Multicentre Retrospective Cohort Study on Current Practices in Treatment of Patients Presenting with Non-A Non-B Aortic Dissection and Factors Predicting the Need for Intervention and Mortality

<b>Objectives:</b> Non-A Non-B (NANB) aortic dissections (ADs) are uncommon. Because of their rarity, their therapeutic pathway is not yet standardized, and anatomic or goal-directed treatments are not reported in current practices. We reviewed the treatment strategies of NANB AD across Europe, aiming to identify factors associated with increased mortality and the need for intervention, outlining optimal management pathways for future care. <b>Methods:</b> This multicentre cohort study was carried out in four European aortic centres, retrospectively including patients affected by NANB AD over the last 10 years. Patients' anatomical clinical and treatment data were collected with the aim of investigating the factors associated with their need for intervention and increased mortality, comparing the characteristics of those requiring surgery with those who responded to medical treatment alone. <b>Results:</b> Thirty-eight NANB patients (26, 68.4% men; mean age 60.6 ± 12.87) were included. The primary entry tear was identified in Ishimaru zone 1 or 2 in most cases (24, 63.2%) and the dissection extended distally to the ilio-femoral arteries in half of the patients (21, 55.3%). Surgical repair was indicated in 21 (55.3%) cases within 90 days of acute onset for end-organ ischemia, impending aortic rupture, or retrograde extension of the dissection (including 11 emergent/urgent operations), with most patients requiring surgery within 15 days of acute onset (17, 44.7%). The mean aortic diameter among patients requiring surgery was significantly higher in both zone 1 (7 37 IQR 3 versus 34 IQR 7, <i>p</i> = 0.043) and 2 (36 IQR 6 versus 32.5 IQR 7, <i>p</i> = 0.044) when compared with patients who underwent medical treatment alone. An increased in-hospital mortality rate was noted among patients with indication for surgery after medical treatment (0% versus 30.8%, <i>p</i> = 0.023). <b>Conclusions:</b> This cohort provides an additional description of clinical aspects and current practices in the treatment of NANB in Europe. Most patients of this series had an indication for surgery within two weeks of acute onset, demonstrating a frequently complicated course; moreover, this raises questions surrounding the most appropriate timing for interventional management. Although a diameter threshold was not identified, the baseline enlarged aortic diameter in zones 1 and 2 seemed to be associated with a need for early intervention. Further study is needed to fully refine the indications for treatment in NANB patients; this will support the study of the independent risk factors for increased mortality risk and complications among this group, and will allow the identification of subgroups of patients that may benefit from more aggressive treatment from acute onset.