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Department of Radiography, Sør-Trøndelag University College (HiST), Trondheim, NorwayFaculty of Medicine, Norwegian Research Centre for Electronic Patient Records (NSEP), Norwegian University of Science and Technology (NTNU), Trondheim, Norway
Department of Sociology and Political Science, Norwegian University of Science and Technology (NTNU), Trondheim, NorwayDepartment of Public Health, University Medical Center Rotterdam, Rotterdam, The Netherlands
Faculty of Medicine, Norwegian Research Centre for Electronic Patient Records (NSEP), Norwegian University of Science and Technology (NTNU), Trondheim, NorwayDepartment of Computer and Information Science, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
To study incidence, handling and outcome of patients hospitalised with symptomatic and ruptured abdominal aortic aneurysm in Norway.
Design, material and methods
Retrospective study of 1291 patients, between January 2008 and August 2010 using the National Patient Registry and a regional vascular surgery registry. We applied a stepwise logistic regression model to detect differences in regional in-hospital mortality.
385/711 (54%) patients hospitalised for aneurysm rupture, rAAA (ICD-10: I71.3), died. The odds of dying varied with a factor 2.3 between the extreme regions. 475/711 (67%) underwent repair, 323 survived, giving an in-hospital mortality rate of 32% after surgery. Older patients were significantly less likely to be transported for surgery. The overall incidence for patients aged >50 was 16.6 rAAA per 100 000 person-years. There was remarkable variation across counties with rates between 7.7 and 26.8. A total of 580 patients were hospitalised with suspected symptomatic aneurysms (ICD-10:I71.4, acute admission); 224 (39%) were treated with aneurysm repair, 356 (61%) were discharged without repair without a significant difference across health regions.
For rAAA, we found substantial geographical variations in incidence, surgery and patient outcome. These results highlight the need for increased awareness about the condition and suggest ways to improve care trajectories to reduce delay to surgery, thereby minimising rupture mortality.
In this study, we investigated the incidence and treatment pattern of patients with emergency, non-ruptured AAA and rAAA in different regions in Norway, based on data from the nationwide Norwegian Patient Registry (NPR) and the Norwegian Vascular Surgery Register, NORKAR. Most of the patients with ruptured AAA are treated with open repair, but some institutions perform EVAR in suitable patients. Norway is divided into four Regional Health Authorities, each with its regional university hospital and several hospital trusts. The main questions of this study are whether there are any regional differences in the incidence of rAAA, the handling of patients with rAAA and how this affects the outcome.
Materials and Methods
The NPR is a nationwide health register containing a variety of data points on health-care services offered in Norwegian hospitals. Reporting is mandatory for all hospitals and reimbursement is based on the reported figures. NORKAR, the national quality registry for vascular surgery, offers de-identified clinical information of patients undergoing vascular surgery, including both elective and emergency aneurysm surgery. Identifiable information is, however, stored by local NORKAR registries at hospital level. Local NORKAR data were linked to the NPR data via the common Norwegian unique person identification number. Unlike NPR, reporting to NORKAR is voluntary and based on written informed patient consent. Permission to use the NPR data was obtained from Norwegian Directorate of Health. The committee of NORKAR permitted the use of the local registry data. This study was approved by the Regional Committee for Medical Research Ethics (reference no. 2010/1980).
We performed a retrospective cross-sectional study of patients with ruptured or symptomatic aortic aneurysm presenting at Norwegian hospitals between 1 January 2008 and 31 August 2010. The main source of data was derived from the national patient registry (NPR). Additional data for a minor subset were obtained from local NORKAR registry. We included all patients hospitalised with ICD-10 diagnosis codes I71.3 for rAAA, and I71.4 combined with acute presentation indicating a symptomatic abdominal aortic aneurysm. The NPR data set provided demographics (gender, age in 10-year intervals, residence and ZIP-codes), principal diagnosis and bi-diagnosis, surgical procedures, discharge status and administrative data (admission and discharge time, readmission(s), hospital and health region identifiers). This data set also included information about the patient contacts before and after the AAA hospitalisation episode, for example, outpatient visits or hospitalisation for other reasons. The local NORKAR data set provided demographics (gender, age and residence), principal diagnosis and risk factors, aneurysm parameters, surgical procedures, complications, discharge status and administrative data (operation and discharge time, readmission(s), hospital and health region identifiers).
The main end point was in-hospital mortality defined as death during the relevant hospitalisation episode. Patients who had contact with the specialist health-care system for abdominal aortic aneurysm prior to the actual admission were considered to have a known aneurysm.
Population figures including age and gender for the calendar years of 2008–2010 were obtained from the Central Bureau of Statistics of Norway. Incidence rates, age and gender standardised rates were calculated using the official figures for 2009.
Following the descriptive analysis, three multiple logistic regression models were conducted to detect differences in in-hospital mortality by health region. Models were made in a stepwise procedure, in which the first model only included the regional variables as explanatory factors. The second model was controlled for demographic variables (age and gender), while the third model also contained a variable describing whether the hospital admission involved a surgical intervention. This stepwise procedure was chosen to identify and rule out the influence of gender, age and surgery on the regional disparities in mortality. Odds ratios were calculated with 95% confidence intervals (CIs). Frequency distribution of number of rAAA cases, mortality and surgery rates is reported in Table 1. CIs were calculated by application of Clopper–Pearson exact method. Differences in proportions were evaluated using Pearson's chi-squared test of independence (p < 0.05). The statistical analyses were performed using Statistical Package for the Social Sciences (SPSS)18 and Minitab 16.
Table 1Ruptured AAA (rAAA) cases, surgery and in-hospital mortality rates by treating hospital regions.
Number of cases presenting at hospitals in the period of 2008–2010 is based on patient's treating region and not on patient's region of residence. The number of cases also includes three patients without Norwegian citizenship.
Mortality rate without surgery 98.7% (95%CI = 96.3–99.7%; n = 233).
% (95% CI; n)
32% (28–36%; 152)
36% (31–42%; 103)
35% (23–48%; 21)
23% (14–34%; 17)
20% (10–32%; 11)
a Number of cases presenting at hospitals in the period of 2008–2010 is based on patient's treating region and not on patient's region of residence. The number of cases also includes three patients without Norwegian citizenship.
b Mortality rate without surgery 98.7% (95%CI = 96.3–99.7%; n = 233).
Between January 2008 and August 2010, 580 patients presented at Norwegian hospitals with an emergency, non-ruptured AAA, emAAA (admission class emergency, ICD-10: I71.4). A total of 224 patients (39%) were operated during the hospital stay, consistent with the diagnosis of symptomatic aneurysm. The other 356 (61%) patients in this group were discharged without repair, indicating that they did not have symptoms caused by their AAA. There was no significant difference in the discharge rate across health regions (Clopper–Pearson exact CI: 95%): ‘South-East’ = 227/361 [58–68%], ‘Central Norway’ = 60/91 [55–76%], ‘West’ = 40/76 [41–64%], and ‘North Norway’ = 29/52 [41–70%]. Furthermore, of the 580 cases, 49 (8%) were readmitted for elective repair within the study period, and 93 (16%) had subsequent outpatient visits for their AAA within the study period. We have no additional data about the remaining 214 (37%) patients, indicating that they did not have further admissions or outpatient visits.
A total of 711 patients were diagnosed as rAAA (ICD-10: I71.3). Using 2009 population as basis, this translates into annual crude incidence rates of 1.8 [95% CI from 1.4 to 2.2] for repaired emAAA, and 5.6 [95% CI from 4.9 to 6.2] rAAA patients per 100 000 inhabitants. The male/female incidence ratio was 3.0:1/4.4:1 for rAAA/emAAA, respectively. The incidence rates in patients aged>50 were, however, (5.2 [95% CI from 4.1 to 6.4] for the emAAA group and 16.6 [95% CI from 14.6 to 18.7]) for the group of rAAA patients. For the rAAA group, incidence rates clearly increased with age, the most marked increased change from the age of 70 (Fig. 1).
For rAAA patients, incidence rates, measured over population age above 50, varied widely between counties, with a 3.5-fold difference between the most extreme values (Fig. 2). On the regional level, the incidence rates ranged from 9.7 to 21.7 (population age ≥50 years).
Trajectory, operation rate and mortality of patients with rAAA
Fig. 3 illustrates the nationwide trajectory of patients admitted to hospitals with aneurysm rupture. A total of 145 of 711 (20%) patients presented at a hospital without AAA surgery service. Of these, 87 (60%) patients were subsequently transferred to a hospital with vascular surgery service. As many as 75 (86%) of the transferred patients underwent repair. Gender did not influence the decision for transportation. However, significant difference was found in age between the patients transferred and the patients that were not transferred (p < 0.001). The majority of the non-transfers belonged to the higher age categories (median age category was 80–89).
Overall, 475 of 711 (67%) patients with rAAA underwent surgery (Table 1); most of these had an open repair. The surgical rates varied substantially across regions, from 53% to 79% (Table 1) even after controlling for age and gender (logistic regression model). A total of 385 of 711 rAAA patients (54%) succumbed during hospital stay, irrespective of age, gender or surgery (Table 1). Even among the patients who underwent surgery, the overall in-hospital mortality rate was as high as 32% (n = 152), ranging from 20% to 36% between regions.
To investigate the effect of having a previously known AAA, we identified a nationwide sub-group of 448 patients presenting with rupture between January 2009 and August 2010. Of these, 43 patients (9.6%) had been registered with an aneurysm less than a year before hospitalisation: median time between the latest outpatient episode and admission date was 93 days (range 2–338 days). For about 75%, this interval was less than 6 months. However, having a prior detected aneurysm did neither exhibit significant influence on surgical rates, nor in-hospital mortality rates: Among the 43 patients having a previously known aneurysm, 30 (70%) underwent repair, nine of these 30 (30%) died. In comparison, in the remaining 405 patients of this sub-group of 448 patients, surgery was carried out on 263 patients (65%), 94 of whom died (36%).
In-hospital mortality: regional disparities
Table 2 presents the odds ratios of in-hospital rAAA mortality that were obtained from three logistic regression analyses, in which the explanatory variables were included in a stepwise procedure. The first logistic regression model contained only hospital regions as explanatory variables, while the second model also included (as an extension of model 1) gender and age category. The final model extended model 2 with a variable for surgery. As can be seen from Table 2, in-hospital mortality varied substantially between health regions. More specifically, the odds of dying were 2.28 times higher in Central Norway compared to ‘North Norway’ (see Model 1 in Table 2). The corresponding odds ratios were 2.11 between the ‘South-East’ and ‘North’ and 1.81 between ‘West’ and ‘North’. Except for the last, these were all statistically significant differences. When we included the demographic variables of gender and age (model 2), these regional effects sustained. After including the variable of surgery (model 3), only the ‘South-East’ versus ‘North’ association still remained significant while the differences between ‘Central Norway’ and ‘North’ and between ‘West’ and ‘North’ were insignificant.
In this report, we used data from a national patient registry to estimate the incidence of rAAA and emAAA in Norway and describe the trajectories and clinical outcomes of these patients. So far, nationwide systematic studies about these trajectories and patterns are lacking.
Both the overall incidence rate, age- and gender-specific incidence rates align well with that reported by others.
The incidence of rAAA varied, however, greatly between the different regions of the country. This could neither be attributed to differences in the overall incidence and prevalence of atherosclerotic disease nor to variations in the number of patients diagnosed with AAA and operated before rupture.
One might speculate that the observed differences are due to differences in awareness of the disease or in other factors within the health-care system, but at present this question remains unanswered.
When it comes to the services that were offered to patients that were admitted with rAAA, we found large differences in the odds of dying for patients operated for rAAA between the health regions, with a factor of 2.3 between the two extremes (see Table 2). In the northernmost region, where relatively fewer patients with rAAA turned up at the hospital, a larger proportion underwent surgery, and of these, a larger proportion survived. By way of comparison, the largest county in Northern Norway, Finnmark has an area the size of Denmark, but a population of only 70 000 served by two hospitals. This leads to speculations that these differences might be due to longer transportation distances in northern Norway, so that only the fittest patients are still operable upon arrival at hospital. This might even influence the decision to transport a patient – but we do not have sufficient data to prove this.
The proportion of rAAA patients that underwent repair varied significantly between regions. However, whether these differences are due to regional differences in selection criteria or due to limited access to vascular surgical services is not known.
Approximately, 86% of patients transferred from hospitals without vascular service were operable. This aligns well with findings by others that critically ill patients can be stabilised at one hospital, transported to an operating hospital and found eligible for surgery at arrival.
Three patients apparently survived rupture without repair (and were not reported dead by NPR later). This may sound surprising, but is in accordance with other observations of survivors after computed tomography (CT) verified aneurysm rupture.
Aneurysm surgery requires extensive support from radiological services. Imaging analyses are critical for making the diagnosis and in deciding whether the patient is eligible for surgery. Imaging analyses also contribute to the analysis as to whether the patient can be stabilised and transported to another hospital, if required. Shared access to all images taken is crucial for decision making, procedure planning and to make necessary preparations, prior to arrival of the patient.
Irrespective of screening facilities, however, our data indicated that 10% of the patients with a known aneurysm developed a rupture. We cannot answer the question how many of the Norwegian patients under surveillance for AAA develop rupture, as there is no surveillance registry, but the proportion of previously known aneurysms in the group with rAAA may well be representative for the national level. However, patients having a previously known aneurysm were not more likely to be operated and did not display a lower rate of in-hospital death than those hospitalised with an unknown aneurysm. Some patients in ‘watchful-waiting’ are possibly ineligible for elective surgery due to co-morbidities or other factors contributing to a significant risk of an unfavourable outcome. However, when a rupture develops, the prospect of immediate death changes the risk assessment, and surgery now becomes a more favourable option.
It is important to note that the majority of the emAAA cases apparently had no symptoms caused by a symptomatic aneurysm during the recorded hospital stay, and did not represent true medical emergencies. This may indicate that threshold for emergency admission for patients with known aortic aneurysm is low. Further research is needed to explore the trajectories and outcomes of these patients,
in particular, for the group of patients discharged without undergoing surgery. A few may have had prohibitive co-morbidity, but most of them were probably followed for their AAA with regularly imaging, administered by their GP, which is usual practice for aneurysms under intervention threshold. However, these patients are difficult to follow with retrospective data collection and should be followed prospectively.
Further research is also necessary to address whether the observed difference in the incidence of rAAA are due to a real difference in the prevalence of AAA or other factors. This would entail screening programmes in at least two regions with different incidences. Considering the transportation factor, we would advocate screening especially in remote areas of Norway.
This study has a number of limitations. Despite the fact that the NPR data represent a valuable information source for research; the data have been collected for reimbursement purpose and not for research objectives. This study collected data based on diagnosis codes and not administrative procedure ones. Surgical procedure codes were not always consistent with the diagnosis codes, thus several cases had to be traced and checked manually. The NPR registry does not record cause of death, only whether or not the patient was discharged alive. We have assumed that for I71.3 and acute I71.4, the diagnosis also was the cause of death. Given that the registry is limited to hospitalisation episodes, we cannot calculate mortality beyond in-hospital. Due to de-identified data in the NORKAR central registry, matching with the nationwide NPR was not possible. However, the person identifiable in the local NORKAR registry data showed good validity compared to NPR data (∼94%).
BB was funded by Sør-Trøndelag University College and The Liaison Committee between the Central Norway Regional Health Authority (RHA) and the Norwegian University of Science and Technology (NTNU). ADL by the Research Council of Norway (VERDIKT).
Conflict of interest
We would like to thank Professor Hans O Myhre for feedback on interim findings of research and Wenche Rønning for data preparation for NORKAR.
In this issue of the Journal, Brattheim et al.1 assessed the regional disparities in incidence, handling and outcomes of patients suffering from ruptured or symptomatic abdominal aortic aneurysm (AAA) in Norway. Analysing their National Patient Registry, they found that 1291 patients developed ruptured or symptomatic AAA during a recent continuous 32-month period. Among those, 711 patients (55%) presented with ruptured AAA (rAAA), or an overall incidence of 16.6 rAAA per 100,000 person-years for patients aged >50 years.
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