Left subclavian artery revascularization as part of thoracic stent grafting^† Free

Abstract

OBJECTIVES

Intentional covering of the left subclavian artery (LSA) as part of thoracic endovascular aortic repair (TEVAR) can cause (posterior) strokes or left arm malperfusion. LSA revascularization can be done as prophylaxis against, or as treatment of, these complications. We report our experience with the surgical technique, indications and the results of LSA revascularization.

METHODS

Between 2000 and 2013, 51 patients of 444 patients who were treated by TEVAR, had LSA revascularization. All elective patients had a preoperative work-up with magnetic resonance angiography to evaluate the circle of Willis. In all, surgical access was through a left supraclavicular incision only.

RESULTS

The majority (90%) had prophylactic LSA revascularization because of incomplete circle of Willis and or dominant left vertebral artery (LVA) (n = 29), patent left internal mammary artery (n = 1), prevention spinal cord ischaemia (SCI) (n = 2), prevention left arm ischaemia due to small LVA (n = 2) and LVA origin in arch (n = 1). Fourteen percent had secondary revascularization, either immediate because of malperfusion of the left arm (n = 2) or late after TEVAR because of persisting left arm claudication (n = 5). In 12 patients, the following early complications were observed: re-exploration for bleeding, n = 1; left recurrent nerve paralysis, n = 2; left phrenic nerve paralysis, n = 1; left sympathetic chain neuropraxia, resulting in Horner's syndrome, n = 3; Chyle duct lesions, resulting in persistent Chyle leakage, n = 3. Neither strokes nor SCI was observed. One patient experienced occlusion of the bypass at 6 months.

CONCLUSIONS

The present study shows that the procedure of LSA revascularization as part of TEVAR is safe with low morbidity consisting of mainly (transient) nerve palsy.

INTRODUCTION

Thoracic endovascular aortic repair (TEVAR) is emerging as a standard treatment modality for various thoracic aortic pathologies mainly thoracic aortic aneurysm (TAA), type B aortic dissection and thoracic aortic injury [1]. Up to 35–40% of patients undergoing TEVAR have thoracic aortic pathology adjacent to the left subclavian artery (LSA) requiring the covering of this vessel to achieve secure proximal sealing [2, 3]. Intentional LSA covering however, is not without risk. Reduced perfusion pressure after LSA coverage can lead to malperfusion of the arm, brain and spinal cord [4]. To reduce these risks, some recommend routine prophylactic revascularization. However, some argue that the risks are negligible without revascularization, unless it is necessary for instance in patients with a patent left internal mammary artery (LIMA) graft or left arm access dialysis. The risk of brain or spinal cord ischaemia (SCI) with LSA covering is controversial with studies showing contradictory findings [5]. From a rational point of view, it can be argued that certain patients are at high risk of (posterior) brain or SCI after LSA covering, i.e. patients with hypoplastic right vertebral artery (RVA) or dominant left vertebral artery (LVA) in combination with incomplete circle of Willis, and previous abdominal aortic surgery and/or occluded hypogastric arteries, respectively. The debate about the effectiveness of reducing these risks by accompanying LSA covering with prophylactic revascularization is still ongoing. The surgical risks of LSA revascularization itself should therefore be well known. In this paper, we report the indications, technical aspects and results of LSA revascularization in a single-institution experience.

METHODS

Between 2000 and 2013, 444 patients were treated by TEVAR at our institution, of whom 51 patients had LSA revascularization periprocedurally. Charts of all patients with subclavian revascularization were reviewed retrospectively for indication, technical aspects and results. The follow-up is 94.1% complete, with a mean follow-up period of 2.3 years (range 0.4–10 years).

We used three types of commercially available stent-grafts approved by the Food and Drug Administration, which were selected only upon availability and surgeon's preference.

Preoperative work-up

All elective patients in whom covering of the LSA for complete exclusion of aortic pathology using TEVAR was anticipated, underwent routine magnetic resonance angiography (MRA), and if not available computed tomography angiography (CTA), for anatomical assessment of the head and neck arteries including collaterals at the circle of Willis. Patients with estimated increased risk of the brain, SCI or left arm ischaemia were scheduled for LSA revascularization prior to or at the TEVAR procedure. In urgent patients, preoperative MRA or CTA was done only if the time was allowed. In emergency, TEVAR always preceded. In cases without the time for proper preoperative evaluation, the caliber of the LVA and RVA on CT scanning together with the measured (reduced) left radial pressure post-procedure, made us decide whether or not to revascularize immediately.

Indications for revascularization

Patients requiring LSA covering with expected (based on preoperative imaging) insufficient collateral blood supply from the contralateral vertebral and/or circle of Willis (carotid circulation), and hence prone to the (posterior) brain and left arm ischaemia, had prophylactic LSA revascularization, including patients with the LVA originating separately from the aortic arch. Other indications for prophylactic LSA revascularization were patients with concomitant long aortic segment covering prone to SCI, and patients with patent LIMA graft prone to myocardial ischaemia. Two patients with an aberrant right subclavian artery (i.e. lusoric artery) had a left and right subclavian artery revascularization prior to TEVAR.

Surgical technique

Bilateral radial artery blood pressure was measured. In all patients with an adequate acoustic window, transcranial Doppler was used to check for inadequate perfusion of the middle cerebral artery during temporary ipsilateral carotid clamping for anastomosing. In cases without proper anterior communication, arterial blood pressure was temporarily raised or (rarely) a shunt was used. For logistic reasons, until 2011 LSA revascularizations were performed as a separate procedure from TEVAR. Since the opening of a fully equipped hybrid operating theatre in our institution, LSA revascularization and TEVAR have been performed concomitantly.

The surgical technique used for cervical reconstruction of subclavian-to-carotid-bypass (SCB) or subclavian-to-carotid-transposition (SCT) is similar to techniques described by others [6, 7]. In brief, through a small transverse supraclavicular cervical incision between the two heads of the sternocleidomastoid muscle, the proximal left common carotid artery (LCCA) and parallel vagus nerve are exposed. Next, a deep retractor is placed and usually between the LCCA and internal jugular vein the proximal part of the LSA can be identified. After 5000 IU of heparin, the LSA is clamped proximal to the vertebral artery and distally. The artery is cut, carefully oversewn with 5–0 Prolene and transposed to the LCCA with care not to kink the LSA. During temporary carotid occlusion, the LSA stump is side-to-end anastomosed to the left lateral side of the LCCA. Following careful deairing, flow is restored.

The preparation for the SCB is the same, except for the anastomosis of a 6–8 mm Dacron graft on the LSA, which is usually created at the level of the thyrocervical trunk. In all patients, the medial approach was applied (i.e. between the two heads of the sternocleidomastoid muscle), since it provides sufficient exposure for SCT as well as SCB procedures. Usually we prefer SCT, unless it is not possible to temporarily interrupt flow in the proximal LSA as in patients with a patent LIMA graft, isolated LVA perfusion to the posterior brain or technical difficulties because of displaced anatomy. At the end of the procedure fibrin glue was sprayed in the wound to prevent chylus leakage, and a redon drain left behind.

Following SCB, it was usually difficult to expose adequately the LSA proximal to the vertebral artery. The LSA was occluded by either the stent-graft covering the ostium or (in case a retrograde Type II endoleak was anticipated) an Amplatzer plug during the endovascular aortic procedure. As an alternative, the proximal LSA may be occluded afterwards by a plug or coils delivered retrogradely through a left brachial artery access.

Postoperative care

Postoperatively all patients (SCB and SCT) started with acetylsalicylic acid lifelong and no coumarine unless there was an indication for its use (e.g. history of atrial fibrillation and mechanical valve prosthesis).

The postoperative follow-up was on regular intervals of 3 months and subsequently 6 months or a year (depending on the results) with control CT and physical examination on the outpatient clinic.

RESULTS

The majority of patients were male and the average age was 67 ± 11 years. The most common comorbidities were hypertension and prior aortic surgery (9 abdominal aortic prosthesis, 2 ascending aorta surgery and 1 TAAA classic repair). Six patients had a history of transient ischemic attack and cerebrovascular accident.

The majority of patients were operated on electively and had degenerative aneurysm disease (Table 1).

Indications for revascularization of the subclavian artery are listed in Table 2. In 23 patients, a SCT was performed and in 28 patients a SCB. A total of 43 patients had subclavian artery revascularization prior to TEVAR with a median interval of 22 days, and 8 patients in the same setting as TEVAR.

In our early experience, 9 elective patients had routine prophylactic LSA revascularization despite adequate circle of Willis, only to extend the proximal landing zone. Subsequent patients were revascularized more selectively, depending on the preoperative risk assessment. The majority of the patients had an incomplete circle of Willis and/or dominant LVA.

In 1 patient with a distal arch aneurysm more than 7 cm, covering of the LSA and LCCA was preceded by a SCB followed by a carotid-to-carotid crossover bypass. Another patient with a separate LVA origin from the arch had SCT followed by a transposition of the LVA to the LSA (end-to-side on the proximal part of the transposed LSA).

Two patients requiring covering of a long aortic segment into the hiatus, had prophylactic LSA revascularization despite adequate cerebral collaterals, to prevent SCI.

Two patients were treated endovascularly for dysphagia lusoria by excluding the lusoric artery at its origin, and transposing it in the neck. The first patient had an incomplete circle of Willis with a dominant LVA, and an RVA originating from the right common carotid artery. To prevent malperfusion of the right arm, first an SCT on the right side was performed. Since, covering of also the LSA was inevitable due to proximity of both ostia, a separate procedure was necessary for an SCT on the left side, followed by the TEVAR procedure. To prevent inadvertent postoperative neuropraxia of the recurrent nerve bilaterally, SCT/SCB of the right side and LSA is always performed as a separate procedure. The second patient had a complete circle of Willis; therefore, first, a SCT on the right side was performed, followed by TEVAR in a separate procedure with successful covering of the origin of the a. lusoria. On control angiography at the end of the procedure, the LSA was partially covered due to the proximity, but well-perfused, without a significant loss of radial artery pressure on the left side. The patient, however, developed arm claudication of the left arm after a year necessitating delayed SCT on the left.

In 2 patients, malperfusion of the left arm developed early after the TEVAR procedure. The first patient was an emergency because of a contained rupture of a distal arch aneurysm, with loss of left radial pulse after deployment of thoracic stent-graft necessitating LSA revascularization. In the other elective patient left arm malperfusion occurred the day after TEVAR despite preoperative assessment of a complete circle of Willis, necessitating LSA revascularization.

Left arm claudication developed in 5 patients late after TEVAR necessitating LSA revascularization. One patient with an aberrant right subclavian artery was described earlier. Two other emergent patients with a subacute Type B aortic dissection developed left arm claudication 1 year and 6 months after TEVAR. Another emergent patient with a contained rupture of a distal arch aneurysm developed left arm claudication 2 years after TEVAR. The last patient who had an elective TEVAR procedure because of a distal arch aneurysm developed left arm claudication 2 months after the procedure despite a preoperative assessed complete circle of Willis.

In all patients, the LSA was successfully revascularized by either SCT or SCB. All complications observed postoperatively and during the long-term follow-up are reported in Table 3. No ipsilateral or contralateral perioperative strokes occurred nor wound infections. One patient (1.9%) required surgical re-exploration of the wound for bleeding after SCT the same day, which was corrected by an additional suture on the LSA stump. Chyle leakage was observed in 3 patients (5.7%), all successfully treated by a period of medium-chain triglyceride diet. No surgery was required. Since the routine use of fibrin glue spray, no chyle leakage has been noted. In 1 patient (1.9%), a 6-mm Dacron bypass graft to the LSA occluded 1 year after surgery despite antiplatelet therapy, resulting in recurrent complaints of left arm malperfusion. A redo SCB to the more distal LSA was performed, which is still functional for more than 3 years now. Predominant (temporary) neuropalsy of the recurrent laryngeal nerve (n = 3, 5.7%), phrenic nerve (n = 2, 3.8%) and sympathetic chain resulting in (partial) Horner's syndrome (n = 3, 5.7%) were observed. Four of them recovered without sequelae, leaving 4 patients (7.5%) with persistent peripheral neural injury, being hoarseness due to recurrent laryngeal nerve palsy (n = 2, 3.8%), paralysis of the left hemidiaphragm due to phrenic nerve palsy (n = 1, 1.9%) or Horner's syndrome (n = 1, 1.9.%).

DISCUSSION

If aortic pathology necessitates LSA covering by a thoracic stent-graft, there is currently no general consensus whether to revascularize prophylactic routinely, selectively or to remain expectant. Risks associated with LSA covering during TEVAR are well described in the literature, but contemporary data on the risks associated with LSA revascularization itself in the TEVAR era are not well described. The current study shows that LSA revascularization itself is a low-risk procedure mainly consisting of temporary neuropraxia.

Most data available are studies with isolated SCB and/or SCT for patients with occlusive subclavian artery disease. These studies have reported complication rates between 10 and 20% [9, 10]. In another study with SCB for occlusive subclavian artery disease in 124 patients over 22 years the complication rate was 8% [11]. In our study, we have observed (transient) complications of LSA revascularization with SCB or SCT in 12 of 53 procedures (22.6%). The study of Domenig et al. [6] in 150 patients spanning 28 years reported an overall complication rate of 23%, which is similar to that of our study. However, their study encompassed mainly occlusive subclavian artery disease as indication for SCT whereas TEVAR as indication for SCT was present in only 17.3% of the patients. Additionally, they reported 12% nerve palsies. A study by Cina et al. [12] reporting results of isolated SCB and SCT for occlusive subclavian artery disease from their own cohort and from reviewing earlier studies on this subject have shown 9.2% nerve injuries with SCB and 11.2% with SCT. In a contemporary study of Lee et al. [13], 32 (22%) patients of a cohort of 145 patients with LSA covering as part of TEVAR had selective LSA revascularization by SCB. Overall complication rate was 9.4% of which 3.1% had transient phrenic nerve palsy. A meta-analysis of Rizvi et al. [4] studying the effect of LSA covering with TEVAR showed that phrenic nerve injuries as complication of revascularization was 4.4% (confidence interval 1.6–12.6%). The majority of complications in our study were neural injuries, of which 7.5% persisted over time. Despite careful dissection, it is not always possible to prevent inadvertent traction on the vagal and/or phrenic nerve (which crosses the anterior scalene muscle superficially). The sympathetic chain cannot be identified dorsal in the neck, and may be (temporarily) injured by local preparation at the level of the proximal LSA and LVA.

The subclavian artery contributes importantly to the posterior brain, spinal cord and left arm. Therefore, intentional covering of the ostium of this artery with thoracic stent-grafting can lead to ischaemia of these territories resulting in stroke, paraplegia/paraparesis and/or arm ischaemia, respectively. The prevention of these complications is the main goal of LSA revascularization by SCB or SCT. However, LSA revascularization itself is not without risk. Older studies with LSA revascularization for occlusive subclavian artery disease have shown stroke rates between <1 and 11% [12, 14–16]. With the advent of TEVAR, subclavian artery revascularization has become, beyond traditional indications, a new treatment adjunct to prevent ischaemic complications from covering LSA with a thoracic stent-graft. A study in the TEVAR era by Lee et al. [13], with a selective prophylactic revascularization approach, showed a 3.1% stroke rate in the revascularized group. A more recent study by Maldonado et al. showed a stroke rate of 6.1% (n = 180) in patients who underwent LSA covering and revascularization during TEVAR [17]. Another very recent study by Madenci et al. [18] showed an overall stroke rate of 5.7% (n = 88) in a separate TEVAR cohort. Our results are, in contrast to these studies, favourable regarding the risk of strokes. It is conceivable, that our routine use of trans cranial doppler monitoring, resulting in induced hypertension or shunting when considered necessary may have contributed to the zero incidence of strokes in our study. To regard LSA revascularization as a safe procedure with a relatively low risk of major adverse events, in particular strokes, it is important to separate postoperative strokes as a result of LSA revascularization from strokes as result of LSA covering by TEVAR.

Some studies report difference in stroke rate between SCB and SCT. In the study of Cina et al. the stroke rate was 6.6% with SCB and 4.4% with SCT. The study of Madenci et al. showed in the TEVAR cohort a stroke rate of 8.3% with SCB vs 3.9% with SCT (difference not significant). In the multivariable analysis, SCB vs SCT was also not a significant predictor for strokes or death. The technique of revascularization, medial versus lateral approach (i.e. lateral from sternocleidomastoid muscle), however, was not described [18]. In our experience, the medial approach gives sufficient exposure for SCT as well as SCB. Interestingly, in the study of Domenig et al. [6] significantly more nerve injuries were noted in the lateral approach group, but strokes (3%), however, were noted only in the medial approach group. In our study, with all patients approached medially, no strokes were observed related to the revascularization itself.

LSA is via the LVA and thyrocervical trunk an important contributor to spinal cord perfusion. The first two posterior intercostal artery branches from the thyrocervical trunk supply partially the dorsal spinal cord trunk; therefore, LSA covering harbours the risk of SCI [19]. Careful selection of patients at risk of SCI (e.g. previous aortic surgery, and/or covering of long aortic segment and/or occlusion of internal iliac artery), cerebrospinal liquor drainage, and prevention of intra- and postoperative hypotension were part of the favourable outcome regarding SCI. A meta-analysis by Cooper et al. [20] showed that in patients with LSA covering, LSA revascularization is protective for SCI. The study by Lee et al. [13] with selective revascularization also showed favourable results for SCI. However, not all studies confirm this favourable outcome for SCI. A recent retrospective review study by Maldonado et al. showed that in patients with LSA covering (n = 394) LSA revascularization was not protective for SCI (nor for strokes) [17].

We have not observed any graft occlusion in the period between LSA revascularization and second-stage TEVAR, despite the parallel flow which exists as long as the origin of the LSA is not occluded. All patients are routinely anticoagulated by aspirin only. It has been suggested, however, that LSA revascularization and TEVAR procedure be performed, respectively, in the same setting [21].

Two of our patients underwent endovascular exclusion of an aberrant right subclavian artery in patients with dysphagia lusoria. This less invasive approach can be used as an alternative to open surgical techniques with resection and graft replacement of the lusoric artery/Kommerell diverticulum through thoracotomy and cardiopulmonary bypass combined with SCB on the right side [22].

With the advent of (single-) branched stent-grafts for the aortic arch, LSA revascularization as part of thoracic stent-grafting may become unnecessary in the near future. However, the success of this innovation will be depending, in addition to the technical feasibility, on the rate of ischaemic complications, in particular strokes and SCI relative to TEVAR and LSA revascularization. Initial experiences are promising but strokes remain a problem [23, 24].

This retrospective study with its limitations was not designed to answer the question whether LSA covering should be prophylactic revascularized selectively or routinely. Nonetheless, we believe that our approach of prophylactic selective revascularization is rational and associated with low risk regarding the very low rate of ischaemic complications during TEVAR. Future prospective studies with large sample size patients comparing LSA covering with and without LSA revascularization should provide a definitive answer to this question. Our study adds to the field of studies that support the notion that LSA revascularization is a low-risk procedure, with mainly transient nerve injuries. In line with recent recommendations [5, 25], we believe that there is a rationale for selective revascularization. Preoperative careful evaluation of the supra-aortic arteries with special attention to the vertebral arteries and circle of Willis, is in our experience, mandatory to decide whether to revascularize LSA prophylactic. This approach might prevent (posterior circulation) strokes and SCI.

In conclusion, the current study shows that LSA revascularization as part of thoracic stent-grafting is safe with low morbidity consisting mainly of (transient) nerve palsy.

Conflict of interest: none declared.

REFERENCES

APPENDIX. CONFERENCE DISCUSSION

Dr J. Benedik(Essen, Germany): I have two questions. First, do you think that the complications rate could be reduced by cooperation with a vascular surgeon? I noticed in the manuscript that you divided the ductus thoracicus. The second question: is it really necessary to divide the ductus thoracicus routinely?

Dr Saouti: As you know, in our hospital we do a lot of aortic surgery, including carotid surgery, so we are very familiar with vascular surgery. We don't do this procedure with vascular surgeons, and I don't think their involvement would diminish the complications rate.

Regarding the second question about the thoracic duct, if it can be spared it, we spare it. But usually in going proximally to the left subclavian artery for exposure, especially with transpositions, you encounter the left vertebral artery and usually it's necessary to ligate the thoracic duct for sufficient exposure. But if you can spare it, yes, it is of course better.

Dr Benedik: I have one additional question. The indication for dysphagia lusoria, do you think that's a good option for TEVAR?

Dr Saouti: There are reports from several surgeons that the classic treatment is by graft replacement and with a cervical reconstruction on the right side. Based on our experience with two patients, we have good results even in the long term. These two patients also had revascularization on the left side, additional to the right cervical reconstruction, with good results. So I think this is a good potential treatment for patients with dysphagia lusoria.

Dr M. Luehr(Leipzig, Germany): You presented a debranching procedure with a bypass procedure. Was that a left subclavian to left carotid bypass? Did you do any of those?

Dr Saouti: Yes, left subclavian to left carotid bypass transposition.

Dr Luehr: My question is, if you perform a bypass procedure, do you ligate the LSA or do you leave it intact? We experienced a lot of Type II endoleaks after TEVAR of zone 2 with intentional LSA coverage.

Dr Saouti: That is an interesting question. Indeed, if possible we ligate the LSA stump to prevent parallel flow potentially causing retrograde Type II endoleaks. But usually when the anatomic exposure of the proximal left subclavian artery was difficult, then we left it and we did a left subclavian artery revascularization, prior to TEVAR, within an average time lapse of three weeks. In that period there is parallel flow through the bypass and antegrade into the left subclavian artery. But we haven't noticed any complication of graft occlusion. Then when we did a TEVAR under control fluoroscopy, if we saw a Type II endoleak, we put an Amplatzer plug through the left brachial artery access. If there was no retrograde Type II endoleak, we leave it and look at the control CT on follow-up.

Dr Luehr: So you would suggest that if you do have a Type II endoleak you would occlude it but it is preferable to ligate the LSA, right?

Dr Saouti: Yes.

Dr D. Dougenis(Patras, Greece): I noticed in your series that you had two cases where, following TEVAR, you decided to do the bypass unexpectedly, after you had problems with perfusion of the hand. We had a similar experience with only one case where we retrospectively understood that the cerebral artery was coming from the aortic arch. So I would like to ask you, what was the problem with these two cases where you closed the subclavian and then there was no perfusion in the hand?

Dr Saouti: One of the two patients was an emergency, so we didn't have a preoperative assessment of the cerebropetal arteries, and when we looked back, we saw on the CT, which was from another hospital, a small calibre left vertebral artery in comparison with the right. But in the emergency situation, the TEVAR proceeded, so we did a TEVAR, and when we saw after the procedure that the left radial artery blood pressure was significantly reduced, then we performed revascularization. The other patient was elective with a complete circle of Willis, not with a dominant left vertebral artery, but, despite that, he developed a significant drop in blood pressure and we had to revascularize.

Dr Dougenis: No particular aetiology?

Dr Saouti: No particular reason, no.

Dr A. Apaydin(Izmir, Turkey): Have you compared the transposition versus bypass in relation to minor complications, i.e., neuropraxia? Have you seen more complications with the transposition technique?

Dr Saouti: If we look at neuropraxia, we saw it most often in the bypass cases, especially the phrenic nerve anterior to the scalene muscle. We had to put traction on that nerve to get enough exposure.

Author notes