Discussion
Nowadays, the most common indication for FET is chronic or acute dissection that involved the ascending aorta followed by degenerative atherosclerosis aneurysm (45). The FET procedure is now potentially indicated for varying aortic arch and descending aorta pathologies, including chronic or acute dissection as well as aneurysmal pathologies. It is well established that each pathology is associated with specific risk profiles, affecting short- and long-term outcomes after aortic arch repair (46). In addition to the type of aorta pathology, cannulation site, concomitant surgery, neurological monitoring, the method surgeon approached to the left subclavian artery, and intra-operative measures would change the course of postoperative outcomes. So, we herein conducted a systematic review focused on the outcome of FET deployment in ATAAD patients who needs total arch replacement, taking into account peri-operative features.
The present meta-analysis, including 35 studies with 3211 patients diagnosed with ATAAD, revealed that the FET procedure in this subset of patients was associated with 3% (95% CI 2 – 4) and 5% (95% CI 4 – 7) of postoperative SCI and stroke, respectively. Additionally, the pooled rate of in-hospital mortality was found to be 7%. A recent meta-analysis by Preventza et al. demonstrated a total pooled operative mortality of 8.8% from 34 reports on patients undergoing FET procedure (7) comparable with rates reported by other meta-analyses (47, 48). In the present meta-analysis, we found that the pooled estimate of in-hospital mortality was 7% (95% CI 5 – 9;I2 = 68.65%) which is less than previous reports. One possible explanation is that they estimated operative mortality (variously reported operative, 30-day, and in-hospital), not specifically in-hospital mortality estimated in our analysis. Another drawback regarding previous reports is that they included heterogenous populations with different pathologies or chronicity of dissection in the final analysis. Although they tried to address this issue by subgroup analysis (7), only 12 studies on patients with ATAAD have been compared with other pathologies (14 studies). Besides, recent meta-analyses (47, 48) included a mixture of patients who underwent total arch replacement, proximal, and hemi arch replacement; meanwhile, they reported a higher mortality rate. It is noteworthy that total arch replacement is a more complex surgery. Hence, total arch replacement in an urgent or emergent situation inheres with a greater peri-operative mortality rate. The observed discrepancy and declining mortality rate during recent years may be attributed to improved diagnostic modalities, enhanced experience of aortic centers and aortic surgeons, and well-established monitoring techniques (49).
Despite the improved results of extensive aortic surgery since the introduction of HCA and brain protection techniques, these procedures are still associated with neurologic impairments. Neurologic complications such as stroke and SCI are the most disastrous complication of aortic surgery, especially after thoracic and arch procedures, with a high burden of morbidity and health-related costs (50). In a single-center series of 25 patients who underwent thoracic aorta aneurysm repair with FET, 24% of patients developed SCI after surgery which is a significant rate of this dreaded complication (6). On the other hand, data from multicenter studies revealed a considerably lower rate of stroke and SCI. A report from the International E-vita Open Registry (IEOR) indicated a 6% and 8% incidence rate of stroke and SCI, respectively (5). We found that the pooled estimate for overall stroke reported in 24 studies was 5%, and 3% for SCI reported in 16 studies. A different definition of SCI and diagnostic criteria and distinct baseline characteristics could explain the inconsistency observed amongst previous reports. However, the impact of the indication of total arch replacement (ATAAD versus chronic dissection and aneurysm) is arguable. This was the main rationale behind including only studies of patients diagnosed with ATAAD in the present meta-analysis. Several hypotheses proposed to explain SCI after FET, including the level of distal landing zone of the stent, hemodynamic instability after cardiopulmonary bypass, age, compromising segmental spinal cord blood supply, and HCA time (6, 51, 52). The effect of the distal stent landing zone on the incidence of SCI has been explored previously; however, different results indicated the possibility of other contributing factors (6, 53). We examined the effect of HCA time on the development of neurologic adverse events. Nowadays, isolated HCA as a protective strategy is not recommended (36). Recent publications indicate that milder hypothermic circulatory arrest in combinations of routine selective antegrade cerebral perfusion improves brain and end-organ protection (54). Unfortunately, we could not evaluate the relationship between core temperature during arch replacement and neurologic events due to lack of data and inconsistency between reports regarding measurements. A total of 19 studies reported circulatory arrest time, and we observed that with a longer duration of circulatory arrest time, a higher rate of neurologic adverse events would be expected. A similar concern regarding the role of HCA time has been raised by Tian et al. while they found a significant strong positive linear relationship between mortality and circulatory arrest time (r = 0.715) (48). Hence, companies and surgeons endeavor to simplify the anastomosis of the prosthesis to the distal aortic stump allowing less HCA time and starting rewarming swiftly (55). In addition to the HCA time, the degree of hypothermia and cerebral perfusion method to achieve the best neurologic outcome is of paramount (56). In the present series of studies included in the meta-analysis, only four authors did not mentioned the cerebral perfusion method, while in all other reports antegrade cerebral perfusion has been utilized.