Addressing the elephant in the room: Conventional versus frozen elephant trunk in complex aortic surgery

Management of complex aortic arch pathologies has evolved since the conventional elephant trunk (CET) was used for the first time almost 40 years ago. The evolvement of frozen elephant trunk (FET) in 2003 created a different horizon within aortic surgery. Depending on the clinical circumstances and expertise available, both conventional and FET procedures can be used in complex aortic surgeries. Traditionally, injuries involving the arch and descending thoracic aorta were treated using CET. This is a two‐stage operation with the first stage involving open repair where a graft tube is placed in the aortic arch and the extension goes down to the descending thoracic aorta. In the second stage, this extension or “trunk” acts as a clamping site to anastomose the trunk to the distal aortic replacement graft at a later stage using left heart bypass rather than deep hypothermic circulatory arrest. The advantage of using FET includes being able to carry out the surgery in a single‐stage approach that encompasses open and endovascular repair; subsequently, FET has been combined with thoracic endovascular aortic repair (TEVAR) to extend the sealing zone and used as a clampable graft for open surgery rather than a landing zone for TEVAR. Other reported advantages of FET when treating aortic dissection include a possible reduction in distal aneurysm growth, decrease in distal aortic malperfusion, helping in the remodeling stage, and possible improvement in the long‐term survival. Di Marco et al. suggested that contraindications to FET surgery included when visceral arteries originated from false lumens and if re‐entries were not possible in the distal descending and thoracoabdominal aorta. While every procedure carries risk, spinal cord ischemia is a particular risk involved with FET and is reported to be around 4%. However, this is a procedure that greatly aids blood flow through the true lumen and compresses the false lumen; ultimately, providing good outcomes in such complex presentations. The current meta‐analysis by Vernice and Wingo compared the differences in survival, intervention, and adverse effects between CET and FET surgery approach. Results from the study showed no significant difference in open reintervention between both surgical approaches; however, FET was found to have an increased likelihood of endovascular reintervention (p = .03). Again, no significant differences were seen in adverse events, specifically no significance in postoperative stroke, renal failure, and spinal cord injury between both surgical approaches. Lastly, when looking at perioperative mortality, Vernice and Wingo reported that FET had a better 1‐year survival rate (p = .03) and a decreased rate of perioperative mortality when compared to the CET approach (p < .001). Although this study proposes important findings of both ET procedures, it is not without limitations. The idea of comparing outcomes for CET and FET is flawed. The procedures are mostly used to treat different pathology and anatomy, therefore the outcomes are merely comparable, as such a direct comparison is not useful. An important criticism that is highlighted in their analysis is the limited number and retrospective nature of the studies included and the heterogenic data analysed. Only five studies were included, none of which were of significant large sample sizes with significant variation in the years of practice. Uniting results from retrospective cohort studies introduces allocation bias and increases heterogeneity among the study populations. Substantial variability within each study also limits the applicability of the significant results of this meta‐analysis to a greater population. For instance, a large discrepancy exists between the number of patients who underwent CET (125) and FET (46) in the study by Leontyev et al. This difference may influence and exaggerate findings in the meta‐ analysis that would otherwise be nonsignificant in a larger cohort of FET cases. Trial sequential analysis may aid in the interpretation of meta‐analyses with a smaller quantity of data and determine