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.