Frozen elephant trunk: the gold standard

Frozen elephant trunk: the gold standardType A aortic dissection (TAAD) is a life-threatening emergency requiring imperative diagnosis and prompt surgical treatment.The primary aim of open surgical repair (OSR) in TAAD is resecting the origin of the intimal tear located in the ascending aorta.Importantly, this may extend to involve the arch and proximal descending thoracic aorta (DTA), hence necessitating partial or complete replacement of the aortic arch with possible ante-/retro-grade stenting of the DTA (1).Borst et al. (2) were the first to describe the elephant trunk (ET) procedure which involves replacing varying portions of the ascending aorta and the arch with a separate free-floating stent extension inserted into the DTA.The latter is performed as a second-stage procedure with retrograde endovascular access to facilitate fixation of the trunk and elimination of the false lumen (FL) distally (2).The frozen elephant trunk (FET), pioneered in 1996, merges the two stages of the conventional ET (CET) procedure into a single-stage hybrid total arch replacement (TAR).This procedure circumvents the cumulative hazards with the twostaged surgery as well as the interval mortality associated with CET.FET follows the same principles as CET in terms of ascending aorta and proximal arch replacement using a Dacron arch prosthesis.However, it utilises antegrade placement of a self-expandable stent-graft into the DTA in a single-step hybrid fashion.This 'freezing' of the trunk facilitates the reestablishment of true lumen (TL), with improved FL thrombosis and subsequent aortic remodelling, leading to more optimal clinical outcomes (3,4).The favourable hybrid profile that FET offers has resulted in a major rise in commercial interest with the development of several FET hybrid prostheses of varying designs and features.As aforementioned, the introduction of FET revolutionised the field of aortic surgery by outperforming the CET techniques in TAR, particularly regarding survival, as mortality rates in the literature have been ascertained to favour FET over CET.A contemporary meta-analysis demonstrated lower perioperative mortality (RR: 0.50, 95% CI: 0.42, 0.60; P<0.001) and improved 1-year survival (HR: 0.63, 95% CI: 0.42.0.95; P=0.03) with FET (5).Still, FET is associated with a non-negligible risk of postoperative complications including endoleak, distal stent-graft induced new entry (dSINE) and spinal cord ischaemia (SCI) amongst other less common events, all of which may require secondary intervention, negating its single-stage advantage.A meta-analysis incorporating four different FET devices and results from 43 studies showed a 7% (95% CI: 5-12%) rate of secondary endovascular reintervention following FET repair.It also demonstrated a 2% pooled rate of dSINE (95% CI: 1-6%), a 6% pooled rate of postoperative cerebrovascular events (95% CI: 4-10%), and an 11% pooled rate of postoperative renal failure (95% CI: 7-16%) following FET repair.However, the results had a high rate of heterogeneity which was explained by the different types of stent-graft used as well as the various study geographical locations (6).Spinal cord ischaemia is considered to be a major drawback of the FET procedure.Two earlier meta-analyses have shown a pooled SCI incidence of 4.7-5.1%,and a 4.9-7.6%rate for postoperative stroke post-FET (7,8).The recent meta-analysis of 5,068 patients by Nakhaei et al. (6) reported a 3% incidence of SCI following FET (95% CI: 2-4%).The position of the stent-graft below the T8 vertebra or of length ≥15 cm and postoperative hypotension (<70 mmHg) have been identified as independent and modifiable risk factors for SCI in FET (7,9).The incidence of SCI where the stent length is ≥15 cm or the coverage extends to T8 or beyond was significantly higher when compared to a stent length of 10 cm (11.6% vs. 2.5%, P<0.001) (7).Retaining the stent-graft above T9 and maintaining an average post-operative systolic blood pressure >90 mmHg were described as prophylactic measures to reduce SCI risk when performing FET (10).Therefore, succeeding practices tended to avoid both longer FET stent-grafts and extended distal aortic coverage.Such improvements were reflected in the contemporary results of a recent meta-analysis highlighting no significant difference in the incidences of postoperative stroke and SCI between FET and CET (5).Longer FET stent-grafts, although increase the risk of SCI, promote more favourable aortic remodelling.Aortic remodelling is well-established in the literature as a significant prognostic factor following TAR, with FET exhibiting excellent aortic remodelling, including optimal FL thrombosis rates and significant positive changes in TL and FL diameters (11).For example, in a meta-analysis of 1,279 FET patients, FL thrombosis was achieved in 96.8% of patients (95% CI: 90.7-98.9%)(12).Similarly, these findings were supported in a review by Di Bartolomeo et al. (13), where complete or partial FL thrombosis was seen in 90% of patients.In addition, the published literature has shown similar remodelling trends in both Editorial