Background

Surgical treatment of thoracic aortic aneurysms and dissections is still an urgent problem due to traumatic intervention with high risk of fatal complications [1 — 6]. Endovascular surgery with hybrid technologies is being actively developed. Hybrid interventions reduce the risk of complications and mortality compared to open procedures. This is achieved via less time of aortic cross-clamping, cardiopulmonary bypass, brain and visceral ischemia. It is especially important for elderly patients and patients with severe comorbidities [7, 9 — 15].

Thoracic aortic aneurysms and dissections are often extended and involve aortic arch. In patients eligible for aortic stenting, proximal and distal necks of the aneurysm should meet certain anatomical requirements for effective fixation. Ideally, the neck should be represented by an intact wall of appropriate diameter and length [16 — 18]. Aortic arch debranching is required if the stent is located in aortic arch and overlaps the orifices of supra-aortic arteries. In this case, debranching with creating a landing zone for supra-aortic arteries precedes stenting [19 — 21].

Type of debranching depends on extent of lesion and anatomical features of supra-aortic arteries. There is intracavitary (with sternotomy) and extracavitary debranching (within the neck) [16, 19, 22].

For intracavitary debranching, the main requirement is the absence of at least one donor vessel on the neck. Then, total debranching from ascending aorta is performed to release the attachment zone (Z0 according to the Mitchell classification) [23].

If there are donor vessels arising from aortic arch outside the area of further stenting, extracavitary debranching is possible. The last one consists in debranching of the left subclavian artery or the left common carotid artery and the left subclavian artery on the neck. Extracavitary debranching provides implantation of a stent-graft into the landing zone Z1 and Z2.

We report own experience in hybrid treatment of thoracic aortic aneurysms and dissections with various methods of debranching.

Material and methods

There were 107 patients with thoracic aortic aneurysms and dissections who underwent debranching as a part of hybrid treatment between 2015 and 2021. There were 28 (26%) women and 79 (74%) men. Mean age of patients was 58±15 years.

All patients underwent standard preoperative examination. Most patients had comorbidities. Hypertension, chronic obstructive pulmonary disease and coronary artery disease prevailed (Table 1).

Table 1. Concomitant diseases

The main diagnostic procedure was contrast-enhanced multislice computed tomography (MSCT). MSCT is necessary to assess the anatomical features of the aneurysm and supra-aortic arteries, as well as to measure the necessary parameters of landing zones. Length of proximal landing zone should be at least 2 cm from the edge of the aneurysm. All patients underwent preoperative Doppler ultrasound of supra-aortic arteries to assess baseline blood flow parameters and detect various lesions. Our patients had no baseline severe lesions of supra-aortic arteries. Postoperative ultrasound was performed to assess cerebral circulation after surgery.

Patients underwent total and partial debranching including subtotal debranching and carotid-subclavian bypass. Debranching was performed in patients with type 3 dissection, type B aneurysms, posttraumatic aortic isthmus and arch aneurysms, thoracoabdominal aneurysms type A and aortic dissection DeBakey type 1 (Table 2).

Table 2. Aortic arch debranching options depending on pathology

Total debranching was performed from ascending aorta. In case of aortic wall lesion, we replaced the ascending aorta before debranching. Moreover, simultaneous aortic valve repair and myocardial revascularization were carried out according to indications. Total debranching was combined with myocardial revascularization in 3 patients and aortic valve replacement in 5 patients.

We tried to form the proximal anastomosis of prosthesis with aorta as close as possible to aortic root to free up more space for convenient upper fixation of the stent-graft.

Before replacement, we carefully analyze the length of prostheses for supra-aortic arteries to avoid its excess. Moreover, their placement should prevent kinking. In case of total debranching, we mandatory replaced all 3 supra-aortic arteries: innominate artery, left common carotid artery and left subclavian artery. The most common option was replacement of innominate artery from ascending aorta with a previously formed trifurcation prosthesis made of linear 12 or 14 mm tube graft and sewn into this graft branches 8 mm in end-to-side fashion. The main branch was used for replacement of innominate artery, other 2 prostheses — for the left common carotid artery and left subclavian artery, respectively (Fig. 1). Anastomosis between prosthesis and ascending aorta was performed in end-to-side fashion.

Fig. 1. Total aortic arch debranching (scheme and intraoperative images).

A — prosthesis of the innominate artery; B — prosthesis of the left common carotid artery; C — prosthesis of the left subclavian artery.

If the left vertebral artery arose from aortic arch, we preserved blood flow in this artery via its implantation into the left common carotid artery in all types of debranching.

Subtotal debranching involved 2 supra-aortic arteries (left common carotid artery and left subclavian artery). In our department, we developed 2 types of subtotal debranching (Fig. 2).

Fig. 2. Subtotal aortic arch debranching in hybrid treatment.

a — subtotal debranching #1; b — subtotal debranching #2.

Subtotal debranching No. 1 (Fig. 2A) is a right-to-left carotid-subclavian bypass with reimplantation of the left common carotid artery into prosthesis and ligation of the first segment of the left subclavian artery [24]. In this case, we performed a standard approach to the right common carotid artery and the second supraclavicular approach to the left common carotid artery and subclavian artery. After cross-clamping the right common carotid artery, we formed anastomosis of this artery with synthetic prosthesis 8 mm in end-to-side fashion between two clamps. Then, we created a canal under pretracheal muscles, and prosthesis was passed in this canal to the left subclavian artery. The left common carotid artery was intersected between two clamps, and anastomosis in end-to-side fashion was formed between the distal part of the left common carotid artery and synthetic prosthesis. Proximal part of the left common carotid artery was ligated. Then, we performed anastomosis between the distal end of prosthesis and the left subclavian artery in end-to-side fashion. The left subclavian artery was ligated proximal to anastomosis and ostium of the left vertebral artery.

Subtotal debranching No. 2 (Fig. 2B) is carotid cross-over bypass with replantation of the left common carotid artery into the left subclavian artery with ligation of the first segment of the left subclavian artery (2 (1.9%) patients) [25].

Debranching was performed through standard accesses to both common carotid arteries and subclavian artery. After cross-clamping of the right common carotid artery, we performed anastomosis between the right common carotid artery and synthetic prosthesis 8 mm in end-to-side fashion. Then, we created a canal under pretracheal muscles, and prosthesis was passed in this canal to the left common carotid artery. Distal anastomosis between synthetic prosthesis and the left common carotid artery was formed in end-to-side fashion. In the area of further anastomosis between the left common carotid artery and left subclavian artery, the left common carotid artery was intersected between two clamps. Proximal part of common carotid artery was sutured and ligated. Anastomosis between the left common carotid artery and left subclavian artery was performed in end-to-side fashion. Left subclavian artery was ligated proximal to the ostium of the left vertebral artery.

Carotid-subclavian anastomosis or bypass

Surgery was performed via left-sided supraclavicular approach. Carotid-subclavian anastomosis has always been preferred over carotid-subclavian bypass. A prerequisite for carotid-subclavian anastomosis is appropriate length of the 1^st segment of the left subclavian artery proximal to the vertebral artery. In our opinion, optimal length of this segment should be 1–2 cm. An excess will lead to kinking of anastomosis and vertebral artery while insufficient length will result tension of anastomosis and kinking of donor common carotid artery. Hemodynamics of carotid-subclavian anastomosis is disturbed in both cases, and there is a risk of thrombosis. The site for subclavian-carotid anastomosis should be carefully selected. It is better to place subclavian-carotid anastomosis slightly proximal to the proposed point of intersection of common carotid artery and subclavian artery. Finally, blood flow through the reconstructed subclavian artery will proceed physiologically from the bottom up from the common carotid artery.

MSCT in early postoperative period was mandatory in all patients for control of location of prostheses, stent displacement, endoleaks, etc. (Fig. 3).

Fig. 3. MSCT after aortic arch debranching.

1 — total aortic arch debranching; 2 — subtotal aortic arch debranching.

One of the most important issues is assessment of cerebral circulation after debranching.

Volumetric blood flow rate is the most valuable parameter for analysis of blood supply (Q, ml/min). To assess cerebral circulation, we compared volumetric blood flow rate in supra-aortic vessels before and after surgery. Time-averaged mean blood flow velocity was used (TAV). We assessed time-averaged mean blood flow velocity in foraminal segments of vertebral arteries and in internal carotid arteries (ICA) above the bifurcation of common carotid artery. Overall Q was defined as the sum of Q in all vessels.

Quantitative values in independent samples were compared using the Student's t-test. Qualitative variables were analyzed using the non-parametric Kruskal-Wallis H-test (Fig. 4).

Fig. 4. Blood flow velocity in supra-aortic vessels after debranching (Kruskal—Wallis H-test).

Volumetric blood flow rate corresponds to cardiac output and obeys the Poiseuille equation. The first equation is Q = P1-P2 / R, where P1-P2 — pressure difference between both ends of the vessel, R — resistance to blood flow. The second equation describes correlations associated with resistance: R = 8ηL/π r2, where L — length of the vessel, η — blood viscosity, π = 3.14, r — radius of the vessel. According to this formula, a longer vessel with less lumen is characterized by higher resistance to blood flow and less volumetric blood flow. Ultrasound revealed a tendency towards decrease of overall Q in supra-aortic vessels for all types of debranching. Moreover, subtotal debranching is followed by significant difference (p<0.05) (Fig. 4).

We observed significant decrease of linear blood flow velocity in the left vertebral artery after subtotal debranching. Linear blood flow velocity in the left vertebral artery decreased after debranching. Moreover, there were blood flow changes in the form of latent steal syndrome. Therefore, we separately analyzed changes of blood flow velocity in the left vertebral artery before and after subtotal debranching and revealed a significant decrease of Q in the left vertebral artery after surgery (p<0.01) (Fig. 4).

Decrease of blood flow velocity after debranching may be due to greater length of vessels (additional grafts) and changes of their diameter. These aspects increase resistance to blood flow. This was especially clearly expressed in decrease of overall Q after subtotal debranching. Nevertheless, even statistically significant reduction of blood flow velocity was not critical and remained sufficient for adequate blood supply to the brain.

Results and discussion

According to CT and ultrasound data, there were no cases of stenosis and thrombosis in early postoperative period after both total and partial debranching. One (0.9%) patient developed thrombosis of the left vertebral artery due to ligation of the first segment of the left subclavian artery near the orifice of the vertebral artery with its subsequent deformity. Postoperative lymphorrhea occurred in 9 (8.4%) patients due to injury of lymphatic duct after reconstruction of the left subclavian artery. Seven (6.5%) patients had dizziness and headaches. One (0.9%) patient died from retrograde dissection and rupture of the thoracic aorta after previous subtotal debranching. Stenting of the aortic arch and descending aorta was scheduled after debranching in this case.

Debranching was followed by certain decrease of blood flow rate in supra-aortic vessels compared to baseline data. After subtotal debranching, we observed significant decrease of blood flow rate in the left vertebral artery. Nevertheless, decrease of blood flow rate was not critical for blood supply to the brain.

The advantage of partial debranching in hybrid treatment is surgical simplicity. Indeed, there is no need for thoracotomy that significantly reduces surgical trauma and duration of intervention. Between two methods of subtotal debranching developed in our center, we prefer the first technique since it is usually feasible. Subtotal debranching No. 2 cannot always be performed, since the length of the left common carotid artery may not be enough for implantation into the left subclavian artery.

The main advantage of total debranching is no need for CPB, aortic cross-clamping and circulatory arrest. However, one should consider that stent-graft is placed highly in distal ascending aorta, and ascending aorta itself may be involved in pathological process. This fact can requires additional intervention.

The main and significant disadvantage of total and subtotal debranching is potential thrombosis of prostheses in delayed postoperative period. This is due to the likelihood of kinking and stenosis of prostheses lying in non-standard positions. After total debranching, thrombosis can be fatal because blood supply to the brain depends on one synthetic graft. According to various data, incidence of occlusions after debranching is 1.9 — 4% [26, 27]. Therefore, control of the length and position of prostheses is very important for debranching to prevent possible kinking and compression by surrounding structures [27].

Importantly, some authors do not always perform carotid-subclavian anastomosis before covering the ostium of the left subclavian artery with a stent-graft [27]. The absolute indications for this anastomosis are dominant left vertebral artery, patent IMA-LAD anastomosis, arteriovenous fistula on the left arm, aberrant origin of the left vertebral artery from the aortic arch, aberrant origin of the right subclavian artery (a. luzoria) in left-handed patients. According to these authors, clinical symptoms are rare and no revascularization of the left subclavian artery is required in other cases. This point of view occurred after the EUROSTAR study in 2007. However, recent reports recommend reconstruction of the left subclavian artery because this approach significantly reduces the incidence of stroke and mortality after hybrid aortic arch repair [16, 18, 20, 21].

In case of partial debranching, we prefer ligation of the first segment of the left subclavian artery to prevent the risk of embolism and thrombosis of the left vertebral artery during subsequent aortic stenting. It is known that debranching of the left subclavian artery before endovascular treatment can reduce the incidence of ischemic stroke in posterior cerebral circulation from 5.5 to 1.2% [23]. Ligation of the first segment of the left subclavian artery should be performed as proximal as possible from the ostium of the vertebral artery. Indeed, its deformation can lead to stenosis and subsequent thrombosis of this artery.

There are also reports devoted to chimney-graft technique instead of surgical debranching. Various authors use double and even triple chimney techniques when stent grafts are installed in all supra-aortic arteries. However, incidence of type 1 endoleaks in early postoperative period is high after complex chimney stenting. These events require various open surgeries or embolization procedures.

Thus, aortic arch debranching is necessary in some patients eligible for hybrid aortic surgery. This is especially true for patients with severe comorbidities. Total and partial debranching has certain advantages and disadvantages. Aortic repair without debranching is a more traumatic treatment. Despite less surgical trauma typical for subtotal and especially total debranching, there is a significant risk of synthetic graft thrombosis with potential fatal outcomes. Therefore, treatment strategy should be always selective. Open reconstructions or fenestrated grafts may be more advisable in young patients eligible for subtotal debranching.

Hybrid procedures (Bavaria type II with total debranching) should be performed in certain patients with high surgical risk. Moreover, alternative and physiological hybrid interventions with anatomical placement of prostheses such as Elephant Trunk and Frozen Elephant Trunk procedures should be preferred [2, 28, 29].

The authors declare no conflicts of interest.