Aortopulmonary Septal Defect

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 is present 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.[1]

Developmentally, the defect results from incomplete separation of the common tube of the truncus arteriosus and the aorticopulmonary trunk.[2, 3] 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 aortopulmonary septal defect.

van Mierop subdivided aortopulmonary septal defect into three subtypes.[4] The first subtype is believed 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; however, this failure of fusion 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 aortopulmonary septal defect itself, it does not account for other anomalies encountered with aortopulmonary septal defect.

Patent ductus arteriosus (PDA) is encountered in almost three fourths of patients with aortopulmonary septal defect.[5, 6] An interrupted aortic arch type A or severe coarctation is present in 10-15% of patients with aortopulmonary septal defect.[7] Discontinuity of the aorta in interrupted aortic arch type A occurs distal to the left subclavian artery, as in a severe form of aortic coarctation. This is quite different developmentally from interrupted aortic arch type B, in which discontinuity occurs between the left carotid artery and left subclavian arteries. Interrupted aortic arch type B is frequently associated with DiGeorge/velocardiofacial/22q-chromosome arm deletion, unlike interrupted aortic arch type A. When interrupted aortic arch occurs without a ventricular septal defect (VSD), an aortopulmonary septal defect is usually present.[8]

Tetralogy of Fallot and anomalous coronary from pulmonary artery are each present in about 5% of cases.[9, 10] Other reported anomalies associated with aortopulmonary septal defect include VSD, aortic atresia, transposition of the great arteries,[11, 12] double aortic arch, and other more complex heart diseases.

Aortopulmonary septal defect has been described in other mammals including dogs, cats, and horses.[13]

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 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.

Aortopulmonary septal defect is likely caused by multifactorial genetic etiologies. No clear inheritance pattern is noted in most patients. Although this defect appears to have clinical similarities with truncus arteriosus and interrupted aortic arch type B, aortopulmonary septal defect is not associated with the 22q-/DiGeorge syndrome as are the other malformations. Note that the aortic arch interruption commonly associated with aortopulmonary septal defect occurs as type A rather than type B.

Rarely, aortopulmonary septal defect 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.[14]

One small case series described three unrelated children with iris hypoplasia and aortopulmonary septal defect.[15] The hypothesized association between the two problems is an error in neural crest development.

United States data

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

International data

A large case series from India reported an overall frequency of surgery for aortopulmonary septal defect of 0.6% of all surgeries performed for congenital heart disease.[16]

Race-, sex-, and age-related demographics

No racial predilection is observed.

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

As a congenital disease, all cases are present from birth. The diagnosis is typically made in infancy but may be delayed if persistently elevated PVR occurs. Because of improved fetal ultrasonography, prenatal diagnosis of aortopulmonary septal defect has also been reported.[17, 18]

Infants with an isolated aortopulmonary septal defect have an excellent prognosis for normal cardiac function and a normal lifestyle.[1]

Patients with a more guarded prognosis include older patients with pulmonary resistance of greater than 8 Wood U/m2 at preoperative assessment and those with more complex associated malformations where prognosis depends more on those lesions than on aortopulmonary septal defect.

A small incidence of reintervention for stenosis of the great arteries has been reported.

Morbidity/mortality

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.[19]

Complications

The most concerning complication in the repair of aortopulmonary septal defect is perioperative death from pulmonary hypertensive crisis in the child with pulmonary vascular obstructive disease (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 using 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.

An experienced healthcare team comprised of nurses, social workers, and spiritual counselors can provide important support to parents of infants with newly diagnosed congenital heart disease.

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

The clinical presentation of aortopulmonary septal defect (APSD) depends on the size of the defect, pulmonary vascular resistance (PVR), and associated anomalies.

In a large defect with falling PVR, aortopulmonary septal defect presents with typical signs and symptoms of congestive heart failure (CHF) indistinguishable from those of a large ventricular septal defect (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 aortopulmonary septal defect 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, some right-to-left shunting and mild cyanosis may be present yet not clinically apparent. Unfortunately, despite lack of symptoms, irreversible pulmonary vascular obstructive disease (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 years pass before diagnosis with serious heart disease.

If a large, nonrestrictive defect with low pulmonary vascular resistance (PVR) is present, then physical examination findings are indistinguishable from those of a large patent ductus arteriosus (PDA). These findings include tachypnea, tachycardia, and increased work of breathing. Note the following:

• 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 no murmur or only a soft systolic murmur may be observed. Pulses are not bounding; little diastolic run-off is noted. 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.

Obtain a CBC count, cross match, and urinalysis preoperatively in patients with an aortopulmonary septal defect (APSD).

If the infant has been on diuretics and digoxin preoperatively, checking electrolyte and digoxin levels is prudent.

Infants with congestive heart failure (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.

In infants and children, this test (if performed by experienced personnel and reviewed by a skilled pediatric echocardiographer) should reveal the defect and associated abnormalities in virtually all cases.[20, 21] See the image below.

Doppler color flow mapping shows retrograde flow in the transverse arch during diastole. By contrast, in an infant with a large left-sided patent ductus arteriosus (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.[22]

When an aortopulmonary septal defect is found, the echocardiographer should be especially careful to look for other abnormalities, which are present in 50% of cases of aortopulmonary septal defect. In addition to identifying the aortopulmonary septal defect, the ventricular septum, origins of the pulmonary arteries, aortic arch, presence of a PDA, and origins of the coronary arteries should be carefully scrutinized.

In addition, 3-dimensional echocardiography has been used to help characterize an aortopulmonary septal defect.[23]

Chest Radiography

Radiography typically reveals cardiomegaly with increased pulmonary blood flow. Pulmonary congestion is proportional to the degree of CHF.

Electrocardiography

ECG typically reveals biventricular hypertrophy or right ventricular hypertrophy. Electrical evidence for left atrial enlargement may present.

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 pulmonary vascular resistance (PVR). If questions or additional incompletely characterized defects are noted, careful hemodynamic and angiographic assessment may be helpful.

Beyond infancy, CC may be required to exclude irreversible pulmonary vascular obstructive disease (PVOD) before performing surgical repair. In older children with a diagnosis of a nonrestrictive aortopulmonary 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.

Medical palliation of aortopulmonary septal defect (APSD) may be performed for several days to weeks to allow elective surgical scheduling. Because an aortopulmonary window does not spontaneously close, surgical repair is necessary to prevent the development of pulmonary vascular obstructive disease (PVOD). Meanwhile, digoxin and diuretics may provide some symptomatic benefit before surgical repair.

Preoperative inpatient care of patients with APSD is directed at managing congestive heart failure (CHF) and completing the diagnostic evaluation in anticipation of surgery. In rare instances (eg, active sepsis), postponing surgery may be desired. 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 because 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 pulmonary vascular resistance (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 congestive heart failure (CHF) with the expectation that he or she would grow and become a "better" surgical candidate. This approach is seldom successful because caloric demands of an infant with CHF typically exceed the amount of nutrition delivered by even the most aggressive means.

Case reports and small case series report closure of small aortopulmonary septal defects in the cardiac catheterization (CC) lab. The Rashkind double umbrella device,[24] the Amplatzer duct occluder,[25] the Amplatzer septal occluder, muscular ventricular septal defect (VSD) occluder, and perimembranous VSD occluder have all been used to close small (type I) defects.[26] 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. See the image below.

Important considerations

The following are essential issues to keep in mind:

• Early recognition of serious heart disease with associated pulmonary hypertension and high pulmonary vascular resistance (PVR) is important, as irreversible pulmonary vascular obstructive disease (PVOD) may develop (one of the most feared scenarios in pediatrics and pediatric cardiology)

• Realization that heart diseases, including large ventricular septal defects (VSDs), patent ductus arteriosus (PDA), and aortopulmonary septal defect (APSD), may present in this fashion (When PVR does not fall after birth, children may not have symptoms of congestive heart failure [CHF] and may feed and grow normally with a paucity of cardiac findings.)

• Recognition of loud and single second heart sounds that indicate the existence of pulmonary hypertension, thereby warranting further workup

• Ensuring clearly discernment of a splitting of the second heart sound with respiration on each cardiac examination on every child, and referral of the patient to a pediatric cardiologist for evaluation if the heart sounds are suspicious

• Identification of aortopulmonary septal defect as the cause of a large left-to-right shunt causing CHF

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.

Transfer

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

Diet and activity

A high-calorie formula may be needed for infants with CHF perioperatively. Generally, activity is not restricted in patients with this defect, except in those with Eisenmenger syndrome.

Various surgical techniques allow correction of this lesion.[7, 27, 28, 29, 30, 31]

Most centers use techniques that involve cardiopulmonary bypass.

The aorta and pulmonary artery may be divided, and the defects in the walls may be 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 larger case series have reported 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; however, in rare instances, a staged approach may be undertaken.

Specific techniques for unique anatomy must be individualized.

A retrospective review (2002-2011) reported good outcomes associated with the use of a single pericardial patch technique for primary repair of an aortopulmonary window with an interrupted aortic arch.[32] In 6 of 11 patients, the interrupted aortic arch was type A; the remaining 5 patients had type B. Median age at the time of surgery was 11 days, with a mean weight of 2.6 kg; mean follow-up was 6 ± 3 years. There were no early and late deaths nor reoperations. There was one case of postoperative stroke without late sequelae. All patients at last follow-up visit had no recurrent aortic arch obstruction or pulmonary artery branch stenosis.[32]

Postoperatively, evidence of a good surgical repair should be confirmed.

Postoperative care should focus on managing pulmonary hypertension, evaluating for residual defects, and aiding convalescence in anticipation of discharge. 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 aortopulmonary septal defect 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. Rarely, cardiac catheterization may be needed to detect residual abnormalities. A case report indicated successful transcatheter closure of a late-onset residual shunt following repair of an aortopulmonary septal defect with the use of a muscular ventricular septal occlude.[33]

Postoperative pulmonary hypertension

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.

Follow-up 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.

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

Endocarditis prophylaxis is no longer recommended for most patients with congenital heart disease with the exception of the following[34] :

• Those who have had prior endocarditis

• Those with prosthetic heart valves

• Those with unrepaired cyanotic congenital heart disease (eg, palliative shunts and conduits)

• Those with completely repaired congenital heart defects that were repaired with prosthetic materials/devices within 6 months of the procedure

• Those with turbulence near patch material

Therefore, most patients with repaired and unrepaired aortopulmonary septal defect do not require endocarditis prophylaxis.[34, 35, 36] Go to Antibiotic Prophylactic Regimens for Endocarditis for more information.

Class Summary

Digitalis may be used in the management of congestive heart failure (CHF). It 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.

Digoxin (Lanoxicaps, Lanoxin)

Cardiac glycoside with direct inotropic effects in addition to indirect effects on the cardiovascular system. Acts directly on cardiac muscle, increasing myocardial systolic contractions. Its indirect actions result in increased carotid sinus nerve activity and enhanced sympathetic withdrawal for any given increase in mean arterial pressure.

May be given as a loading dose followed by a maintenance dose or simply as a maintenance regimen. Digitalis loading increases hazards of this drug. In management of CHF, little, if any, indication for digoxin loading is warranted. For more immediate inotropy, use IV beta-agonists.

Class Summary

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.

Furosemide (Lasix)

Increases excretion of water by interfering with chloride-binding cotransport system, which, in turn, inhibits sodium and chloride reabsorption in ascending loop of Henle and distal renal tubule. It is a very effective diuretic yet may cause significant potassium loss.

Chlorothiazide (Diuril)

Thiazide diuretic acts at the distal part of the nephron to inhibit sodium and chloride reabsorption. Used alone, this agent typically elicits a modest diuresis; however, when combined with furosemide, effects of both agents are potentiated with a potent diuretic effect.

Spironolactone (Aldactone)

Potassium-sparing diuretic that works on the distal tubule to inhibit sodium/potassium exchange at the aldosterone site. Although a weak diuretic alone, it helps limit potassium loss when used with other potent diuretics.