]) cause excess pulmonary blood flow and volume overload, which may lead to signs of HF and during infancy often result in failure to thrive. A large left-to-right shunt also decreases lung compliance, leading to frequent lower respiratory tract infections.

Blood flow is obstructed, causing a pressure gradient across the obstruction. The resulting pressure overload proximal to the obstruction may cause ventricular hypertrophy and HF. The most obvious manifestation is a heart murmur, which results from turbulent flow through the obstructed (stenotic) point. Examples are congenital aortic stenosis, which accounts for 3 to 6% of congenital heart anomalies, and congenital pulmonic stenosis, which accounts for 8 to 12%.

Varying amounts of deoxygenated venous blood are shunted to the left heart (right-to-left shunt), reducing systemic arterial oxygen saturation. If there is > 5 g/dL of deoxygenated Hb, cyanosis results. Detection of cyanosis may be delayed in infants with dark pigmentation. Complications of persistent cyanosis include polycythemia, clubbing, thromboembolism (including stroke), bleeding disorders, brain abscess, and hyperuricemia. Hypercyanotic spells can occur in infants with unrepaired tetralogy of Fallot.

Depending on the anomaly, pulmonary blood flow may be reduced, normal, or increased (often resulting in heart failure in addition to cyanosis), resulting in cyanosis of variable severity. Heart murmurs are variably audible and are not specific.

Some congenital heart anomalies (eg, bicuspid aortic valve, mild aortic stenosis) do not significantly alter hemodynamics. Other anomalies cause pressure or volume overload, sometimes causing heart failure (HF). HF occurs when cardiac output is insufficient to meet the body’s metabolic needs or when the heart cannot adequately handle venous return, causing pulmonary congestion (in left ventricular failure), edema primarily in dependent tissues and abdominal viscera (in right ventricular failure), or both. HF in infants and children has many causes other than congenital heart anomalies (see Table: Common Causes of Heart Failure in Children).

Most left-to-right shunts and obstructive lesions cause systolic murmurs. Systolic murmurs and thrills are most prominent at the surface closest to their point of origin, making location diagnostically helpful. Increased flow across the pulmonary or aortic valve causes a midsystolic crescendo-decrescendo (ejection systolic) murmur. Regurgitant flow through an atrioventricular valve or flow across a VSD causes a holosystolic (pansystolic) murmur, often obscuring heart sounds as its intensity increases.

Patent ductus arteriosus typically causes a continuous murmur that is uninterrupted by the S₂ because blood flows through the ductus during systole and diastole. This murmur is 2-toned, having a different sound during systole (when driven by higher pressure) than during diastole.

Central cyanosis is characterized by bluish discoloration of the lips and tongue and/or nail beds; it implies a low blood oxygen level (usually oxygen saturation < 90%). Perioral cyanosis and acrocyanosis (cyanosis of the hands and feet) without lip or nail bed cyanosis is caused by peripheral vasoconstriction rather than hypoxemia and is a common, normal finding in neonates. Older children with longstanding cyanosis often develop clubbing of the nail beds.

In infants, symptoms or signs of heart failure include

Dyspnea with feeding causes inadequate intake and poor growth, which may be worsened by increased metabolic demands in HF and frequent respiratory tract infections. In contrast to adults and older children, most infants do not have distended neck veins and dependent edema; however, they occasionally have edema in the periorbital area. Findings in older children with HF are similar to those in adults.

In neonates, circulatory shock may be the first manifestation of certain anomalies (eg, hypoplastic left heart syndrome, critical aortic stenosis, interrupted aortic arch, coarctation of the aorta). Neonates appear extremely ill and have cold extremities, diminished pulses, low BP, and reduced response to stimuli.

Chest pain in children is usually noncardiac. In infants, chest pain may be manifested by unexplained marked irritability, particularly during or after feeding, and can be caused by anomalous origin of the left coronary artery from the pulmonary artery. In older children and adolescents, chest pain due to a cardiac etiology is usually associated with exertion and may be caused by a coronary anomaly, myocarditis, or severe aortic stenosis.

Syncope, typically without warning symptoms and often in association with exertion, may occur with certain anomalies including cardiomyopathy, anomalous origin of a coronary artery, or inherited arrhythmia syndromes (eg, long QT syndrome, Brugada syndrome). High school–age athletes are most commonly affected.

Manifestations of congenital heart disease may be subtle or absent in neonates, and failure or delay in detecting CHD, particularly in the 10 to 15% of neonates who require surgical or inpatient medical treatment in the first month of life (termed critical congenital heart disease [CCHD]), may lead to neonatal mortality or significant morbidity. Thus, universal screening for CCHD using pulse oximetry is recommended for all neonates before hospital discharge. The screening is done when infants are ≥ 24 h old and is considered positive if ≥ 1 of the following is present:

All neonates with a positive screen should undergo a comprehensive evaluation for CHD and other causes of hypoxemia (eg, various respiratory disorders, CNS depression, sepsis) typically including a chest x-ray, ECG, echocardiography, and often blood testing. Sensitivity of pulse oximetry screening is slightly > 75%; the CHD lesions most often missed are left heart obstructive lesions (eg, coarctation of the aorta).

Acute, severe heart failure or cyanosis in the first week of life is a medical emergency. Secure vascular access should be established, preferably via an umbilical venous catheter.

When critical congenital heart disease is suspected or confirmed, an IV infusion of prostaglandin E₁ should be started at an initial dose of 0.01 mcg/kg/min. Occasional infants will require higher doses, such as 0.05 to 0.1 mcg/kg/min, to reopen or maintain patency of the ductus arteriosus. Keeping the ductus open is important because most cardiac lesions manifesting at this age are ductal-dependent for either systemic blood flow (eg, hypoplastic left heart syndrome, critical aortic stenosis, coarctation of the aorta) or pulmonary blood flow (cyanotic lesions such as pulmonary atresia or severe tetralogy of Fallot).

Mechanical ventilation is often necessary in critically ill neonates. Supplemental oxygen should be given judiciously or even withheld because oxygen can decrease pulmonary vascular resistance, which is harmful to infants with certain defects (eg, hypoplastic left heart syndrome).

Other therapies for neonatal HF include diuretics, inotropic drugs, and drugs to reduce afterload. The diuretic furosemide is given as an initial bolus of 1 mg/kg IV and titrated based on urine output. Infusions of the inotropes dopamine or dobutamine can support BP but have the disadvantage of increasing heart rate and afterload, thus increasing myocardial oxygen consumption. Milrinone, frequently used in postoperative patients with congenital heart disease, is both a positive inotrope and a vasodilator. Dopamine, dobutamine, and milrinone all have the potential to increase the risk of arrhythmias. Nitroprusside, a pure vasodilator, is often used for postoperative hypertension. It is started at 0.3 to 0.5 mcg/kg/min and titrated to desired effect (usual maintenance dose is about 3 mcg/kg/min).

Therapies often include a diuretic (eg, furosemide 0.5 to 1.0 mg/kg IV or 1 to 3 mg/kg po q 8 to 24 h, titrated upward as needed) and an ACE inhibitor (eg, captopril 0.1 to 0.3 mg/kg po tid). A potassium-sparing diuretic (eg, spironolactone 1 mg/kg po once/day or bid, titrated up to 2 mg/kg/dose if needed) may be useful, particularly if high-dose furosemide is required. Beta-blockers (eg, carvedilol, metoprolol) are often added for children with chronic congestive HF. Digoxin is used less often than in the past but may still have a role in children with heart failure who have large left-to-right shunts, in certain postoperative patients with congenital heart disease, and in some infants with supraventricular tachycardia (dose varies by age; see Table: Oral Digoxin Dosage in Children*).

Supplemental oxygen may lessen hypoxemia and alleviate respiratory distress in heart failure; when possible, fractional inspired oxygen (Fio₂) should be kept < 40% to minimize the risk of pulmonary epithelial damage. Supplemental oxygen must be used with caution, if at all, in patients with left-to-right shunt lesions or left heart obstructive disease because it may exacerbate pulmonary overcirculation.

In general, a healthy diet, including salt restriction, is recommended, although dietary modifications may be needed depending on the specific disorder and manifestations. HF increases metabolic demands and the associated dyspnea makes feeding more difficult. In infants with critical congenital heart disease, particularly those with left heart obstructive lesions, feedings may be withheld to minimize the risk of necrotizing enterocolitis. In infants with HF due to left-to-right-shunt lesions, enhanced caloric content feedings are recommended; these feedings increase calories supplied and do so with less risk of volume overload. Some children require tube feedings to maintain growth. If these measures do not result in weight gain, surgical repair of the anomaly is indicated.

Current guidelines of the American Heart Association for prevention of endocarditis state that antibiotic prophylaxis is required for children with CHD who have the following: