Commentary: Double Graft Wrapping to Prepare a Landing Zone for Stent-Graft Placement: One of the Allies in the Battle for Complete Endovascular Treatment of the Ascending Aorta?

Endovascular treatment of the ascending aorta is appealing. Use of stent-grafts in this segment is the last battleground in the endovascular conquest of the entire aorta. The war began in 1987 when Nikolay Volodos in Ukraine did the first transfemoral aortic stent-graft implantation for posttraumatic descending aortic aneurysm. ¹ The other warrior was Juan Parodi in Argentina, who performed the first endovascular aneurysm repair, ² which triggered the offensive. Today’s broad clinical experiences with stent-graft implantations in the abdominal and thoracic aorta are pushing the boundaries. The ascending aorta is the last stronghold and the biggest challenge in the entire aorta.

The preferable treatment of ascending aorta true aneurysm is open surgery with replacement of the aorta from the sinotubular junction to the innominate artery. If significant aortic valve dysfunction is present, graft implantation combined with aortic valve replacement is necessary. If the aneurysm extends to the aortic arch, treatment is more complex and necessitates additional hemi- or complete arch replacement. All those open surgeries require cardiopulmonary bypass, hypothermic circulatory arrest, and rerouting of aortic blood flow. However, nowadays there are increased numbers of older patients deemed unsuitable for open surgery owing to multiple comorbidities and high or intermediate risk. The alternative treatment might be a hybrid approach (combining open and endovascular) or complete endovascular reconstruction. Complete endovascular treatment of ascending aortic aneurysm means implantation of tubular stent-grafts in the ascending aorta or the use of parallel grafts or branched/fenestrated stent-grafts to extend the distal landing zone if the aneurysm extends to the aortic arch.

Endovascular treatment of the ascending aorta is challenging due to anatomical and hemodynamic constraints. Anatomical obstacles are proximity of the aortic valve and coronary arteries, so the length of the proximal landing zone must be sufficient (general agreement at least 2 cm). Another is a discrepancy in length between the inner and outer curvature of the ascending aorta, which might result in kink or even collapse of the stent-graft. The disparity in the diameter of the aorta above the sinotubular junction and at the level of innominate artery might compromise the use of a single stent-graft. An additional challenge is a conical shape of the ascending aortic aneurysm, which is seen in up to 75% of patients with ascending aortic pathologies. ³

In the October 2019 issue of the JEVT, Kolvenbach and colleagues ⁴ demonstrate a hybrid technique to overcome the challenges in the treatment of true ascending aortic aneurysm in patients unsuitable for open surgery. The authors use double wrapping of the ascending aorta to prepare a landing zone for stent-grafting by reducing the aortic diameter and discrepancy in the outer vs inner curvature lengths. Such a strategy is another step toward facilitating endovascular treatment of the ascending aorta.

The choice of stent-grafts for the ascending aorta is very limited. There are in use standard thoracic models, physician-modified versions (shortened by cutting) to correspond to patient anatomy, or custom-made devices with different diameters (maximum 46 mm). A dedicated tubular graft for the ascending aorta is available but still in its infancy. ⁵ Even if we conquered all the anatomical challenges of stent-grafting in the ascending aorta, the diameter of the proximal landing zone in true aneurysm would remain a concern. The wrapping technique might solve this constraint and be of additional value.

In the hands of Kolvenbach’s team, the wrapping of the ascending aorta is straightforward but also unique. There are 2 layers of wrap: the first a polypropylene mesh and the second a polytetrafluoroethylene (PTFE) tube. The nonabsorbable polypropylene mesh has high tensile strength; its elasticity allows it to adapt almost perfectly to the aortic wall. The PTFE tube graft is sutured loosely over the first wrap to prevent adhesions between the sternum and polypropylene mesh, in the event of resternotomy. Reoperations after wrapping are rare and not well reported, but in patients with long life expectancy, the problem might exist. The free space between the two wrap materials is of concern: nonresorbed or encapsulated fluids harbor the potential for infection. The other particularity is trimming the mesh in a trapezoid shape to accommodate the shorter inner curvature of the ascending aorta. If there is any clinical benefit to this trapezoid shape compared to a square shape, it will be made clear during follow-up. ⁶

Endovascular stent-grafting of the ascending aorta in the Kolvenbach cohort was always staged. This strategy downgrades the complexity of the treatment, giving the patient time to recover. Two patients with significant aortic diameter reduction after wrapping refused the second step and are under surveillance. Five patients underwent stent-grafting in the ascending aorta. Six patients had stent-grafts implanted in the aortic arch, with several different adjunctive procedures depending on the anatomy. The use of parallel grafts in the chimney configuration was intentional in 2 patients and as a bailout in 1 patient after accidental covering of the innominate artery. In 1 patient, an adequate distal stent-graft landing zone was secured through supra-aortic debranching performed during the sternotomy and wrapping.

Since its introduction by Ake Senning in the 1960s ⁷ the wrapping technique has been criticized. The initial idea was to induce reverse remodeling of the aortic aneurysm and reinforce the aortic wall, instead of resecting the affected aortic segment and replacing it. Over time, there have been several modifications of the wrapping technique. ⁸ There is agreement among the physicians that the technique should not be used if there is significant atherosclerosis, mural thrombosis, ulcer, or calcification of the ascending aorta. There is no agreement as to the diameter of the ascending aortic aneurysm that would support the use of the procedure; for most surgeons the threshold is 55 or 60 mm. ⁷ Further-more, there is no consensus as to which mesh to use for wrapping (polypropylene, PTFE, Dacron, nylon, or bovine pericardium). There is no accord on suturing the mesh: a running Blalock suture first followed by an over-and-over fixation of the mesh to aortic wall or using simple interrupted sutures. There is a difference in the number and placement of stitches to affix the mesh to the aorta and prevent migration. All these different modifications make the standardization difficult, as well as the assessment of early and long-term results. Inherent uncertainty in the technique is still alive.

The “believers” in the wrapping technique will continue to use this method to obtain an adequate landing zone and enable stent-grafting in the ascending aorta in patients with true aneurysm. In this manner, they facilitate treatment of true ascending aortic aneurysm in polymorbid patients in whom open surgery has unacceptable risk. For both patient and surgeon, this treatment is a win-win alternative. The “skeptics” of such a hybrid minimally invasive treatment will certainly mention the altered biomechanical behavior of the aorta, with external reinforcement (wrapping) and increased stiffness after ascending aorta stent-grafting. Additional changes in aortic hemodynamics undoubtedly merit evaluation in the clinical setting. The “believers” and “skeptics” of such hybrid techniques must focus on patient safety and try to find a balance between minimal invasiveness and complete ignorance of the procedure. A registry or prospective inclusion of patients treated at different centers by wrapping and stent-grafting in the ascending aorta will shed light on the remodeling of the aorta, the biomechanical properties, and the clinical consequences.

Whether or not the proposed hybrid strategy for ascending aortic aneurysm treatment will be a true ally in the battle to conquer the endovascular treatment of the ascending aorta is difficult to know. The present cohort of patients is paving the way to overcome the anatomical challenges at this time. Despite the skepticism of this technique, some high-risk patients at least have an alternative for treatment.