The management of aortic pathology in the aortic arch and its proximal segments remains a technical challenge for cardiovascular and vascular surgeons, carrying a high risk of stroke, mortality, and other postoperative complications. Currently, the surgical approach is not limited solely to the aortic arch and ascending aorta but also extends to the descending section. The FET technique involves a hybrid device that integrates a traditional graft with a vascular stent graft, allowing treatment of pathological descending thoracic aorta. This approach is increasingly used in both acute aortic syndromes and complex aortic aneurysms affecting the arch and descending aorta as discussed in other blog entries. Among the potential benefits of the FET technique are favorable remodeling of the distal aorta in the short and long term in cases of acute Type 1 DeBakey dissections and improvement or resolution of the distal malperfusion syndrome.
The Thoraflex® hybrid is one of five globally approved devices for FET repair. Since its approval in 2012, satisfactory clinical outcomes have been observed in the short and medium term, with acceptable rates of perioperative mortality, spinal cord ischemia (SCI), and stroke (CV). However, thrombosis in the stented portion of the hybrid graft remains a particular complication, with little knowledge regarding its incidence, clinical impact, and predisposing factors. This study aimed to assess the frequency and clinical impact of thromboembolic (TE) complications post-FET repair using the Thoraflex® hybrid. The study included 128 consecutive patients (average age 67.9 years; 31.0% females) who underwent aortic arch repair with FET using the Thoraflex® from September 2014 to May 2021 across four Canadian centers. Patient characteristics, intraoperative details, and thromboembolic complications were retrospectively collected and analyzed.
Fifteen patients (11.7%) presented thrombi within the Thoraflex® stent graft on imaging studies (n = 8; 53.3%) or experienced a thromboembolic event (n = 9; 60.0%) prior to hospital discharge. The incidence of embolism was: mesenteric (n = 8; 88.9%), renal (n = 4; 44.4%), and iliofemoral (n = 1; 11.1%). Patients with thromboembolic complications were more likely to have a history of autoimmune disease (n = 3; 20.0% vs. n = 2; 1.8%; p = 0.01) and implantation of a longer Thoraflex® stent graft (150 mm vs. 100 mm) (n = 13; 86.7% vs. n = 45; 39.8%; p < 0.001). All patients with thromboembolic complications received therapeutic anticoagulation, and some required surgical (n = 5; 33.3%) or endovascular intervention (n = 2; 13.3%). Radiographic resolution was observed in 86.7% of patients (n = 13). In-hospital mortality occurred in one patient, a stroke in another, and SCI in one.
The authors concluded that thromboembolic complications occur more frequently than previously recognized following aortic arch repair with FET using Thoraflex®, and are associated with increased rates of surgical and endovascular reintervention.
COMMENTARY:
The results from this study of patients treated with FET are notable for several reasons:
Firstly, the series shows excellent outcomes considering 20% had acute aortic dissections, 24% concurrent surgeries, 23% aortic root surgeries, and nearly 40% emergency or urgent surgeries. With a mortality rate of 4.6%, stroke rate of 6.2%, and SCI rate of 5.4%, these complication rates are lower than most published series analyzing FET outcomes. Additionally, comparing groups with or without thromboembolic complications revealed no significant differences in mortality, stroke, or SCI rates. Secondly, it provides invaluable and previously scarce information on the behavior of thrombi and/or distal thromboembolic events related to FET. 12% of all patients in the series met these criteria. Of these, 5% presented a thrombus within the FET alone (without clinical manifestations), another 5% experienced isolated distal thromboembolic events, and 2% had both a thrombus within the FET and a distal thromboembolic event. Notably, most cases were asymptomatic (60%), though all exhibited embolic events confirmed on imaging studies and received systemic anticoagulation therapy. Lastly, in this series, 40% of these patients required surgical or endovascular treatment for their thromboembolic complications. The 12% rate of thromboembolic complications found in this study, higher than expected, might be due to the specific search for this complication in all study patients through systematic computed tomography (CT), unlike previously published studies. This might explain why this complication may have been underestimated in earlier studies with similar surgeries involving the aortic arch and FET.
The distal endoprosthesis of the Thoraflex® prosthesis is made of polyester and nitinol, materials widely used in endovascular implants due to their biocompatibility. However, when in contact with blood, their surface can activate the coagulation cascade and platelets, which can lead to blood clot formation and serious thrombotic events depending on the patient’s predisposition to clotting. This study identified autoimmune disease as a predisposing factor for thromboembolic complications, a finding previously described in clinical cases. Additionally, the association with a longer endoprosthesis (150 mm) is not entirely surprising, as larger prostheses increase the blood-surface interface, which is prone to clot formation. However, no relationship was found between thrombus formation and the appearance or more or less rectified aspect of the Thoraflex® stent graft. Likely, future research in computational fluid dynamics may help better clarify if there are anatomical configurations that predispose to clot formation in FETs.
Recent publications over the last 10 years analyzing the clinical outcomes of the Thoraflex® hybrid prosthesis for FET repair are generally very satisfactory. The perioperative mortality rate varies from 0% to 12%, the SCI rate ranges from 0% to 7%, and the stroke rate can reach up to 18%. These results may be even better today, as suggested by the outcomes analyzed in this study or those derived from the ongoing U.S. Investigational Device Exemption trial for the Thoraflex® device, which is expected to publish one-year clinical outcomes soon. According to this trial, which describes the experience of 74 patients undergoing repair across 12 centers, thromboembolic events were infrequent; they occurred in only 2 (3%) patients, and none of the events resulted in death.
However, until now, we had little information about the rate of thrombosis in the endoprosthesis of this type of device because it has not been a specifically studied complication in most published series. Comparing the ischemic complication rate in TEVAR, which is around 9%, with the one found in this study, we observe similarities. However, the ischemia associated with TEVAR is not exclusively related to arterial thrombosis or embolism, as it can often be secondary to arterial dissection or even arterial obstruction that may occur as a result of endoprosthesis malpositioning. The rates vary depending on the organ under study or the scenario in which the endoprosthesis is implanted, with an SCI incidence of 1-3% or a CV incidence of 4-8%. Therefore, these are relatively high figures for a procedure that is theoretically of lower risk than an FET procedure. Other complications are almost exclusive to TEVAR; the acute thrombotic (almost complete) occlusion of TEVAR, although very rare and described in less than 10 clinical cases in the literature, usually affects young, male patients treated with TEVAR for blunt traumatic injury of the descending aorta, with small aortic diameters, and in whom the oversizing of the prosthesis could reach up to 33%. In this study, there is no occurrence of this complication with the Thoraflex®, as it is logical, since 90% of the patients undergoing FET had aortic aneurysms. Additionally, it was confirmed that 93% of the stent grafts of the prosthesis were well expanded and none were pleated.
The main limitation of this study is its retrospective nature. It concludes that the rates of thromboembolic complications are significantly higher after total aortic arch repair using the Thoraflex® device, but this conclusion is based on the use of a single FET device and lacks a comparative device. No information was collected on the impact of the use of preoperative antiplatelet or anticoagulant agents before FET implantation, which could have influenced the incidence of postoperative thrombus formation in the stent graft. Additionally, the timing of postoperative imaging tests was not protocolized, which prevented precisely determining the exact moment of thrombus formation. Also, there was no standardized treatment algorithm to manage postoperative thromboembolic complications, although all patients with these complications received anticoagulation. Lastly, the observation period was limited to short-term results, and further studies will be necessary to assess the optimal duration of therapeutic anticoagulation and antiplatelet therapy.
Given the 5% mortality rate among 128 patients undergoing total aortic arch replacement, this study supports the excellent results of FET, particularly with the Thoraflex® prosthesis. However, the incidence of thromboembolic complications turned out to be higher than expected (12%), although no significant clinical repercussions were observed after anticoagulation (administered to all patients) or the performance of additional endovascular or surgical procedures (necessary in 40% of patients).
In light of these findings, it is important to consider the possibility of complications after the use of this prosthesis, especially in cases of patients with possible predisposing factors, such as the need for long endoprostheses, autoimmune disorders, or diseases that increase the risk of thrombosis. Prophylactic anticoagulation could be considered as early as possible and/or more stringent monitoring using standardized imaging tests in the immediate postoperative period. In any case, before sounding the alarm about the Thoraflex® prosthesis, these findings should be corroborated in future prospective studies.
REFERENCE:
Ibrahim M, Chung JC, Ascaso M, Hage F, Chu MWA, Boodhwani M, et al.; Canadian Thoracic Aortic Collaborative. In-hospital thromboembolic complications after frozen elephant trunk aortic arch repair. J Thorac Cardiovasc Surg. 2024 Apr;167(4):1217-1226. doi: 10.1016/j.jtcvs.2022.08.005.
