5.2 TEVAR with chimney stent graft

This surgical approach has been shown to be reliable in cases where a suitable proximal landing zone can be established, where a simple left carotid to left subclavian bypass or one chimney stent graft for the left subclavian in sufficient (Carino et al. , 2019). When the aortic pathology involves or is in close proximity to the aortic branches, it is paramount that the endografts must cross their ostia in order to produce an adequate seal (Malina, Resch and Sonesson, 2008). In this scenario, a standard angioplasty/stenting technique otherwise known as a chimney graft can make performing a TEVAR procedure possible using off the shelf devices (Greenberg et al. , 2003; Donas et al. , 2010). This technique, first reported by Greenberg et al. and subsequently described in detail by various other vascular groups, is a means of gaining additional fixation length in order to stabilise the aortic stent grafts whilst also safeguarding perfusion to the vital branches (Greenberg et al. , 2003; Baldwin et al. , 2008; Donas et al. , 2010; Criado, 2007). However, the addition of a chimney stent graft has been shown to increase the risk of type IA endoleak (Ahmad et al. , 2017).
A 2016 study by Huang et al. describes 27 consecutive non-A non-B patient outcomes without adequate proximal landing zones that were treated with the chimney stent graft endovascular technique with a mean follow up time of 17.6 months (Huang et al. , 2016). Chimney stents were deployed parallel to the main endografts in order to preserve blood flow while extending the landing zones. The technical success rate published was 100% with endografts deployed in zone 0 (3), zone 1 (18) and zone 2 (6). Proximal endoleaks were reported in 5 patients immediately after surgery and were treated with kissing balloon technique in order to minimise gutter formation. Computed tomography angiography showed all aortic stent and chimney stent grafts to be patent post-surgery. Huang et al. also report a 0% 30-day mortality rate and a 0% retrograde type A dissection, however 2 out of the 27 patients were reported to have suffered a stroke post operatively (Huanget al. , 2016).
Zhu et al. has also previously reported similar results in terms of success and also the incidence of endoleak whilst utilising this technique in a cohort of 34 patients (Zhu et al. , 2013). The technical success was reported at 82% and immediate type I endoleaks were reported in 5 patients all of which underwent bare chimney stent techniques (Zhu et al. , 2013). No perioperative death or strokes were observed however one perioperative morbidity included an ST-elevation myocardial infarction. The mean follow-up for this study was 16.3 months and primary patency was maintained in all the chimney stents as well as in the surgical bypasses across this period with no incidence of stent fracture or chimney-related endoleak observed in addition. The authors conclude that this technique provides a minimally invasive way of the preservation of arch branch blood flow with favourable mid-term outcomes. However, the study also concluded that the application of the bare chimney stents seemed to be associated with a higher incidence of immediate type I endoleaks and suggests that balloon-expandable stents should be regarded as the first choice because of their greater radial strength (Zhu et al. , 2013).
An earlier study by Shu et al. reported outcomes of the chimney stent-graft technique on 8 patients treated for Non-a non-b aortic dissections with no adequate proximal sealing zones (Shu et al. , 2011). Covered stents were placed parallel to the aortic stent grafts in order to restore flow to the left common carotid artery while extending the proximal fixation zones; the left subclavian arteries were also intentionally covered after cerebrovascular assessment. All 8 procedures were completed successfully with one main aortic stent graft deployed alongside one chimney graft implanted in the left common carotid artery. The authors report two retrograde type II endoleaks that were identified perioperatively but were left untreated but followed closely using computed tomography (Shu et al. , 2011). They also report no instances of any puncture site complication, strokes, death or paralysis during the hospital stay and a 30-day mortality of 0%. Mean follow-up was 11.4 months and during this time there was no mortality with duplex ultrasound and computed tomography displaying patency of stent grafts, enlargement of the true lumen and compression of the false lumen (Shuet al. , 2011). One of the type II endoleaks disappeared in two weeks post-operatively while the other faded gradually until almost disappearance at 11 months post-operatively.
A 2015 study by Liu et al. reported outcomes of 41 consecutive patients treated with the chimney stent graft technique for Non-a non-b aortic dissection including 8 emergent repairs (Liu et al. , 2015). This technique was utilised to reconstruct the left subclavian artery in 5 patients and the left common carotid artery in 34 patients. In 2 cases the double chimney technique was used in order to simultaneously reconstruct the innominate artery and the left common carotid artery. The mean follow-up period for this cohort was 17.3±6.1 months and the authors reported a 0% 30-day mortality rate (Liu et al. , 2015). None of the patients were reported to have a type I endoleak however four had type II endoleak. During the follow-up no patients were reported to have suffered severe neurological complications, migration or occlusion of any stent grafts. Similar results including 0% 30-day mortality, 0% stroke and 0% retrograde type A dissection were reported in a study by Zou et al. while using the chimney stent graft technique in a Non-A non-B dissection cohort (Zou et al. , 2016).