Normothermic frozen elephant trunk: our experience and literature review

Introduction

The Elephant Trunk technique was introduced in 1983 by Borst et al. (1) to facilitate the repair of extensive pathology of the thoracic aorta. During the first surgical step via median sternotomy the ascending aorta and the aortic arch are repaired and a free-floating extension of the arch vascular prosthesis, the “elephant trunk”, is left beyond the proximal descending aorta. This technique aims to prevent difficult tissue dissection in the distal arch/proximal descending aorta area during the second surgical step and can provide a safe landing zone in case of endovascular completion. This approach has been shown to be safe but is burdened by the cumulative risk of two major surgical procedures and poses the hazard of potentially fatal aortic events during the interval time between the first and the second step (2).

The technological and technical evolution has allowed the possibility of a simultaneous treatment of the aortic arch and the descending aorta with the intraoperative implantation of a stent graft. Kato et al. presented in 1996 a series of 10 patients who received a custom-made stented prosthesis implanted at the distal arch anastomotic site for the treatment of descending thoracic aorta aneurysm and dissection (3). Karck et al. in 2003 described the frozen elephant trunk (FET) technique with the implantation of a purposely designed surgical stent graft (4).

Alongside the possibility of treating in a single step extensive aortic pathologies and lesions of the distal aortic arch and proximal descending aorta, FET repair is a valuable strategy in patients with acute aortic dissection especially in presence of complex primary tears, re-entry and aortic rupture at the distal arch or proximal descending (5) or in case of visceral malperfusion sustained by compression of the true lumen (6,7). At mid-term, this approach can also sustain a positive distal aortic remodelling (8) characterised by a higher rate of false lumen thrombosis (8,9) and a reduction in descending thoracic aorta dilatation (5,8,9).

Despite the growing experience at specialised centres with broader practice in aortic arch surgery, in-hospital mortality after FET is still non negligible (up to 17%) and postoperative course is often complicated by the occurrence of cerebral stroke (2.5–20%), spinal cord injury (2–21%) and renal dysfunction (up to 35%) (5,10-14). Operative times and institution of circulatory arrest remain the two main intraoperative negative determinants of early survival and are associated with postoperative brain/spinal cord injury and visceral organs complications (15-22).

Several adjustments in surgical techniques and cardiopulmonary bypass conduction have addressed these issues by reducing cardiopulmonary, cross-clamp and circulatory arrest times. Nevertheless, new approaches have been developed allowing arch surgery and FET repair minimising or completely avoiding systemic circulatory arrest. We present the following article in accordance with the Narrative Review reporting checklist (available at https://cdt.amegroups.com/article/view/10.21037/cdt-22-73/rc).

Methods

A literature search using online platform and database (PubMed, Google, ResearchGate) was performed for FET repair in mild hypothermia or normothermia and avoiding or minimising systemic circulatory arrest. We applied no data restrictions (from origin to January 2022) and we considered only English language publications. Due to the high heterogeneity of definition of these techniques, several searches were conducted using various combinations of the following terms: “frozen elephant trunk”, “elephant trunk”, “aortic arch”, “normothermia”, “hypothermia”, “endoballoon” (Table 1). Associated and similar papers were extensively reviewed. Ultimately, we were able to find four institutional experiences, described in 11 papers, which focused on minimising or avoiding systemic circulatory arrest during total arch replacement plus stenting of the descending thoracic aorta.

We discuss further experiences describing the progressive improvement in management of hypothermia and circulatory arrest and the transition towards the avoidance of systemic circulatory arrest.

Key contents and findings

Reduction of cardiopulmonary bypass time can be achieved avoiding deep hypothermia and shortening cooling and rewarming phases. Different definitions of deep, moderate and mild hypothermia have been used according to cerebral physiology findings (23,24) (Tables 2,3). A systemic cooling at 14–20 °C allows 20–30 minutes of safe hypothermic circulatory arrest (HCA) duration. A longer safe period of circulatory arrest with lower neurological complications can be obtained at higher temperatures 22–26 °C with the adjunct of antegrade selective cerebral perfusion (27-31). Antegrade arterial return flow from right axillary/innominate artery, selective antegrade selective cerebral perfusion through innominate, left carotid and left subclavian arteries, and moderate HCA, provide satisfactory cerebral protection and spinal cord supply (23,27,32). Satisfactory results in terms of early survival, postoperative neurologic complications and organ function preservation, have been reported using antegrade cerebral perfusion and HCA at 30–31 °C (33,34). However, in these series most of the operations were hemiarch repairs with an average duration of isolated cerebral perfusion between 18 and 38 minutes. More complex procedures or redo operations with extensive treatment of the aortic arch and the descending thoracic aorta require longer systemic circulatory arrest periods thus increasing the risk of severe spinal cord injury and paraplegia if the time of arrest exceeds 50 minutes at mild hypothermia (35-37). Similarly, visceral organs can suffer from prolonged arrest time at 28–30 °C, with kidneys tolerating up to 60 minutes of ischaemic time and liver up to 90 minutes before developing organ dysfunction and damage (37).

Proximalization of the distal aortic anastomosis in arch zone ≤2 is a valuable technical advantage of FET repair. It allows the construction of an easier and faster distal anastomosis in a more accessible area avoiding the handling of frail tissue at the distal arch and significantly shortening the circulatory arrest and cardiopulmonary bypass times (38).

The use of a 4-branched arch prosthesis can further reduce the circulatory arrest time. Once the distal side of the arch repair is accomplished, the vascular graft is clamped, and the systemic perfusion resumed from the fourth branch of the graft (39). The proximal aortic repair can be performed thereafter, and heart reperfusion regained before the anastomosis of the epiaortic vessels.

How to minimise circulatory arrest time: the antegrade balloon occlusion technique

Despite these refinements, institution of HCA remains detrimental. Several experiences have tried to overcome the limitations and morbidities associated with conventional arch surgery introducing new approaches and techniques aiming the reduction or the avoidance of systemic circulatory arrest.

Matalanis et al. developed from 2005 the “branch-first” technique (40). The main aim of this approach is to avoid the circulatory arrest and maintain cerebral and systemic perfusion at an average temperature of 27 °C, range 22–28 °C. The first step of this method is the debranching and perfusion of the neck vessels, with intermittent interruption of the flow in each artery—in their experience, 14 (range, 10–18) minutes for innominate artery, 11 (range, 9–14) minutes for the left carotid artery, 18 (range, 13–23) minutes for the left subclavian artery—while avoiding any period of global cerebral circulatory arrest relying on intracranial and extracranial collaterals blood supply (41). The distal organ perfusion is maintained during the arch reconstruction through retrograde femoral artery perfusion with cross-clamp of the proximal descending thoracic aorta or the use of an endo balloon after the deployment of the FET stent graft. With this technique they reported in 64 patients—mean age 65 years old, 49% acute aortic dissection, 11 cases of FET—satisfactory early outcomes: in-hospital mortality 3.1%, cerebral stroke 1.6% and a low occurrence of renal (6.2%) and respiratory (tracheostomy 4.7%) complications. Despite these outstanding results, in a recent paper focusing on their experience with the “branch-first” technique in patients undergoing arch repair and FET procedure from 2008 to 2019, the same group from Melbourne reported the systematic use of circulatory arrest at 25 °C (mean time: 44 minutes) during the deployment of the stent graft and the construction of the distal anastomosis (42).

Touati et al. described in 2007 their experience of normothermic arch replacement with the use of endoballoon occlusion of the descending thoracic aorta to allow distal organ perfusion (43). The perfusion set up provided: normothermic perfusion (between 36 and 37 °C) of the lower half of the body to obtain a femoral artery pressure ≥55 mmHg; normothermic cerebral perfusion through the cannulation of the innominate and left carotid arteries to obtain a right radial pressure of 70 mmHg; intermittent retrograde coronary sinus perfusion. The descending thoracic aorta was usually occluded with a Robicsek Pruitt aortic occlusion catheter after the opening of the aorta or with an inflated balloon of the Djumbodis system in case of stenting of the descending aorta. They reported no distal perfusion interruption during the transverse resection of the aorta and the placement of the endoballoon, manoeuvres that usually required about 5 minutes while maintaining a reduced retrograde flow at 1–1.5 L/min. Twenty-nine patients were treated with this method, 19 chronic aneurysms, 8 acute dissections and 3 chronic dissections. Extension of stenting with the Djumbodis system was performed in fifteen patients. In-hospital mortality was 6.8%, there was no perioperative neurological deficit, no renal and hepatic impairment was observed.

A similar technique (Figure 1) was used by Guo et al. (44) in 16 patients with acute type A aortic dissection who underwent aortic arch replacement between 2010 and 2012. At an average systemic temperature of 31 °C, after exploration of the aortic arch and preparation of the distal aortic stump, a membranous stent graft (MicroPort, Shanghai, China) was anchored to the inner wall of the descending thoracic aorta and occluded with a 16 French urethral catheter. Systemic perfusion through the femoral artery was resumed thereafter for a mean lower body circulatory arrest time of 20±13 minutes. Early results were satisfactory with no 30-day mortality, there was one case of postoperative cerebral stroke and 2 patients required post-operative haemodialysis because of acute renal failure—one of these patients presented already with renal hypoperfusion because of renal artery dissection.

Figure 1 Right axillary and femoral artery perfusion with mild hypothermia for aortic arch replacement from Guo et al. (44).

Mild systemic circulatory arrest for arch and FET repair using and endoballoon occlusion was described by Goto et al. (45) in 8 patients. Their method provided femoral and left subclavian artery cannulation for arterial return, selective antegrade cerebral perfusion and systemic cooling at 30 °C of bladder temperature. After the transection of the aorta, the FET stent graft was deployed during a period of circulatory arrest of 17±4 minutes and was occluded thereafter with a Foley catheter balloon with an immediate resumption of the lower body perfusion from the femoral artery. Total operation time, cardiopulmonary bypass time and cardiac arrest time were significantly lower when compared with patients previously operated on moderate HCA. Mechanical ventilation time and postoperative hospital stay were significantly shorter in patients who had endoballoon FET occlusion. There was no hospital death in both groups, no complications were registered in the group who had reduced circulatory arrest time and FET repair in mild hypothermia. Despite the limited populations size, the authors suggested that endo-clamp with FET graft can safely shorten the circulatory arrest time, enhance the neural protection and avoid coagulopathy and other adverse effects of deep HCA.

In 2019, Sun et al. (46) from Fuwai Hospital in Beijing described their surgical technique with an aortic balloon occlusion for total arch replacement with FET repair (Figure 2). The right axillary artery and the femoral artery are cannulated for cardiopulmonary bypass, and the right axillary artery is used for antegrade selective cerebral perfusion. Circulatory arrest is instituted at the nasopharyngeal temperature of 28 °C and antegrade cerebral perfusion started and maintained at 5–8 mL/kg/min. The aortic arch is transected between the left common carotid and left subclavian arteries. The stented graft is inserted into the descending aorta and an aortic balloon is deployed in the metal part of the FET prosthesis; reperfusion of the lower body starts again thereafter. In their initial experience the average HCA time was 5.36±2.78 min. The results of this technique have been widely reported with separate analyses (up to 134 patients treated with endo aortic balloon) for aortic dissection patients (47-49) and comparison with FET under moderate HCA and arch replacement + endovascular aortic repair (50,51).

Figure 2 Endo aortic balloon occlusion for total arch replacement and FET repair from Sun et al. (46). FET, frozen elephant trunk.

The antegrade balloon occlusion technique seems a feasible way to shorten the circulatory arrest time and avoid deep cooling while providing neurological and visceral protection and reducing postoperative mechanical ventilation time (47,50). This data comes from single institutional practices and, apart from the experience of Fuwai Hospital (46-51), includes small populations of patients, therefore, no robust conclusions about the reproducibility of these techniques can be driven. Furthermore, due to the observational nature of these studies and the heterogeneity of the treated aortic pathologies, it is not possible to strongly and significantly objectify the expected advantages associated with the reduction of the operative times and the shortening of systemic circulatory arrest.

Normothermic FET with NO circulatory arrest. How we do it

To improve surgical outcomes and extend open arch replacement with FET to elderly, comorbid and frail patients, we have proposed a new FET construction based on normothermia and completely avoiding systemic circulatory arrest (Figure 3). This approach involves:

Figure 3 Our approach for normothermic arch + FET repair without circulatory arrest. 1: innominate and femoral artery cannulation; 2: trans-femoral off-pump stent graft deployment and subsequent cardiopulmonary bypass institution; 3: stent graft balloon endoclamp; 4: graft to stent graft anastomosis with cerebral, upper and lower body continuous perfusion. FET, frozen elephant trunk.

• Off-pump retrograde trans-femoral stent graft deployment;
• A combined femoral and innominate artery cannulation for cardiopulmonary bypass arterial return that allows continuous upper and lower body perfusion at 34–35 °C;
• Antegrade selective cerebral perfusion with total brain and subclavian arteries perfusion; either with selective perfusion of innominate, left carotid and left subclavian arteries either with perfusion of innominate artery and left carotid artery after a left carotid to left subclavian bypass;
• Occlusion of the stent graft with a retrogradely inserted balloon;
• Direct suture between the stent graft and the vascular graft.

Primarily this technique was employed in case of type Ia endoleak after TEVAR; afterwards the use of FET without HCA was extended to patients with chronic arch aneurysm (especially involving proximal descending thoracic aorta), with acute or chronic dissection, especially in high-risk and older patients (52-54).

Surgical procedure

The operations were performed through a median sternotomy access. The arch vessels were extensively isolated and the proximal landing zone at the level of the origin of the subclavian artery was marked with multiple large clips. Following systemic heparinization, the innominate artery and the right femoral artery were cannulated for cardiopulmonary bypass arterial return. A vascular aortic stent graft without any free-flow area and supported by an extra-stiff guidewire, was deployed through the left femoral artery and advanced to the proximal landing zone. The stent graft size was chosen considering a 10–20% of oversizing of the distal landing zone in chronic aneurysm and a 0–10% of oversizing of the distal landing zone in acute dissection. Using a 11 French sheath, an endoballoon was then retrogradely advanced into the stent graft and was inflated under fluoroscopy to simulate and evaluated the aortic occlusion. The right atrium was cannulated with a two-stage cannula, a vent line was placed into the left ventricle through the right upper pulmonary vein and finally normothermic cardiopulmonary bypass was instituted. The left subclavian artery was ligated at its origin, anastomosed distally to an 8 mm graft and selectively perfused. The ascending aorta was clamped and cardioplegic arrest obtained with cardioplegia. The left carotid artery was ligated at the origin and distally cannulated and perfused for antegrade selective cerebral perfusion. The innominate artery was then clamped, and the aortic balloon inflated keeping the lower body perfused from the femoral artery. The crossclamp was then removed from the ascending aorta and the proximal aorta was resected from the sinotubular junction to the endoprosthesis. A 4-branched vascular graft was anastomosed to the distal aorta with bites internally taking the endograft and externally reinforced by a Teflon felt. Once the distal anastomosis was completed, the vascular Dacron graft was clamped, and the aortic balloon deflated. The proximal repair was then accomplished and the heart reperfused thereafter. With the heart beating, the three neck vessels were ultimately anastomosed to the three branches of the graft to complete the aortic reconstruction.

In patients with aortic dissection, an endo aortic balloon (Reliant balloon, Medtronic) and a 19 French arterial cannula were introduced in the same sheath and advanced retrogradely from the femoral artery. Once the balloon was inflated, the arterial femoral line was opened and allowed uninterrupted antegrade perfusion of the distal dissected aorta from the descending thoracic aorta (52) (Figure 4).

Figure 4 In case of acute aortic dissection, after transfemoral graft deployment, the sheath is advanced into the stent graft and use to introduce the endo balloon and a cannula for arterial return. This configuration allows a continuous antegrade flow into the dissected thoraco-abdominal aorta. A disadvantage of this technique is the temporary occlusion of the internal iliac artery, which could impair the spinal cord blood supply. For this reason, the sheath is always removed soon after the distal arch anastomosis is complete and the antegrade systemic flow can be re-established through the 4th branch of the vascular prosthesis.

Compared to the techniques reported and discussed in the previous paragraph using an antegradely delivered endoballoon (43-46), our approach:

• Avoids completely circulatory arrest while providing a perfectly bloodless and manoeuvrable operative field as the balloon is retrogradely advanced into the stent graft for aortic clamping;
• Enhances the safety of the procedure with the possibility of testing the endo balloon occlusion before opening the aortic arch;
• Allows a normothermic cardiopulmonary bypass with continuous brain, spinal cord and visceral perfusion.

One of the major concerns in performing open arch surgery in mild hypothermia or normothermia, is the dreadful event of an ineffective endoballoon occlusion causing a difficult exposure and inadequate distal perfusion. However with our approach, the balloon occlusion is tested under fluoroscopy before the institution of cardiopulmonary bypass, and this is of utmost importance especially in case of important back bleeding from a pressurised false lumen during acute aortic dissection repair.

The retrograde insertion of the stent graft and the endoballoon can be prevented by the presence of significant disease of the iliac and femoral vessels. A severe atherosclerotic disease of the iliac and femoral axes could represent a limitation of our technique compared to the antegrade stent graft delivery.

Until today, at our Institution, 13 patients underwent aortic arch replacement using this technique: 7 patients for chronic arch aneurysm, 4 patients for type Ia endoleak and 2 patients for aortic dissection. We registered no cerebral stroke nor spinal cord injury. Two patients suffered postoperative acute renal injury. There was 1 in-hospital death for late pulmonary complications in a patient with history of severe COPD for whom an endovascular approach was deemed not feasible.

Conclusions

Despite numerous refinements in cardiopulmonary bypass conduction and improvement in surgical techniques, HCA is strongly associated with early mortality and postoperative morbidity and remains the most important limitation of conventional arch surgery and FET repair. Minimising or avoiding circulatory arrest can shorten operative times and avoid the systemic effects associated with organ ischaemia and hypothermia. The use of endoballoon occlusion has emerged in recent years as a safe and effective strategy to allow distal perfusion during FET repair. In our experience, the multidisciplinary approach combining surgical and transcatheter techniques provides in selected patients a feasible and safe method for normothermic open arch and descending thoracic aorta surgery completely avoiding systemic circulatory arrest with uninterrupted systemic organ perfusion. Skills and proficiency in catheter-based techniques enhance the interventional armamentarium of the cardiovascular surgeon promoting the progress of the specialty and increasing patients’ safety.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editors (Mohamad Bashir, Mohammed Idhrees and Edward P. Chen) for the series “Frozen Elephant Trunk” published in Cardiovascular Diagnosis and Therapy. The article has undergone external peer review.

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://cdt.amegroups.com/article/view/10.21037/cdt-22-73/rc

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://cdt.amegroups.com/article/view/10.21037/cdt-22-73/coif). The series “Frozen Elephant Trunk” was commissioned by the editorial office without any funding or sponsorship. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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