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A critical neonatal coarctation can be defined as one that is sufficiently severe to keep the neonate prostaglandin-dependent. Perfusion distal to the coarctation must be maintained by ensuring patency of the ductus arteriosus and maintaining elevation of pulmonary vascular resistance by appropriate ventilatory manipulation.
One of the complexities of managing the critical neonatal coarctation is that it is often associated with hypoplasia of the isthmus, distal aortic arch, or proximal aortic arch. It must be remembered that these segments of the aorta are normally smaller than the ascending aorta consequent to the branching of the aortic arch. In general, an isthmic diameter that is less than 40% of the ascending aortic diameter is inadequate. Likewise a distal aortic arch diameter that is less than 50% of the ascending aorta, or a proximal aortic arch that is less than 60% of the ascending aorta, is inadequate. It is exceedingly common to find severe hypoplasia of the isthmus so that resection of the isthmus or a slide plasty as illustrated here are almost routinely incorporated into the management of critical neonatal coarctation. Distal aortic arch hypoplasia is a less frequent but still not rare problem. Severe hypoplasia of the aortic arch proximal to the left common carotid artery is a very rare finding.
The most common technique for dealing with the hypoplastic distal aortic arch has been to perform an extended end-to-end anastomosis as illustrated in the accompanying article by Tsang. However, an alternative approach that we have found particularly helpful in the neonate is to perform a reverse subclavian flap procedure.
Disadvantages of the Left Subclavian Flap Approach
The principal disadvantage of the left subclavian flap approach is that it requires division of the left subclavian artery. It is exceedingly rare for this to result in left upper limb ischemia so long as the branches of the left subclavian artery are not divided. There is a theoretical risk of a left subclavian steal but it is rare in our experience that this is functionally important during childhood.
Advantages of the Left Subclavian Flap Approach
The principal advantage of this approach is that there is less tension on the anastomosis. The toe of the extended end-to-end anastomosis can be difficult to expose, and tearing of tissue at the toe can result in bleeding that can be difficult to control. The relatively long anastomosis required for the extended end-to-end anastomosis also requires a considerably longer clamp time than is generally required for the left subclavian flap approach.
The mediastinal pleura is dissected from the distal left subclavian artery to approximately the midpoint of the descending aorta. Retraction sutures are placed in the anterior pleural flap with care to avoid injury to the vagus nerve and the recurrent laryngeal nerve. The left subclavian artery is dissected free with care to avoid injury to the lymphatic vessel, which frequently passes over the proximal subclavian artery. This vessel when large should be ligated. When smaller the vessel can be carefully cauterized. When dissecting behind the origin of the left subclavian artery care should be taken to avoid injury to “Abbott’s artery,” which is frequently present in this location. The hypoplastic distal aortic arch is dissected free, and dissection is continued until the ascending aorta can be clearly visualized. The left common carotid artery is dissected free over at least its proximal two-thirds within the chest. The ductus arteriosus is dissected free as is the proximal ∼2 cm of the proximal descending aorta. Collateral vessels, usually the initial 2 or 3 intercostal vessels, are carefully preserved.
There is little doubt that the technique of coarctation resection with extended end-to-end anastomosis incorporating the hypoplastic aortic arch is the most popular technique for dealing with arch hypoplastia in association with coarctation. However, individual anatomy can dictate under certain circumstances that the reverse subclavian flap procedure is a preferable approach. For example, more severe degrees of arch hypoplasia are probably best treated with the flap procedure. If there is a long aortic isthmus or if there are other factors that increase the tension on an extended end-to-end anastomosis, then the reverse subclavian flap may be preferable. It should be remembered that the principal advantage of the reverse subclavian flap procedure is that it does reduce the amount of tension on the anastomosis so that long-term outcome, particularly freedom from recoarctation, is likely to be reduced with this procedure.
One report describing a large series of patients undergoing the reverse subclavian flap procedure was published by Kanter and coworkers from Emory University in 2001.
One-hundred sixty-two infants less than 3 months of age underwent repair of coarctation after 1988. Of these, 46 had a reverse subclavian flap aortoplasty at a median age of 11 days and a mean weight of 3.2 kg. There were two hospital deaths, one in a patient who subsequently underwent a Norwood procedure and the other from sepsis. At a mean follow-up of 38 months, 5 patients had recurrent obstruction, of which three were at the coarctation site rather than at the arch repair. The authors concluded from this series that the reverse subclavian aortoplasty procedure is an excellent technique for relief of arch hypoplasia with a low recurrence rate and acceptable operative and intermediate-term survival.
Variations of the reverse subclavian flap procedure have been described. For example Giamberti and coworkers
from Italy described a procedure in 2001 in which the left subclavian artery was left in continuity. This is very likely a more technically challenging procedure than the standard reverse flap procedure. Nevertheless it does offer the important advantage that the left subclavian artery is left in continuity so there is no risk to perfusion of the left arm. The authors describe 5 neonates with a mean age of 4 days and a mean weight of 2.4 kg who underwent this technique in association with coarctation resection and standard end-to-end anastomosis. There were no hospital or late deaths. No patient presented with recurrent coarctation.
In conclusion, coarctation can be a deceptively complex problem that requires careful individual tailoring of the operative approach according to the specific anatomical situation. The reverse subclavian flap procedure provides a helpful tool in the armamentarium for the surgeon who must deal with important distal aortic arch hypoplasia in association with coarctation of the aorta.