Despite technological improvements and advances in radiodiagnosis, aortic dissection is a severe condition with high mortality from its diagnosis. Surgical mortality with new techniques experienced a reduction from 33% in 1999 to approximately 22% in international records. This improvement in mortality and the development of new prostheses have led many surgeons to pursue a more aggressive approach. There is a focus on reducing the amount of aorta with residual dissection, particularly extending the treatment to the aortic arch. Recent studies have warned of the consequences of systematic extension of treatment to the aortic arch and descending thoracic aorta in this patient population, claiming an increase in postoperative stroke, as well as an increase in spinal ischemic injuries and 30-day mortality. All this makes it still a controversial topic, and no standard surgical treatment exists for these patients.

The present study analyzes data recorded in one of the most experienced centers worldwide (Cleveland Clinic) since 1978, with a total of almost 900 patients. To establish a more rigorous analysis, potential significant differences between patient groups were eliminated through propensity analysis adjustment. Comparisons were made between patients with treatment restricted to the ascending aorta only, patients with ascending aorta and aortic arch treatment according to conventional techniques, and those in whom the ascending aorta and aortic arch were replaced using the modified frozen elephant trunk technique. The outcomes of each group were analyzed in relation to aortic clamping and circulatory arrest times, survival, need for reintervention, neurological events, and renal failure.

Regarding surgical times, there were no significant differences in mean aortic clamping or circulatory arrest times. No significant differences were found in postoperative bleeding between the frozen elephant trunk and ascending aorta surgery, but significant differences emerged compared with conventional aortic arch surgery (p = 0.01). Renal failure was lower in patients undergoing modified frozen elephant trunk when compared to those receiving only ascending aorta replacement (p = 0.006), but no significant differences were found in other group comparisons. Neurological events were similar across the three groups, with no significant differences in spinal ischemia rates. Reinterventions for growth of the remaining aortic segments were only 47% in the frozen elephant trunk group, compared to 71% in the group where only the ascending aorta was treated and 75% in the conventional aortic arch approach. All reinterventions in the frozen elephant trunk group could be performed endovascularly.

Finally, the authors highlight that, when comparing survival between groups, greater mortality was observed in the extended classical arch approach compared to the group with ascending aorta replacement only (p = 0.0005). However, there were no significant mortality differences between the modified frozen elephant trunk and isolated ascending aorta treatment groups.

COMMENTARY:

Thanks to propensity analysis adjustment, the heterogeneity of populations observed since the 1980s in this Cleveland Clinic cohort could be rigorously studied. This study observed that patients undergoing modified frozen elephant trunk have similar ischemic times to classical approaches, with similar neurological complications but lower rates of renal failure and reintervention for bleeding when compared to the ascending aorta-only approach or the conventional aortic arch approach. Most importantly, a significant difference in terms of survival was found in favor of the modified frozen elephant trunk compared to the conventional aortic arch approach, with a non-significant trend when compared to ascending aorta-only treatment. Likely, a larger sample size would have achieved statistical significance. In conclusion, in expert hands, the modified frozen elephant trunk in acute DeBakey Type I aortic dissection surgery may show favorable outcomes when compared to more classic approaches and contradicts publications by other groups and international registries.

However, there are criticisms and limitations to this study. Aortic dissection is a pathology with a limited number of annual events. The sample size collected spans a long period, during which different technical and technological advances were not considered in the propensity analysis, which may have influenced the results. Extending treatment to the aortic arch, in early stages, would have been adopted as an obligation (due to the presence of tear or entry at that level) where mere ascending aorta replacement was not feasible, while in recent stages, adopting the elective approach with modified frozen elephant trunk was the result of experience and availability of this type of prosthesis. This and other inherent biases in the retrospective nature of the study, such as follow-up losses, may limit the validity of the conclusions drawn. Thus, while the results are interesting, they should be taken with great caution.

The modified frozen elephant trunk is a complex procedure that adds even more difficulty to a surgery that is already highly demanding in an emergency situation. Therefore, to clarify its role in elective application in this context, registries and collaboration between centers will be essential to shed light on these issues.

REFERENCE:

Roselli EE, Kramer B, Germano E, Toth A, Vargo P, Bakaeen F, et al; Collaborators from Cleveland Clinic Aorta Center. The modified frozen elephant trunk may outperform limited and classic extended repair in acute type I dissection. Eur J Cardiothorac Surg. 2023 Apr 5. doi: 10.1093/ejcts/ezad122.