Longer-term rates of survival and reintervention after thoracic endovascular aortic repair (TEVAR) for blunt aortic injury: a retrospective population-based cohort study from Ontario, Canada

Introduction

In most countries, including Canada, injury remains the leading cause of death in the first four decades of life and accounts for more productive years of life lost than any other disease process.1 2 Blunt thoracic aortic injury (BAI) is the second most common cause of death in blunt trauma (exceeded only by traumatic brain injury), and 80% of patients die at the scene of injury.3–6 If left untreated, many patients will die of aortic rupture.6

Treatment of BAI varies with the severity of injury. In general terms, all BAI types are managed medically with strict blood pressure control (‘impulse control’) to reduce aortic shear wall stress and lower the probability of rupture.7 8 Impulse control alone is likely adequate for low-grade injuries,7 but all higher-grade injuries typically require either thoracic endovascular aortic repair (TEVAR) or open surgical repair.7 In the last two decades, the shift has been towards TEVAR (an endograft stent placed in the aorta to cover the injury) rather than open surgical repair whenever possible9 due to better short-term outcomes. TEVAR has been shown to reduce perioperative mortality (Relative risk 0.49, 95% CI 0.36 to 0.66) and morbidity, particularly stroke and spinal cord ischemia (RR 0.34, 95% CI 0.17 to 0.69), making it the recommended treatment strategy.9

However, during the longer term, patients receiving TEVAR are at risk of delayed complications as the aorta remodels and typically dilates around their endograft.10 11 The medium-term and long-term risks of TEVAR including endoleaks, aneurysm formation, delayed ruptured, and requirements for reintervention are not well characterized.12–14 The largest studies to date have come from Taiwan15 (287 patients) and the USA (296 patients)7 and have shown low rates of mortality in patients receiving TEVAR with relatively low rates of immediate complications, although most patients were only followed for several years after their procedure.

The issue of long-term follow-up is particularly important in trauma as most patients with BAI are young, active, and in good health prior to their injury, so understanding the quality of survivorship in this group is especially relevant. Our study will compare the longer-term outcomes of patients receiving TEVAR versus medical, surgical, or hybrid (TEVAR and surgical) treatment strategies for BAI in Ontario, Canada.

Methods

Study population

BAI cases were defined as patients with an International Classification of Diseases 10th Edition external cause of injury code corresponding to blunt trauma and a diagnosis code indicating aortic injury (S25.0 in National Ambulatory Recording System, Canadian Institute for Health Information Discharge Abstract Database, or the Ontario Trauma Registry (OTR) (figure 1, online supplemental file 1).

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Figure 1

Data creation flow chart. *See online supplemental appendix 2 for ICD-10-CA codes corresponding to blunt trauma and for Canadian Classification of Interventions codes corresponding to the different repair types. ^#This is the number of unique patients with an aortic injury (some patients had aortic injury codes in more than one database). CIHI-DAD, Canadian Institute for Health Information Discharge Abstract Database; ED, emergency department; ICD-10-CA, International Classification of Diseases 10th Edition; NACRS, National Ambulatory Recording System; OTR, Ontario Trauma Registry; TEVAR, thoracic endovascular aortic repair.

We extracted baseline characteristics for patients including age, sex, socioeconomic status and rurality (based on postal codes and the Rurality Index for Ontario),20 comorbidities 2 years prior to BAI using the Elixhauser comorbidity index score,21 mechanism of injury, aortic injury severity, Injury Severity Score (ISS), and associated injuries. Aortic injury grades were captured in the OTR as Abbreviated Injury Scale (AIS). Although AIS scores are used extensively in trauma registries, they are not as widely reported in modern BAI literature. We used previously published methods22 to translate the AIS grades into Society for Vascular Surgery (SVS) grades.23 Patients were excluded if they died within the first 24 hours of hospital admission and had not received an intervention within that period of time.

Results

Outcomes

The median duration of follow-up for the cohort was 3 years (IQR: 1–6 years). Overall, 348 (81.5%) patients survived to maximum follow-up. Of the 79 deaths, 35 (44.3%) occurred in hospital (more than 24 hours after admission) and 44 (55.7%) occurred post-discharge. Survival to maximum follow-up did not differ between treatment groups (table 3). Deaths due to aortic rupture or complication (aorta-related mortality) were very uncommon and were comparable between treatment groups. Similarly, stroke, spinal cord ischemia, endoleak, or renal failure requiring dialysis were very uncommon (less than six patients for each outcome) in the study cohort and did not differ between treatment groups. Aortic reinterventions were required in only 2.6% of surviving patients but were significantly more common in the TEVAR group (p<0.01). Of the 11 total patients who had a reintervention in the follow-up period, 5 underwent either primary or redo TEVAR, 5 had surgery, and 1 underwent a hybrid repair.

Table 3

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Outcomes for blunt aortic injury study cohort (N=427), by repair type

Notably, only 3 (3.8%) of the patients of the 79 patients who died were confirmed to have undergone autopsy. Sixty-nine (87.3%) were confirmed not to have undergone autopsy and a further seven (22.5%) patients had an incomplete autopsy status field in the Ontario Registrar General Database by the time of publication.

The Kaplan-Meier survival plot for survival probability in the four treatment groups is presented in figure 2. There were no significant differences in survival to maximum follow-up between the four treatment groups (log-rank test, p=0.08). In the adjusted analyses, TEVAR was not associated with improved survival to maximum follow-up when compared with either medical management, hybrid repair, or surgical repair (figure 3).

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Figure 2

Kaplan-Meier survival curve for survival to maximum follow-up. TEVAR, thoracic endovascular aortic repair.

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Figure 3

Adjusted HRs for survival to maximum follow-up between TEVAR and alternative repair strategies. TEVAR, thoracic endovascular aortic repair.

Discussion

In this study, we describe the contemporary management and longer-term outcomes of patients suffering BAI in Ontario, Canada. We found that patients were managed with a number of different treatment approaches, but that medical management (58.8%) or TEVAR (24.6%) was the most common. Regardless of the initial management strategy, patients with BAI had a favorable longer-term prognosis, with 81.5% of patients surviving to maximum follow-up, and only 2.6% of patients requiring aortic reintervention. Rates of delayed aorta-related mortality, endoleaks, strokes, and other delayed complications were exceedingly uncommon, providing reassurance that contemporary BAI management strategies are benefiting patients well beyond their survival to hospital discharge. Given the observational nature of our data, we cannot be certain that all patients with a particular grade of aortic injury would do similarly well with any of the treatment approaches. We can, however, be confident that within our trauma system, surgeons are exercising sound clinical judgment in selecting individual treatment approaches for their patients, as evidenced by the favorable outcomes we have observed.

Our study adds to several smaller studies in providing evidence that TEVAR remains safe and effective in the immediate years after aortic injury. For instance, Farber et al25 reported 5-year outcomes for 101 patients treated with one of two TEVAR devices. Although limited by a loss to follow-up rate of 41%, they reported a 9.1% rate of death and only two minor endoleaks during the follow-up period.25 Prendes et al26 followed 46 TEVAR patients for a median duration of 34 months, reporting a 93.3% survival rate and a 2.1% rate of late interventions. However, this study was also limited by a loss to follow-up rate of 43.2%.26

An additional German study that included 19 TEVAR-treated patients reported a 5% rate of aortic reintervention by 5 years but a persistently impaired quality of life, thought to be related to concomitant orthopedic and neurologic injuries.12 Finally, Cheng et al15 reported on the outcomes of 287 TEVAR patients in Taiwan, using a retrospective population-based cohort design.15 Similar to our study, these authors reported a survival advantage to TEVAR (compared with open surgical repair) at both 1 year and 5 years post-repair and low rates of intervention (2%) during follow-up. This study included a smaller sample size than the present study and did not report outcomes for patients treated with medical or hybrid treatment options.

Overall, it seems that the mortality benefit seen with TEVAR, particularly in comparison with open surgical repair, is related to the overall lower rates of perioperative (30-day) mortality, stroke, and paraplegia27 28 seen during the index admission and that patients who survive this tenuous period of acute care can look forward to a highly favorable prognosis, at least in the first several years after injury.

A particular challenge in studying the longer-term course of endovascular interventions like TEVAR relates to high rates of lost to follow-up, particularly in young and otherwise healthy patients. The issue compounds over time as patients’ overall health continues to improve and they become increasingly less inclined to return for follow-up visits and surveillance imaging.25 26 As noted in several studies above, loss to follow-up rates of 30%–40% are not uncommon in this patient population, and some studies have reported that 37.6% of TEVAR-treated patients do not return for stent surveillance imaging.29 It is this loss to follow-up issue that population-based studies like ours are uniquely positioned to address. Our study presents complete outcome data (no loss to follow-up) for a very large population of patients with BAI, thereby providing robust information on the longer-term prognosis of patients receiving TEVAR versus comparator treatment approaches.

In addition to the large sample size and completeness of follow-up, other strengths of our study are the inclusion of patients receiving all the different management strategies for BAI (medical/impulse control, hybrid, open surgical repair), a population that is representative of the entire province of Ontario (11 different treating trauma centers), and the quantification of other important secondary outcomes including aorta-related mortality, endoleaks, stroke, spinal ischemia, and renal failure requiring dialysis, which were all very low.

There are several limitations associated with our study design. First, aortic injury severity was based on AIS codes used in the provincial trauma registry. There is always the possibility of data coding errors resulting in misclassification of aortic injury severity but that would be unlikely to affect the overall findings of the study, particularly as other similar studies have not even included aortic injury severity in their regression models.30 We also had to translate the AIS grades into SVS aortic injury grades using previously described methods and misclassifications of injury grade are possible.

Another limitation is in our definition of ‘medical management’ of an aortic injury. We considered patients as having received this treatment approach if there were no codes to indicate that they had a TEVAR or surgical intervention, however, data coding errors remain possible. Similarly, the included databases do not provide detailed information on the specific treatments a patient being treated with ‘impulse control’ would have received (ie, a particular beta-blocker medication, target heart rate or blood pressure target, duration of therapy, etc) and there was no standardization of medical treatments across trauma centers during the period of study. It is possible that some patients in the ‘medical management’ group would have been eligible for an alternative aortic repair strategy (eg, TEVAR), but did not survive long enough to receive it. We attempted to address this by excluding patients who did not receive TEVAR or open repair and who died within the first 24 hours of admission, but residual confounding could still exist.

Also, in terms of our estimate of aorta-specific mortality (deaths from aortic rupture or complication), it is possible that some patients were misclassified in their cause of death, given that the confirmed autopsy rate was only 3.8% for the entire cohort. This low autopsy rate is partly explained by the inclusion of in-hospital deaths, for which a very lower autopsy rate would generally be expected since essentially all patients would have already had advanced imaging (to confirm they had an aortic injury) and that would have already documented their additional injuries. In this scenario, the cause of death would likely be more clinically apparent (eg, severe traumatic brain injury), and make it much less likely the investigating coroner would request an autopsy to confirm the cause of death.

Conclusions

The longer-term survival from BAI appears highly favorable with low rates of reintervention and death in the years after injury, regardless of the initial treatment approach.