Transposition of the Great Arteries 

Updated: Apr 11, 2017
Author: John R Charpie, MD, PhD; Chief Editor: Howard S Weber, MD, FSCAI 

Overview

Background

Transposition of the great arteries (TGA) is the most common cyanotic congenital heart lesion that presents in neonates. The hallmark of transposition of the great arteries is ventriculoarterial discordance, in which the aorta arises from the morphologic right ventricle and the pulmonary artery arises from the morphologic left ventricle. See the image below.

This right ventricular angiogram shows a patient w This right ventricular angiogram shows a patient with transposition of the great arteries. The aorta arises directly from the right-sided anterior right ventricle (10° left anterior oblique [LAO]).

Although transposition of the great arteries was first described over 2 centuries ago, no treatment was available until the middle of the 20th century, with the development of surgical atrial septectomy in the 1950s and balloon atrial septostomy in the 1960s. These palliative therapies were followed by physiological procedures (atrial switch operation) and anatomic repair (arterial switch operation) (see the videos below). Today, the survival rate for infants with transposition of the great arteries is greater than 90%.

This video shows the repair of a newborn with transposition of the great arteries and ventricular septal defect (VSD) by means of arterial switch and VSD closure. Procedure performed by Giles Peek MD, FRCS, CTh, FFICM, The Children’s Hospital at Montefiore, Bronx, NY. Video courtesy of Montefiore.
Switch ventricular septal defect (VSD hypoplastic right arch). Procedure performed by Giles Peek MD, FRCS, CTh, FFICM, The Children’s Hospital at Montefiore, Bronx, NY. Video courtesy of Montefiore.

The major anatomic classifications of transposition of the great arteries depend on the relationship of the great arteries to each other and/or the infundibular morphology. In approximately 60% of the patients, the aorta is anterior and to the right of the pulmonary artery (dextro-transposition of the great arteries [d-TGA]). However in a subset of patients, the aorta may be anterior and to the left of the pulmonary artery (levo-transposition of the great arteries [l-TGA]). In addition, most patients with transposition of the great arteries (regardless of the spacial orientation of the great arteries) have a subaortic infundibulum, an absence of subpulmonary infundibulum, and fibrous continuity between the mitral valve and the pulmonary valve. Despite these useful classifications, several exceptions are noted, and, hence, discordant ventriculoarterial connection is the only distinguishing characteristic that defines transposition of the great arteries.

From a practical standpoint, the presence or absence of associated cardiac anomalies defines the clinical presentation and surgical management of a patient with transposition of the great arteries. The primary anatomic subtypes are (1) transposition of the great arteries with intact ventricular septum, (2) transposition of the great arteries with ventricular septal defect, (3) transposition of the great arteries with ventricular septal defect and left ventricular outflow tract obstruction, and (4) transposition of the great arteries with ventricular septal defect and pulmonary vascular obstructive disease.

In approximately one third of patients with transposition of the great arteries, the coronary artery anatomy is abnormal, with a left circumflex coronary arising from the right coronary artery (22%), a single right coronary artery (9.5%), a single left coronary artery (3%), or inverted origin of the coronary arteries (3%) representing the most common variants.

Pathophysiology

The pulmonary and systemic circulations function in parallel, rather than in series. Oxygenated pulmonary venous blood returns to the left atrium and left ventricle but is recirculated to the pulmonary vascular bed via the abnormal pulmonary arterial connection to the left ventricle. Deoxygenated systemic venous blood returns to the right atrium and right ventricle where it is subsequently pumped to the systemic circulation, effectively bypassing the lungs. This parallel circulatory arrangement results in a deficient oxygen supply to the tissues and an excessive right and left ventricular workload. It is incompatible with prolonged survival unless mixing of oxygenated and deoxygenated blood occurs at some anatomic level.

The following are 3 common anatomic sites for mixing of oxygenated and deoxygenated blood in transposition of the great arteries:

  • Patent foramen ovale or atrial septal defect

  • Ventricular septal defect (See the images below.)

    This two-dimensional echocardiogram (parasternal l This two-dimensional echocardiogram (parasternal long-axis view) shows a patient with transposition of the great arteries and ventricular septal defect (VSD). The pulmonary artery arises from the posterior (left) ventricle, dives posteriorly, and then bifurcates immediately into the left and right branch pulmonary arteries. A large VSD is present in the outlet septum.
    This two-dimensional echocardiogram (apical 4-cham This two-dimensional echocardiogram (apical 4-chamber view) shows a patient with transposition of the great arteries and ventricular septal defect. The anterior aorta arises from the right-sided right ventricle.
  • Patent ductus arteriosus

One or all of these lesions can be present in concert with dextro-transposition of the great arteries, and the degree of arterial hypoxemia depends on the degree of anatomic mixing.

Etiology

The etiology for transposition of the great arteries is unknown and is presumed to be multifactorial.

The embryology likely involves abnormal persistence of the subaortic conus with resorption or underdevelopment of the subpulmonary conus (infundibulum). This abnormality aligns the aorta anterior and superior with the right ventricle during development.

Epidemiology

United States data

Despite its overall low prevalence, transposition of the great arteries is the most common etiology for cyanotic congenital heart disease in the newborn.[1] This lesion presents in 5-7% of all patients with congenital heart disease. The overall annual incidence is 20-30 per 100,000 live births, and inheritance is multifactorial. Transposition of the great arteries is isolated in 90% of patients and is rarely associated with syndromes or extracardiac malformations. This congenital heart defect is more common in infants of diabetic mothers.

Race-, sex-, and age-related demographics

No racial predilection is known, but transposition of the great arteries has a 60-70% male predominance.

Patients with transposition of the great arteries usually present with cyanosis in the newborn period, but clinical manifestations and courses are influenced predominantly by the degree of intercirculatory mixing.

Prognosis

The prognosis depends on the specific anatomic substrate and type of surgical therapy used (arterial switch operation, atrial switch operation, or Rastelli procedure).

Overall, perioperative survival following arterial switch operation is greater than 90%. Long-term and arrhythmia-free survival is excellent (approximately 97% at 25 years), and late mortality is predominantly due to sudden death and myocardial infarction.[2]

The overall mortality rate following an atrial level switch is low; however, long-term morbidity associated with systemic (right) ventricular dilatation and failure, systemic atrioventricular (tricuspid) valve regurgitation, and atrial bradyarrhythmias and tachyarrhythmias is significant. A subset of patients may experience profound right ventricular failure, but they may do well with left ventricular retraining and late arterial switch.[3]

After arterial switch operation, sequelae may include chronotropic incompetence and stenosis at the supravalve neoaortic, neopulmonary, branch pulmonary arteries, and coronary artery ostia. However, most patients maintain normal systolic function and exercise capacity.[2]

Progressive neoaortic root dilation is common and is a risk factor for neoaortic valve regurgitation following arterial switch operation. Continued surveillance of this population is required.[4]

Morbidity/mortality

The mortality rate in untreated patients is approximately 30% in the first week, 50% in the first month, and 90% by the end of the first year. Long-term complications are secondary to prolonged cyanosis and include polycythemia and hyperviscosity syndrome. These patients may develop headache, decreased exercise tolerance, and stroke. Thrombocytopenia is common in patients with cyanotic congenital heart disease leading to bleeding complications. With improved diagnostic, medical, and surgical techniques, the overall short-term and midterm survival rate exceeds 90%.

Patients with a large ventricular septal defect, a patent ductus arteriosus, or both may have an early predilection for congestive heart failure, as pulmonary vascular resistance falls with increasing age. Heart failure may be mitigated in those patients with left ventricular outflow tract (pulmonary) stenosis.

Arterioplasty in patients with supravalve pulmonary or pulmonary artery branch stenosis following arterial switch surgery may be an effective and durable management option in the immediate term.[5] In a retrospective study (2004-2013) comprising 223 patients who underwent arterial switch for transposition of the great arteries, 38 patients (16%) developed supravalve pulmonary stenosis within 12.5 months. The surgical morbidity (eg, main pulmonary artery plasty) was 13%, without hospital or late mortality. At the 41.2 months postsurgical follow-up, all the patients had New York Heart Association (NYHA) functional grade 0 or 1 symptoms.[5]  Cardiac catheterization and endovascular stenting of the branch pulmonary arteries is an alternative in older patients versus cardiac surgery.

A retrospective study (1995-2016) that evaluated midterm outcomes in 97 patients with congenitally corrected transposition of the great arteries who underwent different management strategies reported similar transplant-free survival in those who underwent a systemic right ventricle (93%), anatomic repair (86%), and Fontan procedure (100%) (there was a 79% transplant-free survival for pulmonary artery band or shunt) (P = 0.33).[6]  Multivariate analysis demonstrated systemic right ventricular dysfunction as a risk factor for death or transplantation.

A small percentage (approximately 5%) of patients with transposition of the great arteries (and often a ventricular septal defect) develop accelerated pulmonary vascular obstructive disease and progressive cyanosis despite surgical repair or palliation. Long-term survival in this subgroup is particularly poor.

Complications

Complications include the following:

  • Congestive heart failure

  • Arrhythmia

  • Eisenmenger syndrome (irreversible and progressive pulmonary vascular obstructive disease)

  • Supravalve pulmonary or branch pulmonary artery stenosis

  • Coronary artery ostial obstruction (coronary ischemia)

Rare cases of supravalvular aortic stenosis as a late complication of transposition of the great arteries have been reported.[7]

Patient Education

Family members should learn cardiopulmonary resuscitation (CPR).

Educate family members about congenital heart disease.

Obtain genetics counseling for future pregnancy, despite the relatively low risk of recurrence.

For patient education resources, see the Heart Health Center, as well as Tetralogy of Fallot.

 

Presentation

History

Infants with transposition of the great arteries (TGA) are usually born at term, with cyanosis apparent within hours of birth.

The clinical course and manifestations depend on the extent of intercirculatory mixing and the presence of associated anatomic lesions. Note the following:

  • Transposition of the great arteries with intact ventricular septum: Prominent and progressive cyanosis within the first 24 hours of life is the usual finding in infants if no significant mixing at the atrial level is evident.

  • Transposition of the great arteries with large ventricular septal defect: Infants may not initially manifest symptoms of heart disease, although mild cyanosis (particularly when crying) is often noted. Signs of congestive heart failure (tachypnea, tachycardia, diaphoresis, and failure to gain weight) may become evident over the first 3-6 weeks as pulmonary blood flow increases.

  • Transposition of the great arteries with ventricular septal defect and left ventricular outflow tract obstruction: Infants often present with extreme cyanosis at birth, proportional to the degree of left ventricular (pulmonary) outflow tract obstruction. The clinical history may be similar to that of an infant with tetralogy of Fallot.

  • Transposition of the great arteries with ventricular septal defect and pulmonary vascular obstructive disease: Progressively advancing pulmonary vascular obstructive disease can prevent this rare subgroup of patients from developing symptoms of congestive heart failure, despite a large ventricular septal defect. Most often, patients present with progressive cyanosis, despite an early successful palliative procedure.

Physical Examination

Newborns with transposition of the great arteries are usually well developed, without dysmorphic features. Physical findings at presentation depend on the presence of associated lesions. Note the following:

  • Transposition of the great arteries with intact ventricular septum: Infants typically present with progressive central (perioral and periorbital) cyanosis. Other than cyanosis and a loud, single second heart sound (S2), the physical examination is often unremarkable.

  • Transposition of the great arteries with large ventricular septal defect: Cyanosis may be mild initially, although it is usually more apparent with stress or crying. Upon presentation, infants often have an increased right ventricular impulse; a loud, single second heart sound (S2); usually no systolic murmurs; possibly a mid-diastolic rumble; and gallop rhythm. Hepatomegaly may be present.

  • Transposition of the great arteries with ventricular septal defect and left ventricular outflow tract obstruction: Cyanosis is prominent at birth, and the findings are similar to those of infants with tetralogy of Fallot. A single second heart sound (S2) and a systolic ejection murmur may be present. Hepatomegaly is rare.

  • Transposition of the great arteries with ventricular septal defect and pulmonary vascular obstructive disease: Progressive pulmonary vascular obstructive disease is not always evident from physical examination findings. A loud, single second heart sound (S2) is present. Cyanosis is usually present and can progress despite palliative therapy in the newborn period.

 

DDx

Diagnostic Considerations

Important considerations

Note the following:

  • Consider transposition of the great arteries (TGA), particularly in a cyanotic newborn

  • Adequately delineate coronary artery anatomy preoperatively

  • Appropriately interpret diagnostic information, including echocardiography, radiography, and oxygenation studies

  • Inform patients and caregivers of young children regarding the potential complications of surgery, including death

Differential Diagnoses

 

Workup

Laboratory Studies

Abnormal pulse oximetry findings with a discrepancy between the upper and lower extremities is consistent with inadequate intracardiac mixing.

A hyperoxia test (for cyanotic congenital heart disease) may be indicated in patients with transposition of the great arteries (TGA).

In a patient with arterial hypoxemia, an arterial blood gas (ABG) measurement is obtained on 100% oxygen for 10 minutes.

Pulmonary disease (not cyanotic congenital heart disease) is suspected if the partial pressure of oxygen increases to more than 150 mm Hg with oxygen.

Note the following:

  • Admit patients with TGA for preoperative testing and surgical interventions.

  • Carefully monitor medication doses and side effects.

  • Monitor adequacy of repair and palliation with periodic physical examinations and possibly echocardiograms.

  • Periodic electrocardiograms and/or 24-hour Holter monitoring to monitor for atrial arrhythmias should be employed, particularly following atrial-level switch operation (ie, Senning or Mustard procedure).

Procedures

Cardiac catheterization

Neonatal diagnostic cardiac catheterization is usually reserved for the subgroup of patients for whom echocardiography does not adequately delineate the coronary artery anatomy. See the angiograms below.

This right ventricular angiogram shows a patient w This right ventricular angiogram shows a patient with transposition of the great arteries. The aorta arises directly from the right-sided anterior right ventricle (70° left anterior oblique [LAO]).
This left ventricular angiogram shows a patient wi This left ventricular angiogram shows a patient with transposition of the great arteries. The pulmonary artery arises directly from the left-sided posterior left ventricle (30° right anterior oblique [RAO]).
This left ventricular angiogram shows a patient wi This left ventricular angiogram shows a patient with transposition of the great arteries. The pulmonary artery arises directly from the left-sided posterior left ventricle (20° cranial).

In addition, cardiac catheterization may be necessary to improve left-to-right shunting at the atrial level (see the following videos demonstrate a restrictive atrial septal communication before and following balloon atrial septostomy).

This echocardiographic video (subcostal view) in a 1-day-old newborn reveals transposition of the great vessels and inadequate intracardiac mixing at the atrial level, resulting in severe desaturation. The video was obtained before the infant underwent balloon atrial septostomy. Video courtesy of Howard S Weber, MD, FSCAI.
This two-dimensional echocardiographic video (subcostal view) was obtained immediately following emergent balloon atrial septostomy in the same newborn discussed in the previous video. It now demonstrates a nonrestrictive atrial communication, which resulted in alleviation of the infant's cyanosis. Video courtesy of Howard S Weber, MD, FSCAI.

Postcatheterization precautions include hemorrhage, vascular disruption after balloon dilation, pain, nausea and vomiting, and arterial or venous obstruction from thrombosis or spasm.

Complications may include rupture of blood vessel, tachyarrhythmias, bradyarrhythmias, and vascular occlusion.

Chest Radiography

The chest radiograph may appear normal in newborns with transposition of the great arteries and intact ventricular septum with adequate atrial level mixing, but it may demonstrate the classic "egg on a string" appearance in approximately one third of patients. In newborns who present with extreme cyanosis, the pulmonary vascularity will appear to be increased, indicating inadequate atrial level mixing.

With a ventricular septal defect, cardiomegaly usually occurs with increased pulmonary arterial vascular markings.

Echocardiography

Echocardiographic images should be diagnostic of transposition of the great arteries by demonstrating the bifurcating pulmonary artery arising posteriorly from the left ventricle in the parasternal long-axis view.

The parasternal short-axis view shows the relationship of the great arteries to one another. The aorta is usually anterior and rightward of the pulmonary artery in cross-section.

Most associated anatomic lesions, including atrial septal defects, ventricular septal defects, and patent ductus arteriosus, are also diagnosed readily by echocardiography.

The coronary artery anatomy needs to be ascertained and may be abnormal in nearly one third of patients. The coronary artery origins and branching pattern are often delineated by echocardiography.

In a retrospective study of the relationship between interatrial communication, ductus arteriosus, and pulmonary flow to help predict postnatal desaturation in transposition of the great arteries and intact ventricular septum in 45 affected fetuses compared with 50 age-matched controls, echocardiography in fetuses with postnatal saturations of 50% or lower revealed a smaller interatrial communication as well as the presence of a retrograde diastolic flow in most of these fetuses relative to those with postnatal saturations over 50%.[8]  Compared with the control fetuses, those with transposition of the great arteries had a lower flow through the ductus arteriosus.

Magnetic Resonance Imaging

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (MRI) studies may have the potential to help clinicians stratify risk in patients with transposition of the great arteries following atrial switch procedure.[9] In a single-center prospective study of 55 patients with transposition of the great arteries who underwent LGE MRI, investigators found that the presence of systemic right ventricular fibrosis was strongly associated with adverse clinical outcomes, particularly new-onset sustained tachyarrhythmias.[9]   MRI studies may be useful in evaluating the supravalve pulmonary, aortic, and branch pulmonary artery regions if significant stenosis is suspected.

 

Treatment

Medical Care

Initial treatment of transposition of the great arteries consists of maintaining ductal patency with continuous intravenous (IV) prostaglandin E1 (PgE1) infusion to promote pulmonary blood flow, increase left atrial pressure, and promote left-to-right intercirculatory mixing at the atrial level. This is particularly important in patients with severe left ventricular outflow tract stenosis or atresia. Administration of PgE1 within the first 48 hours after birth is crucial to reduce early mortality in newborns with transposition of the great arteries, especially in the simple form.[10]

Cardiac catheterization and balloon atrial septostomy is indicated in severely hypoxemic patients with an inadequate atrial level communication and insufficient mixing (preductal saturations significantly lower than postductal saturations). Balloon atrial septostomy is used to increase the atrial level shunt and to improve mixing.

For the ill neonate, metabolic acidosis should be corrected with fluid replacement and bicarbonate administration.

Mechanical ventilation may be necessary if pulmonary edema develops in concert with severe hypoxemia.

Ultimately, the patient requires surgical repair or palliation early in life.

Consultations

Consult with a pediatric cardiologist and a pediatric cardiothoracic surgeon.

Transfer

Transfer is required for specialized diagnostic, therapeutic, and surgical interventions.

Diet and activity

Patients with transposition of the great arteries and a large ventricular septal defect who have not undergone repair may require increased caloric density during infancy (120-130 kcal/kg/d), particularly if they have significant congestive heart failure and poor weight gain.

Following definitive repair, most patients do not need a special diet.

Specific activity restrictions are dependent on the patient's residual hemodynamic abnormalities. Following the arterial switch procedure, exercise stress testing is necessary in older patients who are interested in participating in competitive sports.

Surgical Care

Surgical approach depends on the age of the patient at presentation, the presence of associated congenital cardiac lesions, and the experience of the cardiothoracic surgeon with a given surgical technique. Most full-term neonates with uncomplicated transposition of the great arteries can undergo an arterial switch procedure in one operation, with minimal mortality.

Transposition of the great arteries with intact ventricular septum

The ideal operation is an arterial switch procedure. It represents an anatomic repair and establishes ventriculoarterial concordance. This procedure should be performed when the infant is younger than 4 weeks, as the left ventricle may not be able to handle systemic pressure postoperatively if left too long in the low-pressure, low-resistance pulmonary circuit. Rarely, however, depending on the particular coronary artery anatomy (eg, intramural coronary artery), coronary artery translocation may not be feasible, and an arterial switch is not recommended. In this subgroup, an atrial level switch (Senning or Mustard procedure) has lower surgical and short-term morbidity and mortality.

Transposition of the great arteries with ventricular septal defect

The preferred operation is an arterial switch procedure with ventricular septal defect closure (see the videos below). If the ventricular septal defect is large and nonrestrictive and coronary artery anatomy makes an arterial switch operation inadvisable, a Rastelli-type intracardiac repair may be feasible. With the Rastelli-type procedure, waiting until the infant is older and larger may be preferred because of the need for a right ventricle–pulmonary artery conduit in the Rastelli operation. If the infant has excessive congestive heart failure (with growth failure), it may be advisable to either proceed with reparative surgery or, if not feasible, band the main pulmonary artery during the newborn period to restrict pulmonary blood flow.

This video shows the repair of a newborn with transposition of the great arteries and ventricular septal defect (VSD) by means of arterial switch and VSD closure. Procedure performed by Giles Peek MD, FRCS, CTh, FFICM, The Children’s Hospital at Montefiore, Bronx, NY. Video courtesy of Montefiore.
Switch ventricular septal defect (VSD hypoplastic right arch). Procedure performed by Giles Peek MD, FRCS, CTh, FFICM, The Children’s Hospital at Montefiore, Bronx, NY. Video courtesy of Montefiore.

Transposition of the great arteries with ventricular septal defect and left ventricular outflow tract obstruction

An arterial switch operation may not be feasible due to pulmonary valve (left ventricular outflow tract) stenosis or atresia. If the ventricular septal defect is nonrestrictive and remote from the aorta, a Rastelli intracardiac repair could be possible. Because the Rastelli procedure necessitates a conduit from the right ventricle to the pulmonary artery, delaying repair until the infant is older and larger may be preferable. In this case, placing an aortopulmonary shunt during the newborn period may be necessary to establish adequate pulmonary blood flow while waiting.

Transposition of the great arteries with ventricular septal defect and pulmonary vascular obstructive disease

These patients might not be appropriate surgical candidates because of the progressive increase in pulmonary vascular resistance. This is a small subgroup of patients whose conditions are not often diagnosed until after a palliative or reparative procedure is performed.

Long-Term Monitoring

Evidence from the Boston Circulatory Arrest Trial suggests that neurodevelopmental outcomes for children with dextro-transposition of the great arteries (d-TGA) who undergo arterial switch operation (and other complex neonatal operations) may not be normal and may require further investigation and follow-up.[11]

Many patients do not require any specific medications. Possible discharge medications might include digoxin, furosemide, or both.

 

Medication

Medication Summary

Transposition of the great arteries (TGA) has no specific or recommended drug therapies. Newborn infants with transposition of the great arteries (particularly those with severe left ventricular outflow tract obstruction) may benefit from alprostadil (ie, prostaglandin E1) therapy. Patients with transposition of the great arteries and ventricular septal defect who have not undergone surgical repair, and some patients following complete repair, might potentially benefit from digoxin and diuretic therapy to improve systemic ventricular function and avoid fluid retention.  

For more information, see Antibiotic Prophylactic Regimens for Endocarditis.

All patients require antibiotic prophylaxis prior to dental and indicated surgical procedures in order to reduce the risk of subacute bacterial endocarditis. Thus, all patients require preoperative and postoperative antibiotic prophylaxis for dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa. Antibiotic prophylaxis is also recommended for invasive respiratory tract procedures that involve incision or biopsy of the respiratory mucosa (eg, tonsillectomy, adenoidectomy). Antibiotic prophylaxis is not recommended for bronchoscopy unless the procedure involves incision of the respiratory tract mucosa. For invasive respiratory tract procedures to treat an established infection (eg, drainage of abscess, empyema), administer an antibiotic active against Streptococcus viridans.

See the endocarditis prophylaxis guidelines that were revised by the American Heart Association (AHA).[12]

Inotropic agents

Class Summary

These drugs increase the contractility of cardiac muscle in a dose-dependent manner (ie, positive inotropic effect).

Digoxin (Lanoxin)

Frequently used cardiac glycoside that inhibits the sarcolemmal sodium-potassium adenosine triphosphatase, which leads to an increase in intracellular calcium concentration and increased myocardial contractility.

Loop diuretics

Class Summary

These drugs inhibit electrolyte reabsorption in the thick ascending limb of the loop of Henle, thus promoting diuresis.

Furosemide (Lasix)

This is a commonly used loop diuretic with moderate diuretic potency. Increases excretion of water by interfering with chloride-binding co-transport system which in turn inhibits sodium and chloride reabsorption in ascending loop of Henle and distal renal tubule.

Prostaglandins

Class Summary

Temporary maintenance of patency of ductus arteriosus in neonates with ductal-dependent congenital heart disease.

Alprostadil IV (Prostin VR)

Identical to the naturally occurring prostaglandin E1 (PGE1) and possesses various pharmacologic effects, including vasodilation and inhibition of platelet aggregation. Temporary maintenance of patency of ductus arteriosus in neonates with ductal-dependent congenital heart disease. Relaxes smooth muscle of the ductus arteriosus. Beneficial in infants with congenital defects that restrict pulmonary or systemic blood flow and who in order to get adequate oxygenation and lower body perfusion, depend on a patent ductus arteriosus.