Table 1 : Demographics, clinical presentation, and operative procedure (LAA/ RAA: Left/Right aortic arch, CAVCD: Complete atrioventricular canal defect, PAPVR: Partial anomalous venous return, PDA: Patent ductus arteriosus, TEF: Tracheo-esophageal fistula, CPB: Cardiopulmonary bypass).
Discussion : AA for IAS was first described by Gross in 1948[1]. The patient was a 4 month-old female infant who had recurrent episodes of severe respiratory distress and respiratory tract infections. The AA was performed through a left anterior thoracotomy approach. After a partial thymectomy, an abnormal leftward arising innominate artery was fixed to the retrosterum. The operation was successful with complete relief of the symptoms. Since then, various approaches to AA have been described such a left or right thoracotomy, a thoracoscopic approach, a full median sternotomy and a partial upper median sternotomy [4, 6]. Our preferred technique is the partial upper median sternotomy.
IAS is thought to be due to an abnormal innominate artery arising distally along the aortic arch and hence crossing the trachea anteriorly from a left to right direction. This leads to a potential for a compressive effect and is further facilitated by overcrowding of the upper mediastinum due to the presence of a large thymus especially in the younger children [5, 7].
Common symptoms include stridor, reflex apnea (a sudden respiratory arrest cause by an irritation of the area of compression), and recurrent respiratory tract infections. It can also present as failure to wean from mechanical ventilation. Stridor by itself is not an indication. Strong indication for surgery are reflex apnea, two or more episodes of infection, severe compression (> 70% luminal reduction), and dependence on mechanical ventilation. Of these, reflex apnea is the strongest indication for an intervention as it can lead to mortality [2, 3].
IAS is diagnosed by flexible bronchoscopy, which shows an anterior pulsatile compression in the distal trachea. Besides this, a flexible bronchoscopy facilitates the conduct of the AA operation. It helps determine the number and position of the anchoring sutures and helps evaluate the result of the AA by assessing the degree of resolution of IAS (Figure 1 ). Cross-sectional imaging such as a CT angiogram or an MRI is obtained to further evaluate the anatomy (Figure 2 ).
A partial upper median sternotomy approach to an AA for tracheomalcia from various causes has been previously described by Elliot [6]. In this paper, we describe our technique for AAselectively for IAS. This has become our preferred approach for the following reasons. Firstly, it facilitates the performance of a complete thymectomy. The bilateral phrenic nerves are better visualized and thus at a lesser risk for injury. A complete thymectomy is central to the success of the operation as it increases the available anteroposterior dimension in the upper mediastinum as often these children have a large thymus gland. Without a thymectomy, the degree to which the innominate artery moves towards the sternum is limited and thus the distracting force on the trachea. Secondly, the goal is to get a good anatomic result by accepting only a ≤20 % residual stenosis after an AA. This was evident in our study as the patients who did not achieve a technical success needed an alternative procedure. If this not achieved, one needs to look for alternative factors such as an intrinsic tracheal pathology. A partial sternotomy approach facilitates this as it is easy to convert to a full sternotomy and explore the anterior surface of the trachea between the SVC and the aorta as compared to a thoracotomy approach. In one case, the patient had an intrinsic tracheal stenosis due to isolated tracheal cartilage deficiency which was not diagnosed preoperatively and required a tracheal resection and has been previously published by us [8]. Thirdly, the anatomy of the innominate artery is better appreciated by this approach. Alternative to an AA to treat IAS is an innominate artery reimplantation procedure. As previously described, the innominate artery in IAS arises further leftward along the aortic arch. Hence, it crosses anterior to the trachea from a left to right direction compressing it anteriorly. The innominate artery can be reimplanted in an off- pump manner by re-implanting the artery 1 cm proximal on the greater curvature of the aorta rightward of the trachea [5, 7].Such an reimplantation has an immediate effect of relieving the compression with no long-term consequence [5]. Only one patient needed this approach in this series after a test AA failed to produce an optimal result. Again, a midline approach as compared to the thoracotomy approach greatly facilitated this operation as this approach requires a median sternotomy. Fourthly, a full sternotomy is unnecessary as the operative procedure is limited to the upper mediastinum and an upper partial sternotomy actually facilitates when a future re-sternotomy is needed arises as described next.
AA by an upper partial median sternotomy does not preclude a repeat sternotomy if certain precautions are taken. In an infant with Down syndrome, prune belly syndrome, complete atrioventricular canal defect and recurrent failure to wean from mechanical ventilation, an AA was performed at age 2 months and a complete repair of the canal defect was performed at age 8 months. The patient did well after the aortopexy and was liberated from mechanical ventilation. At redo sternotomy, because the lower pericardium and the sternum were intact after the initial surgery, an easy retrosternal plane could be established and the posterior sternal table in the region of the aortopexy was divided under direct vision by deviating rightwards of it. The repair was intact and did not interfere with the canal repair. As previously described, if the aortic arch is left sided, then the innominate artery is fixed to the left half of the sternal table, distracting it away from the trachea in an anterior and leftward fashion and if the aortic arch is right sided, the aortopexy is done to the right half of the sternotomy. This also helps with a future redosterntomy as the innominate artery is not fixed across the sternotomy incision.
It is critical not to develop a pretacheal plane and we believe is another key step for a successful AA. By dissecting the innominate artery circumferentially away from the trachea, the compressive effect will be relieved. However, if severe tracheomalcia is present, it will lead to collapse of the anterior wall of the trachea. Pulling the innominate artery anteriorly, besides producing a distracting compression relieving effect on the trachea, has an additional suspensory effect. This was evident in the original description by Gross [1] where a residual tracheal stenosis was seen due to underlying tracheomalacia due to such as circumferential dissection of the artery.
The composite suture technique simplifies the operation. While fine sutures are used on the artery, heavy sutures are used for the AA. If the suspension sutures were to snap, they can be easily replaced before the sternum is closed.
The strengths of the study are the description of the technical pearls and pitfalls for a successful AA via an upper partial sternotomy as evidenced by the good operative outcomes. The limitations are the small sample size, absence of a comparator such as another technique for an AA and lack of long-term follow up.
Conclusion : An upper partial sternotomy approach provides a very versatile approach to an AA for IAS. Besides facilitating an adequate AA, it provides options for direct tracheal surgery or an innominate artery reimplantation in case an optimal result is not obtained by an AA.
Funding Source : None
Conflict of Interest : None
Ethics Statement : The study is a retrospective review of a prospectively maintained de-identified database. No further chart-review or any form of patient contact was attempted for this study and hence is IRB exempt. The study was not part of any research protocol and written informed consent was obtained for the operative procedures. No portions of the manuscript and the submitted pictures have any information that can lead to identification of the patient as per the Healthcare Insurance Portability and Accountability ACT of (HIPAA) 1996.