Congenital Defects of the Cardiovascular System

Cyanotic Heart Defects: Poor Mixing

d-Transposition of the Great Arteries

Anatomy and Pathophysiology

In d-transposition of the great arteries (d-TGA), the aorta arises from the venous, desaturated right ventricle, and the pulmonary artery from the systemic, oxygenated left ventricle. The blood flow in these patients is in parallel with the deoxygenated blood entering the aorta and recirculating to the body while the richly oxygenated pulmonary venous return is recirculated to the lungs. In the absence of any shunting across connections between the systemic and pulmonary circulations, this results in systemic hypoxia and is often lethal. In this disorder, three levels where the mixing can occur are at the level of the patent foramen ovale/atrial septal defect, patent ductus arteriosus (PDA), and a ventricular septal defect when present. The best site of blood mixing has been shown to be at the atrial level through patent foramen ovale (PFO) or atrial septal defect (ASD), with the other forms (patent ductus arteriosus and ventricular septal defect) being less reliable. Thus, at birth, it is extremely important to make sure that not only is there an atrial level communication, but also that it is adequate in size.⁹⁴

Associated Defects

Associated defects have a dramatic effect on the presentation and pathophysiology of newborn infants with d-TGA. At a minimum, an atrial septal defect with balanced bidirectional shunting is essential for survival.⁹⁴ The presence of a patent ductus arteriosus also allows for additional shunting from the aorta (oxygen-depleted blood) to the pulmonary artery (oxygen-rich blood) with an equal volume of left-to-right atrial shunt at the atrial level.

The presence of a ventricular septal defect (VSD) occurs in about 25% of infants with d-TGA. Its presence also results in mixing of the oxygen-rich and desaturated blood, but as previously stated, atrial level mixing is the most reliable. Coarctation of the aorta or aortic arch interruption can also occur in association with d-TGA with ventricular septal defect.⁸³

Transposition of the great arteries is the most common cyanotic heart defect identified in the first week of life, and the diagnosis should be considered in any cyanotic neonate. Fetal diagnosis is common but not uniform; however, even with prenatal diagnosis, profound hypoxia owing to a highly restrictive patent foramen ovale can lead to rapid deterioration and death within the first hours of life.52,100 Respiratory symptoms in this disorder are absent or limited to hyperpnea or tachypnea without dyspnea. The patient’s second heart sound is loud and persistently single because of the anterior position of the aorta and the posterior position of the pulmonary artery. A holosystolic murmur, when present, suggests an associated ventricular septal defect; a systolic ejection murmur is auscultated when the patient has pulmonary stenosis. In the absence of these associated defects, murmurs are generally not heard. The peripheral pulses are normal unless coarctation of the aorta is present. Persistent ductal patency or high pulmonary vascular resistance will affect the clinical findings of an associated ventricular septal defect or coarctation of the aorta.

The follow-up data on patients who have undergone the arterial switch operation are quite favorable.65,100,107 Risk factors for early mortality include prematurity and right ventricular hypoplasia.¹⁷ Coronary anatomy (especially intramural coronary arteries), which was a risk factor in the earlier experience, can now be managed effectively, although with higher hospital morbidity.^17,63 Long-term follow-up studies demonstrate excellent ventricular function, normal rhythm, and a low incidence of obstruction at the aortic and coronary suture lines.^23,89 Narrowing in the supravalvular pulmonary area may require subsequent surgeries or catheter interventions.^5,31,75,100 Dilation of the neoaortic root and aortic regurgitation are found in some children, but rarely do these require further intervention.^64,100 Neurodevelopmental outcome is, in general, good in these infants who do not require intraoperative circulatory arrest, but motor deficits, rather than impaired intelligence quotient scores, are seen in infants with transposition of the great arteries who had circulatory arrest.¹⁵

Cyanotic Defects: Restricted Pulmonary Blood Flow

Tetralogy of Fallot

Anatomy and Pathophysiology

In 1888, Fallot described the association of infundibular (subvalvular) and valvular pulmonary stenosis, a large ventricular septal defect, a large aorta overriding the ventricular septum, and right ventricular hypertrophy. The spectrum of lesions can range from a single malaligned VSD (also known as pink tetralogy of Fallot [TOF]) with excellent saturations to pulmonary atresia with ventricular septal defect with very low saturations. Often, infants with atretic or absent pulmonary arteries have multiple aortopulmonary collaterals as their pulmonary blood flow. In TOF, cyanosis is proportional to the right ventricular outflow tract obstruction, with those with severe stenosis having very low saturations. The extent of shunting across the ventricular septal defect is also determined by an intricate balance between the systemic vascular resistance (SVR) and the pulmonary vascular resistance (PVR). Acute narrowing or stenosis from the release of endogenous catecholamines increases PVR more than SVR, resulting in right-to-left shunting.

Associated Defects

A right aortic arch is seen in approximately 25% of these patients. Coronary artery anomalies, where the left comes from the right, must be sorted out before surgery. The branch pulmonary arteries may be discontinuous, supplied by collaterals from the aorta. Many of these patients also have multiple VSDs, atrial septal defects, anomalous systemic venous drainage, and even mitral stenosis. Another rare but difficult form is tetralogy of Fallot with an absent pulmonary valve, which includes hypoplasia of the pulmonary valve annulus and large dilated branch pulmonary arteries that often compress the bronchi.

Clinical Presentation

The spectrum of the clinical presentation of TOF is directly related to the severity of the pulmonary stenosis. The intensely cyanotic newborn infant generally has severe pulmonary stenosis or atresia and markedly diminished pulmonary blood flow. The minimally cyanotic or even acyanotic newborn infant being examined for a systolic murmur has just enough pulmonary stenosis to allow a left-to-right shunting through the ventricular septal defect without producing a right-to-left shunt.

There is usually a palpable right ventricular impulse and often a thrill with a single second heart sound. In the majority of these neonates, the PVR is less than the SVR; therefore shunting across the VSD is left to right. The systolic ejection murmur heard in neonates with tetralogy of Fallot is produced by turbulent blood flow across the pulmonary stenosis. A continuous murmur may suggest systemic-to-pulmonary collaterals as the source of pulmonary blood flow.

Laboratory Evaluation

In the newborn, the classical “boot-shaped” heart caused by the small or absent main pulmonary artery might not be obvious on the chest x-ray, but one must evaluate the pulmonary vascular markings, which often offer a clue as to the severity of the pulmonary stenosis/pulmonary atresia. The electrocardiogram of the neonate with TOF generally is normal. The echocardiogram demonstrates the ventricular septal defect and aortic override (Figure 84-2). Of particular importance when performing an echocardiograph is the documentation of the sites and degree of pulmonary obstruction. Determination of the size of the main and branch pulmonary arteries, presence of a patent ductus arteriosus or collateral vessels, and documentation of other anomalies are also important.

Figure 84-2 Echocardiogram showing parasternal long-axis view in a newborn infant with tetralogy of Fallot. The right ventricle (RV) is anterior, and left ventricle (LV) is posterior, with a large ventricular septal defect (VSD) and overriding aorta (AO). LA, Left atrium.

A diagnostic cardiac catheterization is indicated before surgery only if the pulmonary artery anatomy and sources of pulmonary blood flow cannot be defined noninvasively by echocardiogram, computed tomography, or magnetic resonance imaging or there remains a question about the coronary artery anatomy.

Management and Prognosis

Neonates with severe cyanosis are stabilized by an infusion of prostaglandin E₁ to maintain the patency of the ductus arteriosus and thereby increase pulmonary blood flow. In general, neonates who require PGE need a palliative shunt (Blalock-Taussig shunt) or a complete repair in the newborn period to provide a reliable source of pulmonary blood flow. Balloon dilation or stenting of stenotic pulmonary valves has been favored in a few centers as an alternative to shunts.²⁷ Rehabilitation of branch pulmonary artery stenosis by surgery or interventional catheterization is another important step at the time of primary repair or as part of a staged approach.⁶⁰

Neonatal repair of tetralogy of Fallot is feasible for babies with normal or appropriate pulmonary artery size. This complete repair consists of closure of the ventricular septal defect, relieving the pulmonary stenosis, and enlargement of the right ventricular outflow tract with a patch. In the absence of marked pulmonary artery hypoplasia or unfavorable coronary artery anatomy, surgery can be undertaken at virtually any age.⁸⁷

Tricuspid Atresia

Anatomy and Pathophysiology

Tricuspid atresia (TA) is defined by a platelike tissue in place of the tricuspid valve with no direct communication between the right atrium and the right ventricle. Associated right ventricular hypoplasia and pulmonary artery hypoplasia are proportional to the size of the ventricular septal defect and the degree of subpulmonary and pulmonary valve stenosis.

Systemic venous return from the inferior and superior venae cavae enters the right atrium and crosses the atrial septum, with resultant complete mixing of the systemic and pulmonary venous return in the left atrium. Pulmonary blood flow is supplied by left-to-right shunting through either the ductus arteriosus or the ventricular septal defect. The degree of systemic hypoxia is proportional to the relative systemic and pulmonary blood flow. Neonates with tricuspid atresia, small ventricular septal defect, and severe pulmonary stenosis have severely limited pulmonary blood flow and are ductal dependent. Those with large ventricular septal defects and no pulmonary stenosis have high pulmonary artery pressure and flow. When pulmonary artery resistance falls in these babies, pulmonary flow dramatically increases, hypoxia is minimal, and they are at risk of developing congestive heart failure.

Associated Defects

Tricuspid atresia (TA) is not a diagnosis that occurs in isolation. All neonates with TA must have an atrial septal defect for postnatal survival. Other associated lesions include ventricular septal defect (VSD), transposition of the great arteries, atrioventricular (AV) septal defect, and coarctation of aorta. The size of the ventricular septal defect is extremely important in neonates with the combination of tricuspid atresia and transposition of the great arteries. This is because in transposition of the great arteries, the aorta arises from the right ventricle, the systemic circulation is dependent on the flow through the VSD, and any restriction severely compromises systemic circulation.

Clinical Presentation

The typical neonatal presentation of a patient with TA is cyanosis at or before ductal closure and a murmur. Precordial activity is normal, and the second heart sound is often single. There may be a systolic ejection murmur if there is subpulmonary and/or pulmonary valve stenosis. If the ventricular septal defect is large, tachypnea, a left ventricular impulse, and a third heart sound develop during the first few days of life as the pulmonary vascular resistance falls. Hepatic enlargement is an important sign of the presence of a restrictive atrial septal defect and elevated right atrial pressures.

Laboratory Evaluation

Electrocardiogram is usually diagnostic in neonates with tricuspid atresia. These patients have right atrial enlargement and left axis deviation. The chest radiograph tends to be nonspecific, although severely cyanotic neonates show decreased pulmonary vascularity. Echocardiogram (Figure 84-3) clearly defines the anatomy in this disorder, especially the right ventricular outflow tract, the pulmonary artery, the presence of a ductus arteriosus, and the atrial septal defect, in addition to the presence/absence of d-TGA, coarctation, and pulmonary arteries. Catheterization is needed only to perform a balloon atrial septostomy in those with a restrictive atrial septum.

Figure 84-3 Apical four-chamber view of neonate with tricuspid atresia. Shown are a fibromuscular floor of the right atrium (RA), small ventricular septal defect (VSD), and hypoplastic right ventricle (RV). A large atrial septal defect permits free flow from the right atrium (RA) to the left atrium (LA) and into the left ventricle (LV).

Management and Prognosis

Antegrade pulmonary flow across the ventricular septal defect may be adequate in the first months of life as long as the atrial septal defect remains nonrestrictive. It is generally possible to predict by echocardiogram when babies require a patent ductus arteriosus to maintain adequate arterial saturations. A balloon atrial septostomy is rarely necessary unless there is significant restriction at the atrial septal defect.⁷⁰

If the baby is ductal dependent or if hypoxia increases in the first month of life, a systemic-to-pulmonary shunt is necessary to provide adequate pulmonary blood flow and oxygenation. Conversion to a bidirectional Glenn anastomosis is usually considered when an infant is between 3 and 6 months of age.⁵⁵ Some babies with well-balanced systemic and pulmonary flows can proceed directly to an early bidirectional Glenn operation⁸⁶ or a Fontan operation at about 2 to 3 years of age. Among children who undergo the Fontan type of operation, those with tricuspid atresia have excellent long-term prognosis, with a low prevalence of ventricular dysfunction, mitral regurgitation, arrhythmias, and systemic venous congestion.⁹⁸

Pulmonary Atresia with Intact Ventricular Septum and Critical Pulmonary Stenosis

Anatomy and Pathophysiology

The pulmonary valve in this disorder can range from a well-formed pulmonary annulus with a plate that obstructs outflow to complete absence of the pulmonary artery (pulmonary atresia). Both of these forms lead to extreme right ventricular hypertrophy (peach pit RV) with right ventricular dysfunction to right ventricular hypoplasia. In these cases, the pulmonary blood flow is possible only because of the ductal patency and flow across the atrial septum for mixing of the systemic and pulmonary venous blood.

Associated Defects

Coronary artery fistulas, located between the right ventricle and the coronary arteries, are the most critical associated lesions in this defect. These must be well defined because they are important prognostically for surgical planning. In the case of a coronary fistula that is dependent on the right ventricular pressure for antegrade flow and myocardial perfusion (right ventricular dependent coronary circulation), sudden decompression of the right ventricle can lead to untoward consequences such as severe myocardial ischemia and death.

Clinical Presentation

Fetal diagnosis of this disorder frequently can identify the risk factors for subsequent interventional and surgical management, including tricuspid valve hypoplasia and coronary artery fistulas.³³ Neonates with pulmonary atresia and an intact ventricular septum have severe hypoxia at the time the ductus arteriosus closes. These patients can become unstable and have signs of tachypnea, tachycardia, hepatomegaly, and cardiorespiratory collapse.

Laboratory Evaluation

The chest radiograph often shows cardiomegaly, owing to right atrial enlargement. In-depth evaluation of the echocardiogram is diagnostic, demonstrating the pulmonary atresia, size of the tricuspid valve, and degree of right ventricular hypoplasia. Imaging studies can delineate the presence of coronary artery fistulas. Cardiac catheterization is usually indicated to assess coronary flow, the location and size of the fistula, localization of the pulmonary blood flow, and for consideration of balloon dilation of the pulmonary valve.

Management and Prognosis

Prostaglandin E₁ therapy is essential in maintaining ductal patency. Careful assessment of the anatomy and physiology provides a framework for interventional and surgical management.⁶ Balloon pulmonary valvuloplasty is feasible in babies even with a tiny orifice in the pulmonary valve, and novel techniques including radiofrequency perforation of the valve in the catheterization laboratory may be considered.⁴

If interventional catheterization is unsuccessful, surgical valvotomy is indicated unless there is clear dependence of the coronary flow on the right ventricle. In that circumstance, decompression of the right ventricle can result in coronary hypoperfusion, and in these cases a systemic-to-pulmonary shunt is recommended. In babies with successful surgical or interventional valvotomies, right ventricular growth is possible, and biventricular circulation can be restored.42,46

Severe tricuspid hypoplasia or right ventricle–dependent coronary circulation is an indication to pursue the single-ventricle approach to separate the systemic and pulmonary circulations.³⁸ Babies who have right ventricular hypoplasia should be considered candidates for a bidirectional Glenn operation combined with closure of the atrial septal defect (1.5 ventricle repair). This procedure directs the inferior vena caval blood across the hypoplastic tricuspid valve and uses the right ventricle.

Ebstein Anomaly

Anatomy and Pathophysiology

In this particular cardiac disorder, at least one leaflet of the tricuspid valve annulus is displaced apically with varying amount of tethering of the septal leaflet. The anterior leaflet is redundant and could even obstruct the right ventricular outflow tract, resulting in decreased blood flow and functional or anatomic pulmonary atresia. Because of the displacement, a portion of the right ventricle is atrialized and acts as an inefficient pump. Forward flow is determined based on the severity of the tricuspid valve displacement and dysfunction. If there is a functional/anatomic pulmonary atresia, then there is obligatory right-to-left shunt through the patent foramen ovale. This degree of right-to-left atrial shunt is proportional to the severity of the tricuspid valve abnormality.

Associated Defects

Patients with Ebstein anomaly often have other associated intracardiac lesions. Accessory pathways or Wolff-Parkinson-White syndrome are found in up to 20% of patients with Ebstein anomaly. Other patients have coarctation of the aorta, atrial septal defects, and pulmonary atresia.

Clinical Presentation

The presence of multiple systolic clicks is a notable feature. The level of cyanosis depends on the extent of atrial level right-to-left shunting. A low-frequency holosystolic murmur of tricuspid regurgitation can be heard.

Laboratory Evaluation

The electrocardiogram of babies with severe Ebstein malformation shows an RSR′ pattern across the right side of the chest, suggesting right ventricular dilation. The chest radiograph shows marked cardiomegaly caused by right atrial dilation. The echocardiography helps to assess the extent of tricuspid valve displacement, the direction of shunt at the atrial level, and the presence of pulmonary atresia. The area of the right atrium and the atrialized right ventricle has been a useful sign of severity and outcome.¹⁰⁸

Management and Prognosis

Mild forms of Ebstein anomaly require no specific treatment, and these infants in general do well.⁹⁷ The severely affected neonate with severe displacement of the tricuspid valve and severe tricuspid valve regurgitation often is ductal dependent with no anterograde flow across the pulmonary valve.¹⁰⁸ Maintaining patency of the ductus arteriosus with prostaglandin E₁ can be useful in the short term; however, ductal flow into the pulmonary artery can make anterograde flow more difficult. In severe Ebstein anomaly, measures to lower the pulmonary vascular resistance, including nitric oxide and several attempts to wean the infant from prostaglandin E₁, might be necessary before anterograde flow across the pulmonary valve can be established.⁹ Brief support with extracorporeal membrane oxygenation to facilitate this fetal to neonatal transition has been successful in a few babies. Surgical repair or replacement of the valve is feasible in older children, but this is not useful in neonates. Either surgical exclusion of the right ventricle, with plans for a long-term single-ventricle palliation, or transplantation might be the only alternatives for the neonate with severe Ebstein anomaly and persistent cyanosis.⁵⁸

Cyanotic Defects: Complete Mixing

Total Anomalous Pulmonary Venous Connection

Anatomy and Pathophysiology

Total anomalous pulmonary venous connection (TAPVC) comprises a group of defects in which the pulmonary veins drain into the systemic venous circulation (right heart) rather than to their normal return to the left atrium:

1. Supracardiac type (55%): A vertical vein connects the pulmonary venous confluence from just behind the left atrium and heads superiorly to the innominate vein, which then drains to the superior vena cava and right atrium (Figure 84-4).

Figure 84-4 Three-dimensional reconstruction computed tomography angiogram in a neonate with a total anomalous pulmonary venous connection above the diaphragm showing the pulmonary venous confluence that connects to the vertical vein, which in turn connects to the innominate vein and the superior vena cava. A, Posterior view showing all the pulmonary veins draining anomalously into the confluence and joining the vertical vein. *, Pulmonary venous confluence; VV, vertical vein. B, Anterior view showing the vertical vein draining into the innominate vein and then to the SVC. IV, Innominate vein; SVC, superior vena cava; VV, vertical vein.

2. Infracardiac type: (13%): The confluence of the pulmonary veins that gather just posterior to the left atrium drains into a descending vertical vein that courses through the diaphragm and the liver via the portal venous system and joins the systemic venous circulation in the inferior vena cava and then the right atrium.

3. Cardiac type: This involves the connection between the pulmonary veins and the systemic venous circulation through either the coronary sinus or the right atrium.

4. Mixed type: This is a relatively rare form occurring in 5% of patients with TAPVC. It usually involves the left pulmonary veins draining into the systemic veins through the ascending vertical vein and the right pulmonary veins into the coronary sinus or directly into the right atrium.

The infracardiac type is the one form of TAPVC that generally presents in extremis in the neonatal period, owing to the obstruction of the descending vertical vein either at the diaphragm or the ductus venosus. The supracardiac form can present with obstruction when the vertical vein passes between the left bronchus and the left pulmonary artery or at the junction of the superior vena cava and the innominate vein, but this tends not to be quite so extreme.

In this disorder, the pulmonary venous return mixes completely with systemic venous return in the right atrium. Blood flow to the left side of the heart is dependent on shunting from the right atrium to the left atrium through the foramen ovale. In the absence of any form of pulmonary venous obstruction, pulmonary blood flow is increased and hypoxia is mild. In contrast, if the pulmonary venous connection is obstructed at any point in its attempts to connect with the systemic venous circulation, this results in pulmonary venous hypertension with pulmonary edema and decreased pulmonary blood flow. The combination of decreased pulmonary blood flow and impaired pulmonary function caused by edema results in profound systemic hypoxia.

Associated Defects

An atrial septal defect or a patent foramen ovale is essential for postnatal survival. Left-sided heart defects, transposition of the great arteries, and tetralogy of Fallot have also been reported in association with TAPVC. Neonates with heterotaxy syndrome commonly have associated total anomalous pulmonary venous connection.

Clinical Presentation

The neonatal clinical presentation of unobstructed total anomalous pulmonary venous connection is generally asymptomatic. These patients are either diagnosed at an older age secondary to recurrent pneumonias or are identified by echocardiogram in evaluation for a murmur. Cyanosis and respiratory distress are generally limited to babies with the severe form of obstruction of the pulmonary venous connections. In babies without obstruction, volume overload and increased pulmonary blood flow can gradually develop.

Laboratory Evaluation

A chest x-ray can be very helpful in this disorder because it can show pulmonary edema, which is highly suggestive of pulmonary venous obstruction. Dilated mediastinal veins give an appearance of fullness (snowman sign) to the superior mediastinum, although in neonates this is usually masked by the thymus. An ECG is usually not helpful. The echocardiogram is the gold standard, and careful examination of entry of each pulmonary vein into the confluence and its drainage can be identified. Sites of venous obstruction can also be illustrated by imaging with evidence of turbulent flow by pulse wave and color flow Doppler imaging. The size of the individual pulmonary veins and the confluence should be measured because of a relationship of pulmonary venous diameters less than 2 mm and poor prognosis.⁵¹ The atrial septum must be imaged to document that it is not restrictive. If there is any question of the restriction at the atrial septum, then a balloon atrial septostomy is recommended. If the echocardiogram cannot provide all the necessary information, cardiac CT angiogram (see Figure 84-4), cardiac catheterization, or cardiac magnetic resonance imaging may be necessary.

Management and Prognosis

Unobstructed total anomalous pulmonary venous connection requires little specific medical management until the infant is ready for surgical intervention. Neonates in whom there is evidence of restrictive atrial septal defects should undergo a somewhat urgent balloon atrial septostomy. Neonates with pulmonary venous obstruction tend to be profoundly hypoxic and require significant respiratory and metabolic support. Extracorporeal membrane oxygenation has been used as a bridge to complete repair.

Elective repair—anastomosis of the common pulmonary venous confluence to the left atrium—in the first months of life is appropriate for neonates with unobstructed flow. Urgent surgery is essential for those with pulmonary venous obstruction. Postoperative pulmonary artery hypertension and pulmonary vascular reactivity is most troublesome in neonates with preoperative pulmonary venous obstruction. The long-term prognosis is excellent except in those neonates with hypoplastic pulmonary veins ⁵¹ or single-ventricle anatomy.⁴¹ Recurrent or persistent pulmonary venous obstruction at the anastomosis site or within the veins is difficult to treat either by surgery or interventional catheterization.⁶¹ Arrhythmias and a poor chronotropic response to exercise have been reported in some patients after surgery.¹⁰²

Truncus Arteriosus

Anatomy and Pathophysiology

In truncus arteriosus, there is common origin of aorta and pulmonary artery from a single semilunar valve. This single trunk overrides a large ventricular septal defect that allows for mixing of the systemic venous return and pulmonary venous return. In type I truncus there is a short main pulmonary artery segment arising from the truncus, which then gives rise to branch pulmonary arteries. In type II truncus, both the branch pulmonary arteries have a direct origin from the truncus. In type III truncus, the pulmonary arteries arise from opposite sides of the truncus and are remote from each other.

Both pulmonary and systemic blood flows are determined by the relative systemic vascular resistance and pulmonary vascular resistance. As the pulmonary vascular resistance falls, there tends to be increased pulmonary blood flow, which then results in pulmonary venous overcirculation and increased left atrial and left ventricular size.

Associated Defects

A number of other intracardiac defects are associated with truncus arteriosus. First and foremost, the valve leaflets in truncus arteriosus tend to be thickened and dysplastic. These neonates often suffer from truncal valve regurgitation and/or truncal stenosis. They can have anywhere from one to six leaflets. Unilateral or bilateral branch pulmonary artery stenosis occurs in about 10% of children. If the origin of the pulmonary artery is atretic, there can also be collateral from the aorta supplying the lungs. Coronary artery stenosis and malposition are rare but are surgically important variations.¹ A right aortic arch is found in 15% to 25% of patients with truncus and an interrupted aortic arch may also be present. DiGeorge syndrome is a very common associated lesion that should be screened for in all the patients with truncus arteriosus.

Clinical Presentation

The neonatal presentation of uncomplicated truncus arteriosus can be subtle with mild tachypnea or cyanosis being the only symptom. The pulse oximetry is around 85%. The higher saturation indicates falling pulmonary vascular resistance and increasing pulmonary blood flow. Lower saturations indicate increasing pulmonary vascular resistance, branch pulmonary artery stenosis, or pulmonary dysfunction from edema. Acidosis can be present in infants with associated truncal stenosis and regurgitation or aortic arch interruption. As the pulmonary vascular resistance drops, the pulmonary blood flow increases, resulting in a murmur and signs and symptoms of pulmonary overcirculation. Truncal valve stenosis and a regurgitation murmur also can be easily identified by a thorough physical examination. The patient may have bounding pulses and increased pulse pressure because decreased diastolic pressure is secondary to runoff into the branch pulmonary arteries. Poor perfusion and decreased leg pulses indicate aortic arch interruption. All of these patients should also be screened for the presence of a thymus, and their calcium levels should be measured.

Laboratory Evaluation

An electrocardiogram may show biventricular hypertrophy or may be normal; however, a chest x-ray shows cardiomegaly and pulmonary overcirculation. The echocardiogram is the gold standard for diagnosis. While performing the echocardiogram, attention must be paid to define the truncal valve, branch pulmonary arteries, aortic arch anatomy, and coronary arteries. Cardiac catheterization, CT angiography, and cardiac MRI are reserved for neonates with pending questions after the echocardiogram. All affected neonates should be screened for microdeletion of chromosome 22.

Management and Prognosis

In patients with truncus arteriosus, increased pulmonary blood flow generally responds to anticongestive measures such as diuretics and digoxin. Supplemental oxygen should be avoided because this decreases the pulmonary vascular resistance, which increases pulmonary blood flow. Those with moderate to severe truncal valve stenosis and regurgitation generally do not respond to medical management and require balloon dilation or surgical repair. In those neonates with DiGeorge syndrome, careful management of calcium levels is required.

Truncus arteriosus generally is repaired in the first months of life. This repair includes closure of the ventricular septal defect and placement of a right ventricle to pulmonary artery homograft. Associated defects, including truncal valve stenosis, aortic arch interruption, coronary abnormalities, and branch pulmonary artery atresia, increase the risk of the procedure but do not preclude it.¹⁰³

If truncal stenosis and regurgitation are severe, then a homograft is used to replace the truncal valve to provide a competent neoaortic valve.

The long-term prognosis for this repair is excellent for children with straightforward truncus arteriosus. Homograft replacement is generally required by age 5 years in about 20% of patients, but they must always be replaced at some point in the child’s life.⁴⁴ Neoaortic valve stenosis and regurgitation gradually worsen and can require repair or replacement of the valve in 25% of patients.⁴⁵ Ventricular dysfunction and arrhythmias are generally poor prognostic indicators.

Cyanotic Defects: Variable Physiology

Single Ventricle

Anatomic variations of the cardiac disorder loosely termed single ventricle are massive. A methodic segmental approach of the patient’s venous, atrial, ventricular, and arterial connection can generally allow one to make an accurate diagnosis. In this disorder, there must be complete mixing of the systemic and pulmonary venous return to allow for adequate single-ventricle output. This mixing occurs most effectively at the atrial level through either a PFO or ASD. Additional shunting can and does occur at the VSD and PDA. The blood from this single ventricle is pumped either to the systemic or pulmonary circulation. The predominant circulation must then support the other through a patent ductus arteriosus. The oxygen saturation in these cases is determined by the relative resistances across the pulmonary and systemic vascular beds. It is important to recognize that many babies have lower pulmonary vascular resistance, resulting in unrestricted pulmonary blood flow. Oxygen acts as a pulmonary vasodilator and therefore increases pulmonary blood flow, thus reducing systemic blood flow, resulting in acidosis and hepatic and renal shutdown.

When single-ventricle physiology is determined, the next step is to determine whether the pulmonary or systemic circulation requires support. If the neonate has single-ventricle physiology, then a Norwood surgery is planned with additional variations, including the Damus-Kaye-Stansel procedure as required.⁷³ The long-term surgical planning for babies with single-ventricle physiology must begin in the neonatal period. The Norwood procedure is then followed by a bidirectional Glenn procedure (anastomosing the superior vena cava to the branch pulmonary arteries) between 3 and 9 months of age.^2,86 The staged palliation is completed by the Fontan procedure (IVC to pulmonary artery) at approximately 2 to 3 years of age. At this stage, the pulmonary and systemic circulations are separate, the systemic venous return passively drains to the lungs, and the pulmonary venous return comes back to the atrium that in turn feeds the single ventricle to then support the systemic circulation.

Double-Outlet Right Ventricle

Anatomy and Pathophysiology

In double-outlet right ventricle (DORV), the aorta and the pulmonary artery arise side by side from the right ventricle. Double-outlet right ventricle has four distinct subtypes based on the location of the VSD and its relationship to the great arteries. This includes DORV where the VSD is (1) subaortic, (2) subpulmonary, (3) doubly committed, or (4) remote from the great arteries. The Taussig-Bing malformation is one of the forms of DORV with a VSD that is subpulmonary in addition to transposition of the great arteries.⁹⁰ Patients’ individual physiologies can range from that of a large VSD to that of transposition.

Fastest Obstetric, Gynecology and Pediatric Insight Engine

Congenital Defects of the Cardiovascular System

Share this:

Related

Related posts:

Stay updated, free articles. Join our Telegram channel

Full access? Get Clinical Tree