The 2014 European guidelines recommend a maximum aorta diameter of 40 mm and a minimum proximal landing zone length of over 20 mm to ensure the success of thoracic endovascular aortic repair (TEVAR), thus minimizing the risk of type Ia endoleaks. However, this criterion presents a challenge in acute aortic syndromes (AAS) affecting the distal aortic arch. In these situations, it is common to need to completely or partially occlude the left subclavian artery (LSA) to achieve adequate proximal sealing.

Partial occlusion of the LSA could, theoretically, increase turbulences, the risk of embolisms or even cause a retrograde aortic dissection, not A-not B and even type A. On the other hand, complete occlusion of the LSA carries the risk of ischemia in the upper limb and may affect the flow in the cerebral artery, with possible adverse consequences for the brain or spinal cord. It is noteworthy that the European guidelines already in 2009 recommended the revascularization of the LSA. Since then, this type of surgical procedure has experienced a notable increase, reflecting its growing importance in clinical practice.

This study aims to evaluate the optimal management of the LSA during TEVAR involving the distal aortic arch in an urgent context. For this purpose, a total of 52 patients with AAS underwent TEVAR (from March 2017 to May 2021) requiring a proximal landing zone in the distal aortic arch. The decision to partially or completely cover the ostium of the LSA with an endoprosthesis, with or without additional bypass, was based on aortic pathology (if there was sufficient proximal neck) and vascular anatomy (based on the patency of the circle of Willis and the unilateral dominance of a carotid or vertebral artery). 35% underwent complete LSA coverage (complete LSA group) and 17% partial coverage (partial LSA group), while in 48% there was no need to occlude the LSA (control group). 22% of the complete LSA group underwent an LSA bypass before TEVAR, while 11% underwent cerebrospinal fluid drainage. The primary endpoints were 30-day and 1-year mortality, stroke, spinal cord ischemia (SCI), and malperfusion syndrome.

Technical success was achieved in 96% of the procedures. The length of the endoprostheses was 171 mm (complete LSA group) versus 151 mm (partial LSA group) vs. 181 mm (control group), covering 6±2 vs. 5±1 vs. 7±2 intercostal arteries. The 30-day mortality, stroke, and SCI rates did not differ. A patient with arm malperfusion underwent an LSA bypass after TEVAR. After 1 year, aortic interventions occurred in 6% (complete LSA group) versus 22% (partial LSA group) versus 13% (control group). Mortality at one year (0% vs. 0% vs. 8%), stroke (6% vs. 0% vs. 4%) and SCI (0% vs. 0% vs. 4%) were similar between groups.

The authors conclude that, after adequate analysis of vascular anatomy, the coverage of the LSA for TEVAR is safe and may offer similar results to TEVAR that starts distal to the LSA.

COMMENTARY:

The outstanding results of this study, achieved in the group of patients with partial or total occlusion of the LSA, are highlighted by the absence of deaths and neurological complications, along with a single case of arm hypoperfusion. This case was timely identified and effectively treated, demonstrating that these achievements are not due to chance. The implementation of a decision-making algorithm specially designed for TEVAR cases in AAS, combined with the vast experience of a hospital specialized in these procedures, are the fundamental pillars behind these successful results.

Emergency TEVAR requiring proximal anchorage in zones Z1 or Z2 involves the total or partial occlusion of the subclavian artery. It is crucial to ensure that after implantation the blood flow to the brain, the anterior spinal cord (SC) and the left arm is not compromised. This involves meticulous preoperative assessment to identify any vascular anomalies that may affect blood flow, such as a pronounced dominance of the left vertebral artery (VA), a hypoplastic right VA, carotid artery stenosis, or a non-patent circle of Willis. In addition, in cases of endoprosthesis that occlude 7 intercostal arteries, or those exceeding 20 cm or covering more than a third of the descending thoracic aorta, prophylactic cerebrospinal fluid (CSF) drainage is recommended. The implementation of this practice should be personalized and performed with care, as it can improve blood flow in the SC through the anterior spinal artery, potentially reducing the incidence of SCI from 9% to 2%, although the complication rate is not negligible, ranging between 6 and 7%. The execution of the procedure in several stages would facilitate ischemic conditioning of the paravertebral collateral network after the occlusion of the first intercostal arteries, as well as the development of collaterals in the vascularization of the affected SC. This staged approach, particularly in the treatment of aortic aneurysms, has proven effective in reducing the incidence of SCI.

This team establishes, first and foremost, that if the indication for TEVAR is urgent and the patient is hemodynamically unstable or in hypovolemic shock, performing a carotid-subclavian bypass prior to TEVAR is not practical or realistic.

The visual algorithm for decision-making they propose is practical and easy to follow. If the patient is hemodynamically stable but exhibits symptoms (persistent pain, paraplegia or other neurological deficits), the first step should be to obtain detailed images of the supra-aortic vessels, including the vertebral arteries, the basilar artery, and the circle of Willis. Furthermore, they emphasize that, depending on the location and extent of the aortic pathology, it is essential to make a pre-procedure decision on whether to partially or completely cover the LSA, the estimated length of the endoprosthesis, and the likely number of intercostal arteries to be occluded. Therefore, they suggest the following recommendations:

Partial coverage of the LSA is viable as long as it does not compromise and ensures the safety of the proximal anchorage zone. In cases where TEVAR requires an endoprosthesis with a total length greater than 200 mm, they recommend performing prophylactic CSF drainage 48 hours before the procedure and consider performing TEVAR in two stages. This same strategy applies if it is necessary to cover more than 7 intercostal arteries, although this entails some risk of type Ib leakage (which could be treated in a secondary procedure). In case of complete coverage of the LSA, a carotid-subclavian bypass could be avoided if the circle of Willis is confirmed to be intact, the vertebral arteries are compensated and there is no significant stenosis of the left carotid artery. A prophylactic carotid-subclavian bypass should be performed if these conditions are not met, as well as in cases where the left vertebral artery is dominant or emerges directly from the aortic arch. In this study, only 22% of complete LSA occlusions required prior bypass. To assess arm ischemia, the decision to perform revascularization post-TEVAR is primarily based on the detection of clinical symptoms of malperfusion during the first hours after the intervention.

However, in the case of elective surgeries involving endoprosthesis with occlusion of the LSA, this team prefers to perform a carotid-subclavian bypass prophylactically in most patients, regardless of the specific vascular anatomy they present.

In the recent multicenter study by Luehr et al., which has included the largest number of patients to date to assess the impact of LSA occlusion after TEVAR, based on whether they underwent LSA revascularization, it was observed that, although only 50% of the procedures were emergencies, there were no significant differences in terms of mortality (12.7% vs. 19.8%), incidence of stroke (5.5% vs. 7.4%) and paraplegia rates (5.5% vs. 6.6%). However, it is important to note that the rate of arm malperfusion was 10 times higher in those patients who did not receive subclavian revascularization. This study, unlike the one we are analyzing today, obtained worse clinical outcomes, was multicenter and did not have homogeneous action protocols, which makes extrapolation and interpretation of these results difficult.

On the other hand, prophylactic open revascularization of the LSA could increase the risk of minor perioperative complications (such as seroma, nerve damage, lymphatic leakage) and major (neurological) ones. It is known that this practice is associated with an operative mortality that ranges from 1.2% to 5%. For this reason, some researchers propose prophylactic revascularization of the LSA only when there is a high risk of neurological complications, especially stroke or SCI, predicted by angioCT. Additionally, given the difficulty that can entail performing a carotid-subclavian bypass prophylactically in an emergency context with the patient unstable, it seems reasonable to refrain from performing such in these circumstances.

Although it is a retrospective study with a relatively limited patient sample, the most significant finding that emerges from this study is that, in an urgent context, TEVAR with partial or complete occlusion of the LSA can be safely performed without a prophylactic carotid-subclavian bypass, as long as the angioCT predicts that cerebral and spinal vascularization will be sufficient to prevent complications. Therefore, following decision-making algorithms like the one presented in this study is very valuable, safe and its implementation should be recommended in any hospital that handles this type of pathology.

REFERENCE:

Haldenwang PL, Heute C, Schero KJ, Schlömicher M, Haeuser L, et al. Urgent Endovascular Aortic Repair Requiring Coverage of the Left Subclavian Artery. Thorac Cardiovasc Surg. 2023 Oct 16. doi: 10.1055/a-2125-3173.