Determining surgical indications for aortic arch aneurysms. Aortic arch pathologies often pose significant challenges to surgical or endovascular treatment. Conditions affecting the aortic arch relevant to the vascular surgeon include degenerative aneurysms and the acute aortic syndromes (e.g. penetrating ulcers, intramural hematoma and aortic dissections) (5). However, in 2019 EACTS and ESVS published an expert consensus document in which they mentioned/listed less common/rare aortic arch pathologies, such as: arteria lusoria, Kommerell diverticulum, traumatic, infectious, giant-cell and Takayasu's arteritis (6).
The incidence of degenerative aortic arch aneurysms is increasing with advances of imaging. The growth of aortic arch aneurysm is an indolent process with a mean annual growth rate from 0.07 to 0.2 cm/y (7). Main risk factors include increasing age, female sex, presence of chronic obstructive pulmonary disease, hypertension and positive family history (8). However, no researches specifying in aortic arch or rate of expansion or the risk of true aneurysms rupture are presented. Scientists from Yale University report that annual growth rate of aorta is about 1 cm/y and for aneurysms exceeding 6 cm in diameter rupture can occur at 6,9% per year. The annual risk of rupture generally increases with the diameter growth, so they recommend performing operative intervention when the aneurysms measures 5.5-6 cm (9). Moreover, some other scientists state that aneurysm size beyond 6.5 cm is associated with faster expansion (with an average rate of 2.5 mm/y) and hyperlipidemia (5). Twenty-two percent of aneurysms of that size ruptured with 80% mortality rate, they note.
Tracheobronchial compression syndrome with the aortic arch aneurysms is one of the urgent conditions that needs emergency surgery (3). There is no accurate data presenting the frequency of this complication, although some researchers suggest 5–10% (10).
Airway compression syndrome is also an independent predictor of emergency surgery in patients with double aortic arch, arteria lusoria, pulmonary artery sling, and Kommerell diverticulum (11). Most of the authors consider urgent aortic arch surgery the only option for patients with tracheobronchial compression syndrome.
Purpose of separate examination of indications for aortic arch surgical treatment as immediate is related to existing relative contraindications for a surgery in conditions of CPB and visceral arrest in our patient. A giant false aneurysm leads to tracheobronchial compression, which caused bronchial drainage disruption. It resulted in nonresolving community-acquired pneumonia, which a priori complicated peri- and postoperative prognosis.
The main risks of aortic arch interventions include neurological, cardiac, renal and pulmonary disorders in the early postoperative period. Accordingly, the purpose of preoperational patient preparation is to maximize the levelling of conditions which deteriorate the results of surgery with CPB and visceral arrest (12).
However, in case of our patient the emergency intervention seems justified, as he had both vascular (thrombosis, rupture and size more than 9 cm) and extravasal (tracheobronchial compression syndrome, high degree of respiratory failure and as a result, fever due to pneumonia) indications for aortic arch replacement. Also, considering the respiratory tract compression, complex therapy of pneumonia in this case was not possible. This fact once again indicates the inexpediency and unsuccess of conservative therapy in the tracheobronchial tree block and the justification of urgent surgery.
Ways to improve the results of simultaneous total prosthetic replacement of the aortic arch and coronary bypass. Simultaneous coronary arteries bypass graft is performed in 15–30% of all patients with aortic arch surgeries (13). CABG following the total prosthetic replacement of the aortic arch is considered as significant risk factor of increased operative mortality and morbidity (2). However, in a number of modern works it is suggested that there is no significant difference in mortality rate between patients with and without simultaneous coronary revascularization (14). For this reason, it seems relevant to optimize coronary bypass in this patient cohort via minimizing the period of CPB time and myocardial ischemia.
For that purpose, in our patient's case, distal anastomoses of autoveins with obtuse marginal artery and posterior descending artery of right coronary artery were carried out on parallel perfusion during cooling process and proximal – during warming process.
Further, mammary coronary bypass of anterior interventricular artery was performed on parallel CPB during patient warming.
Chosen approach is confirmed by a number of major studies. For example, Toshihiro Fukui presents a similar order of coronary artery bypass graft in 56 patients who underwent total prosthetic replacement of the aortic arch (2). The fatality rate in the examined group was 3.6% (2 patients), and it had no connection to follow-up coronary bypass. Postoperative coronary bed CT was performed in 51 patients and revealed complete permeability of all anastomoses. Similar technique of myocardial revascularization in patients with aortic arch pathology is followed by Yokoyama H. (except of the LITA use) (13).
It stands to mention that the use of the LITA graft is controversial in patients with total prosthetic replacement of the aortic arch. Thus, Yokoyama H. did not use these grafts due to the reasons, which include 1) the possibility of cardioplegia administration through free grafts after forming the anastomoses; 2) hemodynamic instability after arch replacement (which is not uncommon for this complex operation) can decrease blood flow in small compressed LITA; 3) anastomosis of the LSA with the prosthesis can predispose to LITA dissection (13). Whereas, Kuniyoshi et al. used LITA for revascularization of anterior interventricular branch in this group of patients with good permeability indications confirmed by coronaro/shuntography (15). Several authors recommend LITA for coronary bypass in patients undergoing total arch replacement due to the proven long-term permeability of this graft, and also based on evidence that myocardial infarction is one of the main causes of late postoperative death in this patient cohort (13).
We believe that usage of LITA graft as a conduit is a choice for the anterior interventricular branch revascularization in all patients, including those who need aortic arch surgeries.
Optimization of anesthesiological practices and surgical approach for vascular compression of the respiratory tract. Trachea intubation, providing of optimal and safe artificial lung ventilation is a significant problem in patients with large aortic arch aneurysms which are accompanied by airway compression. It may be explained by the expressed anatomical distortion due to vascular compression (16). Trachea intubation in such cases can be performed with endotracheal tube with a double lumen on the left or right side if there is significant compression of the entrance to the left main bronchus (17). A number of authors mention the danger of using a left-side double-lumen tube in patients with the compression of the left bronchus trunk bottom, as using of ALV in this method increases the risk of aneurysm rupture. In addition, contraindications for the use of double lumen tubes include anatomical aspects, such as damage of the cardinal or bronchial veins, coarctation and vessel compression by aortic aneurysm (16). Most thematic publications point to the vital importance and effectiveness of intraoperative bronchoscopic monitoring while airway decompression (18). In such cases, the flexible bronchoscope allows to inspect all available areas of the respiratory tract, evaluate the properties of endoluminal tissue of walls and carry out effective direct purification of the remaining excretions after decompression (3).
In case of our patient, we preferred to use a single lumen tube, and trachea intubation was controlled by bronchoscopy. Constant monitoring within the lumen allowed us to control decompression results, and to turn on the left lung after releasing the main trunk of the left bronchus. Distinction of our case is aorta-tracheal fistula found after aneurysm dissection and complete release of the trachea. Turning to the literature, we found that most modern works describe the successful decompression of the respiratory tract after aneurysmectomy and absence of the need for prosthetics or endovascular repair of trachea and bronchi (19). However, the literature describes the case of tracheomalacia detected intraoperatively after resection of the syphilitic aneurysm of the aortic arch, which was successfully corrected by implantation of a 14 mm Y-shaped silicone stent explanted after 6 months with complete stabilization of tracheal and main bronchi walls (20). Treatment of irreversible compression lesions of trachea involves straight or step-by-step reconstruction. However, in cases with cardiosurgical patients, these methods may not be applicable due to development of life-threatening respiratory failure. Most authors confirm the effectiveness and safety of implantation of the above-described temporary endotracheal stent as an alternative to reconstructive airway interventions (21). After aneurysmectomy and airway decompression, control bronchoscopy revealed no signs of tracheomalacia, which allowed us to eliminate fistula performing only effective suture plastic of trachea. Therefore, regardless of the presence or lack of integrity of trachea or bronchi wall, for patients of this group we recommend to use bronchoscopy at all stages of treatment, from intubation in the operating room to extubation in the intensive care unit.
Modern view on aortic arch surgery. Since Hans Borst described the "elephant trunk technique” in 1983, many cardiac surgery centers have accumulated enormous experience in performing this operation (22). Over the years, new improvement methods of a complex aortic arch repair were developed and widely implemented. The most important developments now include synthetic multi-branch prostheses, homographs, stent grafts, all of which have become commercially available over the past decade (12).
We believe that multi-branch prosthesis has a number of advantages justifying its routine usage in complex aortic arch repair. Thus, there is a potential to minimize the visceral arrest time and the period of myocardial ischemia. In addition, hemostasis significantly improves, and patients with connective tissue diseases potentially reduce their risks of repeated interventions (23, 24).
It should be noted that the experience gained in aortic arch surgery allows to identify preferred "candidates" for a particular graft. Thus, some authors recommend implantation of freshly frozen homographs to patients with DeBakey type I aortic dissections and do not recommend their usage for people with Marfan syndrome due to the high risk of reoperations (25). Developing over the last years endovascular and hybrid techniques for implanting stent grafts in the treatment of aortic arch aneurysms may be useful, but they are still associated with a number of technical and economic difficulties, and with the high risk of neurological complications (26).
In case of our patient, use of a synthetic multi-branch prosthesis was the only option. We assume that frozen homografts are preferable to relatively "scheduled" patients, and the endovascular technique in that case didn't allow us to perform airway decompression.
Patients with aortic arch aneurysms may develop an airway compression. Urgent indications for surgery in such cases include both significant size of the aneurysm and high risk of rupture, as well as potential for developing critical respiratory failure and recurrent nonresolving pneumonias. Preoperative CT enables to find out the exact location and evaluate the degree of airway compression, which determines further intraoperative actions. We recommend to use bronchoscopy at all steps of treatment of such patients, from intubation in operating room to extubation in intensive care unit. Surgical planning and accurate preoperative diagnostic are essential to a successful outcome in case of these patients. Simultaneous aortic arch replacement and coronary bypass needs further optimization of time for myocardial ischemia.
Patients with large degenerative aortic arch aneurysms may have airway compression. Urgent indications for intervention in case of such patients include not only the significant size of the aneurysm but also high risk of rupture, and potential for developing critical respiratory failure and recurrent nonresolving pneumonias. Pre-operative CT scan allows to clarify the location and degree of airway compression, which determines further intraoperative tactics. We recommend to use bronchoscopy at all stages of treatment of similar patients - from intubation in the surgery room till extubation in the intensive care. Thus, aggressive surgical tactics along with careful pre-operative diagnostic are the key to success and the only chance for such patients.
Literature data analysis revealed no published cases of CHD in combination with thoracic aortic aneurysms, with obstructive respiratory complications and aorta-visceral fistulas. Simultaneous aortic arch replacement and coronary bypass require optimization aimed to reduce myocardial ischemia time.