Frozen elephant trunk procedure for complex aortic arch surgery: The Salerno experience with Thoraflex hybrid

Abstract Background and Aim of the Study To report early clinical outcomes of the frozen elephant trunk (FET) technique for the treatment of complex aortic diseases after transition from conventional elephant trunk. Methods A single‐center, retrospective study of patients who underwent hybrid aortic arch and FET repair for aortic arch and/or proximal descending aortic aneurysms, acute and chronic Stanford type A aortic dissection with arch and/or proximal descending involvement, Stanford type B acute and chronic aortic dissections with retrograde aortic arch involvement. Results Between December 2017 and May 2020, 70 consecutive patients (62.7 ± 10.6 years, 59 male) were treated: 41 (58.6%) for emergent conditions and 29 (41.4%) for elective. Technical success was 100%. In‐hospital mortality was 14.2% (n = 12, 17.1% emergent vs. 10.3% elective, P = NS); 2 (2.9%) major strokes; 1 (1.4%) spinal cord injury. Mean follow‐up was 12.5 months (interquartile range, 3.7–22.3). Overall survival at 3, 6, 12, and 24 months was 90% (95% confidence interval [CI], 83.2—97.3), 85.6% (95% CI, 77.7–94.3), 79.1% (95% CI, 69.9–89.5), 75.6% (95% CI, 65.8–86.9) and 73.5% (95% CI, 63.3–85.3). There were no aortic re‐interventions and no distal stent graft‐induced new entry (dSINE); 5 patients with residual type B dissection underwent TEVAR completion. Conclusions In a real‐world setting, FET with Thoraflex Hybrid demonstrated feasibility and good clinical outcomes, even in emergent setting. Our implant technique optimize cerebral perfusion reporting good results in terms of neurological complications. Techniques to perfect the procedure and to reduce remaining risks, and consensus on considerations such as standardized cerebral protection need to be reported.


| INTRODUCTION
The frozen elephant trunk (FET) procedure has become established as a proven and attractive option to treat aortic disease when the arch and the thoracic aorta are involved to facilitate the conventional two-stage access. 1 In acute and chronic aortic dissection, the use of FET can help to expand and stabilize the true lumen and cover eventual supplementary tears but the perceived technical complexity of the operation may be restricting its adoption, especially in the acute setting. [2][3][4] Undoubtedly, the constant development of new branched prostheses, which increases the surgeons' armamentarium in the treatment of complex aortic arch pathology, plays an important role in reducing the risk of procedural failure. 5 At present, there is little evidence weighing the burden of replacing the aortic arch as an additional procedure during elective or emergency proximal aortic repair, thus making comparison with patients undergoing secondary total arch replacement difficult. 6 The aim of this study was to evaluate safety and short-term outcomes after FET with the Thoraflex™ Hybrid (Terumo Aortic) prosthesis in aortic arch reconstruction both in emergency and elective setting at a single institution.

| METHODS
This is a single-center, retrospective, observational study based on prospectively collected data obtained from institutional cardiac surgery data set at University Hospital San Giovanni di Dio and Ruggi d'Aragona in Salerno, Italy. The study was conducted in accordance with the principles of the Declaration of Helsinki. Institutional board approval was obtained for the study, and patient consent was waived.
All patients who underwent FET for acute and chronic arch and thoracic aorta pathologies between December 2017 and May 2020 were included. The dates were chosen to capture all routine use of the Thoraflex Hybrid FET device which consists of a proximal unstented tubular gelatin-coated Dacron graft and a distal stent-graft polyester made with a self-expandable nitinol skeleton, deployable antegrade during circulatory arrest over a guidewire. We use exclusively the Plexus configuration with four integrated lateral branches: three for the reconstruction of supra-aortic vessels and one for systemic perfusion.
We size the stent-graft portion according to the aortic diameter of the distal landing zone as evaluated by preoperative CT angiogram: 0% oversizing in acute and chronic aortic dissections; 10%-15% oversizing in ascending aorta and/or arch aneurysms, particularly when a second stage was anticipated. To minimize the risk of spinal cord ischemia, we only implant the 100 mm length.

| Surgical technique
All cases are operated under general anesthesia after invasive arterial pressure monitoring of bilateral radial arteries and a femoral artery.
We cannulate the right jugular vein after oro-tracheal intubation and position a Swan-Ganz catheter. All patients are monitored with a continuous transesophageal echocardiography (TEE) and bilateral cerebral oxymetry (INVOS™ system). Median sternotomy is performed in all cases: the usual incision is extended in a small right or bilateral supra-clavicular cervicotomy to improve access and harvesting of supra-aortic vessels. Central cannulation is routinely via the right intrathoracic subclavian artery via side graft. Our approach is "branch-first" and beating heart arch vessel reconstruction. During the initial cooling phase, on a beating heart, the left carotid artery The aortic arch is then opened and inspected.
The landing zone (usually zone 2) is reinforced with Teflon strip and, eventually, bioglue. At this stage, the distal stent-graft of the FET device is released into the descending thoracic aorta. The reinforced collar of the prosthesis is sutured to the aorta and, after cannulation of the fourth lateral branch and careful de-airing, systemic perfusion is resumed, starting to rewarm the body. The anastomosis between the surgical graft and sinotubular junction (either native or prosthetic, depending on the proximal repair) is completed and cross-clamp released allowing the heart to start beating. The prosthesis-elongated supra-aortic vessels are then end-to-end sequentially re-anastomosed to the corresponding branches of the graft, starting with the LSA to LCA and finally brachiocephalic artery.
The correct deployment and fully expansion of the prosthesis is assessed by TEE. When the brachiocephalic artery is clamped, the flow is lowered to 10-12 ml/kg/min for isolated cerebral perfusion. After the circulatory arrest time the full flow was restarted via prosthetic side branch and single cerebral vessels.

| Endpoints
The primary endpoints of the study were 30-day and in-hospital mortality, defined as death due to any cause during postoperative course at 30 days and until discharge, usually to a rehabilitation unit,   in elective group, p < .01) Patients presenting in emergency setting had a higher incidence of malperfusion but this difference did not reach statistical significance.
No intraoperative deaths were recorded. Operative characteristics and their distributions among the two groups are showed in Another interesting finding from our study is the very low rate of spinal cord injury which occurred in only one patient (1.4%) operated for acute aortic dissection. We believe that our good results are due to the use of a combination of 100 mm stented length (less intercostal arteries coverage), Thoraflex Hybrid deployment in zone 2, short circulatory arrest time, and correct sizing of the stented graft. 12 Fiorentino et al. reported a low overall incidence of SCI (two cases of temporary isolated papaparesis) but only in 150 mm distal stented grafts. 13 Flores et al reported a very high incidence of SCI in FET when the stented was deployed at the lower level of the thoracic aorta. 14 It has been reported that in Thoraflex implant the LSA anastomosis remains the Achilles heel being too close to the collar device. 11 We overcome this problem by extending the surgical incision with a small left supra-clavicular cervicotomy and "elongating" the LSA with a tubular prosthesis, thus making the anastomosis technically easier and achieving success in all cases. In one case, not included in this series, we successfully used a custom-made Thoraflex Hybrid, in which the plexus is separated from the main part of the prosthesis, to make anastomosis easier, improve operating times and correctly position the intra-thoracic vessels. 15 Overall survival for the entire cohort at 30 days was 90% (95% repair by the highest volume care providers. 16 We think that the future treatment of acute type A aortic dissection is going toward a total arch approach with standardized cerebral protection that should more and more be delivered by specialist aortic centers with expertize in this technique. In this case, the Thoraflex Hybrid proved to be an easy-toimplant prosthesis, making the brain protection strategy easier and reporting a low complication rate.
Finally, an important aspect of our study is the relatively large number of cases done in a short period of time in a single institution, thus allowing for a significant reduction of multicenter studies bias.
Other series available in literature report results of a similar cohort of patients but operated in different centers: the Canadian experience enrolled 40 consecutive cases in 9 different centers, in about 3 years of activity while the English experience counts 66 cases in 4 years from 9 centers throughout UK. 17 F I G U R E 4 Kaplan-Meier survival curves between the two groups (raw data). AAD, acute aortic disease treated in emergency setting; CAD, chronic aortic disease treated in elective setting MASIELLO ET AL. | 113

| STUDY LIMITATIONS
Due to the relatively low complication rate and limited follow-up, it was not possible to detect differences between the groups or pathologies. At present, the follow-up has a shorter duration compared to other series.

| CONCLUSIONS
Surgical techniques involving stenting of the descending thoracic aorta during primary surgery for both acute and chronic complex aortic disease involving the arch are associated with promising early and midterm results. Result of this study and growing evidence in the literature suggest that FET in acute aortic dissection should also be routine when performed by experienced operators in dedicated aortic centers.