Treatment of right-sided aortic arch aneurysms with aberrant left subclavian artery with Kommerell’s diverticulum using the frozen elephant trunk technique

Abstract OBJECTIVES The ideal treatment for aneuryms of aberrant left subclavian arteries with Kommerell's diverticulum arising from right aortic arches remains open. METHODS Between January 2015 and December 2020, 5 patients with aneurysms from a right-sided aortic arch with aberrant left subclavian artery and Kommerell’s diverticulum underwent repair by using the frozen elephant trunk technique in 3 aortic centres. Patients’ characteristics were retrospectively reviewed and the surgical procedure and outcomes are presented. RESULTS The median age of the 2 male and 3 female patients was 59 (range from 49 to 63) years. The median operative times were as follows: surgery 405 min (range from 335 to 534), cardiopulmonary bypass time 244 min (range from 208 to 280) and aortic clamp time 120 min (from 71 to 184). The mean core temperature was 25.94°C (from 24 to 28). The intensive care unit stay was 4 days (range from 1 to 8) and the in-hospital stay 21 days (from 16 to 34). All patients were discharged and we observed no stroke or spinal cord ischaemia postoperatively. During the median follow-up time of 1003 days (range from 450 to 2306), 3 patients required subsequent thoracic endovascular distal stent graft extension. CONCLUSIONS The frozen elephant trunk technique is a good treatment option for patients with aneuryms of an aberrant left subclavian artery with Kommerell's diverticulum arising from right aortic arches. Secondary stent graft extension is a frequently needed component of the treatment concept.


INTRODUCTION
The most common variant of the aortic arch branching represents 'the bovine aortic arch' with the prevalence of 11-27% in the adult population [1].With a prevalence of 0.4-2.3%, the aberrant right subclavian artery named alternatively arteria lusoria is the most common anomaly of the aortic arch.The aberrant artery usually arises directly from the aortic arch just distal to the left subclavian artery and passes into posterior mediastinum on its way to the right upper extremity [2].The abnormal vessel course can have important clinical and surgical relevance due to oesophageal or tracheal compression syndromes, important anatomical relations and risk of injury during surgery [2,3].The mirror image pathology with an aberrant left subclavian artery arriving from a right-sided aortic arch is far less common [2].A sac-like widening or bulging of the aortic arch or the descending aorta in the case of an aberrant right subclavian artery is called Kommerell's diverticulum [4,5].
In case of aneurysmal formation with or without a dissection component, there are several different treatment options including classical open surgical repair, hybrid approaches or even total thoracic endovascular aortic repair (TEVAR) but due to specific procedure-related limitations, none of them emerged as standard treatment strategy.The frozen elephant trunk (FET) technique has become a broader and increasing treatment option for all aortic arch pathologies.This concept allows for both, repair of the underlying aortic disease and rerouting as well as re-vascularization of the supra-aortic branches [6][7][8][9].
We report a series of 5 patients with an aberrant left subclavian artery with Kommerell's diverticulum arising from a rightsided aortic arch treated using the FET technique.

Ethics statement
This research project has been approved by the ethics committee of the University of Freiburg, Freiburg, Germany.Approval number: 20-1302.The reason for formal consent was not obtained due to anonymity of the patients data.

Patients
The prospectively maintained respective aortic databases were screened for patients with right-sided aortic arch aneurysms and an aberrant left subclavian artery originating from a Komerell's diverticulum on the convex part of the aorta (Figs 1 and 2).Finally, between January 2015 and December 2020, a total of 5 patients underwent total aortic arch replacement using the FET technique in patients with aberrant left subclavian artery.The rationale for the surgery was either tracheal compression of extended vessel size.Two of them were treated at the University Heart Centre Freiburg, Germany, next 2 at the West-German Heart Center Essen, Germany, and one at the Tampere University Hospital Heart Center, Finland.Their baseline characteristics, including previous cardiac surgical procedures, were collected.Their intraoperative data, clinical outcomes after surgery and follow-up data were reviewed.The respective institutional review boards approved this retrospective study, and the need for informed consent was waived.

Definition of clinical parameters
The primary outcomes were perioperative mortality and stroke.Stroke was defined as a new postoperative physiciandiagnosed neurologic deficit persisting >24 hours confirmed by imaging methods-computed tomography or magnetic resonance imaging.

Surgical technique
E-vita open plus (Jotec, Hechingen, Germany) and Thoraflex Hybrid (Terumo Aortic, Inchinnan, UK) prostheses were used.The FET size in dissection cases was the length plus width of true lumen divided by 2 added 10%.In aneurysm cases size in relation to distal landing zone, so that TEVAR extension has a 10% oversize to the distal landing zone with also a 10% oversize to the diameter of the stent graft component of the FET.The surgical techniques from all 3 centres have previously been reported [7,10,11].In our series, we ligated the arteria lusoria distal to the diverticulum to prevent retrograde flow to the aneurysm.The endograft of the hybrid prosthesis excluded antegrade flow to the Kommerell's diverticulum (Fig. 3).Spinal cord protection with a cerebrospinal fluid drain was used in every case.

Statistical analysis
Continuous variables are presented as the median and range.Categorical and binary variables are presented as frequencies (n) and percentages (%).Statistical analysis was performed using Stata statistical software for macOS (Stata/MP version 13.0; StataCorp, Texas).

Baseline and aortic characteristics
The median age of the 2 male and 3 female patients was 59 (range from 49 to 63) years.The pathomorphological substrate was aneurysmal disease in 4 patients and aneurysm on the basis of a residual dissection after previous type A repair in the case of 1 patient.This patient underwent previous supracoronary ascending and hemiarch aortic replacement.The baseline and aortic data are summarized in Table 1.

Operative data
Three E-vita open plus (Jotec, Hechingen, Germany) and 2 Thoraflex Hybrid (Terumo Aortic, Inchinnan, UK) prostheses were used.The median operative times were as follows: surgery 405 min (range from 335 to 534), cardiopulmonary bypass time 244 min (range from 208 to 280), aortic clamp time 120 min (from 71 to 184).The mean core temperature was 25,94 C (from 24 to 28).One patient required re-vascularization of both subclavian arteries performed by aorto-axillary bypasses due to extension of the pathology.Detailed data are shown in Table 2.
Detailed surgical procedure (patients 1 and 2).The left or right subclavian artery was cannulated via an 8 mm side graft.After (re-)sternotomy, the left innominate vein and the supraaortic vessels were isolated.The target core temperature for hypothermic circulatory arrest was 25 C.Both patients were operated on beating-heart normothermic myocardial perfusion technique.The carotid arteries were clamped and cannulated   for bilateral selective antegrade cerebral perfusion.The left subclavian artery was resected at the origin from the Kommerell's diverticulum and mobilized.The diverticulum was closed and the left subclavian artery anastomosed end-to-end to an 8-mm Dacron graft which to maintain the perfusion in the posterior cerebral circulation.The right subclavian artery was also resected and anastomosed end-to-end to an 8-mm graft.A Thoraflex Hybrid graft were deployed and the descending aortic anastomosis was performed in Ishimaru zone 2. Overstenting of the Kommerell's diverticulum offspring was achieved.Afterwards, lower body perfusion was established via the side branch of the arch prosthesis.In the next step, the right subclavian artery was anastomosed to the subclavian branch of the arch prosthesis.After discontinuation of right vertebral perfusion, the artery was anastomosed to the common carotid branch of the prosthesis.The left common carotid artery was anastomosed end-to-end to the innominate branch of the prosthesis and the left subclavian artery was anastomosed end-to-side to the same prosthetic branch.
Detailed surgical procedure (patients 3 and 4).Right subclavian cannulation was used.The aim temperature was 28 C. The left subclavian artery was resected at the origin from the Kommerell's diverticulum and mobilized.E-vita open prosthesis anastomosed to zone 2. Overstenting of the Kommerell's diverticulum offspring was achieved.In patient 4 carotid arteries were re-implanted in the ascending aortic graft using 8-mm polyester grafts.Re-vascularization of both subclavian arteries was performed by aorto-axillary bypass.In addition, the E-vita open stent graft was extended distally by a stent graft in order to exclude the aortic aneurysm over the aortic kinking close to tracheal bifurcation.Detailed surgical procedure (patient 5).Cardiopulmonary bypass was established via prosthetic 10-mm dacron side branch to the left femoral artery and a central venous cannula after sternotomy.Cooling was targeted to 24 C. Cardioplegia was administered retrogradely using a Custodiol bolus and to the right coronary ostium.Sequence from proximal to distal, of arch vessels takeoff was left common carotid, right common carotid, right subclavian, and left subclavian aortery.First, the left subclavian was exposed at the left border of the trachea, double ligated but not transsected in this case because no dilatation or dysphagia or airway compression was present.An end-to-side bypass was done using a 8-mm dacron prosthesis.The remaining arch vessels were sequentially cut, proximally ligated and individually reconstructed using 8-mm dacron prostheses and perfused with Le Maitres until proximally anastomosed.The ascending aorta was transsected at zone 0. A stiff Jotec (Jotec/ CryoLife, Kennesaw, GA, USA) guidewire was advanced to iliac artery level under angioscopic control, through the encoscope working channel.An E-vita open plus 36 mm Â 16 cm was inserted, and a Teflon felt reinforced anastomosis made in zone 0. Overstenting of the Kommerell's diverticulum offspring was achieved.A Jotec occlusion balloon was inserted into the endograft, and lower body perfusion begun via the femoral cannula.
Rewarming was begun.The ascending aorta was replaced to the sinotubular junction with a 32-mm dacron prosthesis and anastomosed to the trimmed end of the E-vita prosthesis.The sinotubular junction anastomosis was reinforced with Teflon felt.The 4 arch vessel prostheses were anastomosed thus: both subclavian artery prostheses and the left carotid prosthesis were anastomosed to the ascending aortic prosthesis.An arterial cannula was inserted into the ascending aortic prosthesis, de-airing completed, antegrade perfusion commenced and femoral perfusion stopped.The right carotid prosthesis was anastomosed to the side of the right subclavian prosthesis.
In-hospital outcome characteristics.The intensive care unit stay was 4 days (range from 1 to 8) and the in-hospital stay 21 days (from 16 to 34).No patient suffered of stroke.One patient developed a left-sided recurrent nerve palsy.The patient cannulated via the femoral artery suffered from a seroma of the femoral cannulation site and delayed wound healing.There was no in-hospital mortality.All patients were discharged home.Detailed data are shown in Table 3.
Follow-up and reinterventions.The follow-up time was 1003 days (range from 450 to 2306).In the follow-up computer tomography scan, no perfusion of the Kommerell's diverticulum was observed.Three patients underwent a subsequent TEVAR extension.In particular, 1 patient had a residual type II and type Ib endoleak.The type II endoleak was treated typically by coiling of an intercostal artery followed by TEVAR extension of the Ib endoleak (Fig. 2).There was no mortality in the follow-up time observed.Detailed data are shown in Table 4.

DISCUSSION
The FET technique is a good treatment option for patients with aneuryms of an aberrant left subclavian artery with Kommerell's diverticulum arising from right aortic arches.Secondary TEVAR extension is a frequently needed component of the treatment concept.

Literature background
The main reason for treatment in this group of patients is the presence of symptoms of oesophageal or airway compression.Another reason is the prevention of aneurysm rupture in asymptomatic patients.Limited literature regarding aneurysms from a

The advantages of the FET technique Komerell's diverticulum treatment
Basically, both stent graft implantation and the FET technique are options available with regard to occluding Kommerell's diverticulum orifice.However, steep transition from the arch to the descending aorta represents a common anatomy in this patients' cohort often provides an inappropriate proximal landing zone for stent graft placement.The FET technique providing total arch replacement can overcome the unfavourable anatomy and concomitantly enables sufficient reconstruction of the aortic arch branches [12,16].When using FET, 1 aspect is important: how to address with the offspring of the Arteria lusoria, as the Kommerell's diverticulum offspring is often large.We ligated the arteria lusoria distal to the diverticulum to prevent retrograde flow to the aneurysm.The endograft of the hybrid prosthesis excluded antegrade flow to the Kommerell's diverticulum.This is the main adventage of the FET in this setting: the hard to be surgically reached Komerell's diverticulum can be treated by excluding it.Alternatively, a big-sized Amplatzer can be implanted [17].

Postoperative results
All of the patients in our study were discharged home and we observed no stroke or spinal cord ischaemia postoperatively.In a study of Berger et al., 250 patients underwent total aortic arch replacement via the FET technique between March 2013 and November 2020 for acute and chronic aortic pathologies.In these series, we reported noticeable in-hospital mortality and stroke rate [9].In fact, the cohorts of these 2 studies are comparable.In the former study patients with all of the pathologies were included.Patients with right-sided aortic arches have no presence of coronary artery disease and arterial atherosclerosis, they reflect the dilatative aortopathy only.
In our another study, 63 patients were treated with FET on for acute or chronic aortic dissection after previous proximal and/or distal open or endovascular thoracic aortic repair.This study reflects a group of patients with dilatative aortopathy with lower incidence of atherosclerosis.The in-hospital mortality was 3%.Postoperative strokes occurred in 8% of patients [8].Overall, our operating results reflect the experience of FET implantation in previous years and the large volume of our centres.

Two-staged treatment and reinterventions
During the follow-up time, the descending aortic treatment was completed by TEVAR extension in 3 patients.As previously reported, patients commonly require secondary aortic procedures, emphasizing the need for thorough primary conceptual planning and stringent follow-up.We consider the reinterventions to be the next step in the multi-component treatment of aortic pathology, not the treatment of complications.In our study of the FET technique for the treatment of penetrating aortic ulcers involving the aortic arch in 34 patients, 8 additional endovascular interventions were performed [18].Basically, the main reasons for secondary interventions after FET implantation are distal stent graft-induced new entry, endoleak and negative aortic remodelling and graft kinking or aortooesophageal fistulae.Kandola et al. [19] reported the endoleak occurrence after FET of 28% in 25.8 ± 5.7 months of follow-up.38% of the patients with endoleak needed treatment with TEVAR.The secondary TEVAR should be seen as staged treatment as we do not see distal stent graft-induced new entry in our series.
Singh et al. reported on successful intraoperative retrograde stent graft placement to control an endoleak after emergent total arch replacement and FET repair for ruptured Kommerell's diverticulum and type A aortic heamatoma.The Ia endoleak was managed immediately with proximal extension.Performing of this procedure in a hybrid operating room facilitated optimal management and outcome [20].

Limitations
The study is limited by the rare occurrence of pathology.The cooperation of the 3 centres allowed to slightly increase the number of reported patients.In our cases, we did not observe tracheal compression after surgery.It cannot be ruled out that the lack of diverticulum resection may not be sufficient in some cases.
To summarize, the FET technique is a good treatment option for patients with aneuryms of an aberrant left subclavian artery with Kommerell's diverticulum arising from right aortic arches.Secondary TEVAR extension is a frequently needed component of the treatment concept.

Figure 3 :
Figure 3: A schematic drawing of the hybrid prosthesis excluded antegrade flow to the Kommerell's diverticulum.

Figure 1 :
Figure 1: A computer tomography scan reconstruction of aberrant left subclavian artery with Kommerell's diverticulum marked with a red arrow.

Table 1 :
Baseline and aortic characteristics

Table 3 :
In-hospital outcome characteristics

Table 4 :
Follow-up data

Table 5 :
Selected literature Continued right-sided aortic arch with aberrant left subclavian artery and Kommerell's diverticulum is available.It mainly contains case reports.Selected current literature is presented in Table 5 [2, 12-17].Basically, 3 types of treatment are reported: classical surgical technique by lateral thoracotomy, hybrid treatment using a combination of supra-aortic transpositions and TEVAR, and the use of the FET technique.Kommerell's diverticulum resection is the standard treatment approach.Vinnakota et al.