The risk of spinal cord injury during the frozen elephant trunk procedure in acute aortic dissection

The risk of spinal cord injury during the frozen elephant trunk procedure in acute aortic dissection Abstract OBJECTIVES The aim of the study was to access the extended occlusion of the intercostal arteries by a stent graft in the development of postoperative spinal cord injury during aortic arch surgery using the frozen elephant trunk technique. METHODS A total of 37 consecutive patients underwent total aortic arch surgery using the frozen elephant trunk technique between March 2012 and July 2017. The mean age of the patients was 54.7 ± 10.5 years. Type A and Type B aortic dissections were the indications for surgery. Moderate hypothermia and antegrade cerebral perfusion via the innominate artery were utilized. The mean diameter of the implanted stent graft was 27.7 ± 2 mm (range 24–30 mm). RESULTS No permanent spinal cord injuries occurred. The distal edge of the stent graft was in the T7–T12 range. Its lower edge was implanted at the T9–T12 level in 25 (67.6%) cases. Preoperatively, the mean number of intercostal arteries was 10 ± 1 on the left side and 10 ± 2 on the right side (P = 0.59). Postoperatively, the mean number of open segmental arteries was 3 ± 2 on the left and 4 ± 1 on the right (P = 0.003). CONCLUSIONS The frozen elephant trunk procedure is associated with the occlusion of most (two-thirds) of the intercostal arteries. Maintenance of adequate blood flow in the subclavian and iliac arteries is an integral prerequisite for a favourable outcome. The level of the deployment of the distal edge of the stent graft does not play a defining role. Unilateral cerebral perfusion, Innominate artery, Frozen elephant trunk, Spinal cord ischaemia, Intercostal arteries INTRODUCTION The concepts of blood supply to the spinal cord are being revised. Thus, the theory that the Adamkiewicz artery plays a key role in supplying blood to the spinal cord is now primarily historical in nature [1]. The current perception of spinal cord perfusion is based on the presence of ‘vertical and horizontal’ collateral networks, where subclavian, iliac, and segmental arteries play a major role in spinal cord perfusion [2]. Spinal cord injury (SCI) is one of the most devastating complications after aortic arch repair. Rare cases of paraplegia have been reported after the conventional elephant trunk procedure. The reported incidence rate of permanent or transient ischaemic SCI after conventional elephant trunk implantation reaches 3%. In contrast, the reported incidence rate of SCI in patients undergoing the frozen elephant trunk (FET) procedure is about 8%. Some single-centre studies have reported incidences as high as 21–24% after FET implantation and have hypothesized various mechanisms to explain SCI [3]. According to the literature, the lack of left subclavian artery perfusion, a previous abdominal aortic operation, severe atherosclerosis, diabetes, postoperative mean aortic pressure <70 mmHg and distal deployment of the stent graft (below T9) with extensive coverage of intercostal arteries were found to be associated with an increased occurrence of SCI [4–6]. In this regard, malperfusion of the intercostal arteries can be one of the causes of SCI. Thus, the aim of the study was to access the extended occlusion of the intercostal arteries by the stent graft in the development of postoperative ischaemia of the spinal cord during aortic arch reconstruction using the FET technique. PATIENTS AND METHODS A total of 37 consecutive patients underwent total aortic arch surgery using the FET technique between March 2012 and July 2017. All the patients underwent single-stage repair of the aortic arch with the implantation of a hybrid stent graft, the E-vita Open Plus (Jotec® GmbH, Hechingen, Germany), into the descending thoracic aorta. The data were prospectively collected in a database, and the study was approved by the local ethics committee. Individual patient consent was waived. 3D computed tomography (CT) was used as the basic instrument for diagnosis in patients with thoracic aortic disease. Additionally, the total number of intercostal arteries and an evaluation of patency were recorded pre- and postoperatively. The lumen of origin of the segmental artery ostia was also verified. Attention was also paid to the patency of subclavian and iliac arteries. All patients underwent postoperative CT within 2–4 weeks after the operation to evaluate the proximal anastomosis and the distal attachment site of the stent graft. All patients had a postoperative neurological examination to determine whether the sensitivity and the motion of the lower extremities were normal. Operative technique The FET procedure was performed according to a surgical management procedure used in our clinic (Table 1). Table 1: Surgical management procedure Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% Table 1: Surgical management procedure Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% A hybrid stent graft, the E-vita Open Plus, with a diameter of 22–40 mm and a length of 150 mm, was used in all cases. The diameter of the graft should be 110% of the diameter of the aortic segment chosen as the landing zone in cases of aortic aneurysms. Cerebral perfusion during circulatory arrest was controlled by directly monitoring the arterial pressure in both radial arteries and by using near-infrared spectroscopy (Invos 5100, Medtronic Corp., Minneapolis, MN, USA). The target haematocrit level during circulatory arrest was above 25%. Cerebrospinal fluid (CSF) drainage and pressure monitoring were not performed. Unilateral perfusion was carried out through the innominate artery while the left common carotid artery and left subclavian artery were clamped. After the administration of heparin at a dose of 1 mg/kg, the innominate artery was side clamped and monitored simultaneously using near-infrared spectroscopy and by determining the arterial pressure level in both radial arteries. The innominate artery was opened to decrease the arterial pressure in the right radial artery by no more than 50% and to decrease the cerebral venous saturation on the right side to not lower than 20% compared to the baseline values. Then, an anastomosis was formed with continuous 5-0 sutures with an 8–10 mm linear vascular prosthesis in an end-to-side fashion. After washing off possible debris and eliminating air from the prosthesis, it was connected to the arterial line of the cardiopulmonary bypass system; heparin was added so that the total dose was 3 mg/kg, with the active clotting time controlled (480–600 s). The stent graft was inserted into the descending thoracic aorta without a guidewire. In most cases, the stent graft was attached by continuous suturing with 4-0 polypropylene sutures distal to the left subclavian artery. In several cases, the stent graft proximal anastomosis was performed in other zones (Table 2). Transoesophageal echocardiography was used to monitor the deployment of the stent graft. After the distal anastomosis was completed, a clamp was placed on the aortic prosthesis; systemic blood perfusion was resumed through an additional cannula, which was inserted into the prostheses distal to the clamp; the patient was gradually rewarmed. Supra-aortic vessel reconstruction was performed en bloc (70.3%) or separately (29.7%). The unilateral cerebral perfusion was discontinued. The proximal aortic anastomosis was then carried out, and the coronary blood flow was restored. Concomitant operations, such as coronary artery bypass grafting, could be performed during the rewarming period. Table 2: Demographics, preoperative clinical characteristics and operative data (n = 37) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) CPB: cardiopulmonary bypass; uACP: unilateral antegrade cerebral perfusion; SCI: spinal cord injury; SD: standard deviation; TND: temporal neurological deficit. Table 2: Demographics, preoperative clinical characteristics and operative data (n = 37) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) CPB: cardiopulmonary bypass; uACP: unilateral antegrade cerebral perfusion; SCI: spinal cord injury; SD: standard deviation; TND: temporal neurological deficit. After cardiopulmonary bypass weaning, heparin was inactivated by protamine in a ratio of 1:1. Infusion of red blood cell units was performed in case the haemoglobin level dropped lower than 90 g/l. If the platelet level was less than 60 × 109, platelet infusion was carried out. Fresh frozen plasma infusion was carried out to a target level of 30 ml/kg [7]. The mean arterial pressure was maintained at a level no lower than 70 mmHg immediately after protamine infusion and for the next 3 days. Definition ‘Permanent’ SCI was defined as irreversible paraplegia, and ‘temporary’ SCI was defined as reversible neurological deficit of the spinal cord. Operations were considered ‘emergent’ if performed within 24 h of hospital admission for cardiovascular instability and ‘urgent’ if performed within 72 h of admission. Neurological complications were defined as ‘permanent neurological deficit’ for patients with a stroke, and ‘temporary neurological deficit’ for patients with reversible deficits. Statistical analysis Continuous variables are not normally distributed and are reported as mean ± standard deviation; categorical data are reported as proportions throughout the article. These variables were compared using the Wilcoxon rank-sum test. The differences were considered significant at P < 0.05. RESULTS A total of 37 consecutive patients underwent total replacement of the aortic arch using the FET technique. Type A aortic dissection was diagnosed in 21 (56.8%) patients. Among these, 15 (71.4%) were acute and subacute. Type B aortic dissection (TBAD) was diagnosed in 16 (43.2%) patients. Acute and subacute TBADs were found in 10 (62.5%) of cases. Two (5.4%) patients and 1 (2.7%) patient had previous cardiac and thoracic aortic operations, respectively. No patients had previous abdominal aortic surgery (Table 2). No patient had signs of SCI. According to the preoperative CT scans, the length of the descending part of the aorta was 271 ± 39 mm. The preoperative number of patent arteries was 10 ± 1 to the left and 10 ± 2 to the right (P = 0.59). The distribution of the patent intercostal arteries was asymmetric due to their involvement in the pathological process, and, in some cases, was accompanied by vessel occlusion. It should be noted that before the operation, 25.1% of the ostia of the intercostal arteries on the left and 28% on the right side originated from a false lumen (P = 0.42). According to postoperative CT scans, the distal edge of the implanted stent graft was in the T7–T12 range. It is important to mention that the lower edge of the FET was implanted at the ‘critical’ level of T9–T12 in 25 (67.6%) cases. Thus, the implanted stent graft overlapped up to two-thirds of the segmental arteries, and the number of non-occlusive intercostal arteries in the lower part of the descending aorta was 3 ± 2 on the left and 4 ± 1 on the right (P = 0.003). After the operation, it was noted that only 13.6% of the intercostal arteries originated from the false lumen. Thus, the length of the descending aorta not covered by the stent graft after the operation was 83 ± 57 mm. The total number of intact intercostal arteries was 35% of the initial number. In 6 (16.2%) patients, stenotic and occlusive lesions of subclavian arteries were revealed before the operation: left subclavian artery stenosis/occlusion was detected in 4 (10.8%) patients; right subclavian artery stenosis/occlusion was detected in 2 (5.4%) patients. These haemodynamic disorders were caused by the dissection of these arteries with significant compression or thrombosis of the true lumen. The blood flow in all supra-aortic vessels was simultaneously restored in 36 (97.3%) cases. One (2.7%) patient underwent revascularization of the left subclavian artery as a second stage due to the extended occlusion of the subclavian artery. The incidence of permanent neurological deficit and temporary neurological deficit was 2.4% (n = 1) and 4.8% (n = 2), respectively. The 30-day mortality rate was 4.8% (n = 2). The in-hospital mortality rate was 10.8% (n = 4). The causes of death were abdominal aortic rupture (n = 1), profuse intraoperative bleeding due to disseminated intravascular coagulation (n = 1) and multiorgan failure (n = 2). DISCUSSION The issue of SCI after stent graft implantation into the descending aorta has been debated in the literature. Some authors believe that the occlusion of a large number of intercostal arteries with the implanted stent graft can be one of the causes of ischaemic SCI after the FET procedure [8]. Therefore, it is recommended that the stent graft be implanted not lower than level T7–T10 in order to prevent ischaemic accidents [4]. However, Griepp et al. [2] reported that, if the number of intercostal arteries in the upper and middle part of the descending aorta that are excluded from the blood flow is <11, then spinal ischaemia is rare. These observations point to the important role of the collateral network, which is fed not only through intercostal arteries but also through the branches of vertebral and iliac arteries. Thus, the authors found that the number of occluded intercostal arteries has no significant effect on the development of SCI. At the same time, an assumption was made that the level of segmental artery blockage is of greater significance. Thus, the occlusion of lower thoracic or lumbar segmental arteries provokes spinal ischaemia more often than the occlusion of upper intercostal arteries. Therefore, taking into account these data and striving for maximum stabilization of the descending aorta, some surgeons consider it safe to implant the distal end of the stent graft even at level T10–T12 [9]. Inspired by the results obtained by Griepp et al. [2], we deliberately implanted the stent graft as deep as possible in the thoracic aorta, striving for the best stabilization of the descending aorta. According to our data, the distal end of the stent graft was in the ‘critical’ zone T9–T12 in 25 (67.6%) cases. Therefore, about two-thirds of the segmental arteries were ‘excluded’ from the blood flow, whereas the lower thoracic segmental arteries and both subclavian and iliac arteries remained patent. The absence of spinal cord complications in our patients confirms the work of Griepp et al. [2]. We believe that with adequate supply of the collateral network, implantation of the distal end of the stent graft at level T9 and lower can be considered relatively safe in terms of SCI. According to the data published by Flores et al. [8], the risk of SCI increases significantly in the presence of thoracic aorta atherosclerosis in the stent graft implantation zone and if the patient had previous interventions on the abdominal aorta. Although the difference between the incidence of SCI among patients with or without severe atherosclerosis was not significant, there was a tendency for SCI to develop in patients with atherosclerotic lesions in the thoracic aorta landing zone (36% vs 9%, P = 0.1218). The univariate logistic regression analysis conducted by this group identified that the history of abdominal aortic aneurysm repair was a significant independent risk factor for SCI (P = 0.0296). Moreover, the authors reported that the combination of the distal landing zone T7 or below and the history of abdominal aortic aneurysm repair was the strongest predictor for SCI (71 vs 6%, P = 0.0047). Surgical intervention on the abdominal aorta damages the branches of the aortoiliac bed, which represent a main source of the spinal cord supply. Therefore, the patients with previous intervention on the abdominal aorta comprise a group with increased risk in comparison with those with an intact abdominal aorta. In cases with TBAD, we intentionally used the FET procedure instead of thoracic endovascular aortic repair. According to the literature, there is a risk of retrograde aortic dissection after stent graft deployment. Although the incidence of this adverse outcome is low (1.3–6%), the mortality rate is high (42%) [10, 11]. Thus, we consider the FET procedure to be a viable alternative for the treatment of TBAD in lieu of thoracic endovascular aortic repair. Furthermore, in our study, some patients required simultaneous aortic valve surgery and coronary artery bypass grafting. The FET technique was used to minimize the risk of aortic complications. Drainage of CSF is a well-known method for SCI prophylaxis in thoracic aortic surgery. Nevertheless, we do not use it for several reasons. Firstly, according to work of Griepp et al. [2], we do not compromise the adequate blood supply of the spinal cord covering the upper and middle segmental arteries by the stent graft. Secondly, we strive to restore the main antegrade blood flow in the descending aorta and in all of the supra-aortic branches during aortic arch surgery as soon as possible. The combination of adequate blood flow in both the subclavian and iliac regions is the keystone of success to prevent SCI. Lastly, CSF drainage itself is associated with a number of complications: direct spinal cord or nerve root injuries, intracranial haemorrhage and infection. Moreover, these complications may lead to death. The published mortality rate attributed to drain complications reaches 11% [12]. We believe that it is not necessary to drain the CSF during the FET procedure if the above-mentioned conditions are fulfilled. The issue of regional perfusion during circulatory arrest remains controversial. Most authors tend to use bilateral perfusion especially in the case of prolonged circulatory arrest [13]. We use only unilateral antegrade cerebral perfusion through the innominate artery during aortic arch surgery. We perform perfusion at a flow rate of 8–10 ml/kg/min, which maintains the pressure range in the arterial line above 60 mmHg. Based on the evaluation of cerebral metabolism conducted by Tanaka et al. [14] and histopathological findings in canine models, an assumption was made that the values of cerebral perfusion mentioned above about 50% of the brain’s physiological needs, which is more than adequate during moderate hypothermia. We believe that the right-sided perfusion conducted during circulatory arrest with a mean pressure of more than 60 mmHg is sufficient to protect not only the brain but also the spinal cord. This conclusion was based on the anatomical features of spinal cord perfusion. The spinal cord blood supply is realized mainly through the anterior and posterior spinal arteries, which in turn are supplied from the vertebral, ascending cervical and deep cervical arteries. Therefore, the spinal cord blood supply can be mediated by the preservation of adequate blood flow in supra-aortic branches [15]. In addition, the advantage of right-sided unilateral perfusion can be explained from the following perspective: Gailloud et al. [16] showed that left-sided deviation of the aorta causes inflection of the intercostal arteries to the left, which results in the formation of non-ostial stenoses in 92% of patients. Right-sided antegrade perfusion through the innominate artery, therefore, provides the blood supply of the spinal cord through the most direct route. These conditions create anatomical prerequisites for satisfactory perfusion of the spinal cord. Therefore, it seems logical that haemodynamic obstruction in the left subclavian artery in some patients does not have any negative effects on the spinal cord. The assessment of unilateral perfusion through the innominate artery should be based on the mean blood pressure in the left radial artery. A target value of at least 30 mmHg is acceptable. According to Urbanski et al. [17], maintaining this pressure in the radial artery during unilateral antegrade perfusion was considered sufficient for perfusion protection during circulatory arrest. Similarly, we believe that maintaining the given level of pressure in the left radial artery allows for adequate perfusion of both the brain and the spinal cord. Moderate hypothermia (25–28°C) is also important for the prevention of spinal ischaemia. This temperature regime allows minimizing the risk of hypothermia-associated bleeding complications and at the same time ensures the necessary protection of the spinal cord. Conversely, high temperatures may jeopardize effective protection with as yet unpredictable consequences for long-term outcome, particularly for the spinal cord [18]. The maintenance of haematocrit values within the range of 25–30% plays an important role, because a lower haematocrit level requires an increased cerebral perfusion flow rate, which leads to the phenomenon of ‘luxury perfusion’ resulting in brain oedema and increasing the risk of air embolism. As was shown in the experimental studies, an elevated haematocrit level promotes better and earlier neurological recovery [18]. Limitations This study has several limitations. It was conducted on a relatively small number of patients, which does not allow for definitive conclusions regarding the incidence of SCI after the FET technique. The patient cohort was slightly heterogeneous, including cases with acute and subacute dissections. Nevertheless, it reflects the clinical reality of this surgical approach in patients undergoing aortic arch surgery using the FET technique. CONCLUSIONS The FET technique leads to extensive occlusion of the intercostal arteries arising from the descending aorta. In our clinic, we have adopted a surgical management protocol for aortic arch surgery. The basis of this protocol is innominate artery cannulation for cerebral perfusion, moderate hypothermia and perfusion pressure. We consider that strict adherence to the accepted surgical management protocol is the key to adequate intraoperative prophylaxis of SCI. The maintenance of sufficient main blood flow in the subclavian and iliac arteries is equally important. Under these circumstances, the distal attachment site of the stent graft does not play a defining role. Conflict of interest: none declared. REFERENCES 1 Adamkiewicz A. Die Blutgefässe des menschlichen Rückenmarkes. I Teil. Die Gefässe der Rückenmarksubstanz // Siteungsber. k. Akad. Wiss. Wien Math. Natur. Klass. 1882. Bd. 85. S. 101. 2 Griepp EB , Di Luozzo G , Schray D , Stefanovic A , Geisbüsch S , Griepp RB. The anatomy of the spinal cord collateral circulation . Ann Cardiothorac Surg 2012 ; 1 : 350 – 7 . Google Scholar PubMed 3 Shrestha M , Bachet J , Bavaria J , Carrel TP , De Paulis R , Di Bartolomeo R et al. . Current status and recommendations for use of the frozen elephant trunk technique: a position paper by the Vascular Domain of EACTS . Eur J Cardiothorac Surg 2015 ; 47 : 759 – 69 . Google Scholar CrossRef Search ADS PubMed 4 Tian DH , Wan B , Di Eusanio M , Black D , Yan TD. 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Google Scholar PubMed 8 Flores J , Kunihara T , Shiiya N , Yoshimoto K , Matsuzaki K , Yasuda K. Extensive deployment of the stented elephant trunk is associated with an increased risk of spinal cord injury . J Thorac Cardiovasc Surg 2006 ; 131 : 336 – 42 . Google Scholar CrossRef Search ADS PubMed 9 Damberg A , Schalte G , Autschbach R , Hoffman A. Safety and pitfalls in frozen elephant trunk implantation . Ann Cardiothorac Surg 2013 ; 2 : 669 – 76 . Google Scholar PubMed 10 Eggebrecht H , Thompson M , Rousseau H , Czerny M , Lonn L , Mehta RH et al. . Retrograde ascending aortic dissection during or after thoracic aortic stent graft placement insight from the European registry on endovascular aortic repair complications . Circulation 2009 ; 120 : 276 – 81 . Google Scholar CrossRef Search ADS 11 Cambria RP , Conrad MF , Matsumoto AH , Fillinger M , Pochettino A , Carvalho S et al. . Multicenter clinical trial of the conformable stent graft for the treatment of acute, complicated type B dissection . J Vasc Surg 2015 ; 62 : 271 – 8 . Google Scholar CrossRef Search ADS PubMed 12 Fedorow CA , Moon MC , Mutch WAC , Grocott HP. Lumbar cerebrospinal fluid drainage for thoracoabdominal aortic surgery: rationale and practical considerations for management . Anesth Analg 2010 ; 111 : 46 – 58 . Google Scholar CrossRef Search ADS PubMed 13 Misfeld M , Mohr FW , Etz CD. Best strategy for cerebral protection in arch surgery—antegrade selective cerebral perfusion and adequate hypothermia . Ann Cardiothorac Surg 2013 ; 2 : 331 – 8 . Google Scholar PubMed 14 Tanaka H , Kazui T , Sato H , Inoue N , Yamada O , Komatsu S. Experimental study on the optimum flow rate and pressure for selective cerebral perfusion . Ann Thorac Surg 1995 ; 59 : 651 – 7 . Google Scholar CrossRef Search ADS PubMed 15 Arslan M , İbrahim H , Cömert A , Tubbs RS. The cervical arteries: an anatomical study with application to avoid the nerve root and spinal cord blood supply . Turk Neurosurg 2017 ; doi:10.5137/1019-5149.JTN.19469-16.1. 16 Gailloud P , Ponti A , Gregg L , Pardo CA , Fasel JHD. Focal compression of the upper left thoracic intersegmental arteries as a potential cause of spinal cord ischemia . AJNR Am J Neuroradiol 2014 ; 35 : 1226 – 31 . Google Scholar CrossRef Search ADS PubMed 17 Urbanski PP , Lenos A , Zacher M , Diegeler A. Unilateral cerebral perfusion: right versus left . Eur J Cardiothorac Surg 2010 ; 37 : 1332 – 7 . Google Scholar CrossRef Search ADS PubMed 18 Spielvogel D , Tang GHL. Selective cerebral perfusion for cerebral protection: what we do know . Ann Cardiothorac Surg 2013 ; 2 : 326 – 30 . Google Scholar PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Interactive CardioVascular and Thoracic Surgery Oxford University Press

The risk of spinal cord injury during the frozen elephant trunk procedure in acute aortic dissection

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
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1569-9293
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1569-9285
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10.1093/icvts/ivx432
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Abstract

Abstract OBJECTIVES The aim of the study was to access the extended occlusion of the intercostal arteries by a stent graft in the development of postoperative spinal cord injury during aortic arch surgery using the frozen elephant trunk technique. METHODS A total of 37 consecutive patients underwent total aortic arch surgery using the frozen elephant trunk technique between March 2012 and July 2017. The mean age of the patients was 54.7 ± 10.5 years. Type A and Type B aortic dissections were the indications for surgery. Moderate hypothermia and antegrade cerebral perfusion via the innominate artery were utilized. The mean diameter of the implanted stent graft was 27.7 ± 2 mm (range 24–30 mm). RESULTS No permanent spinal cord injuries occurred. The distal edge of the stent graft was in the T7–T12 range. Its lower edge was implanted at the T9–T12 level in 25 (67.6%) cases. Preoperatively, the mean number of intercostal arteries was 10 ± 1 on the left side and 10 ± 2 on the right side (P = 0.59). Postoperatively, the mean number of open segmental arteries was 3 ± 2 on the left and 4 ± 1 on the right (P = 0.003). CONCLUSIONS The frozen elephant trunk procedure is associated with the occlusion of most (two-thirds) of the intercostal arteries. Maintenance of adequate blood flow in the subclavian and iliac arteries is an integral prerequisite for a favourable outcome. The level of the deployment of the distal edge of the stent graft does not play a defining role. Unilateral cerebral perfusion, Innominate artery, Frozen elephant trunk, Spinal cord ischaemia, Intercostal arteries INTRODUCTION The concepts of blood supply to the spinal cord are being revised. Thus, the theory that the Adamkiewicz artery plays a key role in supplying blood to the spinal cord is now primarily historical in nature [1]. The current perception of spinal cord perfusion is based on the presence of ‘vertical and horizontal’ collateral networks, where subclavian, iliac, and segmental arteries play a major role in spinal cord perfusion [2]. Spinal cord injury (SCI) is one of the most devastating complications after aortic arch repair. Rare cases of paraplegia have been reported after the conventional elephant trunk procedure. The reported incidence rate of permanent or transient ischaemic SCI after conventional elephant trunk implantation reaches 3%. In contrast, the reported incidence rate of SCI in patients undergoing the frozen elephant trunk (FET) procedure is about 8%. Some single-centre studies have reported incidences as high as 21–24% after FET implantation and have hypothesized various mechanisms to explain SCI [3]. According to the literature, the lack of left subclavian artery perfusion, a previous abdominal aortic operation, severe atherosclerosis, diabetes, postoperative mean aortic pressure <70 mmHg and distal deployment of the stent graft (below T9) with extensive coverage of intercostal arteries were found to be associated with an increased occurrence of SCI [4–6]. In this regard, malperfusion of the intercostal arteries can be one of the causes of SCI. Thus, the aim of the study was to access the extended occlusion of the intercostal arteries by the stent graft in the development of postoperative ischaemia of the spinal cord during aortic arch reconstruction using the FET technique. PATIENTS AND METHODS A total of 37 consecutive patients underwent total aortic arch surgery using the FET technique between March 2012 and July 2017. All the patients underwent single-stage repair of the aortic arch with the implantation of a hybrid stent graft, the E-vita Open Plus (Jotec® GmbH, Hechingen, Germany), into the descending thoracic aorta. The data were prospectively collected in a database, and the study was approved by the local ethics committee. Individual patient consent was waived. 3D computed tomography (CT) was used as the basic instrument for diagnosis in patients with thoracic aortic disease. Additionally, the total number of intercostal arteries and an evaluation of patency were recorded pre- and postoperatively. The lumen of origin of the segmental artery ostia was also verified. Attention was also paid to the patency of subclavian and iliac arteries. All patients underwent postoperative CT within 2–4 weeks after the operation to evaluate the proximal anastomosis and the distal attachment site of the stent graft. All patients had a postoperative neurological examination to determine whether the sensitivity and the motion of the lower extremities were normal. Operative technique The FET procedure was performed according to a surgical management procedure used in our clinic (Table 1). Table 1: Surgical management procedure Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% Table 1: Surgical management procedure Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% Surgical steps 1. Unilateral cerebral perfusion via innominate artery 2. Near-infrared spectroscopy 3. Moderate hypothermia (25–28°C) 4. Monitoring of arterial pressure in both radial arteries 5. Perfusion pressure: 60–80 mmHg 6. Flow rate: 8–10 ml/kg/min 7. Pre- and postoperative control of arterial blood flow more distal from the implanted stent graft (abdominal aorta branches, iliac arteries) 8. Haematocrit values above 25% A hybrid stent graft, the E-vita Open Plus, with a diameter of 22–40 mm and a length of 150 mm, was used in all cases. The diameter of the graft should be 110% of the diameter of the aortic segment chosen as the landing zone in cases of aortic aneurysms. Cerebral perfusion during circulatory arrest was controlled by directly monitoring the arterial pressure in both radial arteries and by using near-infrared spectroscopy (Invos 5100, Medtronic Corp., Minneapolis, MN, USA). The target haematocrit level during circulatory arrest was above 25%. Cerebrospinal fluid (CSF) drainage and pressure monitoring were not performed. Unilateral perfusion was carried out through the innominate artery while the left common carotid artery and left subclavian artery were clamped. After the administration of heparin at a dose of 1 mg/kg, the innominate artery was side clamped and monitored simultaneously using near-infrared spectroscopy and by determining the arterial pressure level in both radial arteries. The innominate artery was opened to decrease the arterial pressure in the right radial artery by no more than 50% and to decrease the cerebral venous saturation on the right side to not lower than 20% compared to the baseline values. Then, an anastomosis was formed with continuous 5-0 sutures with an 8–10 mm linear vascular prosthesis in an end-to-side fashion. After washing off possible debris and eliminating air from the prosthesis, it was connected to the arterial line of the cardiopulmonary bypass system; heparin was added so that the total dose was 3 mg/kg, with the active clotting time controlled (480–600 s). The stent graft was inserted into the descending thoracic aorta without a guidewire. In most cases, the stent graft was attached by continuous suturing with 4-0 polypropylene sutures distal to the left subclavian artery. In several cases, the stent graft proximal anastomosis was performed in other zones (Table 2). Transoesophageal echocardiography was used to monitor the deployment of the stent graft. After the distal anastomosis was completed, a clamp was placed on the aortic prosthesis; systemic blood perfusion was resumed through an additional cannula, which was inserted into the prostheses distal to the clamp; the patient was gradually rewarmed. Supra-aortic vessel reconstruction was performed en bloc (70.3%) or separately (29.7%). The unilateral cerebral perfusion was discontinued. The proximal aortic anastomosis was then carried out, and the coronary blood flow was restored. Concomitant operations, such as coronary artery bypass grafting, could be performed during the rewarming period. Table 2: Demographics, preoperative clinical characteristics and operative data (n = 37) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) CPB: cardiopulmonary bypass; uACP: unilateral antegrade cerebral perfusion; SCI: spinal cord injury; SD: standard deviation; TND: temporal neurological deficit. Table 2: Demographics, preoperative clinical characteristics and operative data (n = 37) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) Demographics and preoperative clinical characteristics Total (%) Age (years), mean ± SD 54.7 ± 10.5 Men, n (%) 24 (64.8) Diabetes mellitus, n (%) 1 (2.7) Hypertension, n (%) 28 (76.7) Emergent procedure, n (%) 11 (29.7) Urgent procedure, n (%) 9 (24.3) Elective procedure, n (%) 17 (45.9) Severe carotid artery stenosis, n (%) 1 (2.7) Severe subclavian artery stenosis/ occlusion, n (%) 6 (16.2) Abdominal aortic aneurysm, n (%) 1 (2.7) Type A aortic dissection, n (%) 21 (56.8)  Acute 7 (33.3)  Subacute 8 (38.1)  Chronic 6 (28.6) Type B aortic dissection, n (%) 16 (43.2)  Acute 4 (25)  Subacute 6 (37.5)  Chronic 6 (37.5) Aortic dissection extension, n (%)  Above the diaphragm 13 (35.1)  Below the diaphragm 24 (64.9) Previous cardiac surgery 2 (5.4) Previous thoracic aortic surgery 1 (2.7) Operative data CPB (min), mean ± SD (range) 219.2 ± 61.7 min (131–422) Cardioplegic arrest (min), mean ± SD (range) 139 ± 48.1 min (63–249) Lower body circulatory arrest (min), mean ± SD (range) 61.7 ± 21.8 min (27–70) uACP (min), mean ± SD (range) 45.1 ± 12.7 min (28–114) Supra-aortic vessels reimplantation, n (%)  En bloc 26 (70.3)  Separate 11 (29.7) E-vita Open Plus diameter, mean ± SD (range) 27.7 ± 2 (24–30) Proximal stent graft level, n (%)  Z0 1 (2.7)  Z1 0  Z2 9 (24.3)  Z3 27 (73) Postoperative data, n (%) Permanent SCI 0 Stroke 1 (2.7) TND 2 (5.4) 30-day mortality rate 2 (5.4) Distal landing zone, n (%)  T7 3 (8.1)  T8 9 (24.3)  T9 11 (29.7)  T10 6 (16.2)  T11 6 (16.2)  T12 2 (5.4) False-lumen thrombosis, n (%)  Along the stent graft 37 (100)  Down to the stent graft end 7 (29.2) CPB: cardiopulmonary bypass; uACP: unilateral antegrade cerebral perfusion; SCI: spinal cord injury; SD: standard deviation; TND: temporal neurological deficit. After cardiopulmonary bypass weaning, heparin was inactivated by protamine in a ratio of 1:1. Infusion of red blood cell units was performed in case the haemoglobin level dropped lower than 90 g/l. If the platelet level was less than 60 × 109, platelet infusion was carried out. Fresh frozen plasma infusion was carried out to a target level of 30 ml/kg [7]. The mean arterial pressure was maintained at a level no lower than 70 mmHg immediately after protamine infusion and for the next 3 days. Definition ‘Permanent’ SCI was defined as irreversible paraplegia, and ‘temporary’ SCI was defined as reversible neurological deficit of the spinal cord. Operations were considered ‘emergent’ if performed within 24 h of hospital admission for cardiovascular instability and ‘urgent’ if performed within 72 h of admission. Neurological complications were defined as ‘permanent neurological deficit’ for patients with a stroke, and ‘temporary neurological deficit’ for patients with reversible deficits. Statistical analysis Continuous variables are not normally distributed and are reported as mean ± standard deviation; categorical data are reported as proportions throughout the article. These variables were compared using the Wilcoxon rank-sum test. The differences were considered significant at P < 0.05. RESULTS A total of 37 consecutive patients underwent total replacement of the aortic arch using the FET technique. Type A aortic dissection was diagnosed in 21 (56.8%) patients. Among these, 15 (71.4%) were acute and subacute. Type B aortic dissection (TBAD) was diagnosed in 16 (43.2%) patients. Acute and subacute TBADs were found in 10 (62.5%) of cases. Two (5.4%) patients and 1 (2.7%) patient had previous cardiac and thoracic aortic operations, respectively. No patients had previous abdominal aortic surgery (Table 2). No patient had signs of SCI. According to the preoperative CT scans, the length of the descending part of the aorta was 271 ± 39 mm. The preoperative number of patent arteries was 10 ± 1 to the left and 10 ± 2 to the right (P = 0.59). The distribution of the patent intercostal arteries was asymmetric due to their involvement in the pathological process, and, in some cases, was accompanied by vessel occlusion. It should be noted that before the operation, 25.1% of the ostia of the intercostal arteries on the left and 28% on the right side originated from a false lumen (P = 0.42). According to postoperative CT scans, the distal edge of the implanted stent graft was in the T7–T12 range. It is important to mention that the lower edge of the FET was implanted at the ‘critical’ level of T9–T12 in 25 (67.6%) cases. Thus, the implanted stent graft overlapped up to two-thirds of the segmental arteries, and the number of non-occlusive intercostal arteries in the lower part of the descending aorta was 3 ± 2 on the left and 4 ± 1 on the right (P = 0.003). After the operation, it was noted that only 13.6% of the intercostal arteries originated from the false lumen. Thus, the length of the descending aorta not covered by the stent graft after the operation was 83 ± 57 mm. The total number of intact intercostal arteries was 35% of the initial number. In 6 (16.2%) patients, stenotic and occlusive lesions of subclavian arteries were revealed before the operation: left subclavian artery stenosis/occlusion was detected in 4 (10.8%) patients; right subclavian artery stenosis/occlusion was detected in 2 (5.4%) patients. These haemodynamic disorders were caused by the dissection of these arteries with significant compression or thrombosis of the true lumen. The blood flow in all supra-aortic vessels was simultaneously restored in 36 (97.3%) cases. One (2.7%) patient underwent revascularization of the left subclavian artery as a second stage due to the extended occlusion of the subclavian artery. The incidence of permanent neurological deficit and temporary neurological deficit was 2.4% (n = 1) and 4.8% (n = 2), respectively. The 30-day mortality rate was 4.8% (n = 2). The in-hospital mortality rate was 10.8% (n = 4). The causes of death were abdominal aortic rupture (n = 1), profuse intraoperative bleeding due to disseminated intravascular coagulation (n = 1) and multiorgan failure (n = 2). DISCUSSION The issue of SCI after stent graft implantation into the descending aorta has been debated in the literature. Some authors believe that the occlusion of a large number of intercostal arteries with the implanted stent graft can be one of the causes of ischaemic SCI after the FET procedure [8]. Therefore, it is recommended that the stent graft be implanted not lower than level T7–T10 in order to prevent ischaemic accidents [4]. However, Griepp et al. [2] reported that, if the number of intercostal arteries in the upper and middle part of the descending aorta that are excluded from the blood flow is <11, then spinal ischaemia is rare. These observations point to the important role of the collateral network, which is fed not only through intercostal arteries but also through the branches of vertebral and iliac arteries. Thus, the authors found that the number of occluded intercostal arteries has no significant effect on the development of SCI. At the same time, an assumption was made that the level of segmental artery blockage is of greater significance. Thus, the occlusion of lower thoracic or lumbar segmental arteries provokes spinal ischaemia more often than the occlusion of upper intercostal arteries. Therefore, taking into account these data and striving for maximum stabilization of the descending aorta, some surgeons consider it safe to implant the distal end of the stent graft even at level T10–T12 [9]. Inspired by the results obtained by Griepp et al. [2], we deliberately implanted the stent graft as deep as possible in the thoracic aorta, striving for the best stabilization of the descending aorta. According to our data, the distal end of the stent graft was in the ‘critical’ zone T9–T12 in 25 (67.6%) cases. Therefore, about two-thirds of the segmental arteries were ‘excluded’ from the blood flow, whereas the lower thoracic segmental arteries and both subclavian and iliac arteries remained patent. The absence of spinal cord complications in our patients confirms the work of Griepp et al. [2]. We believe that with adequate supply of the collateral network, implantation of the distal end of the stent graft at level T9 and lower can be considered relatively safe in terms of SCI. According to the data published by Flores et al. [8], the risk of SCI increases significantly in the presence of thoracic aorta atherosclerosis in the stent graft implantation zone and if the patient had previous interventions on the abdominal aorta. Although the difference between the incidence of SCI among patients with or without severe atherosclerosis was not significant, there was a tendency for SCI to develop in patients with atherosclerotic lesions in the thoracic aorta landing zone (36% vs 9%, P = 0.1218). The univariate logistic regression analysis conducted by this group identified that the history of abdominal aortic aneurysm repair was a significant independent risk factor for SCI (P = 0.0296). Moreover, the authors reported that the combination of the distal landing zone T7 or below and the history of abdominal aortic aneurysm repair was the strongest predictor for SCI (71 vs 6%, P = 0.0047). Surgical intervention on the abdominal aorta damages the branches of the aortoiliac bed, which represent a main source of the spinal cord supply. Therefore, the patients with previous intervention on the abdominal aorta comprise a group with increased risk in comparison with those with an intact abdominal aorta. In cases with TBAD, we intentionally used the FET procedure instead of thoracic endovascular aortic repair. According to the literature, there is a risk of retrograde aortic dissection after stent graft deployment. Although the incidence of this adverse outcome is low (1.3–6%), the mortality rate is high (42%) [10, 11]. Thus, we consider the FET procedure to be a viable alternative for the treatment of TBAD in lieu of thoracic endovascular aortic repair. Furthermore, in our study, some patients required simultaneous aortic valve surgery and coronary artery bypass grafting. The FET technique was used to minimize the risk of aortic complications. Drainage of CSF is a well-known method for SCI prophylaxis in thoracic aortic surgery. Nevertheless, we do not use it for several reasons. Firstly, according to work of Griepp et al. [2], we do not compromise the adequate blood supply of the spinal cord covering the upper and middle segmental arteries by the stent graft. Secondly, we strive to restore the main antegrade blood flow in the descending aorta and in all of the supra-aortic branches during aortic arch surgery as soon as possible. The combination of adequate blood flow in both the subclavian and iliac regions is the keystone of success to prevent SCI. Lastly, CSF drainage itself is associated with a number of complications: direct spinal cord or nerve root injuries, intracranial haemorrhage and infection. Moreover, these complications may lead to death. The published mortality rate attributed to drain complications reaches 11% [12]. We believe that it is not necessary to drain the CSF during the FET procedure if the above-mentioned conditions are fulfilled. The issue of regional perfusion during circulatory arrest remains controversial. Most authors tend to use bilateral perfusion especially in the case of prolonged circulatory arrest [13]. We use only unilateral antegrade cerebral perfusion through the innominate artery during aortic arch surgery. We perform perfusion at a flow rate of 8–10 ml/kg/min, which maintains the pressure range in the arterial line above 60 mmHg. Based on the evaluation of cerebral metabolism conducted by Tanaka et al. [14] and histopathological findings in canine models, an assumption was made that the values of cerebral perfusion mentioned above about 50% of the brain’s physiological needs, which is more than adequate during moderate hypothermia. We believe that the right-sided perfusion conducted during circulatory arrest with a mean pressure of more than 60 mmHg is sufficient to protect not only the brain but also the spinal cord. This conclusion was based on the anatomical features of spinal cord perfusion. The spinal cord blood supply is realized mainly through the anterior and posterior spinal arteries, which in turn are supplied from the vertebral, ascending cervical and deep cervical arteries. Therefore, the spinal cord blood supply can be mediated by the preservation of adequate blood flow in supra-aortic branches [15]. In addition, the advantage of right-sided unilateral perfusion can be explained from the following perspective: Gailloud et al. [16] showed that left-sided deviation of the aorta causes inflection of the intercostal arteries to the left, which results in the formation of non-ostial stenoses in 92% of patients. Right-sided antegrade perfusion through the innominate artery, therefore, provides the blood supply of the spinal cord through the most direct route. These conditions create anatomical prerequisites for satisfactory perfusion of the spinal cord. Therefore, it seems logical that haemodynamic obstruction in the left subclavian artery in some patients does not have any negative effects on the spinal cord. The assessment of unilateral perfusion through the innominate artery should be based on the mean blood pressure in the left radial artery. A target value of at least 30 mmHg is acceptable. According to Urbanski et al. [17], maintaining this pressure in the radial artery during unilateral antegrade perfusion was considered sufficient for perfusion protection during circulatory arrest. Similarly, we believe that maintaining the given level of pressure in the left radial artery allows for adequate perfusion of both the brain and the spinal cord. Moderate hypothermia (25–28°C) is also important for the prevention of spinal ischaemia. This temperature regime allows minimizing the risk of hypothermia-associated bleeding complications and at the same time ensures the necessary protection of the spinal cord. Conversely, high temperatures may jeopardize effective protection with as yet unpredictable consequences for long-term outcome, particularly for the spinal cord [18]. The maintenance of haematocrit values within the range of 25–30% plays an important role, because a lower haematocrit level requires an increased cerebral perfusion flow rate, which leads to the phenomenon of ‘luxury perfusion’ resulting in brain oedema and increasing the risk of air embolism. As was shown in the experimental studies, an elevated haematocrit level promotes better and earlier neurological recovery [18]. Limitations This study has several limitations. It was conducted on a relatively small number of patients, which does not allow for definitive conclusions regarding the incidence of SCI after the FET technique. The patient cohort was slightly heterogeneous, including cases with acute and subacute dissections. Nevertheless, it reflects the clinical reality of this surgical approach in patients undergoing aortic arch surgery using the FET technique. CONCLUSIONS The FET technique leads to extensive occlusion of the intercostal arteries arising from the descending aorta. In our clinic, we have adopted a surgical management protocol for aortic arch surgery. The basis of this protocol is innominate artery cannulation for cerebral perfusion, moderate hypothermia and perfusion pressure. We consider that strict adherence to the accepted surgical management protocol is the key to adequate intraoperative prophylaxis of SCI. The maintenance of sufficient main blood flow in the subclavian and iliac arteries is equally important. Under these circumstances, the distal attachment site of the stent graft does not play a defining role. Conflict of interest: none declared. REFERENCES 1 Adamkiewicz A. Die Blutgefässe des menschlichen Rückenmarkes. I Teil. Die Gefässe der Rückenmarksubstanz // Siteungsber. k. Akad. Wiss. Wien Math. Natur. Klass. 1882. Bd. 85. S. 101. 2 Griepp EB , Di Luozzo G , Schray D , Stefanovic A , Geisbüsch S , Griepp RB. The anatomy of the spinal cord collateral circulation . Ann Cardiothorac Surg 2012 ; 1 : 350 – 7 . Google Scholar PubMed 3 Shrestha M , Bachet J , Bavaria J , Carrel TP , De Paulis R , Di Bartolomeo R et al. . Current status and recommendations for use of the frozen elephant trunk technique: a position paper by the Vascular Domain of EACTS . Eur J Cardiothorac Surg 2015 ; 47 : 759 – 69 . Google Scholar CrossRef Search ADS PubMed 4 Tian DH , Wan B , Di Eusanio M , Black D , Yan TD. 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Multicenter clinical trial of the conformable stent graft for the treatment of acute, complicated type B dissection . J Vasc Surg 2015 ; 62 : 271 – 8 . Google Scholar CrossRef Search ADS PubMed 12 Fedorow CA , Moon MC , Mutch WAC , Grocott HP. Lumbar cerebrospinal fluid drainage for thoracoabdominal aortic surgery: rationale and practical considerations for management . Anesth Analg 2010 ; 111 : 46 – 58 . Google Scholar CrossRef Search ADS PubMed 13 Misfeld M , Mohr FW , Etz CD. Best strategy for cerebral protection in arch surgery—antegrade selective cerebral perfusion and adequate hypothermia . Ann Cardiothorac Surg 2013 ; 2 : 331 – 8 . Google Scholar PubMed 14 Tanaka H , Kazui T , Sato H , Inoue N , Yamada O , Komatsu S. Experimental study on the optimum flow rate and pressure for selective cerebral perfusion . Ann Thorac Surg 1995 ; 59 : 651 – 7 . Google Scholar CrossRef Search ADS PubMed 15 Arslan M , İbrahim H , Cömert A , Tubbs RS. The cervical arteries: an anatomical study with application to avoid the nerve root and spinal cord blood supply . Turk Neurosurg 2017 ; doi:10.5137/1019-5149.JTN.19469-16.1. 16 Gailloud P , Ponti A , Gregg L , Pardo CA , Fasel JHD. Focal compression of the upper left thoracic intersegmental arteries as a potential cause of spinal cord ischemia . AJNR Am J Neuroradiol 2014 ; 35 : 1226 – 31 . Google Scholar CrossRef Search ADS PubMed 17 Urbanski PP , Lenos A , Zacher M , Diegeler A. Unilateral cerebral perfusion: right versus left . Eur J Cardiothorac Surg 2010 ; 37 : 1332 – 7 . Google Scholar CrossRef Search ADS PubMed 18 Spielvogel D , Tang GHL. Selective cerebral perfusion for cerebral protection: what we do know . Ann Cardiothorac Surg 2013 ; 2 : 326 – 30 . Google Scholar PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Interactive CardioVascular and Thoracic SurgeryOxford University Press

Published: Jan 17, 2018

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