Thoracic Aortic Injury in Japan

– Nationwide Retrospective Cohort Study –

Abstract

Background: The epidemiology of traumatic thoracic aortic injury has not been reported in many countries, so we investigated the current trends in Japan.

Methods and Results: Patients with traumatic thoracic aortic injury from July 2007 to March 2013 were identified using a Japanese nationwide administrative database, the Diagnosis Procedure Combination inpatient database. The trends in crude in-hospital mortality and proportion of endovascular repair use among patients with repair were evaluated over time. A total of 617 incident cases of thoracic aortic injury were identified at 234 hospitals, and categorized into endovascular repair (n=126), open repair (n=76), and non-repair (n=415) groups. The in-hospital mortality rate for each of these groups was 5.6%, 15.8%, and 45.3%, respectively. The in-hospital survival rate was higher in the endovascular repair group than in the open repair group (log-rank χ²=4.9; P=0.03). Although the crude in-hospital mortality did not change significantly during the study period (Mantel-Haenszel trend test, P=0.10), the proportion of endovascular repair use among all repair cases increased significantly (P<0.001).

Conclusions: The results of the present nationwide study suggest that the endovascular approach to treatment of thoracic aortic injury in Japan gained in popularity from 2007 to 2012. (Circ J 2015; 79: 55–60)

Traumatic thoracic aortic injury is a life-threatening condition that requires repair in most patients, and is the second cause of death after head injury.¹ However, only approximately 20% of individuals survive long enough after thoracic aortic injury to receive treatment.^1,2 Although the conventional method for repair of traumatic thoracic aortic injury is emergency surgical repair (open repair), endovascular stent-grafting (endovascular repair) was developed in 1997 for treatment of aortic injury.^3,4 The first thoracic device for treating aneurysms was approved by the Food and Drug Administration in the United States in 2005, and subsequently received approval from the Japanese Ministry of Health, Labour and Welfare in Japan in 2008.⁵ Since then, endovascular repair has been rapidly adopted as the treatment modality of choice for anatomically suitable patients with thoracic aortic injury, similar to the treatment trend for other aortic diseases (eg, abdominal aortic aneurysms or aortic dissections).^6–9

It is unlikely that randomized trials will be performed to compare open repair and endovascular repair for treatment of this life-threatening injury, but comparisons of major morbidity and mortality from retrospective case reviews and meta-analyses suggest a benefit for endovascular repair.^10–17 However, to the best of our knowledge, only one study from Canada has reported a nationwide incidence of hospitalization, surgical management, and in-hospital mortality for thoracic aortic injury,¹⁸ and there have been no nationwide studies from countries outside North America.

Therefore, we investigated the current trends in patient background characteristics, in-hospital mortality, and selection of treatment options (endovascular repair, open repair, or no repair) among patients with traumatic thoracic aortic injury in Japan, using a large, nationwide dataset available through the Japanese Diagnosis Procedure Combination (DPC) inpatient database.

Methods

This study was approved by the Institutional Review Board of The University of Tokyo Hospital. Requirement for informed patient consent was waived because of the anonymous nature of the data.

Data Source and Patient Selection

The DPC database includes administrative claims and discharge abstract data for all inpatients discharged from more than 1,000 participating hospitals, covering approximately 92% (244/266) of all tertiary-care emergency hospitals in Japan.^19,20 The database includes the following information for each patient: age; sex; primary diagnosis, comorbidities at admission, and post-admission complications classified according to International Classification of Diseases 10th Revision (ICD-10) codes and text data in Japanese; medical procedures, including types of surgery, coded with original Japanese codes; daily records of drug administration and devices used; length of stay; death within 24 h (ie, one of the following: died in emergency room before admission, died within 24 h of admission, or survived at least for more than 24 h after admission); and discharge status.^19,20 The dates of hospital admission, surgery, bedside procedures, drugs administered, and discharge are recorded using a uniform data submission format. The data collection period for the database was July to December 2007–2010, and throughout the year since 2011.

The present study used data for 51 months from 1 July 2007 to 31 March 2013. We included patients aged ≥18 years with a confirmed diagnosis of thoracic aortic injury. We excluded patients with readmission, planned admission for elective surgery, or “suspected” thoracic aortic injury.

Variables and Endpoint

In addition to the baseline characteristics at the time of admission, several other variables were evaluated in this study. The Japan Coma Scale (JCS) score at the time of admission was recorded for all patients. The JCS score is well correlated with the Glasgow Coma Scale (GCS) score, and a JCS score of 100 is equivalent to a GCS score of 6–9.^19,20 The hospital type was categorized as academic or non-academic, and teaching or non-teaching. Hospital volume was defined as the number of patients with thoracic aortic injury admitted within the study period (ie, 51 months). The primary endpoint for the study was all-cause in-hospital mortality.

Statistical Analysis

We compared the patients background characteristics, treatment selection, and mortality between an open repair group and endovascular repair group. We also presented data of a non-repair group for reference. Continuous variables were compared using a t-test or Mann-Whitney U test, as appropriate. Categorical variables were compared using the χ² test or Fisher’s exact test. Kaplan-Meier plots with log-rank statistics were used to assess the difference in survival between the open repair and endovascular repair groups. The trends in crude in-hospital mortality and proportion of endovascular repair use among patients with repair were tested over time (fiscal years 2007–2012) using the Mantel-Haenszel test for trend. Values of P<0.05 were considered statistically significant. All statistical analyses were performed using IBM SPSS version 22 (IBM Corp, Armonk, NY, USA).

Results

During the 51-month study period, 617 patients were admitted with a diagnosis of thoracic aortic injury (Figure 1). The background characteristics of the patients are presented in Table 1. The open repair group was younger than the endovascular repair group (48.2 vs. 56.5 years, P=0.005), and more open repairs than endovascular repairs were performed in the age group of 18–29 years (Figure 2). More endovascular repairs were performed in academic hospitals than in non-academic hospitals. Conversely, more open repairs were performed in non-academic hospitals. Endovascular repair was performed more often in higher-volume hospitals than in lower-volume hospitals. There were fewer head injuries in the open repair group than in the endovascular repair group (7.9% vs. 20.6%, P=0.02). More blood transfusions and albumin were administered in the open repair group than in the endovascular repair group (Table 2).

Figure 1.

Patient selection for analysis in a nationwide retrospective cohort study of thoracic aortic injury in Japan. ER, emergency room.

Table 1. Background Characteristics of the Patients Analyzed in a Nationwide Retrospective Cohort Study of Thoracic Aortic Injury in Japan

	Non-repair (n=415)	Endovascular repair (n=126)	Open repair (n=76)	P value (open vs. endovascular)
Age (years), mean±SD	59.1±20.5	56.5±18.5	48.2±22.4	0.005
Male sex, n (%)	269 (64.8)	85 (67.5)	58 (76.3)	0.20
Academic/non-academic hospitals, n (%)				0.001
Academic	135 (32.5)	76 (60.3)	28 (36.8)
Non-academic	280 (67.5)	50 (39.7)	48 (63.2)
Teaching/non-teaching hospitals, n (%)				0.12
Teaching	278 (84.2)	110 (87.3)	60 (78.9)
Non-teaching	59 (14.2)	16 (12.7)	16 (21.1)
Hospital volume, n (%)				0.01
1	92 (22.2)	12 (9.5)	17 (22.4)
2–5	184 (44.3)	59 (46.8)	38 (50.0)
>5	139 (33.5)	55 (43.7)	21 (27.6)
Consciousness level (JCS score), n (%)				0.46
0	167 (40.2)	60 (47.6)	40 (52.6)
1–3	52 (12.5)	24 (19.0)	10 (13.2)
10–30	35 (8.4)	15 (11.9)	13 (17.1)
100–300	161 (38.8)	27 (21.4)	13 (17.1)
Coexisting injury, n (%)
Head injury	50 (12.0)	26 (20.6)	6 (7.9)	0.02
Hemothorax	85 (20.5)	29 (23.0)	14 (18.4)	0.48
Lung contusion	44 (10.6)	16 (12.7)	12 (15.8)	0.54
Abdominal injury	49 (11.8)	25 (19.8)	10 (13.2)	0.25
Kidney injury	11 (2.7)	4 (3.2)	2 (2.6)	1.0
Pelvic fracture	78 (18.8)	25 (19.8)	12 (15.8)	0.57
Spinal fracture	66 (15.9)	14 (11.1)	6 (7.9)	0.63

JCS, Japan Coma Scale.

Figure 2.

Treatment procedure by age group in a nationwide retrospective cohort study of thoracic aortic injury in Japan. There is a significant difference in the proportion of endovascular repairs to open repairs between the age group of 18–29 years and the other groups (36.3%, 12/39 vs. 67.5%, 114/169, P<0.001).

Table 2. Treatments, Complications, and Outcomes of the Patients Analyzed in a Nationwide Retrospective Cohort Study of Thoracic Aortic Injury in Japan

	Non-repair (n=415)	Endovascular repair (n=126)	Open repair (n=76)	P value (open vs. endovascular)
Blood transfusion, n (%)
Red blood cells	151 (36.4)	90 (71.4)	57 (75.0)	0.63
Fresh-frozen plasma	96 (23.1)	64 (50.8)	53 (69.7)	0.009
Platelets	42 (10.1)	37 (29.4)	49 (64.5)	<0.001
Total amount of blood transfusion, mean±SD	2,145±2,517	2,593±2,763	4,498±4,326	0.001
Albumin use, n (%)	93 (22.4)	60 (47.6)	53 (69.7)	0.002
Interventions, n (%)
Cardiopulmonary bypass	6 (1.4)	0 (0)	60 (78.9)	<0.001
ECMO	6 (1.4)	0 (0)	3 (3.9)	0.05
Intermittent hemodialysis	3 (0.7)	7 (5.6)	6 (7.9)	0.73
Continuous renal replacement therapy	14 (3.4)	7 (5.6)	6 (7.9)	0.56
Cerebral infarction after admission	6 (1.4)	3 (2.4)	3 (3.9)	0.67
Outcome, n (%)
Died in emergency room	85 (20.5)	0 (0)	0 (0)	–
Death within 24 h	170 (41.0)	2 (1.6)	6 (7.9)	0.06
In-hospital mortality	188 (45.3)	7 (5.6)	12 (15.8)	0.02
Median length of hospital stay, days (quartile)	4 (35)	31 (39)	35 (43)	0.36

ECMO, extracorporeal membrane oxygenation.

The in-hospital mortality rate for the endovascular repair, open repair, and non-repair groups was 5.6%, 15.8%, and 45.3%, respectively. The Kaplan-Meier survival plots after admission for the difference between the open repair group and endovascular repair group are presented in Figure 3. Although there was no significant difference in the length of hospital stay, the survival rate was higher in the endovascular repair group than in the open repair group (log-rank χ²=4.9; P=0.03).

Figure 3.

Kaplan-Meier survival plots after admission for differences between the open repair group and endovascular repair group in a nationwide retrospective cohort study of thoracic aortic injury in Japan. The in-hospital survival rate was higher in the endovascular repair group than in the open repair group (log-rank χ²=4.9; P=0.03). The non-repair group is also shown for reference.

There was no difference in the interval from admission to operation between the endovascular and open repair groups (median days, open repair group vs. endovascular repair group, 1 day vs. 2 days, P=0.75) (Figure 4).

Figure 4.

Interval from admission to treatment procedure and mortality among patients in a nationwide retrospective cohort study of thoracic aortic injury in Japan. The days from admission to treatment procedure were categorized into 3 groups (1, 2–6, and ≥7). (A) No association in the proportion between the interval and treatment procedures (P=0.56). (B) Significant difference in mortality between the endovascular and open repair groups at day 1 (*endovascular vs. open, 8.1% vs. 25.6%, P=0.02).

Figure 5 shows the proportion of endovascular repair use among patients with repair over time. The proportion of repairs performed using an endovascular approach increased significantly (Mantel-Haenszel trend test, P<0.001). During the study period, the crude in-hospital mortality did not change significantly (Mantel-Haenszel trend test, P=0.10) (Figure 6).

Figure 5.

Proportion of endovascular repair among patients with repair over time in a nationwide retrospective cohort study of thoracic aortic injury in Japan. The proportion of endovascular repair use among all repairs performed increased significantly (Mantel-Haenszel trend test, P<0.001).

Figure 6.

Crude in-hospital mortality over time (Mantel-Haenszel trend test, P=0.10) in a nationwide retrospective cohort study of thoracic aortic injury in Japan.

Discussion

The results from the present Japanese nationwide database study of 234 hospitals suggested that the in-hospital survival rate of thoracic aortic injury was higher in the endovascular repair group than in the open repair group. Although the crude in-hospital mortality did not change significantly during the study period, the proportion of repairs performed using an endovascular approach increased significantly from 2007 to 2012 for treatment of thoracic aortic injury in Japan.

The strength of the present study was the evaluation of thoracic aortic injury, a life-threatening and relatively rare injury, using a nationwide database. In fact, approximately 30% of all study patients died within 24 h. Most of them did not receive curative treatment, including endovascular treatment or open surgery. We speculate that immediate aortic repair was not feasible for many injured patients, particularly those with serious coexisting injuries such as head, pulmonary, or cardiac injuries, or other serious medical comorbidities. The present nationwide results from Japan are similar to the results of a recent systematic review that included 139 studies.¹⁴ Specifically, the mortality rate for patients who were not repaired was 46% (45.3% in the present study), while the mortality rates for patients who were managed by endovascular repair and open repair were 9% and 19%, respectively (5.6% and 15.8% in the current study).¹⁴

Our study suggested that the proportion of endovascular repairs to open repairs has been increasing recently in Japan. Moreover, patients who were able to undergo endovascular repair had better in-hospital survival than those who underwent open surgery. These results are consistent with the recent nationwide report from Canada¹⁸ and several previous observational studies.^10–16 The choice between open and endovascular repair for thoracic aortic injury should be individualized, taking into account the patient’s specific injuries, age, anatomy, and other comorbidities. In fact, as clearly shown in Figure 2, more open repairs were performed than endovascular repairs in the age group of 18–29 years. We speculate that this may relate to the special anatomy of an acutely angled aortic arch in young people and the unknown long-term results of endovascular treatment for young patients.⁵ Several studies have suggested that high-risk patients with favorable anatomy may be best-suited to endovascular repair if appropriate equipment and expertise are available.^18,21–25 However, patients with unfavorable anatomy may be better served by open repair.^1,23 The present study was not able to determine which procedure was related to better survival, and this issue should be determined in future studies. However, because it may be difficult to perform randomized trials for this life-threatening and rarely hospitalized injury, the present nationwide study may provide the best attainable level of evidence on this issue.

Although the number of cases in this nationwide study (n=617) was similar to that in the nationwide report from Canada (n=487),¹⁸ we evaluated data from 234 hospitals during a 51-month period. Our data suggested that thoracic aortic injury is only encountered at an average level of 0.62 cases/institution/12 months in Japan. Interestingly, our results indicated that physicians in charge of high-volume institutions and academic hospitals were more likely to choose endovascular repair than open repair. Although our sample size was too small to discuss the relationship between hospital volume and in-hospital mortality, the present study will add new information to the debate about regionalization of severe trauma patients (ie, trauma-care center).²⁶

Study Limitations

First, although the study population was large and covered more than 90% of tertiary-care emergency hospitals (where all patients with aortic injury must be transported within the emergency medical system), it was not a complete population-based study. Second, information on the type and degree of aortic injury, aortic anatomy, physiologic data, and cause of death were not available in the DPC database. Third, some of the out-of-hospital cardiopulmonary arrest patients with multiple traumatic injuries could not be diagnosed as thoracic aortic injury in clinical practice. Thus, the number of aortic injury patients who died in the emergency room might be underestimated in the current study. Thus, all of these limitations should be addressed in the future by well-designed, large-sample, multination, prospective studies.

In conclusion, the present nationwide study suggests that the proportion of repairs performed using an endovascular approach for the treatment of thoracic aortic injury in Japan increased from 2007 to 2012. Future large, prospective, multination trials are required to further evaluate the effects of endovascular repair in patients with thoracic aortic injury.

Disclosures

Conflict of Interest statement: The authors declare no conflicts of interest.

Funding: Dr Horiguchi, Professor Fushimi, and Professor Yasunaga received grant support from the Ministry of Health, Labour and Welfare of Japan (Research on Policy Planning and Evaluation, Grant No. H26-Policy-011). The funders had no role in the execution of this study or interpretation of the results.

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