This study presents the trends in the treatment of thoracic aortic aneurysms in a nationally representative database since FDA approval of thoracic stent grafts in 2005. As anticipated, the utilization of TEVAR has increased. During this period, unadjusted mortality and complication rates following TEVAR have not changed, while the case-complexity of patients undergoing TEVAR has increased. Importantly, the adjusted mortality following TEVAR has improved over time. Furthermore, the adjusted mortality for patients undergoing open aneurysm repair has also improved since 2005. The net result of these case-mix adjusted mortality data for both TEVAR and open surgery confirm that overall mortality in all patients undergoing DTAA repair in the US is improving following the availability of thoracic endografts.
Patients treated with TEVAR are different in many regards from those being treated with open repair. Specifically, TEVAR recipients were nearly 10 years older, had a larger number of comorbidities, and were more frequently non-elective. Despite this disparity, multivariate analysis in our study indicated that TEVAR was associated with improved mortality, a finding that is well supported by other series.4, 6, 7, 20-23
A study published in 2005 comparing TEVAR and open repair showed that endovascular repair was associated with good early outcomes, lower mortality and shorter hospital lengths of stay.24
Since then, several studies have evaluated TEVAR in various populations. One small study comprising 44 patients evaluated the effect of age on TEVAR and found no difference in 30-day mortality between octogenarians (mean age, 84±2.7 years) and non-octogenarians.21
In contrast, our study found that both in-hospital mortality and complications were influenced by increasing age. More recently, a study reviewing data over a 9-year period found that TEVAR had improved mortality, shorter hospitalization and lower intensive care unit stay.26
Similarly, in the current study hospital length of stay was shorter with TEVAR as noted in other series.
In 2005, most centers performing TEVAR were still early in their learning curve with thoracic endografting procedures. Given the increase in use and wider application of TEVAR, it was anticipated that complication rates and in-hospital mortality would improve over time. However, the unadjusted complication rates did not improve as expected, likely due to “sicker” and more complex patients undergoing TEVAR each subsequent year. When these comorbidities were accounted for, the risk adjusted complication rates still did not improve. The unadjusted mortality with TEVAR remained constant, when comorbidities were accounted for, the risk adjusted mortality improved yearly. There are several potential explanations for these observations. First, it is possible that with FDA approval, experience with TEVAR is becoming more dilute such that more low volume centers are performing this procedure with liberalized inclusion criteria. Although TEVAR is less complex than open surgical repair, the subtleties of TEVAR cannot be overstated and greater individual center experience should decrease morbidity. Second, TEVAR is increasingly being performed in “sicker” patients with marginal anatomy. Although we are unable to comment on anatomic criteria, we speculate that less suitable patients with borderline anatomy for thoracic endografting, such as short necks/landing zones, angulated aortic arches, and heavily diseased iliofemoral vessels are being offered TEVAR. Thus as experience with TEVAR increases, more complex patients are being treated with this approach likely resulting in a greater unadjusted complication and mortality rate seen in our findings. A final potential explanation is that TEVAR has already reached the nadir of complication risk. However, this explanation is the least likely given that many centers are still learning this procedure. The annual improvement in adjusted mortality for TEVAR conceptually supports the fact that, greater experience since FDA approval of stent grafts is directly influencing outcomes.
Aneurysm morphology and anatomic location within the thoracic aorta (arch or supra-celiac) are expected to impact outcomes. Anecdotally, patients with less complex aortic aneurysm morphology during the early learning curve period were treated with stent grafting, and with improving confidence more patients with even complex disease were offered endografts. Significantly, early outcomes in the OPEN group might be slightly better a little earlier compared to later given certain patients with intermediate or complex comorbidities were less likely to be treated by endograting early in our analysis. Conversely, later “sicker” patients were more likely to receive TEVAR with improving experience. These trends within groups might partially explain the OPEN results over time, and perhaps support the improvement in outcomes after TEVAR.
The improved unadjusted and adjusted mortality for open aneurysm repairs is interesting and has several potential explanations. First, with the availability of stent grafts, there appears to be a shift in the treatment of “sicker” patients including those with ruptured DTAA and those with higher premorbid risk towards TEVAR. This also suggests that surgeons are appropriately selecting patients for TEVAR and open surgical repair. Another potential explanation is that patients who require open thoracic aneurysm repair are increasingly being treated at high volume and/ or regional aortic centers. Finally, the techniques to minimize morbidity during open surgical repair including hybrid approaches, routine use of lumbar drains, and partial/ left heart bypass may be becoming more prevalent, although cannot be studied in this database.
As the experience with TEVAR grows and devices improve, the proportion of patients undergoing open repair is expected to decline. Patients who traditionally may not be considered candidates for TEVAR including those patients with connective tissue disorders appears to be increasing.27
However, the utilization of TEVAR from 2006 to 2007 also remained constant, a finding that was not expected. This is most likely due to defined anatomic limitations of commercially available stent grafts. As newer generation devices evolve, these anatomic criteria will be broadened and the range of patients with descending thoracic aneurysms will increase. It should be noted that this study was designed to only evaluate thoracic aneurysm disease, the only FDA approved indication for thoracic stent grafts. As such, patients with off-label use of TEVAR, including those with dissection, intramural hematoma, or blunt aortic injury were not included. It is likely that the utilization of TEVAR is increasing with the inclusion of these off-label diagnoses.
There are several important considerations that are highlighted through this analysis. Paramount is the fact that our observational work provides empirical evidence for effective evaluation of outcomes between groups by randomized trial. As confounders and effect modifiers are expected to be homogenous and distributed across both groups, we anticipate that randomization would resolve the better treatment for thoracic aneurysm repair. Importantly, cross over patients would help identify risk factors and characteristics for improved patient selection and reducing treatment mismatch in the future. Another important aspect to remember is that patients included in this research may not have met all criteria of instructions for use (IFU). Although the current study assumes compliance with IFU among recipients, the reality is that with increasing surgeon- and center-specific experience, IFU standards were likely marginalized.
There are a number of other limitations to note in this study. In this retrospective analysis, there is an inherent selection bias with limited data on the specific anatomy to assess the feasibility of TEVAR. The focus of this study was not to compare TEVAR to open surgery but rather to understand the utilization and morbidity trends over time after approval of endograft devices. Next, the NIS is a large database with the potential for erroneous miscoding among ICD-9-CM diagnostic and procedure codes. However, the NIS represents a random sampling of discharge level data that is externally and internally validated. Coding errors are expected to be homogenously distributed across all groups, thus equally effecting the groups in this evaluation. Importantly, since the NIS contains only discharge data, real perioperative mortality and morbidity may be unknown if it occurs after discharge from the index operation. Moreover, specific techniques to decrease the morbidity with these approaches including the use of cardiopulmonary bypass or cerebrospinal fluid drainage cannot be evaluated in our analysis. Finally, the potential for an unmeasured confounder may remain, which is inherent to the constraints of the NIS data points. We are unable to adjust for other well-established surgical risk factors such as low perioperative albumin levels or poor nutritional status.