Aortic arch surgery represents a field with considerable clinical variability within cardiac surgery. Owing to its low incidence and the relatively small number of cases per center compared to other pathologies. Non the less, a broad range of strategies and therapeutic options are used, experience is therefore minimally represented in the literature. Cerebral protection in arch surgery is a critical component in the surgical management of this pathology. Following the implementation of deep hypothermic circulatory arrest (DHCA), two other types of cerebral protection have emerged. Firstly, retrograde cerebral perfusion (RCP), often associated with DHCA, involves cerebral perfusion from the venous system via cannulation in the superior vena cava. Secondly, anterograde cerebral perfusion (ACP), which can be executed under deep or moderate hypothermia, encompasses unilateral perfusion (PCAu), typically on the right side through cannulation of the axillary or innominate arteries, where contralateral flow depends on the presence and patency of the Circle of Willis; and bilateral ACP (PCAb), which can leverage the PCAu setup and incorporate one or more perfusion cannulas to directly perfuse the supra-aortic trunks. The choice between these cerebral protection techniques primarily depends on the surgical team’s experience.
In 2022, Abjigitova and colleagues published in Interactive Cardiovascular and Thoracic Surgery the most comprehensive meta-analysis to date comparing various cerebral protection methods in aortic arch surgery. Over 43,500 patients undergoing aortic arch repair through median sternotomy were included, sourced from 222 observational studies and two randomized trials, and divided into four groups based on the employed cerebral protection strategy: RCP, PCAu, PCAb, and isolated DHCA. Results were pooled using a random-effects model to estimate inter-study variance, assessing perioperative mortality as the primary outcome and the incidence of paraplegia, disabling stroke, renal failure, and respiratory failure as secondary outcomes. Additionally, the authors conducted a sub-analysis stratifying results by underlying pathology: degenerative aneurysms and type A aortic dissection.
The PCAu group exhibited lower postoperative pooled mortality (6.8%) compared to the other groups. RCP showed a mortality rate of 7.1%, while the DHCA and PCAb groups each had a 9% mortality rate. Regarding intraoperative technique characteristics, surgery with ACP was performed under moderate hypothermia compared to the DHCA used in the other two groups (25.8°C vs. 20.4°C). The incidence of disabling stroke was also lower in the PCAu group (4.8%) compared to 7.3% and 6.3% in the PCAb and other groups, respectively. The incidence of paraplegia stood at 2.5% in both types of PCA compared to 3.4% and 4.7% in RCP and DHCA. On the other hand, the incidence of renal failure was notably high in the PCAu group (15%), particularly when compared to the DHCA group (0.8%); however, the need for postoperative dialysis was similar across all groups.
The authors conclude that their work summarizes the outcomes of various neuroprotection techniques in arch surgery over recent decades. Nevertheless, they acknowledge that their data should be cautiously interpreted within the context of their study’s limitations.
COMMENTARY:
The article by Ablitgova et al. summarizes the existing literature on neuroprotection techniques in aortic arch surgery up to the current date. They report the PCAu technique as yielding the best outcomes in their analysis, marking it as the first meta-analysis to date to identify significant differences between unilateral and bilateral anterograde perfusion, despite several limitations that must be highlighted.
We are discussing heterogeneous groups where the lack of matching in the majority of the observational studies contributing to the work results in imbalances. This imbalance appears to disadvantage the PCAb technique based on the reported data. For instance, considering the assessed neurological outcomes, the PCAb group includes more patients with a history of cerebrovascular disease than other groups, exceeding twice the frequency of the PCAu group (14.6% vs. 6.4%). Additionally, the PCAb group was more frequently associated with complex surgeries: in 62% of patients with PCAb, total arch replacement was performed compared to 28.7% in DHCA, and PCAb was associated with longer cardiocirculatory arrest times (48 minutes compared to 27.7 and 23.1 minutes in PCAu and DHCA).
Another significant limitation of the study is the unspecified rate of crossover between techniques. This is particularly crucial when comparing unilateral or bilateral PCA, where many surgeons might switch the perfusion technique to bilateral following an asymmetric drop in NIRS readings. Ultimately, factors such as temperature, times, etiology (aneurysmatic vs. SAA), and the type of procedure (hemiarch vs. total arch replacement) seem to act as confounders in this article.
Over the past year, two new studies have retrospectively compared PCAu and PCAb using moderate hypothermia (28°C) in patients with aortic dissection. The study by Piperata et al. found significant differences between the groups with shorter cardiocirculatory arrest times and a lower incidence of neurological events in the PCAu group, arguing that “blind” insertion of perfusion catheters into the left carotid artery might cause disruption or mobilization of atherosclerotic plaques, increasing the risk of periprocedural stroke. The study by Song et al. found no differences between groups, even though the perfusion techniques were similar in both studies. Additionally, some centers employ a combination of retrograde and anterograde neuroprotection strategies, yet this has been scarcely studied in the literature, and one study showed no superior results compared to RCP. While some literature supports the use of PCAu with moderate hypothermia, it should be noted that other meta-analyses have not highlighted the differences underscored in this article.
As with other cardiac procedures, time matters in arch surgery. Angleitner et al. reported lower long-term mortality in PCAb than in PCAu if the cardiocirculatory arrest exceeded 50 minutes. A meta-analysis by Angeloni et al. showed an increase in mortality in patients with longer times, but only if unilateral protection was used. Based on these findings, the 2022 American guidelines suggest that in cases of cardiocirculatory arrest times over 30 minutes, PCAb may be advantageous.
In my view, this study helps us understand where we stand, where the literature is as of today, and it opens new avenues for analysis. However, its results are inconsistent, owing to a high heterogeneity that prevents extrapolation to clinical practice, a point already emphasized by the authors themselves. The answer to the question posed in the title requires conducting studies that evaluate perfusion techniques by differentiating the type of pathology (acute aortic syndrome vs. aneurysm), conducting a radiological analysis of the Willis polygon anatomy, estimating the crossover rate between PCA techniques, and developing a comprehensive neurological analysis that includes neuroimaging and neurocognitive tests.
REFERENCES:
Abjigitova D, Veen KM, van Tussenbroek G, Mokhles MM, Bekkers JA, Takkenberg JJM, et al. Cerebral protection in aortic arch surgery: systematic review and meta-analysis. Interact Cardiovasc Thorac Surg. 2022 Aug 3;35(3). doi: 10.1093/icvts/ivac128.
Piperata A, Watanabe M, Pernot M, Metras A, Kalscheuer G, Avesani M, et al. Unilateral versus bilateral cerebral perfusion during aortic surgery for acute type A aortic dissection: a multicentre study. Eur J Cardiothorac Surg. 2022 Mar 24;61(4):828-835. doi: 10.1093/ejcts/ezab341.
Song SJ, Kim WK, Kim TH, Song SW. Unilateral versus bilateral antegrade cerebral perfusion during surgical repair for patients with acute type A aortic dissection. JTCVS Open. 2022 May 13;11:37-48. doi: 10.1016/j.xjon.2022.05.006.
