425.1 D-Transposition of the Great Arteries

Transposition of the great vessels, a common cyanotic congenital anomaly, accounts for ≈5% of all congenital heart disease. In this anomaly, the systemic veins return normally to the right atrium and the pulmonary veins return to the left atrium. The connections between the atria and ventricles are also normal (atrioventricular concordance). The aorta arises from the right ventricle and the pulmonary artery from the left ventricle (Fig. 425-1). In normally related great vessels, the aorta is posterior and to the right of the pulmonary artery; in d-transposition of the great arteries (d-TGA), the aorta is anterior and to the right of the pulmonary artery (the d indicates a dextropositioned aorta, transposition indicates that it arises from the anterior right ventricle). Desaturated blood returning from the body to the right side of the heart goes inappropriately out the aorta and back to the body again, whereas oxygenated pulmonary venous blood returning to the left side of the heart is returned directly to the lungs. Thus, the systemic and pulmonary circulations exist as two parallel circuits. Survival in the immediate newborn period is provided by the foramen ovale and the ductus arteriosus, which permit some mixture of oxygenated and deoxygenated blood. About 50% of patients with d-TGA also have a ventricular septal defect (VSD), which usually provides for better mixing. The clinical findings and hemodynamics vary in relation to the presence or absence of associated defects (e.g. VSD or pulmonary stenosis). d-TGA is more common in infants of diabetic mothers and in males (3 : 1). d-TGA, especially when accompanied by other cardiac defects such as pulmonic stenosis or right aortic arch, can be associated with deletion of chromosome 22q11 (DiGeorge syndrome [Chapter 418]). Before the modern era of corrective or palliative surgery, mortality was >90% in the 1st yr of life.

Figure 425-1 Physiology of d-transposition of the great arteries (d-TGA). Circled numbers represent oxygen saturation values. Right atrial (mixed venous) oxygen saturation is decreased secondary to systemic hypoxemia. Desaturated blood enters the right atrium, flows through the tricuspid valve into the right ventricle, and is ejected into the transposed aorta with resultant severe aortic desaturation. Fully saturated pulmonary venous blood flows into the left atrium, across the mitral valve into the left ventricle, and across the transposed pulmonary artery into the lungs. Pulmonary arterial oxygen saturation is thus increased. This lesion would not be compatible with life were it not for the ability of blood to shunt via two fetal pathways: the patent foramen ovale (PFO) and patent ductus arteriosus (PDA). Blood may shunt left to right or bidirectionally at the PFO. Because systemic vascular resistance tends to be higher than pulmonary vascular resistance, blood tends to shunt across the PDA mostly from the aorta to the pulmonary artery. As pulmonary resistance drops in the 1st few weeks of life, pulmonary blood flow will gradually increase in patients with d-TGA.

425.2 D-Transposition of the Great Arteries with Intact Ventricular Septum

Daniel Bernstein

D-TGA with an intact ventricular septum is also referred to as simple TGA or isolated TGA. Before birth, oxygenation of the fetus is only slightly abnormal, but after birth, once the ductus arteriosus begins to close, the minimal mixing of systemic and pulmonary blood via the patent foramen ovale is usually insufficient and severe hypoxemia ensues, generally within the 1st few days of life.

Clinical Manifestations

Cyanosis and tachypnea are most often recognized within the 1st hrs or days of life. Untreated, the vast majority of these infants would not survive the neonatal period. Hypoxemia is usually moderate to severe, depending on the degree of atrial level shunting and whether the ductus is partially open or totally closed. This condition is a medical emergency, and only early diagnosis and appropriate intervention can avert the development of prolonged severe hypoxemia and acidosis, which lead to death. Physical findings, other than cyanosis, may be remarkably nonspecific. The precordial impulse may be normal, or a parasternal heave may be present. The 2nd heart sound is usually single and loud, although it may be split. Murmurs may be absent, or a soft systolic ejection murmur may be noted at the midleft sternal border.

Diagnosis

The electrocardiogram is usually normal, showing the expected neonatal right-sided dominant pattern. Roentgenograms of the chest may show mild cardiomegaly, a narrow mediastinum (the classic “egg-shaped heart”), and normal to increased pulmonary blood flow. In the early newborn period, the chest roentgenogram is generally normal. As pulmonary vascular resistance drops during the 1st several weeks of life, evidence of increased pulmonary blood flow becomes apparent. Arterial PO₂ is low and does not rise appreciably after the patient breathes 100% oxygen (hyperoxia test), although this test may not be totally reliable. Echocardiography is diagnostic and confirms the transposed ventricular-arterial connections (Fig. 425-2). The size of the interatrial communication and the ductus arteriosus can be visualized and the degree of mixing assessed by pulsed and color Doppler examination. The presence of any associated lesion, such as left ventricular outflow tract obstruction or a VSD, can also be assessed. The origins of the coronary arteries can be imaged, although echocardiography is generally not as accurate as catheterization for this purpose. Cardiac catheterization may be performed in patients for whom noninvasive imaging is diagnostically inconclusive, where an unusual coronary artery anomaly is suspected, or in patients who require emergency balloon atrial septostomy. Catheterization will show right ventricular pressure to be systemic because this ventricle is supporting the systemic circulation. The blood in the left ventricle and pulmonary artery has a higher oxygen saturation than that in the aorta. Depending on the age at catheterization, left ventricular and pulmonary arterial pressure can vary from systemic level to <50% of systemic-level pressure. Right ventriculography demonstrates the anterior and rightward aorta originating from the right ventricle, as well as the intact ventricular septum. Left ventriculography shows that the pulmonary artery arises exclusively from the left ventricle.

Figure 425-2 Subcostal four-chamber two-dimensional echocardiographic demonstration of d-transposition of the great arteries. The pulmonary artery (PA) can be seen arising directly from the left ventricle (LV). The immediate bifurcation of this great vessel into the branch pulmonary arteries differentiates it from the aorta, which branches more distally from the heart. LPA, left pulmonary artery; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle.

Anomalous coronary arteries are noted in 10-15% of patients and defined by an aortic root injection or by selective coronary arteriography.

Treatment

When transposition is suspected, an infusion of prostaglandin E₁ should be initiated immediately to maintain patency of the ductus arteriosus and improve oxygenation (dosage, 0.01-0.20 µg/kg/min). Because of the risk of apnea associated with prostaglandin infusion, an individual skilled in neonatal endotracheal intubation should be available. Hypothermia intensifies the metabolic acidosis resulting from hypoxemia, and thus the patient should be kept warm. Prompt correction of acidosis and hypoglycemia is essential.

Infants who remain severely hypoxic or acidotic despite prostaglandin infusion should undergo Rashkind balloon atrial septostomy (Fig. 425-3). A Rashkind atrial septostomy is also usually performed in all patients in whom any significant delay in surgery is necessary. If surgery is planned during the 1st 2 wk of life, and the patient is stable, catheterization and atrial septostomy may be avoided.

Figure 425-3 Rashkind balloon atrial septostomy. Four frames from a continuous cineangiogram show the creation of an atrial septal defect in a hypoxemic newborn infant with transposition of the great arteries and an intact ventricular septum. A, Balloon inflated in the left atrium. B, The catheter is jerked suddenly so that the balloon ruptures the foramen ovale. C, Balloon in the inferior vena cava. D, Catheter advanced to the right atrium to deflate the balloon. The time from A to C is <1 sec.

A successful Rashkind atrial septostomy should result in a rise in PaO₂ to 35-50 mm Hg and elimination of any pressure gradient across the atrial septum. Some patients with TGA and VSD (Chapter 425.3) may require balloon atrial septostomy because of poor mixing, even though the VSD is large. Others may benefit from decompression of the left atrium to alleviate the symptoms of increased pulmonary blood flow and left-sided heart failure.

The arterial switch (Jatene) procedure is the surgical treatment of choice for neonates with d-TGA and an intact ventricular septum and is usually performed within the 1st 2 wk of life. The reason for this time frame is that as pulmonary vascular resistance declines after birth, pressure in the left ventricle (connected to the pulmonary vascular bed) also declines. This drop in pressure results in a decrease in left ventricular mass over the 1st few weeks of life. If the arterial switch operation is attempted after left ventricular pressure (and mass) has declined too far, the left ventricle will be unable to generate adequate pressure to pump blood to the high pressure systemic circulation. The arterial switch operation involves dividing the aorta and pulmonary artery just above the sinuses and re-anastomosing them in their correct anatomic positions. The coronary arteries are removed from the old aortic root along with a button of aortic wall and reimplanted in the old pulmonary root (the “neoaorta”). By using a button of great vessel tissue, the surgeon avoids having to suture directly onto the coronary artery (Fig. 425-4); this is the major innovation that has allowed the arterial switch to replace previous atrial switch operations for d-TGA. Rarely, a two-stage arterial switch procedure, with initial placement of a pulmonary artery band, may be used in patients presenting late who already have had a reduction in left ventricular muscle mass and pressure.

Figure 425-4 Method for translocating the coronary arteries in the arterial switch (Jantene) procedure. A, The aorta (anterior) and the pulmonary artery (posterior) have been transected to allow visualization of the left and right coronary arteries. The coronaries have been excised from their respective sinuses, including a large flap (button) of arterial wall. Equivalent segments of the wall of the pulmonary artery (which will become the neoaorta) are also removed. B, The aortocoronary buttons are sutured into the proximal portion of the neoaorta. With this technique all sutures are placed in the button of aortic wall rather than directly on the coronary arteries. C, Completed anastomosis of the left and right coronary arteries to the neoaorta.

(Adapted from Castañeda AR, Jonas RA, Mayer JE Jr, et al: Cardiac surgery of the neonate and infant, Philadelphia, 1994, WB Saunders.)

In experienced centers, the arterial switch procedure has a survival rate of 95% for uncomplicated d-TGA. It restores the normal physiologic relationships of systemic and pulmonary arterial blood flow and eliminates the long-term complications of the previously used atrial switch procedure.

Previous operations for d-TGA consisted of some form of atrial switch procedure (Mustard or Senning operation). These procedures produced excellent early survival (≈85-90%), but had significant long-term morbidities. Atrial switch procedures reverse blood flow at the atrial level by the creation of an inter-atrial baffle that directs systemic venous blood returning from the vena cavae to the left atrium, where it will enter the left ventricle and then, via the pulmonary artery, the lungs. The same baffle also permits oxygenated pulmonary venous blood to cross over to the right atrium, right ventricle, and aorta. Atrial switch procedures involve significant atrial surgery and have been associated with the late development of atrial conduction disturbances, sick sinus syndrome with bradyarrhythmia and tachyarrhythmia, atrial flutter, sudden death, superior or inferior vena cava syndrome, edema, ascites, and protein-losing enteropathy. The atrial switch procedure also leaves the right ventricle as the systemic pumping chamber and these “systemic” right ventricles often begin to fail in young adulthood. Atrial switch operations are currently reserved for patients whose anatomy is such that they are not candidates for the arterial switch procedure.

425.3 Transposition of the Great Arteries with Ventricular Septal Defect

Daniel Bernstein

If the VSD associated with d-TGA is small, the clinical manifestations, laboratory findings, and treatment are similar to those described previously for transposition with an intact ventricular septum. A harsh systolic murmur is audible at the lower left sternal border, resulting from flow through the defect. Many of these small defects eventually close spontaneously and may not be addressed at the time of surgery.

When the VSD is large and not restrictive to ventricular ejection, significant mixing of oxygenated and deoxygenated blood usually occurs and clinical manifestations of cardiac failure are seen. The degree of cyanosis may be subtle and sometimes may not be recognized until an oxygen saturation measurement is performed. The murmur is holosystolic and generally indistinguishable from that produced by a large VSD in patients with normally related great arteries. The heart is usually significantly enlarged.

Cardiomegaly, a narrow mediastinal waist, and increased pulmonary vascularity are demonstrated on the chest roentgenogram. The electrocardiogram shows prominent P waves and isolated right ventricular hypertrophy or biventricular hypertrophy. Occasionally, dominance of the left ventricle is present. Usually, the QRS axis is to the right, but it can be normal or even to the left. The diagnosis is confirmed by echocardiography, and the extent of pulmonary blood flow can also be assessed by the degree of enlargement of the left atrium and ventricle. In equivocal cases, the diagnosis can be confirmed by cardiac catheterization. Right and left ventriculography indicate the presence of arterial transposition and demonstrate the site and size of the VSD. Systolic pressure is equal in the 2 ventricles, the aorta, and the pulmonary artery. Left atrial pressure may be much higher than right atrial pressure, a finding indicative of a restrictive communication at the atrial level. At the time of cardiac catheterization, Rashkind balloon atrial septostomy may be performed to decompress the left atrium, even when adequate mixing is occurring at the ventricular level.

Surgical treatment is advised soon after diagnosis, because heart failure and failure to thrive are difficult to manage and pulmonary vascular disease can develop unusually rapidly in these patients. Preoperative management with diuretics lessens the symptoms of heart failure and stabilizes the patient prior to surgery.

Patients with d-TGA and a VSD without pulmonic stenosis can be treated with an arterial switch procedure combined with VSD closure. In these patients, the arterial switch operation can be safely performed after the 1st 2 wk of life because the VSD results in equal pressure in both ventricles and prevents regression of left ventricular muscle mass. At major centers, however, there is no reason to delay repair, as results are excellent whether the surgery is performed in the neonatal period or later.

425.4 L-Transposition of the Great Arteries (Corrected Transposition)

Daniel Bernstein

In l-transposition (l-TGA), the atrioventricular relationships are discordant: the right atrium is connected to the left ventricle and the left atrium to the right ventricle (also known as ventricular inversion). The great arteries are also transposed, with the aorta arising from the right ventricle and the pulmonary artery from the left. In contrast to d-TGA, the aorta arises to the left of the pulmonary artery (hence the designation l for levo-transposition). The aorta may be anterior to the pulmonary artery, although often they are nearly side by side.

The physiology of l-TGA is quite different from that of d-TGA. Desaturated systemic venous blood returns via the vena cavae to a normal right atrium, from which it passes through a bicuspid atrioventricular (mitral) valve into a right-sided ventricle that has the architecture and smooth wall morphologic features of the normal left ventricle (Fig. 425-5). Because transposition is also present, however, the desaturated blood ejected from this left ventricle enters the transposed pulmonary artery and flows into the lungs, as it would in the normal circulation. Oxygenated pulmonary venous blood returns to a normal left atrium, passes through a tricuspid atrioventricular valve into a left-sided ventricle, which has the trabeculated morphologic features of a normal right ventricle, and is then ejected into the transposed aorta. The double inversion of the atrioventricular and ventriculoarterial relationships result in desaturated right atrial blood appropriately flowing to the lungs and oxygenated pulmonary venous blood appropriately flowing to the aorta. The circulation is thus physiologically “corrected.” Without other defects, the hemodynamics would be nearly normal. In most patients, however, associated anomalies coexist: VSD, Ebstein-like abnormalities of the left-sided atrioventricular (tricuspid) valve, pulmonary valvular or subvalvular stenosis (or both), and atrioventricular conduction disturbances (complete heart block, accessory pathways such as Wolff-Parkinson-White syndrome).