This study aimed to compare the late clinical outcomes of zone 2 hybrid TEVAR according to the various types of thoracic aortic disease being treated. We yielded three main findings: first, zone 2 TEVAR showed acceptable and durable mid-term outcomes for various thoracic aortic diseases, particularly acute type B complicated AD, PAU, and TAI. Second, the concomitant left carotid artery to left subclavian artery bypass with left subclavian artery embolization procedure during zone 2 TEVAR was performed safely and resulted in lasting bypass graft patency. Third, large AAs with an initial diameter of > 60 mm were associated with higher risks of persistent aneurysmal growth and endoleaks after zone 2 TEVAR.
The indications for hybrid TEVAR with the debranching arch procedure have been gradually extended. This procedure provides an adequate proximal landing zone for TEVAR in patients with aortic disease with aortic arch involvement. However, there are still fatal problems with this procedure, such as retrograde type A AD, stroke, and persistent endoleak in regard to the long-term outcomes. Previous studies have reported higher aortic reintervention rates after TEVAR with the hybrid arch procedure than after open aorta replacement for AA [4, 5]. A recent study investigating the late outcomes of hybrid aortic arch repair for both AD and degenerative AA revealed a high incidence of complications within a median follow-up period of 60 months and recommended life-long surveillance in order to achieve better outcomes .
As TEVAR became more common, clinical studies began to focus not only on mortality, but also on aortic remodeling in association with late complications. Our current study found favorable aorta-related results of zone 2 hybrid TEVAR for acute type B AD, PAU, and TAI relative to previous studies. In cases of acute type B AD, the rate of positive aortic remodeling (true lumen re-expansion and thoracic false lumen thrombosis) was as high as 77%. This was slightly lower than the rate of 80–90% reported in previous studies investigating remodeling rates of general TEVAR for AD . However, we exclusively reported the outcomes of zone 2 hybrid TEVAR for acute type B AD with a low number of procedure-related complications and sustainable mid-term aortic remodeling rates. Since the aortic remodeling rate is also associated with the follow-up duration, it is expected to increase after a longer period of observation. Multiple studies of type B AD have demonstrated that TEVAR promotes aortic remodeling as early as 6–12 months postoperatively [8, 9]. Our data support that early aortic remodeling after zone 2 TEVAR is observed even in the immediate postoperative period and can be consistently identified on follow-up CT. Good results were also obtained for PAU and TAI, relative to previous findings. A Chinese group published the 5-year outcomes of TEVAR for symptomatic PAU; they reported two cases of early type II endoleaks, but no aortic expansion was observed and no patients needed reintervention. They also found that PAU typically appeared in the segment extending from the left subclavian artery to the middle descending aorta (24/28, 89%) . Therefore, zone 2 TEVAR is a good option for most patients with PAU. However, despite the good early outcomes for TAI, there are concerns regarding the long-term aorta-related outcome . Secondary aortic interventions rates were high (22%) in a previous study of the efficacy of zone 2 TEVAR for TAI . However, our current study demonstrated sustainable mid-term outcomes of zone 2 TEVAR with near complete resolution for PAU and TAI without the need for aortic reintervention.
Another topic of ongoing debate is the revascularization of the left subclavian artery, the coverage of which in patients undergoing TEVAR involves substantial risk of ischemic complications in the upper limb and central nervous system. Teixeira et al. found that revascularization of the left subclavian artery significantly reduced the risk of spinal cord ischemia . Moreover, Zamor et al. showed that coverage of the left subclavian artery without revascularization significantly increased the risk of stroke and upper arm ischemia . However, despite numerous reports of the benefit of left subclavian artery revascularization, the local surgical complications should be clarified together. We reported early complications related to the left subclavian artery bypass procedure including nerve injury in several patients. However, all of these local surgical complications improved during follow-up. Furthermore, these complications are considered to be minor in comparison to the possible adverse effects of subclavian artery coverage without revascularization. Neither left-arm claudication nor spinal cord ischemia were observed in our study, because the left subclavian artery revascularization procedure was successful. Therefore, our study supports the efficacy of zone 2 hybrid TEVAR with concomitant left subclavian artery bypass for the treatment of thoracic aortic diseases involving the left subclavian artery. Since we routinely performed left subclavian artery embolization simultaneously, the risk of type II endoleak was virtually eliminated.
TEVAR in general has been demonstrated to be safe, but the possibility of subsequent reintervention with endoleak is a well-known risk. Our study observed five cases of endoleaks (10.4%) with two cases of secondary reinterventions (13.3%) for increasing AAs due to endoleak. This result is consistent with those of previous studies, which revealed an incidence of endoleaks of 5–20% [15, 16]. All patients who underwent aortic reintervention for persistent endoleaks were initially diagnosed with AA with a maximal diameter of > 60 mm. Furthermore, 50% of the patients with large AA (diameter > 60 mm) showed persistent aneurysmal enlargement during the follow-up period. Endoleaks were significantly more common in patients with AA than in those with other aortic pathologies. In open surgical repair, the aneurysmal sac is completely removed, but in the case of TEVAR, only exclusions through stent-graft are allowed. The fate and impact of the residual aneurysm sac after TEVAR remains poorly defined. One study demonstrated that several preoperative morphological factors significantly affected the probability of sac expansion after TEVAR for thoracic aortic aneurysm . The known predictors of endoleak include the anatomy of the arch, the lengths of the stent grafts covering the aorta, the diameter of the AA, the length of the proximal landing zone, and zone types [18–20]. Our data support that patients with large AAs are at a higher risk of endoleak and sac expansion. The strategy and selection of zone 2 hybrid TEVAR should thus potentially be based on the aortic pathology rather than only as an alternative to open repair for high-risk patients.
There are several limitations to this study. First, this was a retrospective observational study in which the data were gathered from review of the medical records. Second, all patients were enrolled from a single center and the number of patients was relatively small. Third, the statistical analysis was not performed to draw general conclusions. However, the follow-up data were complete in 100% of the patients, and all patients had annual CT scan records to compare the mid-term aortic measurements. Further studies should include larger samples to further validate the findings of our study.