The protocol was registered on the International Prospective Register of Systematic Reviews (PROSPERO) with the number of CRD42021247609. The analysis was performed according to the recommendations in the Preferred Reporting of Systematic Reviews and Meta-Analysis (PRISMA) statement (14). The analysis objectives were to investigate pre-operative characteristics, peri-operative (early) and post-operative (late) outcomes of patients undergoing TEVAR for uTBAD in acute vs. subacute period. The P.I.C.O. (patient: patients with uTBAD; intervention: TEVAR; comparison: acute vs. subacute period; outcome: 30-day complications and mortality et al.) model was used to select relevant articles (15).

Three databases (EMBASE/Medline, PubMed, and Cochrane Library) were adopted in this study. The literature search strategy includes: (“stent” OR “endovascular”) AND (“DeBakey III” OR “type B”) AND “uncomplicated” AND “aortic dissection” AND (“timing” OR “phase” OR “period”) and were assessed until November 2021. Studies were identified if reporting the outcomes of TEVAR for patients with uTBAD. The searching evidence was limited to the English language and human studies.

This review was conducted and reported according to the preferred reporting items of the systematic review and meta-analysis report published in 2009 (16). The selection criteria are as follows: Studies reporting outcomes in cohorts of more than 20 patients undergoing the TEVAR procedure and providing data for postoperative outcomes; studies that have compared the outcomes of TEVAR utilized to treat patients with acute uTBAD and subacute uTBAD. Exclusion criteria included removing papers based on study type, namely, case reports, cases series, single-arm studies, and literature reviews; studies that referred to type A dissections or to a combined hybrid endovascular or open thoracic aorta repair were excluded unless they included a subgroup of patients that were treated or further treated with TEVAR for a form of type B dissection; articles containing insufficient data <25% of predefined variables extractable) were excluded from the analysis; if various publications on the same population of patients were identified or if study populations overlapped then only the latest report was included unless the outcomes were mutually exclusive. After excluding duplicated citations, all titles and abstracts were reviewed by independent reviewers; the full-text of studies that met inclusion criteria were obtained and those were reviewed to extract data. Study data were extracted by another independent reviewers, and if necessary, a second was consulted to reach a consensus by rereviewing the full text of articles (Figure 1).

Each article was analyzed with respect to 41 predefined variables regarding clinical characteristics, procedural data, in-hospital, and long-term outcomes using a standardized protocol [see Appendix, as modified according to Eggebrecht's meta-analysis (17)]. Extraction of data was performed by the first authors and independently verified by co-authors. Unspecified information was classified as not available. As a result, the number of patients (denominator) varies with the specific variables reported in the analysis.

The quality assessment was evaluated with the latest version of the ROBINS-I checklist for non-randomized studies (18). Non-randomized studies were judged for confounding bias, selection bias, bias in classification of interventions, bias in deviation from intended interventions, bias due to missing data, bias in measurement of outcome and bias in selection of the reported results. Each study was assigned a “low of risk,” “high of risk,” or “unclear” risk of bias (Figure 2).

TBAD was classified according to the Stanford classification. In this review, dissection was classified into two period including acute (within the first 14 days from onset of symptoms) and subacute (beyond 14 days from onset of symptoms). Thoracic stent–grafts placed in the TEVAR procedure were deployed retrograde via percutaneous femoral artery access employing the pre-closing technique. Procedural success was defined by the technically successful deployment of the endoprosthesis at the intended target location. Aortic-related death referred to death caused by aortic reasons, like aortic rupture. The complications occurred in hospital stay was classified into 30-day complications included aortic rupture, organ failure (renal failure and heart failure), heart complications (myocardial infarction and congestive heart failure), renal complications (renal ischemia and renal failure), respiratory complications, endoleak, neurological complications (spinal cord ischemia, paraplegia, and dialysis). A re-intervention was defined as the need for any surgical conversion or additional endovascular stent–graft procedures. The data that were not reported in the articles were recorded as “n.a.”

As with the included studies, two groups were analyzed in this study. The patients with acute uTBAD were referred to acute group and those with subacute uTBAD were included in subacute group.

The continuous variables were compared between the two groups using t-test and the categorical variables were compared using the χ²-test. The random effects model was used to evaluate the results. The proportion was compared between the two groups to see if there was an overlap of 95% confidence intervals (CI) to assess statistical significance. Statistical analysis was performed using R software v.4.1.

Comprehensive literature search resulted in 490 citations published within the predetermined time span of the analysis. Thereafter, 18 studies' full-text were assessed for eligibility after excluding duplicates and studies that have little correlation with our purpose. Of these, one was excluded for non-English language; four were excluded for comment, letter or abstract only; five were excluded for no acute or subacute details; three were excluded for about cTBAD. In addition, two of the studies were excluded for different definitions of acute and subacute period. Wang et al. (22) considered dissection as an acute event if it occurred within the first 30 days from onset of symptoms. And Schwartz et al. (23) stratified timing of intervention into early (within 180 days of initial presentation) and late (181 days and later). All three articles were non-randomized, retrospective studies. The total number of patients included in the analysis was 1,193 and data was extracted from three studies (19–21). Among them, 718 patients were categorized as acute uTBAD and 475 as subacute uTBAD. The major information of each study including patients, procedure success, emergency conversion, 30-day complications and so on are presented in Table 1.

The characteristics of the selected patient population are shown in Table 2. Patients undergoing interventions for acute uTBAD and subacute uTBAD were of similar age (p = 0.792) and sex (p = 0.186). There was no difference in the diabetes mellitus, hypertension, chronic obstructive pulmonary disease, coronary artery disease, cerebrovascular disease, renal insufficiency between both groups(p>0.05).

The procedural success was obtained in 90.8% of patients with acute uTBAD and 93.6% of patients with subacute uTBAD (p = 0.329, Table 3). In addition, both groups of the patients did not receive emergency surgical conversion during hospital. There was a significantly higher proportion of in-hospital complications in the patients with acute uTBAD as compared to the patients with subacute uTBAD (20.5 vs. 13.7%; p <0.05; Figure 3). Within all of the in-hospital complications that reported by these studies, the incidence of respiratory complications was higher in the patients with acute uTBAD (10.8 vs. 5.0%; p <0.05), while no difference was observed in other in-hospital complications (Table 3). Within the 30-day period, the patients with acute uTBAD presented a significantly higher proportion of mortality (4.6 vs. 1.3%; p <0.05; Figure 4).

Regarding the follow-up data, two of these articles (19, 21) offered 1 year follow-up data,and two (19, 20) provided their follow-up data of more than 3 years. No significant difference can be concluded in late mortality (Figure 5), late reintervention, late complications and aortic rupture during follow-up between the two groups (p > 0.05; Table 4).