In a systematic review and meta-analysis, outcome data of best medical therapy (BMT) were available for 2347 patients from 15 studies who underwent conservative medical management for acute type B aortic dissection (Moulakakis et al. 2014). The pooled 30-day/in-hospital mortality rate was 2.4%. The pooled rate for cerebrovascular events was 1%, for spinal cord ischemia 0.8% and for overall neurologic complications 2%. Survival rates ranged from 86.2% to 100% at 1-year and from 59.0% to 97.2% at 5-years, whereas freedom from aortic events ranged from 34% to 83.9%.

Although medical therapy is recommended for uncomplicated acute type B aortic dissection, the risk of aneurysm development with subsequent rupture in the long-term run should not to be neglected. Van Bogerijen et al. (2014) systematically reviewed and summarized the current available literature on prognostic variables related to aortic enlargement during follow-up in uncomplicated type B aortic dissection. A total of 18 full-text articles were found. The following predictors of aortic growth in these patients were identified: age <60 years, white race, Marfan syndrome, high fibrinogen-fibrin degradation product level (≥20 μg/mL) at admission, aortic diameter ≥40 mm on initial imaging, proximal descending thoracic aorta false lumen (FL) diameter ≥22 mm, elliptic formation of the true lumen, patent FL, partially thrombosed FL, saccular formation of the FL, presence of one entry tear, large entry tear (≥10 mm) located in the proximal part of the dissection, FL located at the inner aortic curvature, fusiform dilated proximal descending aorta, and areas with ulcer-like projection. In conclusion, a significant group of patients develops aneurysmal degeneration along the dissected segments during follow-up and might benefit from closer follow-up or early endovascular intervention.

Risk factors for failure of conservative treatment in acute type B aortic dissection (TBAD) were identified by Grommes et al. (2014) in a retrospective analysis of 104 patients. During the follow-up period, the initial medical treatment was converted to surgical treatment in 21 patients (20.2%) after a median of 333 days. In 5 patients (4.8%), endovascular surgery was performed during the acute dissection phase (within 14 days) because of acute complications, despite best medical treatment. In 16 patients (15.4%), surgery was performed after a median of 189 days. Surgical treatment was indicated because of aortic enlargement (n = 14), rupture (n = 1), or lower-limb ischemia (n = 1). In total, 16 patients (15.4%) died after a median of 774 days. Two patients died of aortic rupture during the acute phase of dissection, and further 14 patients died during the chronic phase of dissection, 6 of them due to dissection-related causes. Patients aged more than 66 years with a maximum aortic diameter greater than 40 mm at admission had a 6.87-fold higher mortality risk than younger patients and patients with smaller aortic diameters. Whether particularly older patients and those with early aortic dilatation benefit from prophylactic TEVAR, has to be questioned.

Durham et al. (2015b) identified a total of 298 patients with initially medical managed acute type B aortic dissections. Failure of medical therapy was defined as any death or aorta-related intervention. Early failure occurred within 15 days of presentation. There were 37 (12.4%) early failures, of which were 15 deaths and 25 were operative interventions. Thus, early mortality was 5%. The indication for early operation in a majority of patients was either renal ischemia (36.0%) or mesenteric ischemia (28.0%). Early aneurysmal degeneration was the indication for intervention in 24.0% of early operations. During a mean follow-up of 4.3 ± 3.5 years, failure of medical therapy occurred in 174 patients (58.4%). There were 87 (29.2%) aorta-related interventions and 119 (38.3%) deaths. An open operative approach was taken in 63 cases (72.4%). In 57 patients (65.5%), the indication for operation was aneurysmal degeneration. The actuarial freedom from intervention was 77.3% ± 2.4% after 3 years and 74.2% ± 2.5% after 6 years. Moreover, the intervention-free survival of the entire cohort was only 41% at 6 years, with end-stage renal disease being the only predictor of medical failure. These authors in addition presented 200 patients (61% men) with medically managed acute type B dissections receiving multiple imaging studies (Durham et al. 2015a). Mean follow-up was 5.3 years. At 5 years, only 51% of patients were free from aortic growth. Fifty-six patients (28%) required operative intervention (50 open, 6 endovascular repair) for aneurysmal degeneration, and the actuarial 5-year freedom from intervention was 76%. After excluding five patients (2.5%) with early rapid degeneration requiring intervention within the first 2 weeks, the mean rate of aortic growth was 12.3 mm/y for the total aortic diameter, 3.8 mm/y for the true lumen diameter, and 8.6 mm/y for the false lumen diameter. Complete thrombosis of the false lumen was protective against growth (odds ratio, 0.19). In conclusion, further study is needed to determine which patients presenting with acute type B dissection will benefit from early intervention (e. g., thoracic endovascular aortic repair) to prevent late aneurysm formation.

In contrast, Charilaou et al. (2016) reported nearly normal 6-year survival in patients with uncomplicated acute TBAD who underwent BMT. In this study, all 65 uncomplicated patients (100%) were treated medically and survived the initial hospitalization. Long-term survival in uncomplicated patients was 91%, 87%, 78%, and 55% at 1, 3, 5, and 8 years. That is, medically treated patients with uncomplicated acute TBAD achieved similar long-term survival as apparently healthy, age-matched and gender-matched controls. These good long-term results are contrary to the perspective of routine thoracic endovascular aortic repair for all TBAD patients.

Luebke and Brunkwall (2014b) reviewed comparative studies of patients treated either with TEVAR or best medical treatment for uncomplicated type B aortic dissection (TBAD). Although the selected studies were not homogenous (with the risk of selection bias), the review strongly suggested that TEVAR may be beneficial compared to BMT in the treatment of uncomplicated Stanford Type B dissection, which is in agreement with the findings of the INSTEAD-XL trial. However, the early TEVAR-related deaths and complications, as well as trends toward higher paraplegia and stroke rates, raise concerns that moderate the better survival with TEVAR at 5 years.

The ADSORB (“acute dissection stent grafting or best medical treatment”) – study (Brunkwall et al. 2012) is the first prospective randomized multi-center-trial on acute dissections (symptom onset to diagnosis ≤14 days) comparing BMT with BMT and stent grafting of the proximal tear in patients having an uncomplicated acute dissection of the descending aorta. The objective of the study was to assess whether stent grafting will produce thrombosis and remodelling of the false lumen with a reduction in aneurysm formation and re-intervention. The primary endpoint of the study was a combination of incomplete/no false lumen thrombosis, aortic dilatation, or aortic rupture at 1 year. Thirty-one patients were randomised to the BMT group and 30 to the BMT + stent graft group (Brunkwall et al. 2014). During the first 30 days, no deaths occurred in either group, but there were three crossovers from the BMT to the BMT + stent graft group, all due to progression of disease within 1 week. At the 1-year follow up there had been another two failures in the BMT group: one malperfusion and one aneurysm formation. One death occurred in the BMT+ stent graft group. Incomplete false lumen thrombosis, was found in 13 (43%) of the BMT + stent graft group and 30 (97%) of the BMT group. The false lumen reduced in size in the BMT + stent graft group, whereas in the BMT group it increased. The true lumen increased in the BMT + stent graft group whereas in the BMT group it remained unchanged. The overall transverse diameter was the same at the beginning and after 1 year in the BMT group (42.1 mm), but in the BMT+ stent graft group it decreased (38.8 mm). In this trial remodelling with thrombosis of the false lumen and reduction of its diameter was induced by the stent graft. However, the question remains as to whether endovascular treatment with a stent graft in the acute phase of type B aortic dissection is associated with improved survival compared with medical treatment alone.

Shah et al. (2014) identified 4706 patients with uncomplicated TBAD from the National Inpatient Sample (NIS) for the years 2009 and 2010. Five-hundred and four patients were treated with TEVAR, 4202 were treated by medical management. The overall adjusted in-hospital mortality was similar for both groups (8.5% for TEVAR vs 10.3% for medical management). The TEVAR carried higher risk of stroke (odds ratio = 1.61). The TEVAR was associated with prolonged LOS (12 vs 5.6 days) and patients were less likely to be discharged home (odds ratio 0.73). Whether these findings support the more widespread use of TEVAR to treat patients with uncomplicated TBAD cannot be decided.

A meta-analysis of the literature identified 2531 patients with acute complicated type B dissection that were treated with TEVAR (Moulakakis et al. 2014). The pooled rate for 30-day/in-hospital mortality was 7.3%. The pooled estimates for cerebrovascular events, spinal cord ischemia (SCI) and total neurologic events were 3.9%, 3.1% and 7.3%, respectively. Survival rates ranged from 62% to 100% at 1-year and from 61% to 87% at 5-years, whereas freedom from aortic events ranged from 45% to 77%. Comparative data for open treatment of acute complicated type B dissection in this meta-analysis were rather unfavorable. A total of 1276 patients from nine studies who underwent open surgical repair for acute complicated type B aortic dissection were analyzed. The pooled rate for 30-day/in-hospital mortality was 19.0%. The pooled rate for cerebrovascular events was 6.8%, for SCI 3.3% and for total neurologic complications 9.8%. Survival rates ranged from 74.1% to 86.0% at 1-year and from 44.0% to 82.6% at 5-years, whereas freedom from aortic events could not be estimated as there were no available data. The findings from Moulakakis et al. (2014) regarding in-hospital mortality with TEVAR were confirmed by a further systematic review where overall mortality and morbidity rates for TEVAR were 8.07% and 30.8%, respectively, in 1574 patients with symptomatic Stanford-B-dissection (Ramdass 2015).

Hogendoorn et al. (2014) assessed the comparative effectiveness of TEVAR vs. open surgical repair (OR) of complicated acute type B aortic dissections (cTBAD) using decision analysis. Main outcomes were quality-adjusted life years (QALYs). In the reference case, a cohort of 55-year-old men, TEVAR was preferred over OR: 7.07 QALYs vs. 6.34 QALYs for OR. The difference of 0.73 QALYs is equal to 8.5 months in perfect health. TEVAR was more effective in all analyzed cases and age groups. Perioperative mortality was the most important variable affecting the difference between OR and TEVAR, followed by the relative risk and percentage of aortic-related complications. Total expected reinterventions were 0.43/patient (TEVAR) and 0.35/patient (OR). The results of this decision model for the treatment of complicated acute TBAD suggest that TEVAR is preferred over OR. Although a higher number of reinterventions is expected, the total effectiveness of TEVAR is higher for all age groups. OR should be reserved for patients whose aortic anatomy is unsuitable for endovascular repair. Luebke and Brunkwall (2014a) also weighed the cost and benefit of TEVAR vs open repair (OR) in the treatment of acute complicated TBAD. In this cost-utility analysis OR appeared in terms of QALYs to be more expensive (incremental cost of €17,252.60) and less effective (−0.19 QALYs) compared with TEVAR. TEVAR yielded more QALYs and was associated with lower 1-year costs compared with OR in patients with an acute complicated TBAD and is therefore the dominant therapy over OR for this disease.

Results of a prospective, nonrandomized, multicenter clinical trial for TEVAR of acute, complicated type B aortic dissection were reported by Bavaria et al. (2015). The trial enrolled 50 patients who were a mean age of 57.2 ± 12.9 years. All 50 patients had dissection-related symptoms at enrollment, including malperfusion (80%), rupture (14%), and malperfusion and rupture (6%). Thirty-day mortality was 8%. All 4 early deaths were considered dissection related. The Kaplan-Meier estimate of freedom from all-cause mortality was 14.6% at 12 months. Three patients (6%) required stent graft-related secondary procedures up to 30 days after implant, and an additional 3 patients (6%) underwent four late secondary procedures between 30 days and 12 months.

Excellent long-term results with TEVAR in 50 patients with acute complicated type B dissection, and in another 10 patients with acute complications, including rupture, end-organ ischaemia and acute dilatation during the primary hospitalisation, but >14 days after onset of symptoms were reported by Steuer et al. (2011). Within 30 days, two (3%) deaths, one (2%) paraplegia and three (5%) strokes were observed. Five-year survival was 87% and freedom from re-intervention at 5 years was 65%. Long-term results were also presented by Hanna et al. (2014). Fifty consecutive patients underwent TEVAR for management of acute complicated TBAD. Indications for intervention included rupture in 10 (20%), malperfusion in 24 (48%), and/or refractory pain/impending rupture in 17 (34%) patients. One patient (2%) had both rupture and malperfusion indications. In-hospital and 30-day rates of death were both 0%; 30-day/in-hospital rates of stroke, permanent paraplegia/paraparesis, and new-onset dialysis were 2%, 2%, and 4% respectively. Overall survival at 5 and 7 years was 84%, with no deaths attributable to aortic pathology. Thirteen (26%) patients required a total of 17 reinterventions over the study period. These data support the use of TEVAR for acute complicated type B aortic dissection but also highlight the importance of life-long aortic surveillance.