AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

Section 2 of 11  

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Background

Aortopulmonary septal defect (APSD), an uncommon congenital cardiac defect, is a deficiency in the septum between the aorta and pulmonary artery resulting in a communication between the two. This defect exists as an isolated lesion in about one half of patients and in conjunction with another defect or more complex heart disease in the other half of patients.

Developmentally, the defect results from incomplete separation of the common tube of the truncus arteriosus and the aorticopulmonary trunk. During early embryonic development, the aorta and pulmonary arteries separate by growth of a spiral septum dividing the common trunk into the aorta and the pulmonary artery. The spiral septum is created by fusion of a truncal septum growing cephalad from the semilunar valves and the aorticopulmonary spiral septum growing caudally from the pulmonary bifurcation. Incomplete development of these septa results in APSD.

van Mierop subdivided APSD into 3 subtypes. The first subtype is thought to result from nonfusion between the aorticopulmonary septum above and the truncal septum below, resulting in a small-to-moderate defect midway between the semilunar valves and the pulmonary bifurcation. The second type is also believed to arise from a failure of fusion of the aorticopulmonary septum above and the truncal septum below but results in a large, nonrestrictive defect without a continuous posterior border in which the defect describes more than one spiral turn. The third type is absence of the aorticopulmonary septum; the defect is large and without a posterior border, and the right pulmonary artery may arise directly from the aorta. Although this classification system may correlate with the various embryologic origins of APSD itself, it does not account for other anomalies encountered with APSD.

Patent ductus arteriosus (PDA) is encountered in almost three fourths of patients with APSD. An interrupted aortic arch type A or severe coarctation is present in 10-15% of patients with APSD. Discontinuity of the aorta in type-A interruption occurs distal to the left subclavian artery, like a severe form of aortic coarctation. It is quite different developmentally from interrupted aortic arch type B in which discontinuity occurs between the left carotid and left subclavian arteries. Type-B interruption is frequently associated with DiGeorge/velocardiofacial/22q-chromosome arm deletion, unlike type A. When interrupted aortic arch occurs without a ventricular septal defect (VSD), an APSD is usually present.

Tetralogy of Fallot and anomalous coronary from pulmonary artery are each present in about 5% of cases. Other reported anomalies associated with APSD include VSD, aortic atresia, transposition of the great arteries, double aortic arch, and other more complex heart diseases.

APSD has been described in other mammals including dogs, cats, and horses.

Pathophysiology

The fetus is unaffected by this defect. Problems arise after birth with the fall in pulmonary vascular resistance (PVR) that typically takes place over the first days and weeks of life. As PVR falls, progressive shunting of blood from the systemic circuit to the pulmonary circuit results in pulmonary edema and signs and symptoms of congestive heart failure (CHF) similar to those seen with a large VSD or patent ductus arteriosus (PDA). Left untreated, irreversible pulmonary vascular obstructive disease (PVOD) is likely to develop. In some cases, PVR does not fall significantly after birth and the phase of CHF is not apparent. In these instances, PVOD is a consequence nonetheless.

Frequency

United States

APSD is a rare defect comprising about 0.1-0.3% of congenital heart diseases in children. No attempt to assess regional or worldwide variation in incidence has been made.

Mortality/Morbidity

Left untreated, an aortopulmonary window results in irreversible pulmonary vascular changes and early mortality. With surgical treatment in the absence of PVOD, the prognosis for isolated aortopulmonary window is good. In the presence of more complex heart disease, prognosis depends more on the nature of other lesions.

Race

No racial predilection exists.

Sex

The male-to-female ratio is approximately 1.8:1.

Age

As a congenital disease, all cases are present from birth. The diagnosis typically is made in infancy but may be delayed if persistently elevated PVR exists. Because of improved fetal ultrasonography, prenatal diagnosis of APSD has also been reported.

CLINICAL

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History

The clinical presentation depends on the size of the defect, PVR, and associated anomalies.

• In a large defect with falling PVR, aortopulmonary septal defect (APSD) presents with typical signs and symptoms of CHF indistinguishable from those of a large VSD or ductus arteriosus.
• • Symptoms usually emerge between the second and eighth weeks of life.
  • Caregivers typically report signs of CHF as tachypnea and diaphoresis (especially with feeds), poor feeding, and usually poor growth.
• If APSD is associated with interrupted aortic arch or severe coarctation, the infant may present with signs and symptoms of shock in newborn period as the ductus arteriosus closes.
• In less common scenarios (about 10% of patients), the defect is small and restrictive and presents as an asymptomatic murmur in the first weeks to months of life.
• In presence of a large, nonrestrictive defect, PVR in some patients may not fall significantly, CHF does not develop, and the patients may be relatively asymptomatic.
• • Because pulmonary and systemic resistances are comparable, there may be some right-to-left shunting, and mild cyanosis may exist, yet not be clinically apparent.
  • Unfortunately, despite lack of symptoms, irreversible PVOD typically develops with time. At this stage, fatigue, exercise intolerance, and cyanosis may appear.
  • Children with persistently elevated PVR are most difficult to identify clinically, and many go years before being diagnosed with serious heart disease.

Physical

• If a large, nonrestrictive defect with low PVR exists, then physical examination findings are indistinguishable from those of a large PDA. These findings include tachypnea, tachycardia, and increased work of breathing.
• • Continuous run-off into the pulmonary circuit during diastole, in combination with an elevated stoke volume, causes a wide pulse pressure with bounding pulses.
  • Palpation reveals a hyperdynamic precordial impulse from increased volume load on the left ventricle.
  • Auscultation reveals a loud and single second heart sound with a continuous murmur at the left upper sternal border. Often, a gallop rhythm and an apical diastolic rumble from increased volume load are present.
  • Hepatic congestion and hepatomegaly develop in proportion to the degree of heart failure.
  • Failure to thrive is concomitant with the degree of heart failure.
• In situations in which PVR fails to fall significantly after birth, findings may be subtler.
• • The second heart sound is single, yet there may be no murmur or only a soft systolic murmur. Pulses are not bounding, as there is little diastolic run-off.
  • Subtle cyanosis may be present from a small amount of right-to-left shunt when pulmonary and systemic resistances are comparable. With irreversible pulmonary vascular changes and Eisenmenger syndrome, cyanosis may become more prominent. Cyanosis will be present if other cyanotic lesions are present (eg, transposition of the great vessels, tetralogy of Fallot).
• A continuous murmur may be the only physical finding if the defect is small and restrictive.

Causes

• APSD likely is caused by multifactorial genetic etiologies. No clear inheritance pattern exists in most patients. Although this defect appears to have clinical similarities with truncus arteriosus and interrupted aortic arch type B, APSD is not associated with the 22q-/DiGeorge syndrome as are the other malformations. Note that aortic arch interruption commonly associated with APSD occurs as a type-A interruption rather than type-B interruption.
• Rarely, APSD has been described in children affected by other syndromes, including vertebral, anorectal, cardiac, tracheoesophageal, renal, and limb (VACTERL) association, with one case report of an infant with terminal 2q deletion.
• One small case series described 3 unrelated children with iris hypoplasia and APSD. The hypothesized association between the 2 problems is an error in neural crest development.

DIFFERENTIALS

Section 4 of 11  

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WORKUP

Section 5 of 11  

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Lab Studies

• Preoperatively, obtain a complete blood count, cross match, and urinalysis. If the infant has been on diuretics and digoxin preoperatively, it may be prudent to check electrolytes and a digoxin level. Infants with CHF are at risk for potassium depletion from diuretics and may be at risk for digoxin toxicity from routine dosing during decreased renal perfusion. The combination of a volume-loaded circulation with potassium depletion and an elevated serum digoxin level may be a risk factor for ventricular fibrillation at the time of sternotomy.

Imaging Studies

• Chest radiograph typically shows cardiomegaly with increased pulmonary blood flow. Pulmonary congestion is proportional to the degree of CHF.
• ECG typically shows biventricular hypertrophy or right ventricular hypertrophy. Electrical evidence for left atrial enlargement may present.
• Echocardiogram
• • In infants and children, this test (if performed by experienced personnel and reviewed by a skilled pediatric echocardiographer) should show the defect and associated abnormalities in virtually all cases. Doppler color flow mapping shows retrograde flow in the transverse arch during diastole. By contrast, in an infant with a large left-sided PDA and a left aortic arch, diastolic flow in the arch is antegrade. For patients with poor echocardiographic windows, transesophageal echocardiography or cardiac MRI may be an option.
  • When an aortopulmonary septal defect (APSD) is found, the echocardiographer should be especially careful to look for other abnormalities, which are present in 50% of cases of APSD. In addition to identifying the APSD, the ventricular septum, origins of the pulmonary arteries, aortic arch, presence of a PDA, and origins of the coronary arteries should be carefully scrutinized.
• Cardiac catheterization
• • Cardiac catheterization (CC) should not be required if anatomy has been well defined by noninvasive means and if the clinical and noninvasive data are both consistent with low PVR. Where questions or additional incompletely characterized defects exist, careful hemodynamic and angiographic assessment may be helpful.
  • Beyond infancy, CC may be required to exclude irreversible PVOD before performing surgical repair. In older children with a diagnosis of a nonrestrictive AP window, CC is advisable to establish pulmonary vascular reactivity before performing surgical repair. In the rare instance of a small restrictive defect, catheter therapy with device occlusion of the defect may be an option.

TREATMENT

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Medical Care

• Medical palliation of this condition may be performed for several days to weeks to allow elective surgical scheduling. Since an aortopulmonary window does not close spontaneously, surgical repair is necessary to prevent the development of pulmonary vascular obstructive disease. Meanwhile, digoxin and diuretics may provide some symptomatic benefit before surgical repair.

  In rare instances (eg, active sepsis), it may be desirable to postpone surgery. In this situation, provide medical therapy (ie, digoxin, inotropic drugs, diuretics) for a brief time in anticipation of surgery

• • The effect of vasodilator agents (eg, angiotensin-converting enzyme [ACE] inhibitors, phosphodiesterase inhibitors, nitrates) is uncertain, as these drugs all affect pulmonary resistance in addition to systemic resistance.
  • Intubation and positive pressure ventilation with permissive hypercarbia and limiting inspired oxygen concentration to 21% may help limit pulmonary blood flow in infants with torrential pulmonary flow requiring medical palliation. Consider using lower inspired oxygen concentrations (15-19%) to elevate PVR in more extreme cases. Sedation and muscle relaxants may prove necessary to limit spontaneous ventilation.
• Previous common practice consisted of medically treating a small infant with CHF with the expectation that he or she would grow and become a "better" surgical candidate. This approach is seldom successful, as caloric demands of an infant with CHF typically exceed the amount of nutrition delivered by even the most aggressive means.
• Case reports exist of closure of small aortopulmonary septal defects (APSDs) in the CC lab. The youngest child to undergo this procedure was aged 6 months. The Rashkind double umbrella device, the Amplatzer duct occluder, and Amplatzer septal occluder have all been used to close small (type I) defects. The limiting factor to catheter closure of these defects is the anatomy. Only relatively small defects with circumferential tissue rims are amenable to transcatheter device closure, limiting this therapeutic option to a relatively small number of patients.

Surgical Care

A variety of surgical techniques exist to correct this lesion.

• Most centers use techniques that involve cardiopulmonary bypass.
• • The aorta and pulmonary artery may be divided and the defects in the walls closed primarily or with patch material. Alternatively, the aorta or pulmonary artery may be opened and the defect patched using autologous, homologous, xenograft, or synthetic material. Two recent, larger case series have found that transaortic repair is associated with a more favorable outcome and has less risk of causing late pulmonary artery stenosis.
  • Other defects may be addressed at the same operation, although, in rare instances, a staged approach may be undertaken.
  • Specific techniques for unique anatomy must be individualized.
• Postoperatively, evidence of a good surgical repair should be confirmed. Residual anatomic problems may be anticipated from preoperative anatomy and include, but not be limited to, pulmonary artery stenosis or distortion, residual left-to-right shunt at the APSD site, and ascending aortic obstruction or distortion. Postoperative data should be consistent with a complete repair.
• • If a pulmonary artery catheter was left in place, it should indicate low pulmonary artery pressure and pulmonary artery oxygen saturation less than 80%.
  • An elevated pulmonary artery pressure may indicate pulmonary artery vasoreactivity or a persistent left-to-right shunt. Pulmonary artery saturation and left atrial pressure should differentiate the two conditions. If concerns persist, transthoracic or transesophageal echocardiography may be informative. On rare occasions, cardiac catheterization may be needed to detect residual abnormalities.
• Apart from anatomic concerns, an older infant or child with elevated preoperative PVR is at risk for postoperative pulmonary hypertension that may require aggressive management.
• Apart from anatomic concerns, an older infant or child with elevated preoperative PVR is at risk for postoperative pulmonary hypertension that may require aggressive management.
• • Inhaled nitric oxide may be useful in the management of postoperative pulmonary hypertension by acting as a selective pulmonary arteriolar vasodilator.
  • Other drugs such as sildenafil or calcium channel blockers may provide ongoing pulmonary vasodilatation.

Consultations

Consult a pediatric cardiologist for diagnosis. Then, refer the patient to a competent cardiovascular surgical team experienced in the repair of congenital heart disease.

Diet

High-calorie formula may be needed for infants with CHF perioperatively.

Activity

Activity generally is not restricted in patients with this defect, except in those with Eisenmenger syndrome.

MEDICATION

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Digitalis and diuretics may be used to palliate this condition for a short time before surgical repair as discussed in Medical Care.

Drug Category: Cardiac Glycoside

Digitalis may be used in the management of CHF. Exerts positive inotropic effect, which increases the force of contraction of the myocardium. The mode of action by which digitalis improves symptoms is complex, but probably results from both increased cardiac contractility and neurohormonal actions.

Drug Category: Diuretics

These agents improve symptoms by decreasing total body water, thereby decreasing pulmonary fluid and improving breathlessness. They promote excretion of water and electrolytes by the kidneys. They are used to treat heart failure or hepatic, renal, or pulmonary disease when sodium and water retention has resulted in edema or ascites. Use multiple strategies to medically manage CHF in infancy. Carefully monitor fluid status and electrolyte balance of infants on anticongestive medications.

FOLLOW-UP

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Further Inpatient Care

• Preoperative inpatient care (if required) is directed at managing CHF and completing the diagnostic evaluation in anticipation of surgery. Postoperative care should focus on managing pulmonary hypertension, evaluating for residual defects, and aiding convalescence in anticipation of discharge.

Further Outpatient Care

• Provide follow-up care within 1-2 weeks following discharge. Patients are commonly discharged on diuretics, but if a good repair is achieved, most patients can be weaned from cardiac medications soon after discharge. Even in the absence of clinically evident problems, at least one postoperative echocardiogram should be performed during follow-up to evaluate for potentially silent problems.

In/Out Patient Meds

• In patients with postoperative aortic regurgitation or residual left-to-right shunting, bacterial endocarditis prophylaxis is indicated. Locate current American Heart Association (AHA) recommendations for endocarditis prophylaxis at American Heart Association. For more information, see Antibiotic Prophylactic Regimens for Endocarditis.

Transfer

• Transport patients, if needed, to a facility with the appropriate pediatric and/or pediatric cardiac surgical services.

Complications

• The most concerning complication in the repair of APSD is perioperative death from pulmonary hypertensive crisis in the child with PVOD. Other generic surgical complications include, but are not limited to, infection, brain injury, and permanent heart block. Although these are considerations, they should be of no higher risk in this procedure than they are in other cardiac procedures employing cardiopulmonary bypass. Specific anatomic risks of repair include incomplete closure of the defect and aortic or pulmonary artery distortion. Other complications may relate to repair of associated defects.

Prognosis

• Currently, infants with an isolated APSD have an excellent prognosis for normal cardiac function and a normal lifestyle. Patients with a more guarded prognosis include older patients with pulmonary resistance of greater than 8 Wood units/m² at preoperative assessment and those with more complex associated malformations where prognosis is more dependent on those lesions than on APSD. A small incidence of reintervention for stenosis of the great arteries has been reported.

Patient Education

• An experienced health care team comprised of nurses, social workers, and spiritual counselors can provide important support to parents of infants with newly diagnosed congenital heart disease.
• For excellent patient education resources, visit eMedicine's Heart Center. Also, see eMedicine's patient education article Tetralogy of Fallot.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Failure to recognize serious heart disease with associated pulmonary hypertension and high PVR until irreversible PVOD has developed (one of the most feared scenarios in pediatrics and pediatric cardiology)
• Failure to realize that heart diseases, including large ventricular septal defects, patent ductus arteriosus, and APSD, may present in this fashion (When PVR does not fall after birth, children may not have symptoms of CHF and may feed and grow normally with a paucity of cardiac findings.)
• Failure to recognize loud and single second heart sounds that indicate the existence of pulmonary hypertension, warranting further workup
• Failure by physician to ensure that he or she can clearly discern a splitting of the second heart sound with respiration on each cardiac examination on every child and refer the patient to a pediatric cardiologist for evaluation if heart sounds are suspicious
• Failure to identify APSD as the cause of a large left-to-right shunt causing CHF

MULTIMEDIA

Section 10 of 11  

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Media file 1:  Echocardiographic image of a 1-month-old infant with a large isolated aortopulmonary septal defect (APSD). The image is a parasternal short-axis view just below the pulmonary artery bifurcation. Aorta at this level is to the right and in the same anterior-posterior plane as the main pulmonary artery (MPA). Right pulmonary artery is seen posterior to the aorta at this level, but the origin of the pulmonary arteries is not visible; it is more superior than this axial image. Normally, a complete wall should be visible for both aorta and pulmonary artery. This image shows the absence of that wall, resulting in the large defect between aorta and pulmonary artery.
	View Full Size Image
Media type:

Media file 2:  Angiogram of a small-to-moderate APSD in a 4 year-old child. Complete occlusion of the APSD with an Amplatzer Duct Occluder.Ao = Ascending aortaPA = Pulmonary artery
	View Full Size Image
Media type:  X-RAY

REFERENCES

Section 11 of 11

• Authors and Editors
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• Differentials
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Article Last Updated: Jun 15, 2006