Frozen versus conventional elephant trunk technique: application in clinical practice

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1 European Journal of Cardio-Thoracic Surgery 51 (2017) i20 i28 doi: /ejcts/ezw335 Cite this article as: Di Bartolomeo R, Murana G, Di Marco L, Pantaleo A, Alfonsi J, Leone A et al. Frozen versus conventional elephant trunk technique: application in clinical practice. Eur J Cardiothorac Surg 2017;51:i25 i33 Frozen versus conventional elephant trunk technique: application in clinical practice Roberto Di Bartolomeo,GiacomoMurana*,, Luca Di Marco, Antonio Pantaleo, Jacopo Alfonsi, Alessandro Leone and Davide Pacini Department of Cardiovascular Surgery, S. Orsola-Malpighi Hospital, Alma Mater studiorum University of Bologna, Bologna, Italy * Corresponding author. Department of Cardiovascular Surgery, S. Orsola-Malpighi Hospital University of Bologna, Via Massarenti 9, Bologna, Italy. Tel: ; fax: ; giacomo.murana@hotmail.com (G. Murana). Received 14 May 2016; received in revised form 22 July 2016; accepted 10 August 2016 Summary Treating complex aortic arch disease with proximal and distal aortic segment involvement is challenging. In recent years, different surgical and endovascular techniques have been applied in a single or multiple-stage approach with the aim to cure and simplify these conditions. The first procedure available for this purpose was the conventional elephant trunk technique. Its recent evolution is the frozen elephant trunk, which treats the descending thoracic aorta using the antegrade release of a self-expandable stent graft. In the following review article, we analyse the advantages and drawbacks of both techniques from clinical and practical perspectives. Keywords: Aortic arch Frozen elephant trunk Elephant trunk Aortic Cerebral perfusion INTRODUCTION Aortic diseases involving the ascending aorta or aortic arch and extending downstream into the descending thoracic or thoracoabdominal aorta are medically challenging [1 3]. They usually require more than one surgical and endovascular intervention, depending on type of disease, anatomy, patient comorbidities and centre experience [4 7]. Reliable methods of brain and organ protection along with appropriated surgical or endovascular techniques play a central role in obtaining a favourable outcome. The aim of this review article is to analyse the benefits and pitfalls of the frozen elephant trunk (FET) technique compared with the conventional elephant trunk (cet) technique in clinical practice. OPEN ARCH AND DESCENDING THORACIC AORTA REPAIR USING CONVENTIONAL AND FROZEN ELEPHANT TRUNK TECHNIQUES Table 1 illustrates the main advantages and disadvantages of the surgical strategies currently available for the treatment of extensive aortic arch lesions. The conventional elephant trunk technique The cet procedure was initially introduced to simplify further descending thoracic aorta interventions [2, 8]. The first two authors contributed equally to the development of the paper and should be considered co-first authors. The basic principle of the conventional cet resides in the protrusion of a length of tubing into the downstream descending aorta during the time of arch reconstruction to facilitate further distal aortic procedures. Briefly, in the first operation, the aortic arch is replaced, and a free-floating extension of the arch prosthesis (elephant trunk) is left behind in the proximal descending aorta [2, 8, 9]. In the second operation, the prosthetic trunk can be extended to the desired level through an open lateral thoracotomy or with the less invasive release of an endovascular stent graft [9, 10]. According to Borst s original suggestion, the length of the elephant trunk should not exceed 7 8 cm because a longer trunk is more likely to cause complications due to kinking and graft occlusion [4]. This constraint has also been supported by Crawford s finding of the increased risk of paraplegia as a result of clot formation around the graft [8]. The main advantages of the elephant trunk technique become obvious during the second operation and include (i) reduced dissection and surgical preparation of the distal segment of the arc where nerve, bronchial, gastrointestinal and lymphatic structures may potentially be injured; (ii) a facilitated and shortened clamping time during open thoraco-abdominal aneurysm and (iii) no need to clamp proximally the left subclavian artery (reduced risk of stroke and paraplegia). The frozen elephant trunk technique A way to achieve one-stage repair of extensive aortic arch disease by combining the concepts of the cet principle and the VC The Author Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

2 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery i21 Table 1: Elephant trunk procedure options for extensive aortic arch and descending thoracic aorta pathologies Surgical technique Advantage Disadvantage Conventional elephant trunk Simplify distal aortic arch anastomosis [10, 20, 49] Facilitate thoracoabdominal aortic interventions [2, 5, 10, 49] FET Allows single-stage treatment [1, 19, 26, 38] Facilitates thoracoabdominal aortic interventions [17, 28, 19] Reduces the risk of additional distal aortic surgery [26, 28, 30, 41] Branched FET Allows single-stage treatment [1, 19, 26, 38] Facilitates thoracoabdominal aortic interventions [17, 28, 19] Reduces the risk of additional distal aortic surgery [26, 28, 30, 41] Facilitates reconstrunction of the supra-aortic vessels compared to the assembled FET prosthesis [13, 50, 51] Reduces time for hypothermic circulatory arrest and myocardial ischaemia compared to the assembled FET prosthesis [13, 50, 51] Need a II stage procedure [4, 19, 20, 49] Interval mortality [4, 5, 44] Increased risk of spinal cord injury [7, 39, 44, 47] Technically demanding [31, 37] Cost of the device [52] Increased risk of spinal cord injury [7, 39, 44, 47] Technically demanding [31, 37] Cost of the device [51] Only one device currently available [13, 51] FET: frozen elephant trunk. endovascular stenting of descending aortic aneurysms was introduced in 2003 as the frozen elephant trunk [11] procedure. It necessitates the use of a preassembled or custom-made hybrid prosthesis. The proximal portion is non-stented and consists of a Dacron sleeve for conventional surgical handling; the distal part consists of a stent graft [12]. Two commercially available hybrid prostheses are available in Europe for FET interventions: the E- evita Open Plus hybrid stent graft system provided by JOTEC (Hechingen, Germany) and the Thoraflex TM Hybrid provided by Vascutek (Inchinnan, Scotland). Available in different sizes and with different delivery systems, they both have a sewing collar to facilitate distal anastomosis. The stented portion of these prostheses is available in diverse diameters (28 40 mm for the Thoraflex TM Hybrid and mm for the E-vita Open Plus) and lengths (100 or 150 mm for the Thoraflex TM Hybrid and 130, 150 or 160 mm for the E-vita Open Plus). The more advanced Thoraflex TM Hybrid graft has a quadrifurcated proximal vascular portion (tubular in the E-vita) to facilitate reimplantation of the epiaortic vessels and a more rapid reperfusion of the lower part of the body once the distal anastomosis is completed [13]. The main surgical steps of FET include (i) total resection of the aortic arch; (ii) preparation of the distal aortic stump with obliteration of the false lumen (FL) use of 4 or 5 U stitches with pledgets inside and a Teflon felt outside; (iii) advancement of the hybrid system in the descending thoracic aorta over a guidewire that has been retrogradely positioned via the femoral artery into the true lumen; (iv) deployment of the stent graft; (v) suturing of the vascular collar to the distal aorta before or after the origin of the left subclavian artery; (vi) complete reimplantion of the arch vessels and (vii) completion of the proximal anastomosis [1]. Practical advice for implantation of the hybrid prosthesis Based on the experience at our centre, we identified nine useful tips that could facilitate FET implantation: 1. Search for re-entry tears in the downstream aorta on the preoperative CT angiograms. 2. Drain the cerebrospinal fluid (spinal pressure <12 mmhg) before surgery. 3. View inside the descending thoracic aorta endoscopically before and immediately after release of the stent graft. 4. Use transesophageal echocardiography for guidance during device implantation. 5. Restart systemic perfusion and rewarming immediately after completing the distal aortic arch anastomosis. 6. Avoid stent oversize in acute aortic dissection (AAD). 7. Consider using branched aortic arch grafts when epiaortic vessels are involved. 8. Avoid long stent graft trunks (>_150 mm) to reduce the risk of spinal cord injuries (SCI). 9. Keep mean systemic pressure >80 mmhg after device implantation to better perfuse spinal cord. APPLICATIONS OF THE ELEPHANT TRUNKS IN CLINICAL PRACTICE Chronic degenerative and post-dissection aortic aneurysms During surgery for chronic degenerative aneurysm, the conventional surgical approach is first to perform open surgical replacement of the aortic arch using the cet technique, followed by open repair of the aneurysmal descending or thoraco-abdominal aorta [4, 5, 9]. The rationale behind the cet technique for staged thoracic aortic repair is linked to the advantages of avoiding dissection near the distal arch anastomosis and eliminating the need to clamp the aorta proximal to the left subclavian artery during the second operation (Fig. 1). Although this elegant approach has allowed patients to be treated satisfactorily, it is limited by the failure to complete the repair [4, 5, 14 16]. These shortcomings can be partially attenuated by the alternative FET technique. This hybrid procedure is extremely effective in patients whose aneurysms are confined to the arch and proximal descending thoracic aorta and in those presenting with saccular aneurysms of the mid-distal arch for which treatment with stent

3 i22 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery Figure 1: (A) Extensive thoraco-abdominal aortic aneurysm angio-ct 3D-reconstruction. (B) The images show the surgical result after the first conventional elephant trunk procedure and (C) after the second hybrid procedure (open visceral rerouting + stent graft coverage of the thoracic aorta). grafting is deemed technically unsuccessful (Fig. 2) [17]. As with the cet, the use of stent grafts in chronic aortic dissection is questionable because it does not constitute a definitive repair. The partially thrombosed and fibrotic arterial wall will not allow the stent graft to obliterate the FL, and distal re-entries often do not permit depressurization and thrombosis of the distal FL. This situation ultimately puts patients at risk for further distal reinterventions. The main disadvantage of the elephant trunk techniques in both degenerative and chronic post-dissection aneurysms is the increased risk of SCI. The reported incidence of permanent or transient ischaemic SCI after cet implantation ranges between 0.4 and 2.8% [18]. A significantly higher rate is described after FET implantation, with studies reporting incidences greater than 10% [19 21]. Possible explanations are the prolonged hypothermic circulatory arrest time required to implant the FET device and/or the occlusion of intercostal arteries at the level of stent-graft deployment [18]. Acute type A aortic dissection Despite improvements in diagnostic techniques and refinements in management strategies, surgical mortality still ranges from 17 to 26%, and type A-AAD continues to represent a great challenge for aortic surgeons [21 23]. For this reason, a conservative tearoriented approach aimed at performing the simplest and shortest operation with the least adverse impact on the patient has generally been adopted [23]. In this acute scenario, the cet, and more recently, the FET techniques are two surgical alternatives available despite their opposite approaches to the treatment of the dissected descending aorta [13, 24 26]. At primary intervention, the FET technique aims to depressurize and induce thrombosis of the dilated Figure 2: Degenerative aortic arch aneurysm (A) before and (B) after implantation of the Thoraflex TM Hybrid 4-branched hybrid device. Courtesy of Vascutek Ltd. persistent FL (Fig. 3). Conversely, the cet technique, by requiring a wide distal surgical intimal fenestration, results in high pressurization of the FL and little chance for late FL thrombosis. The FET technique is also a valuable adjunct in patients with distal aortic malperfusion, re-entry tears involving the proximal descending thoracic aorta, distal arch or descending thoracic aorta rupture, an aneurysmal distal arch and a severely damaged aortic arch hindering safe distal aortic arch anastomosis [17, 27]. In patients with malperfusion syndrome, the rationale for the FET technique lies in its potential to fully open the compressed true lumen and to cover additional entry tears located in the proximal descending thoracic aorta, which maintain

4 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery i23 pressurization of the FL. Also, by inducing both coverage of secondary entry tears and obliteration of the FL at the level of the proximal descending thoracic aorta, the FET is assumed to further diminish distal aortic dilatation and therefore reduce late aorticrelated deaths and the need for complex distal aortic reinterventions [27 29]. A length of approximately 10 cm beyond the left subclavian artery usually seems to be enough to stabilize the dissected arterial wall and favour true lumen expansion downstream. An oversized stent must be avoided to prevent formation of new intimal tears distal to the stent graft [1]. Accordingly, data from imaging studies have shown favourable positive aortic remodelling only at the stent-graft level, with 20% of patients remaining at risk for secondary reintervention due to the negative remodelling in the distal aortic tracts [30]. For this reason, long-term clinical data are still needed to demonstrate a clear survival benefit from aggressive versus conservative management of the aortic arch at primary surgery [31]. Figure 3: Type A AAD (A) before and (B) after implantation of the Thoraflex TM Hybrid 4-branched hybrid device. Courtesy of Vascutek Ltd. Acute type B aortic dissection The FET technique constitutes an alternative therapeutic option in complicated type B-AAD when thoracic endovascular aortic repair (TEVAR) is contraindicated [18, 32, 33]. The most unfavourable anatomical conditions that may hamper an endovascular approach are: A proximal landing zone on the aortic arch >40 mm [18, 34] Concomitant aneurysm of the aortic arch requiring surgical correction (Fig. 4) Steep angulated aortic arch Dissected left subclavian artery with additional distal intimal tears (which may maintain perfusion of the FL despite correct stent-graft deployment) [34]. Recent aortic guidelines mentioned open aortic replacement via left thoracotomy as the only available surgical option in the case of complicated type B-AAD when TEVAR is not feasible [35]. The aim of open surgical repair is to replace the descending aorta with a vascular prosthesis, to direct the blood flow into the true lumen of the downstream aorta and to improve perfusion and decompression of the true lumen, which may resolve malperfusion [35]. Owing to the fact that in most patients, the proximal entry tear is located near the origin of the left subclavian artery or the distal arch is dilated, the operation has to be performed in deep hypothermic circulatory arrest with an open proximal anastomosis. Although the surgical results have improved over the years, they remain suboptimal, with early mortality ranging from 25 50% [35, 36]. At the moment, an expert consensus opinion from the Vascular Disease Domain of EACTS is alone in recommending (Class IIb) FET in type B-AAD when primary TEVAR is not feasible or the risk of retrograde type A-AAD is high [18]. Its use is particularly recommended for dilated aortic arch to reduce the extremely high-mortality rate associated with the aortic replacement through a left thoracotomy under deep hypothermic circulatory arrest. Figure 4: (A) Preoperative angio-ct scan showing an acute type B aortic dissection with an intimal tear located at the aortic isthmus. The aortic arch is severely dilated (maximum diameter 52 mm) at its distal portion. (B, C) Postoperative final result after FET surgery.

5 i24 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery The first multicentre experience published in 2014 on type B- AAD using FET reported an acceptable in-hospital mortality rate of 14% [33]. The incidence of SCI was particularly encouraging (<4%), although the distal landing zone of the FET prosthesis was located at TH 8 9 or below for most patients (72%). The study also confirmed the ability of the prosthesis to induce obliteration of the FL in the perigraft space, with a complete FL thrombosis of 75% in the predischarge CT scan increasing to 97% during follow-up [33]. These results should be attributed to the proximal surgical fixation of the FET prosthesis to the native aortic tissue and to the proximal graft attachment that prevents endoleak formation and stent-graft migration (Fig. 5). LITERATURE SEARCH CRITERIA Selection of articles from the literature was performed in three steps. First, to achieve maximum sensitivity of the search strategy and to identify all studies, PubMed databases were searched from inception through April 2016, using elephant trunk OR frozen elephant trunk OR stented elephant trunk OR antegrade stenting descending thoracic aorta OR aortic arch replacement OR conventional aortic arch repair as either keywords or MeSH terms. The lists of recovered articles were cross-searched to reveal pertinent papers missed in the previous search. Case reports, editorials, expert opinions, comments and review articles were excluded because of potential doubling of results. Studies involving <10 cases also were not included. Only articles in English were considered. In the second step, the articles comparing the FET to the cet repair and coming from single centres were identified for assessment. In the third step, we considered only the most recent series followed up by the same group over the years. For each case series, the number of patients treated, aetiology, hospital mortality rate, SCI including paraplegia and paraparesis, and follow-up survival rates were extracted (Table 2). RESULTS OF SINGLE-CENTRE OBSERVATIONAL STUDIES Assessing outcomes of the FET versus the hemiarch, complete arch and cet procedures could be awkward, mainly due to differences in surgical indications, extent of the aortic repair, type of prosthesis and length of study period. Table 2 summarizes the experience of single centres comparing the FET to conventional arch repair [19, 26, 37 41]. The two major series comparing the hybrid approach and the cet were from Leipzig and Hannover in Germany; they compared 46 vs 125 and 180 vs 97 patients, respectively [39, 19]. The first group [39] reported a 30-day mortality rate for the entire cohort of patients of 16.4% (n = 28), with a trend towards a higher mortality rate in the cet group (19.2 vs 8.7% FET) and, conversely, significantly higher onset of paraplegia in the stented group (21.7 vs 4.0% cet). The type of elephant trunk procedure performed did not have a significant influence on mid-term survival (cet, 5.5 ± 0.3 vs FET, 3.8 ± 0.5 years; log-rank P = 0.9). The authors concluded that the FET procedure can be performed with a relatively low-mortality rate, but, considering the increased incidence of ischaemic SCI, a more pronounced hypothermia should be used especially if prolonged circulatory arrest times are necessary [39]. The group from Hannover [19] showed that the patients who underwent an FET procedure had more favourable postoperative outcomes (especially for type A-AAD) and fewer downstream procedures required at follow-up. The cet is freezing, in the sense that it is being replaced by the FET approach [19]. In a landmark paper, Sun and co-workers [26] reported the largest experience in China in which 411 patients had acute and chronic aortic dissections (stented elephant trunk = 291; conventional surgical repair = 120). In-hospital, mortality was 4.7 and 6.1% in the stented and non-stented groups, respectively. The overall prevalence of stroke and SCI was very low (1.95%, 8/411), and no significant differences were found between groups [26]. At follow-up, the prevalence of thrombosis of the FL was lower in the standard group compared to that in the hybrid population for acute (14.5 vs 94.2%) and for chronic (10.3 vs 92.0%) dissections. Secondary surgical intervention (thoraco-abdominal aortic replacement) was more frequently required with the conventional arch repair (4:1) [26]. All studies reported satisfactory and comparable mid-tem survival rates for both trunk procedures at the 7-year follow-up, ranging from 60% at the University of Pennsylvania to 95% of the Hiroshima General Hospital [19, 26, 37 41] (Table 2). DISCUSSION Figure 5: Type B AAD (A) before and (B) after implantation of the Thoraflex TM Hybrid 4-branched hybrid device. Courtesy of Vascutek Ltd. Since the introduction of the classic ET procedure in the early 1980s, several gains have been made in the surgical treatment of aortic arch disease including new methods for organ protection and new prostheses [1 4]. The FET technique is probably the latest introduced to the armamentarium of the cardiac surgeon to treat extensive lesions of the thoracic aorta. Although the cet procedure has satisfactory early and long-term outcomes, the chance to perform a simultaneous antegrade stenting of the descending aorta in just one step led most surgeons to switch to this treatment option [19, 42]. However, both procedures have advantages and disadvantages, and a careful selection should always be guided by aetiology and anatomical indications [18, 43, 44].

6 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery i25 Table 2: Observational studies from a single centre experience that compare the frozen elephant trunk procedure with conventional arch repair Authors Aortic centre Number of patients (surgical procedure) Aetiology Hospital mortality Acute type A dissection Chronic dissection Degenerative Aneurysm rate Spinal cord injuries Follow-up survival Jakob [37] 2008 Essen, Germany Uchida [38] 2009 Hiroshima, Japan Sun [26] 2011 Beijing, China Leontyev [39] 2013 Di Eusanio [40] 2014 Vallabhajosyula [41] 2014 Shrestha [19] 2015 Leipzig, Germany Bologna, Italy Philadelphia, USA Hannover, Germany FET: 22 (E-vita Open, Jotec) CAR: 23 (ET) FET: 65 (Z-shaped stent, William Cook) CAR: 55 (transverse arch) FET: 291 (Gianturco-type, Microport Medical) CAR: 120 (ET) FET: 46 (E-vita Open, Jotec) CAR: 125 (ET) FET: 21 (E-vita Open, Jotec) CAR: 36 (ET) FET: 62 (GoreTAG, WL Gore & Associates) CAR: 180 (transverse arch) FET: 180 (Thoraflex TM Hybrid, Vascutek; E-vita open, Jotec; Chavan- Haverich, Curative GmbH) CAR: 97 (ET) FET: 100% CAR: 100% FET: 100% CAR: 100% FET: 50.9% CAR: 55% FET: 17.4% CAR: 53.6% FET: 9% CAR: 22% FET: 3% CAR: 3.6% FET: 49.1% CAR: 45% FET: 4.3% CAR: 4% FET: 0.7% CAR: 0 FET: 58.7% CAR: 33.6% FET: 100% CAR: 100% FET: 100% CAR: 100% FET: 26.1% CAR: 64.9% FET: 8.7% CAR: 21.6% FET: 9.5% CAR: 13.9% FET: 10% CAR: 14% FET: 28.3% CAR: 7.2% FET: 34.4% CAR: 44.3% FET: 12% CAR: 25% FET: CAR: FET: 0% CAR: 0% FET: 3.1% CAR: 5% FET: 21.7% CAR: 4% FET: 4.8% CAR: 2.9% FET: 0% CAR: 1% FET: 4.8% CAR: 2.9% FET: 80% (2 years) CAR: 75.8% (4 years) FET: 95.3% (5 years) CAR: 69% (5 years) FET: 92.9% (4 years) CAR: 91% (4 years) FET: 68% (5 years) CAR: 70% (5 years) FET: 72.8% (4 years) CAR: 75.8% (4 years), 68.4% did not undergo II stage FET: 81% (7 years) CAR: 60% (7 years) FET: 62% (4 years) CAR: 48% (4 years) and only 24% underwent a II stage procedure ET: elephant trunk; FET: frozen elephant trunk; CAR: conventional arch repair; ER: endovascular repair; OR: surgical repair. Secondary aortic intervention FET: 10% (50% ER, 50% OR) CAR: 33% (22% ER, 11 OR) FET: 6.2% (only OR) CAR: 9.1% (40% ER, 60% OR) FET: 1.7% (20% ER, 80% OR) CAR: 5% (only OR) FET: 10.9% (only ER) CAR: 13.6% (23.5% ER, 76.5% OR) FET: 100% (only ER) CAR: 30.6% (only OR) FET: 17.7% (91% ER, 9% OR) CAR: 8.9% (31.2% ER, 68.8 OR) FET: 26.1% (46.8% ER, 53.2% OR) CAR: 23.7% (21.7% ER, 78.3% OR)

7 i26 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery The cet technique is usually preferable in extended aortic aneurysm involving the thoraco-abdominal aorta in view of a second future open repair [14, 44]. The recommendations are similar for the two procedures for all of the other complex arch lesions involving the descending thoracic aorta [18, 19, 46]. The principal concern regarding the cet operation resides in the cumulative risks of two major surgical procedures, in the undeniable interval mortality and, most relevant, in the fact that a large number of patients are lost to the second operation [4, 17, 19]. According to the literature, most patients did not receive a second operation (from 32 to 50% after the first procedure) because they did not show, or they refused, or more importantly, because there was no proper indication [4, 5, 20]. On the other hand, the main advantages of the FET are that it often does not necessitate a second procedure and, if required, it is not precluded. A recent position paper from the Vascular Disease Domain of EACTS suggested that the FET technique should be considered (IIa, Level of evidence C) in patients with extensive thoracic or thoraco-abdominal aortic disease when a second procedure, either open surgical or endovascular in downstream aortic segments, can be anticipated [18]. In our institution, aortic arch surgery comprises extensive resections of all diseased aortic tissues at primary elective interventions, with liberal use of either the cet or FET technique. Since 2007, when we performed the first FET procedure, indications have been extended and currently include a wide variety of diseases, ranging from degenerative aneurysms of the aortic arch to acute or chronic aortic dissections, type A or B. Until May 2016, 201 patients received this procedure using the Jotec E-vita Open Plus and the Vascutek Thoraflex TM Hybrid in 157 and 44 cases, respectively. Overall, 35 (17.4%) deaths occurred, including 16 (15.2%) in elective and 5 (29.4%) in urgent patients, respectively. This relatively high-mortality rate reflects the complexity of our surgical population, with a considerable proportion of patients presenting with extensive disease of the thoracic aorta, AAD, reinterventions and associated procedures. The endovascular technique was more frequently performed for distal completion and has become our preferred method in patients with feasible anatomy, especially for those considered high risk for open replacement. During surgery for AAD, patients with complex arch tears involving the distal arch and/or proximal descending thoracic aorta represent an interesting subset for FET application [26, 27, 31, 46, 47]. In this setting, as compared to conventional arch replacement, a stent graft in the descending thoracic aorta may open the true lumen, obliterate secondary entry tears and induce FL thrombosis and remodelling that can result in improved freedom from distal redo and survival [29 31]. Unfortunately, the pathological disorder in the descending aorta is often transferred more distally to the visceral and abdominal aorta and a careful follow-up is always necessary. In an interesting series, Dohle et al. [30] investigated the changes in the lumen volumes along the downstream aorta towards the remodelling in patients undergoing FET. The results for patients with acute type A-AAD (70/102) in the postoperative CT examination revealed an 88% FL thrombosis at the stent graft compared with a 25% FL thrombosis down to the coeliac trunk. Within the first year, positive or stable aortic remodelling was found again in 90% of patients at the level of stent graft vs 58% at the origin of visceral arteries [30]. In our experience about one in every four patients necessitated an endovascular extension using the hybrid prosthesis as the proximal landing zone for endograft deployment. All of this evidence suggests the effectiveness of the FET technique for a durable treatment up to the mid-descending aorta with close surveillance of the remaining downstream aorta. Encouraging results of the antegrade stenting of the descending thoracic aorta have also been described for chronic degenerative aneurysm [47, 48]. In the last report of the E-vita Open international registry accounting for 509 patients from 9 European heart centres, the overall in-hospital mortality rate was 15.9% and no significant differences were found between aortic dissection and chronic degenerative aneurysm (17.1 and 13.2%, respectively) [47]. Far higher early survival rates were reported in the last report from Cleveland Clinic when they used the cet as preventive repair for a moderately dilated descending aorta [49]. Operative mortality in patients with degenerative aneurysm and dissection was 0.8% (1/117), thus encouraging the use of this technique for a more aggressive approach at the time of initial intervention to offer long-term benefits in patients with extensive aortic disease [49]. Despite these excellent early results reported by the authors, a not negligible mortality rate between the first and second operations was observed (9% died during follow-up with 8/10 for unknown reasons) [49]. These results demonstrate that, even in the era of less-invasive approaches such as TEVAR after the conventional or the FET procedure, close surveillance is fundamental to reduce mortality at follow-up. Moreover, it should always be kept in mind that sudden death may occur whenever one is dealing with diffuse aortic diseases. Unlike with the cet, the main drawback of the FET is the increased risk of paraplegia, which ranges from 0 to 21.7% in the literature [47, 48]. According to our experience with more than 200 FET implantations, SCI remains the most catastrophic complication observed postoperatively (8.5% including paraplegia and paraparesis). Likewise, in the multicentre study of Leontyev et al. [47], the authors reported an overall rate of paraparesis and paraplegia of 7.5% with similar rates among different aortic pathologies: 6.5% in type A-AAD, 10% in type B-AAD, 10.9% in chronic type A aortic dissection and 7.6% in thoracic aortic aneurysm 48]. A distal landing zone of T10 or more was identified as the only independent predictor for the occurrence of SCI. Neither body core temperature nor circulatory arrest time influenced neurological outcome, emphasizing the fact that mechanical coverage of intercostal arteries plays a central role in the development of this complication [47]. Other potential pathogenic mechanisms for the onset of SCI after the FET procedure are periods of circulatory arrest, embolization and postoperative hypotension [17]. To reduce these kinds of complications, strict protocols for the protection of the cerebral and visceral organs should always be pursued during and immediately after the operative time. Refinement of the technique along with the implementation of the hybrid devices has strongly contributed to reducing major postoperative complications [50, 51]. The ultimate evolution of the elephant trunk prosthesis represented by a quadruple branched FET graft facilitates arch vessel reimplantation and above all allows quick restart of perfusion to the lower part of the body and the heart once the distal anastomosis is completed [50, 51]. These measures have strongly contributed to shorten myocardial, spinal cord and visceral ischaemia times. Both the cet and the FET techniques are still considered complex operations; however, the refinement of organ protection together with new prostheses will continue to further simplify and increase the use of these surgical techniques. Given the risk

8 R. Di Bartolomeo et al. / European Journal of Cardio-Thoracic Surgery i27 of paraplegia and the higher costs of the FET devices, a prophylactic cet technique should be preferred to the conventional prosthesis. Only future research accompanied by longer followup data will clarify the actual benefit of the new over the old trunk procedure. CONCLUSIONS Conventional or FET procedures represent the most significant technical improvements to the treatment of complex aortic arch pathologies in the last 30 years. Recent technical advances have given us the opportunity to reduce the surgical invasiveness. Facilitated graft implantation along with further improvement in the stented portion of the FET-hybrid prosthesis will probably be used more widely. ACKNOWLEDGEMENTS We thank Vascutek Ltd. for the support received on the Thoraflex TM Hybrid prosthesis illustrations. Conflict of interest: none declared. 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