A Rare Case of Pulmonary Artery Sling and Complete Atrioventricular Canal Defect in an Infant With Trisomy 21

Case Presentation

A five-week-old infant girl with trisomy 21 and complete atrioventricular (AV) canal defect was admitted from cardiology clinic to the cardiac intensive care unit with acute onset of respiratory distress and stridor. On the day prior to admission, she was noted to have mild nasal congestion, noisy breathing, and was refusing to eat. The patient did not have a history of fever or known ill contacts. She was diagnosed with complete AV canal defect at birth. The patient was started on furosemide two weeks prior to this presentation due to tachypnea with feeding and seemed to be doing well and gaining weight on the current treatment. On examination, patient was noted to have severe respiratory distress, stridor at rest with poor air entry. A bedside nasopharyngoscopy showed mild laryngmalacia but no vocal cord edema. The patient was intubated and placed on mechanical ventilation with low settings. Respiratory viral polymerase chain reaction came back positive for rhinovirus. An echocardiogram was interpreted as unchanged from her newborn study with a complete AV canal defect and a small patent ductus arteriosus (PDA).

During admission, the patient started having episodes of desaturation while agitated. These were attributed to bronchospasm because of the notable decreased air entry associated with these spells. Extubation was attempted on hospital day 8 but was unsuccessful as she had very poor air entry, stridor, and was extremely tachypneic.

By hospital day 15, her clinical status remained unchanged on the ventilator. A flexible bronchoscopy was performed, which showed severe circumferential tracheal compression above the carina, with 90% narrowing (Figure 1). The presence of tracheal stenosis due to complete tracheal rings could not be ascertained. A computer tomography (CT) angiogram showed a left pulmonary artery sling with external compression of the distal trachea (Figure 2). The left pulmonary artery sling was also seen on repeat echocardiogram. Rigid bronchoscopy showed no evidence of complete tracheal rings. The patient underwent surgical correction with repair of the AV canal defect, PDA closure, and pulmonary artery sling via reimplantation of the left pulmonary artery onto the main pulmonary artery. Postoperative bronchoscopy showed improved tracheal diameter (Figure 1). The patient was extubated successfully six days postoperatively and was weaned to room air.

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Figure 1.

A, External tracheal compression above the carina by the pulmonary artery sling. B, After operation, distal trachea markedly improved, and the carina is easily visualized.

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Figure 2.

Computer tomography angiogram showing left pulmonary artery (LPA) arising from the right pulmonary artery (RPA) and passing behind the trachea (arrow) causing tracheal compression.

Discussion

Left pulmonary artery sling is characterized by an abnormal origin of the left pulmonary artery from the posterior aspect of the right pulmonary artery. The abnormal left pulmonary artery passes between the trachea and the esophagus and causes posterior compression of the right mainstem bronchus and the lower trachea producing upper airway symptoms. The presentation is usually within the first weeks to months of life with respiratory symptoms and decompensation is often precipitated by acute respiratory infection. ¹ Left pulmonary artery sling is associated with complete tracheal rings in 79% of cases creating a ring-sling abnormality. ² The diagnosis of complete tracheal rings is usually made by rigid bronchoscopy. Other congenital heart defects are found in around 20% of cases of pulmonary artery sling with the most common abnormalities being atrial and ventricular septal defects and tetralogy of Fallot. ²

The diagnosis can be made with echocardiogram; however, it can be initially missed as it was in our case. This unusual anomaly can be easily overlooked in patients with trisomy 21 when looking for more common congenital heart defects. In two recent studies, echocardiogram identified cases of suspected pulmonary artery sling in 37% to 87% of the cases. ^{3 –5} The subxiphoid long- and short-axis sweeps are useful in identifying the origin and initial course of the left pulmonary artery. ⁵ The presence of PDA might give a false impression of a normal pulmonary artery bifurcation (Figure 3), and careful Doppler examination will allow differentiation between the PDA and the normal bifurcation of the pulmonary artery. However, CT angiogram is the gold standard. ¹ Prenatal diagnosis with fetal echocardiogram is unusual, and there is only one case report in the medical literature. ⁶

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Figure 3.

Parasternal short-axis view showing the main pulmonary artery (MPA) and the patent ductus arteriosus (PDA). This view can mimic the normal pulmonary artery bifurcation. Careful Doppler examination will allow differentiation between the PDA and the normal bifurcation of the pulmonary artery.

Children with trisomy 21 are at increased risk of respiratory infections and airway abnormalities, which might delay the diagnosis of vascular rings and slings as they may have similar presentation. A comprehensive literature review showed only one case report of pulmonary artery sling in an infant with trisomy 21. ⁷ This case was also associated with a complete AV canal defect. Recognizing the possibility of pulmonary artery slings in patients with trisomy 21 is extremely important to the cardiologist as the diagnosis can be missed on the echocardiogram while looking for other common congenital heart disease. Vascular rings and pulmonary artery slings should be on the differential in children with trisomy 21 and stridor.

Treatment involves surgical correction of the pulmonary artery sling and the associated congenital heart defect. Surgery has excellent outcomes when no tracheal surgical intervention is required. ⁸ The surgical approach usually involves a median sternotomy, cardiopulmonary bypass, and left pulmonary artery reimplantation to the main pulmonary artery. ^2,8

Conclusion

Pulmonary artery sling is a very rare but important congenital defect that should be recognized and corrected early. Airway abnormalities and other comorbidities associated with trisomy 21 make the diagnosis more challenging in this population. Early diagnosis is extremely important, and airway evaluation is required before surgical correction.