The total aortic arch replacement using the frozen elephant trunk (FET) procedure has shown to promote beneficial aortic remodeling and facilitate future interventions on the descending aorta, as previously discussed in our blog.
Spinal cord ischemia (SCI), especially paraplegia, represents a devastating complication after aortic repair for acute type A aortic dissection (ATAAD). Specifically, one of the major challenges associated with the FET procedure is the observation of an increased incidence of postoperative paraplegia in patients with ATAAD. However, these previous studies have been limited by the small size of patient cohorts, and the risk factors for paraplegia remain unclear due to the limited application of the FET procedure in this population.
A large extension of the false lumen (FL) after ATAAD has been previously associated with an increased risk of late aortic reintervention and distal aortic dilation, as has been discussed in recent publications also addressed in our blog. What had not yet been studied was whether the location of the FL within the descending aorta could significantly affect the blood supply to the spinal cord in ATAAD. When the FL is located in the most posterior position closest to the spinal column, it is reasonable to assume that the bilateral segmental arteries (SAs) will be compromised by the dissection, increasing the risk of paraplegia. This study aimed to investigate the association between the number of segments of the posterior false lumen (PFL) and paraplegia after an FET procedure in patients with ATAAD.
From January 2013 to December 2018, this study included 544 patients with ATAAD who underwent FET procedures at Fuwai Hospital (China). The number of PFL segments between T9 and L2 levels was calculated. Hospital outcomes and long-term survival were analyzed based on the number of PFLs.
The average age was 46.5 ± 9.9 years and 19.5% of the patients were women in this cohort. The incidence of postoperative paraplegia significantly increased when PFL was present in 3 or more segments. Patients were divided into a high PFL group (3-6 segments; n = 124) and a low PFL group (0-2 segments; n = 420). Demographic characteristics were similar between both groups. The involvement of the celiac artery and the superior mesenteric artery was significantly lower in the high PFL group (p < 0.05). Other baseline characteristics and variables were statistically balanced. The incidence of postoperative paraplegia was significantly higher in the high PFL group (7.3% vs 1.9%; p = 0.006). Multivariable logistic regression analysis revealed that high PFL was independently associated with postoperative paraplegia after an FET procedure (odds ratio, 3.812; 95% CI, 1.378-10.550; p = 0.010). Additionally, a moderate nasopharyngeal temperature during hypothermic circulatory arrest (>23.0 °C) was identified as a protective factor for paraplegia (odds ratio, 0.112; 95% CI, 0.023-0.535; p = 0.006).
Patients with ATAAD who present a high PFL between T9 and L2 levels have a significantly elevated risk of postoperative paraplegia if they undergo an FET procedure.
COMMENTARY:
The FET procedure has been increasingly used in ATAAD to extend the repair distally, especially in patients with intimal tears in the aortic arch and distal malperfusion syndrome, almost invariably in patients with DeBakey type I dissections (as was the case for all patients included in this study). The expectation is that the FET procedure will improve long-term aortic remodeling and reduce the need for reintervention.
However, the incidence of SCI associated with the FET (approximately 5%) seems to be consistently higher than the incidence observed with DAA intervention without FET. A hypothesis related to this association is the use of an excessively long endoprosthesis (>15 cm) or extended coverage of the descending aorta beyond T8, as demonstrated in the meta-analysis conducted by Preventza and colleagues. The study by Yamamoto et al., recently discussed in detail in this blog, showed a reduction in malperfusion syndrome and SCI, provided the distal end of the FET does not exceed T8-9, even when using long prostheses with a 150 mm stent, implanted from the aortic zone 0. On the other hand, besides the length of the endoprosthesis, another possible cause of SCI could be thrombosis of the PFL in its posterior part, in the area corresponding to the SAs. Indeed, a single-center observational study in Germany showed that extensive thrombosis of the PFL is associated with SCI.
In the study by Wei et al. that we discuss today, they go a step further and try to analyze the association between the degree of involvement of the PFL in patients undergoing the FET procedure for ATAAD and the incidence of SCI. Their hypothesis is that, since the SAs originate in the posterior part, the FET procedure will promote thrombosis of a greater number of these arteries if a greater proportion of the FL is located in a posterior position. The implication is that, because the FET procedure promotes FL thrombosis, patients with a greater number of segmental arteries originating from the FL will experience more SCI.
One of the study’s limitations to highlight is the youth of the operated patients and that they were operated on by experienced surgeons. Although this was a retrospective study conducted at a single center, it has great merit, as they were able to collect image data from a cohort of 544 patients undergoing ATAAD repair. Wei et al. found a significantly higher incidence of postoperative SCI (7.3%) among patients with PFL in more than 3 spinal segments, compared with the cohort with PFL in 2 segments or less (1.9%). This very explicit association has been demonstrated for the first time. Furthermore, they discovered that moderate hypothermia is protective against postoperative paraplegia.
The relevance of this study lies in that its results validate for the first time the idea that acute thrombosis of a significant number of SAs after the FET procedure can trigger SCI. This conclusion suggests that the risk of SCI could be assessed by a detailed review of preoperative computed tomography (CT). The surgical planning of ATAAD through a thorough review of CT is crucial; however, this study provides us with another variable of utmost importance to consider in surgical decision-making. If an increase in the presence of PFL is observed, avoiding the FET procedure, opting for revascularization of the left subclavian artery, or adopting a more aggressive approach in spinal cord protection strategies during the procedure and in the Intensive Care Unit might be considered. On the other hand, if the presence of PFL is minimal, proceeding with the FET operation in patients with marginal indications for extended aortic arch repair might be justified, given its presumed long-term benefits. The upcoming randomized controlled trial, Hemiarch vs Extended Arch in Type 1 Aortic Dissection (HEADSTART; NCT03885635), which will compare standard hemiarch surgery with extended aortic arch surgery in patients with ATAAD type I from DeBakey, will surely shed light on many of the uncertainties related to the FET procedure. Meanwhile, we will continue applying common sense based on the available evidence.
REFERENCE:
Wei J, Hu Z, Wang W, Ding R, Chen Z, Yuan X, Xu F. Posterior False Lumen and Paraplegia After FET Procedure in Acute Type A Aortic Dissection. Ann Thorac Surg. 2024 Jun;117(6):1136-1143. doi: 10.1016/j.athoracsur.2024.01.026.
