Diseases that encompass congenital malformations and their respective physiologic disturbances affect nearly 1 in 3,000 or 0.1 to 2 percent of all live births. Genetics and environmental factors contribute to the significant worldwide incidence of these defects. Some of the environmental factors investigated include intrauterine environment, cardiotoxic medications or substances consumed by the pregnant mother, maternal age, and birth order. Low birth weight, folate deficiency, and maternal infection such as rubella are contributory, if not causative, of congenital heart disease in developing nations.
Congenital heart diseases caused by malformation can be classified into three discrete groups. Defects causing impaired oxygen transfer from the lungs to the heart, or hypoxemia, include transposition of the great arteries (TGA), tetralogy of Fallot (TF), hypoplastic right-heart syndrome, and critical pulmonary stenosis. Second, those malformations impairing the flow or perfusion of oxygenated blood to the systemic circulation include hypoplastic left-heart syndrome, and coarctation of the aorta (COA). The third classification includes both impaired oxygenation and flow of oxygenated blood. These malformations are shunts that divert blood intended for either the pulmonic or systemic circulation, and include patent ductus arteriosus (PDA) and ventricular septal defects (VSD). There are many more malformations such as atrial septal defects (ASD), valvular defects, or single chambers. However, only those occurring with greatest global incidence will be discussed in greater detail.
Transposition of the great arteries is a malformation characterized by anomalous emergence of the aorta from the morphologic right ventricle and the pulmonary artery from the morphologic left ventricle. Oxygen-depleted blood returning from the body enters the superior and inferior vena cavae from the upper and lower extremities, respectively. The deoxygenated blood then enters the right atrium (RA), passes through the tricuspid valve, into the right ventricle (RV). From here, the already oxygen-depleted blood reenters the systemic circulation via the aberrant connection of the aorta to the RV, possibly causing a life-threatening hypoxemia. Likewise, oxygenated blood from the lungs enters the pulmonic vein and passes into the left atrium (LA). The oxygen-rich blood then passes into the left ventricle (LV) via the mitral valve, and due to the aberrant emergence of the pulmonary artery from the LV, further contributes to the patient’s hypoxic state.
The only way a neonate might survive with a TGA is by way of an additional malformation that aids in mixing the oxygen-depleted blood with oxygen-rich blood. Among these are ASDs, VSDs, but most importantly, a PDA. In patients with only an ASD, adequate mixing of the blood may not occur due to low atrial pressures; therefore, a PDA may be necessary for further mixing to occur. Because PDAs close completely only after a few days, the clinical presentation of a cyanotic infant may be delayed. However, if a TGA patient is born with a VSD, depending on the size of the defect, extreme cyanosis may not occur until weeks later due to adequate shunting of oxygen-rich blood from the left heart with oxygen-depleted blood in the right heart. This is known as the Taussig-Bing complex.
Survival of a neonate with TGA is contingent upon early surgical intervention. However, medical management is required immediately and prior to surgery. This includes maintaining patency of the ductus arteriosus (DA) with prostaglandins, namely PGE-1. Treated surgically, oxygen-depleted blood from the body is redirected to the mitral valve to flow into the pulmonary circuit and oxygen-rich blood is redirected from the lungs to the tricuspid valve to flow into the systemic circulation via the aorta, known as an atrial baffle repair. This type of surgical correction is only successful with a simultaneous arterial switch repair. This operation accounts for the perfusion of the coronary arteries with oxygen-rich blood, and thus the viability of the heart parenchyma.
Further problems in management of TGA patients include congestive heart failure, especially in those with a large VSD. Tetralogy of Fallot affects nearly 6 percent of all patients with congenital heart disease. It has been shown that patients affected by TF are more likely to be afflicted with various extracardiac defects including vertebral, tracheal, esophageal, renal, genital, and ear aberrancies. Commonly characterized by four specific cardiac anatomic abnormalities, a child born with TF may present with little to no cyanosis, a subtle murmur, or more urgently, marked cyanosis. The four anomalies include pulmonic outflow tract obstruction, also known as stenosis or narrowing of the area leading up to the pulmonic valve, with resultant hypertrophy of the RV, an interventricular septal defect, and last, an aorta that overrides the VSD allowing for easy communication of blood from the RV to the aorta.
Because of increased left heart pressure in comparison to the right heart, blood moves from the LV through the VSD into the RV. Because the aorta sits over the VSD, both oxygen-rich blood from the LV and mixed-oxygenated blood from the RV can enter it. Thus, patients can survive with these defects and present with only mild cyanosis, if at all detectable. However, during physical activity, increased return to the right heart may reverse the flow of blood through the VSD, from the right heart to the left heart, also known as a right-to-left shunt. In these instances, patients become markedly cyanotic and must rest or assume a knee-to-chest position to ensure adequate delivery of oxygenated blood to the brain and body.
In contrast to cyanosis associated with exertion, some patients may experience “tetralogy spells,” which are periods of hypoxemia of unknown cause. The spells typically last 15 to 30 minutes and have been associated with near-total occlusion of the RV outflow tract (RVOT) and are speculated to be elicited by fright, activity, or injury. As the cyanosis worsens, the patient begins to take shorter, deeper breaths to compensate for the concomitant acid-base changes in the blood.
TF can be medically or surgically managed. Medical management of a tetralogy spell entails placement of the child in a knee-to-chest position, which increases blood flow to the lungs and decreases blood flow to the extremities for optimal oxygenation. If a spell occurs within a hospital, intravenous morphine and fluids are given to aid in RV filling. Beta-blockers, which are medications that slow the heart rate, can also be given to relax the RVOT. Associated cardiac and extracardiac abnormalities should also be attended to accordingly, and careful prevention of systemic infection, blood clots, and anemia is advised.
Surgical treatment entails either complete repair of all four anomalies or “palliative” anastomoses between the pulmonary and systemic circulatory systems are created to help mix the blood adequately. In a total repair, the VSD is patched, and the area of stenosis in the pulmonary infundibulum is broadened. If a patient is not a candidate for total correction, the Blalock-Taussig procedure has proven to be effective as well. In this procedure, a piece of GOR-TEX® tubing is used to connect the aorta and pulmonary artery, creating a shunt that aids in mixing oxygenated with deoxygenated blood.
The prevalence of hypoplastic left heart syndrome is 1.4 to 3.8 percent of infants born with cardiac malformation. This syndrome consists of an underdevelopment of left heart anatomical structures, including the LA, mitral valve (leading to severe mitral stenosis), LV, aortic valve (resulting in aortic atresia), and the aorta itself. Treatment of this syndrome entails maintaining the patency of the DA, followed by early palliative surgical intervention.
Coarctation of the aorta makes up 6 to 8 percent of all congenital heart defects and, thus, is one of the most common malformations of all congenital heart defects. There is a 2–5:1 ratio of male to female occurrences. With no familial risk of COA recurrence in subsequent children per se, there is an increased risk of left ventricular outflow tract obstructions in families with a member who has COA. This defect occurs in high incidence with bicuspid aortic valve in which the aortic valve has only two leaflets instead of three. It is also a well-known characteristic of the chromosomal disorder Turner’s syndrome or 45 XO.
The malformation is characterized by a stricture in the aorta. Most typically, the stricture occurs at the junction of the aortic arch with the descending aorta, either before, immediately opposite, or slightly after the intersection of the DA or the left subclavian artery with the aorta, but can occur anywhere along the aorta’s path.
Clinical presentations of this malformation include a rise in blood pressure above the narrowing and a decrease in blood pressure below the narrowing, leading to hypertension, or high blood pressure, in the upper extremities, and hypotension in the lower extremities. However, if the DA is maintained, neonatal COA patients may remain asymptomatic. An important diagnostic finding in infants is a delayed or reduced femoral pulse, when compared to the brachial pulse. Standard studies for infants suspected of COA include electrocardiogram, and a chest X-ray, which may show cardiac enlargement and pulmonary edema with pulmonary venous congestion, all of which are associated with backflow of blood from the constricted aorta into the left heart. Last, a two-dimensional echocardiogram will reveal the site of coarctation and the extent of narrowing.
Initial management upon discovery of the COA should include maintaining patency of the DA or reopening it with a prostaglandin, namely intravenous PGE-1. Anticongestive medications should be used to prevent fluid leakage into the lung space. Examples include short-acting inotropic agents such as dobutamine or dopamine, diuretics to encourage urine output, and last, oxygen. If a patient is not a candidate for surgical intervention, a balloon angioplasty can be used to temporarily widen the stricture. There are various surgical procedures that help COA patients, namely resection of the narrowed area, and anastomosing or reconnecting the two free ends of the aorta. Second, a patch aortoplasty works when the aorta opened longitudinally at the coarctation site and a synthetic patch is used to support the previously strictured area. These surgical interventions should be considered urgent when the infant develops congestive heart failure early in life. In young patients with high upper extremity blood pressure, renal function should be assessed because lack of blood flow to the kidneys can initiate a cascade of blood pressure–enhancing mechanisms, particularly the renin-angiotensin pathway, exacerbating the heart disease.
A PDA is an abnormally open DA communicating blood from the aorta directly into the pulmonary arteries. Its etiology is suspected to be genetic but is not completely understood. There is a strong familial risk for siblings of patients with PDAs as it occurs with a 2 to 4 percent increased frequency in affected families. Its incidence has markedly risen to .02 to .04 percent among term infants in the past two decades because of decreased infant mortality. It is often detected in premature infants, those born at high altitudes, and those born to mothers infected with rubella during pregnancy. There is a significant association between low birth weight infants and PDAs, and thus, these defects may occur in higher frequencies in developing countries. There is also a correlation between those infants suffering from respiratory distress syndrome (usually preterm infants) and PDAs.
Functional closure of the DA normally occurs with the onset of delivery, as the infant takes his or her first breaths of air; complete occlusion of the vessel, however, may take up to one month, especially in preterm infants. A DA that remains patent is thus abnormal as it allows for continued diversion of blood from the systemic circulation to the pulmonary circulation.
Depending on the size of the DA and the gestational age at delivery, a patient’s murmur can be a mild systolic murmur or a machine-like holosystolic murmur. A large or nonrestrictive PDA will present in the term infant as respiratory distress, heart failure, and poor feeding. Bounding pulses as well as palpable precordial impulses felt on the anterior chest are also present. In the preterm patient, apnea, which is periods of no respiration, or any respiratory distress should be medically followed for possible PDA. Although diagnosis can be made from physical exam findings, confirmatory tests include echocardiogram, which can reveal the size of the PDA and the degree of shunting, chest X-ray, which may show darkened lung markings and left atrial and/or ventricular enlargement, and last, an electrocardiogram, which can show ventricular hypertrophy.
Small PDAs can be medically treated by a nonsteroidal antiinflammatory agent, such as indomethacin or ibuprofen. The former is rarely used because it is toxic to the kidneys. These agents block the cox-1 and cox-2 pathways that produce prostaglandins, in turn inducing closure of the vessel. The standard of care for premature infants who are unresponsive to indomethacin or ibuprofen treatment is surgical ligation of the PDA. Coil occlusion is an innovative technique that employs a coil inserted into the PDA. The coil serves as a site for embolization that will ultimately completely occlude the vessel. The amplatzer duct occluder is a cone-shaped device that is inserted into the PDA from the aorta. It is effective for patients with large PDAs, but the risk of embolization to the aorta accompanies it.
Ventricular septal defects are present in 3 to 6 out of 10,000 live births, and comprise 30 to 60 percent of all congenital heart defects, making them the most common type of CHD. They often accompany other cardiac malformations, most notably truncus arteriosus, where one outflow tract exists for both ventricles, and the double-outlet right ventricle or the Taussig-Bing anomaly.
Many types of VSDs exist because of the complex nature of embryological fetal heart formation. A defect in any of the three components of the interventricular septum can result in a shunt upon delivery. The three components are the membranous septum, which lies immediately between the aortic and tricuspid valves; the muscular septum, which comprises the breadth of the interventricular septum; and the conal septum, which lies from between the aortic and pulmonic valves to immediately subjacent to them. Seventy-five percent of VSDs occur in the membranous septum subjacent to the aortic valve and posterior to the tricuspid valve.
As discussed above, the resistance from the pulmonary circuit declines drastically within the first week of life, often more rapidly in preterm infants. Therefore, with the LV pumping against resistance from the entire body, and the RV pumping against the low resistance of the lungs, blood is forced from the LV through the VSD into the RV. While some oxygenated blood is lost through the VSD in this left-to-right shunt, the body can still be adequately perfused depending on the size of the VSD, and if small, the patient may be asymptomatic. If the defect is 6 to 10 millimeters in diameter, it is classified as a large or nonrestrictive VSD. The pressures between both ventricles become normalized, and they functionally become one ventricle.
The Eisenmenger phenomenon occurs when increases in pulmonary blood flow result in increases in pulmonary vascular resistance. To accommodate the increasing blood volume as well as the increased outflow resistance, the RV hypertrophies. As time elapses, the RV may produce pressures that exceed those of the LV and can ultimately reverse the flow of blood through the VSD, creating a right-to-left shunt. At this point, patients present with mild-to-severe cyanosis and palliative surgical treatment is necessary.
Adult Congenital Heart Association (ACHA); American Academy of Pediatrics (AAP); American Heart Association (AHA); Birth Defects; Cardiology; Cleft Lip and Palate; Failure to Thrive; Infant and Toddler Development; Neonatology; Pregnancy and Substance Abuse; Premature Babies; Turner’s Syndrome; World Health Organization (WHO).
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