Thoracic Endovascular Aortic Repair for Type B Aortic Dissection

Analysis Among Acute, Subacute, and Chronic Patients

Thoracic endovascular aortic repair (TEVAR) has been increasingly applied for type B aortic dissection with encouraging results. However, the timing of therapy remains undefined, especially for those who do not need emergent interventions. There was a hypothesis that the dissecting membrane was fragile in acute phase and intervention in the subacute phase would be safer because of the stabilization of the intimal flap (1). The 5-year results of the INSTEAD-XL (Investigation of Stent Grafts in Aortic Dissection with extended length of follow-up) trial also showed advantages of TEVAR for subacute dissection over medical therapy (2). However, the differences of results after TEVAR for different stages of dissection have not been fully studied. The VIRTUE Registry found a similar degree of aortic remodeling in acute and subacute dissections but failed to demonstrate any clinical post-TEVAR differences between the 3 groups (3).

In our department, 403 patients were diagnosed as type B aortic dissection during January 2009 and December 2013, of which 314 patients who received TEVAR were enrolled in the study. The indications for TEVAR were complicated dissections with refractory hypertension, intractable pain, rupture or impending rupture, malperfusion, or aneurysmal dilation. They were divided into 3 groups depending on interval between dissection onset to TEVAR: acute (≤14 days, 165 patients), subacute (15 to 90 days, 115 patients), and chronic (>90 days, 34 patients) (4). Comparative analysis of clinical results and aortic remodeling was conducted. Aortic remodeling after TEVAR was defined as complete obliteration of false lumen based on different aortic parts. All percentages were calculated with the Kaplan-Meier method and the p values were from a log-rank test comparing 3 groups.

Follow-up time (through December 2014) was 37.63 ± 17.54 months (range, 2 to 72 months). Cumulative all-cause mortality in subacute group was significantly lower than any of acute and chronic (log-rank test, p = 0.042; Figure 1A). The 30-day and 1-, 3-, and 5-year cumulative mortalities were 3.0%, 9.8%, 14.1%, and 17.1% (acute), 0%, 2.7%, 3.7%, and 7.0% (subacute), and 2.9%, 5.9%, 12.5%, and 12.5% (chronic) for the 3 groups, respectively. Cumulative aorta-specific mortality (death due to dissection-related aortic rupture) displayed the same tendency but the statistical significance was not strong enough (p = 0.091; Figure 1B). The 30-day, and 1-, 3-, and 5-year cumulative aorta-specific mortalities were 2.4%, 8.0%, 10.4%, and 10.4% (acute), 0%, 1.8%, 2.8%, and 2.8% (subacute), and 2.9%, 2.9%, 6.0%, and 6.0% (chronic) for the 3 groups, respectively. Furthermore, cumulative reintervention rate (4.8%, 7.1%, 12.5%, and 15.7% [30-day and 1-, 3-, and 5-year, acute], 0%, 1.9%, 4.4%, and 6.3% [subacute], and 5.9%, 8.6%, 13.0%, and 17.1% [chronic]; p = 0.027) and major complication rate (13.3%, 24.5%, 30.1%, and 37.4% [acute], 5.2%, 11.0%, 16.4%, and 20.2% [subacute], 11.8%, 22.7%, 28.5%, and 35.1% [chronic]; p = 0.041) was also lower in subacute group than any of acute and chronic. On the other hand, the chronic dissection had a lower rate of aortic remodeling than any of acute and subacute dissection in the stented thoracic aorta (90.4%, 90.1%, and 48.5%, acute, subacute, and chronic; p = 0), the distal thoracic aorta (58.6%, 59.5%, and 15.2%; p = 0), and the abdominal aorta (28.0%, 21.6%, and 0%; p = 0.031).

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Figure 1

Survival Times

Cumulative all-cause mortality curves (A) and aorta-specific mortality curves (B) in acute, subacute, and chronic patients. The number of patients at risk at each year is listed in the bottom of the figure. Cumulative all-cause mortality in the subacute group was statistically lower than any of the acute and chronic group (log-rank test; p = 0.042). Cumulative aorta-specific mortality displayed the same tendency but the statistical significance was not strong enough (log-rank test; p = 0.091).

Our study illustrated that the subacute patients gained better clinical results after TEVAR, which supports the hypothesis that the dissecting intimal flap matures and stabilizes in the subacute phase and would make the delivery of stent grafts safer. We also found that both acute and subacute patients exhibited greater aortic remodeling in any part of the aorta than the chronic. This may be due to the aortic susceptibility to remodel in acute and subacute phase, which is defective in chronic phase with thick and fixed intimal septum. The maintenance of intimal compliance to stent grafts in the subacute phase favors the clinical prognosis after TEVAR for subacute patients and raises the attention to the timing of intervention, especially for those uncomplicated dissections.

The unstable type B aortic dissections usually require emergent interventions. However, the optimal timing of TEVAR for those who do not need emergent procedures remains unclear. With better clinical results and aortic remodeling, the subacute phase (15 to 90 days) may be an optimal timing of TEVAR for those patients. However, future prospective randomized clinical studies are required to confirm the observational evidence.

There were limitations in our study. First, it was a retrospective review and the grouping of patients was not randomized. There may be selection bias in the comparison results. Secondly, there has been no uniform definition of subacute phase of aortic dissection. In different studies, 8 to 30 days (5), 15 to 30 days, 2 to 6 weeks, and 15 to 90 or 92 days (3,4) were reported as the subacute phase. The results of comparative analysis may differ based on different definition. The most proper definition of subacute phase needs to be explored in future studies.

• 2016 American College of Cardiology Foundation