eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology

Aortopulmonary Septal Defect

Author: Barry A Love, MD, Assistant Professor, Department of Medicine, Division of Cardiology, Assistant Professor, Division Pediatric Cardiology, Pediatrics and Medicine, Division of Pediatric Cardiology, Mount Sinai School of Medicine
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Updated: Mar 16, 2009

Introduction

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 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.

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 aortopulmonary septal defect.

van Mierop subdivided aortopulmonary septal defect into 3 subtypes.¹ 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.^2,3 An interrupted aortic arch type A or severe coarctation is present in 10-15% of patients with aortopulmonary septal defect.⁴ 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.

Tetralogy of Fallot and anomalous coronary from pulmonary artery are each present in about 5% of cases,⁵ Other reported anomalies associated with aortopulmonary septal defect include VSD, aortic atresia, transposition of the great arteries,⁶ double aortic arch, and other more complex heart diseases.

Aortopulmonary septal defect has been described in other mammals including dogs, cats, and horses.⁷

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 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

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

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.⁸

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 is observed.

Sex

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

Age

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.⁹

Clinical

History

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.

Physical

• If a large, nonrestrictive defect with low 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.
  • 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.

Causes

• 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,¹⁰
• One small case series described 3 unrelated children with iris hypoplasia and aortopulmonary septal defect.¹¹ The hypothesized association between the 2 problems is an error in neural crest development.

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