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Editor's Choice – Distribution of Care and Hospital Incidence of Carotid Endarterectomy and Carotid Artery Stenting: A Secondary Analysis of German Hospital Episode Data

Open ArchivePublished:May 06, 2021DOI:https://doi.org/10.1016/j.ejvs.2021.03.021

      Objective

      This is a description of the German healthcare landscape regarding carotid artery disease, assessment of hospital incidence time courses for carotid endarterectomy (CEA) and carotid artery stenting (CAS), and simulation of potential effects of minimum hospital caseload requirements for CEA and CAS.

      Methods

      The study is a secondary data analysis of diagnosis related group statistics data (2005–2016), provided by the German Federal Statistical Office. Cases encoded by German operation procedure codes for CEA or CAS and by International Classification of Diseases (ICD-10) codes for carotid artery disease were included. Hospitals were categorised into quartiles according to annual caseloads. Linear distances to the closest hospital fulfilling hypothetical caseload requirements were calculated.

      Results

      A total of 132 411 and 33 709 patients treated with CEA and CAS from 2012 to 2016 were included. CEA patients had lower rates of myocardial infarction (1.4% vs. 1.8%) and death (1.2% vs. 4.0%), and CAS patients were more often treated after emergency admission (38.1% vs. 27.1%). Age standardised annual hospital incidences were 67.2 per 100 000 inhabitants for CEA and 16.3 per 100 000 inhabitants for CAS. The incidence for CEA declined from 2005 to 2016, with CAS rising again until 2016 after having declined from 2010 to 2013. Regarding distance from home to hospital, centres offering CEA are distributed more homogeneously across Germany, compared with those performing CAS. Hypothetical introduction of minimum annual caseloads (> 20 for CEA; > 10 for CAS) imply that 75% of the population would reach their hospital after travelling 45 km for CEA and 70 km for CAS.

      Conclusion

      Differences in spatial distribution mean that statutory minimum annual caseloads would have a greater impact on CAS accessibility than CEA in Germany. Presumably because of a decline in carotid artery disease and a transition towards individualised therapy for asymptomatic patients, hospital incidence for CEA has been declining.

      Keywords

      This study includes the first simulation study to estimate effects of potential minimum caseload requirements for carotid endarterectomy (CEA) and carotid artery stenting (CAS). It demonstrates that centres performing CEA are distributed more homogeneously across Germany compared with those offering CAS. Therefore, with respect to accessibility of care, the introduction of minimum caseload regulations would have a greater effect on CAS than CEA. Furthermore, this paper describes hospital incidence time courses of CEA and CAS, and complication rates dependendent on annual centre volumes in Germany.

      Introduction

      The European population is affected by approximately 1.4 million strokes and 1.1 million stroke related deaths annually, and thus faces a major burden of disease.
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      and others not detecting significant outcome differences.
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      Until recently, no guideline recommendations have been released claiming minimum annual caseload thresholds to perform CEA or CAS safely.
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      The 2020 German-Austrian Guidelines on diagnostics, treatment, and aftercare of carotid artery disease for the first time recommended that CEA and CAS procedures be offered only by institutions with annual caseloads exceeding 20 and 10, respectively.
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      Possibly beneficial effects of treatment centralisation (e.g., lower peri-operative complication rates, shorter hospital stays, lower treatment costs) are intrinsically tied to greater infrastructure capacity use (e.g. transportation to, from, and between hospitals, with associated costs). Furthermore, centralisation necessitates re-allocation of resources towards a number of high volume centres, alongside an inversely directed outsourcing of less specialised sectors, and mandates re-organisation of surgical training.
      This study aimed to describe the German healthcare landscape on carotid artery disease regarding hospital incidence time courses for CEA and CAS, and peri-operative complication rates in dependency of annual centre volumes. Furthermore, simulation studies were performed to assess the potential effects of minimum hospital caseload requirements for CEA and CAS on accessibility of care.

      Methods

      Data extraction

      The principal methods of this study have been described elsewhere.
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      Nationwide analysis of risk factors for in-hospital mortality in patients undergoing abdominal aortic aneurysm repair.
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      • et al.
      Editor's choice - high annual hospital volume is associated with decreased in hospital mortality and complication rates following treatment of abdominal aortic aneurysms: secondary data analysis of the nationwide German DRG statistics from 2005 to 2013.
      Data were extracted from diagnosis related group (DRG) statistics of the German Federal Statistical Office (GFSO) from 2005 to 2016 for secondary data analysis.
      As virtually all (excluding military and psychiatry services) case related data on patient hospital episodes are obliged to be submitted to the GFSO by the German Institute for the Hospital Remuneration System (InEK) by §21 Hospital Finance Act (Krankenhausentgeltgesetz), this analysis by approximation is a full survey of German population and hospitals. The legal basis for the use of DRG statistics for secondary data analysis is the German Federal Statistics Act (§3a; §16). The study protocol was approved by the ethics committee of the Medical Faculty, Technical University of Munich. The study was conducted in compliance with good practice of secondary data analysis,
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      • Grobe T.G.
      • et al.
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      and the manuscript was written in accordance with the STROSA guideline (2nd version).
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      • Harling M.
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      • Horenkamp-Sonntag D.
      • et al.
      [A consensus German reporting standard for secondary data analyses, version 2 (STROSA-STandardisierte BerichtsROutine fur SekundardatenAnalysen)].
      Controlled remote data processing was used to access data on servers of the GFSO according to data protection rules.
      • Kuhnl A.
      • Erk A.
      • Trenner M.
      • Salvermoser M.
      • Schmid V.
      • Eckstein H.H.
      Incidence, treatment and mortality in patients with abdominal aortic aneurysms.
      • Krautz C.
      • Nimptsch U.
      • Weber G.F.
      • Mansky T.
      • Grutzmann R.
      Effect of hospital volume on in-hospital morbidity and mortality following pancreatic surgery in Germany.
      • Nimptsch U.
      • Haist T.
      • Krautz C.
      • Grutzmann R.
      • Mansky T.
      • Lorenz D.
      Hospital volume, in-hospital mortality, and failure to rescue in esophageal surgery.
      • Nimptsch U.
      • Krautz C.
      • Weber G.F.
      • Mansky T.
      • Grutzmann R.
      Nationwide in-hospital mortality following pancreatic surgery in Germany is higher than anticipated.
      • Nimptsch U.
      • Mansky T.
      Trends in acute inpatient stroke care in Germany--an observational study using administrative hospital data from 2005-2010.
      Data on the GFSO and Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBSR; INKAR database) were linked. Case specific DRGs were linked to the DRG catalogue of the InEK. Sex and age specific population, district type (settlement structure, defined by BBSR), and length of hospital stay were linked. To identify the treating hospital, the institutional identification (“Institutskennung”) was linked to individual hospital addresses (conducted by the GFSO). This allowed calculation of distances between patients’ homes (centre of postcode area) and actual hospital location. Data protection regulations were realised by GFSO employees.

      Study population

      Administrative codes used in this analysis are listed in Table S1. All DRG cases encoded by German operation procedure codes (OPS) for CEA or CAS, and by International Classification of Diseases (ICD-10) codes for carotid artery disease were included. Patients not undergoing treatment for carotid artery disease and those transferred to another hospital without treatment were excluded. Furthermore, patients were excluded if treated for traumatic injury of the carotid artery.
      Although patients undergoing both, CEA and CAS are few, exclusion of double counts was not possible with the current study design.
      All analyses refer to cases rather than patients, as a link to individual data was not feasible.

      Hospital incidence, patient and hospital characteristics, outcomes

      To report treatment and hospital incidence trends, data from 2005 to 2016 were used (Fig. 1). Incidences were age standardised using the European standard population 2013.

      Gesundheitsberichterstattung des bundes: Standardbevölkerung. Available at: http://www.gbe-bund.de [Accessed 31 March 2016.].

      The annual volume analyses covered the years 2012–2016.
      Recent patient and treatment characteristics and outcomes are reported for 2016 (patient level). The ICD-10 and OPS codes used for the description of comorbidities and complications are listed in Table S1.

      Statistical analyses

      Absolute numbers and percentages are given for categorical variables. Medians with first (Q1) and third quartiles (Q3) are given for continuous variables. For hospital level characterisation of patients, Q1 and Q3 are reported to describe the variance within the respective hospital volume group.
      In a hypothetical approach for minimum caseload requirements, the linear distance to the closest hospital fulfilling the arbitrary set caseload requirement (i.e., 1, 10, 20, 25, 30, 40, 50 cases per year) was calculated for the whole population and for both CEA and CAS. Furthermore, the hypothetical reduction of hospitals treating carotid artery disease was estimated for the same minimum caseload requirements.
      As the database is a full survey, calculation of confidence intervals or p values was considered not reasonable.
      Controlled remote data processing was carried out using SAS (version 9.2 for Microsoft Windows, Copyright 2015, SAS Institute Inc., Cary, NC, USA). Analyses and graphics were performed using R (version 3.5.1, the R Foundation, www.r-project.org) and Microsoft Excel (Version 2013, Microsoft Corporation, Redmond, USA).

      Results

      Patient characteristics

      A total of 33 340 patients were documented to have been treated for carotid artery disease in 2016 (Table 1). More than three quarters of the cohort underwent CEA . CAS patients achieved higher Elixhauser Scores (median score 7 vs. 5) compared with those who underwent CEA. CAS patients covered longer distances to reach the hospital (median linear distance 12.63 vs. 11.26 km) and had longer journey times (median driving time 18.35 vs. 16.39 minutes).
      Table 1Characteristics of all patients treated by carotid endarterectomy (CEA) or carotid artery stenting (CAS) in Germany in 2016
      CEA (n = 25 824)CAS (n = 7 516)Total (n = 33 340)
      Age – y73 (65–78)70 (62–77)72 (64–78)
       < 65 y6 279 (24.3)2 348 (31.2)8 627 (25.9)
       65 – 75 y10 115 (39.2)2 916 (38.8)13 031 (39.1)
       > 75 y9 430 (36.5)2 252 (30.0)11 682 (35.0)
      Male sex17 528 (67.9)5 181 (68.9)22 709 (68.1)
      Elixhauser Score5 (0–10)7 (2–13)5 (0–10)
      Hospital incidence per 100 000 inhabitants
      Directly standardised with European standard population 2013.
       Men42.912.355.2
       Women16.84.821.6
      Cerebrovascular diagnosis
       I65.2 as principal diagnosis or secondary diagnosis23 959 (92.8)5 675 (75.5)29 634 (88.9)
       I63 as only principal diagnosis1 431 (6.0)1 606 (21.4)3 037 (9.1)
       Others428 (1.8)228 (3.0)656 (2.2)
       I65.0/1 or I646 (0)7 (0)13 (0)
      Documented comorbidities
       Chronic ischaemic heart disease, I257 603 (29.4)2 129 (28.3)9 732 (29.2)
       Peripheral arterial occlusive disease, I70.223 075 (89.4)5 396 (71.8)28 471 (85.4)
       Hypertension21 746 (84.2)5 760 (76.6)27 506 (82.5)
       Chronic pulmonary disease2 652 (10.3)668 (8.9)3 320 (10.0)
       Diabetes mellitus7 754 (30.0)2 145 (28.5)9 899 (29.7)
       Renal failure4 361 (16.9)1 303 (17.3)5 664 (17.0)
      Patient residency
       Administratively independent city, KT16 493 (25.1)2 247 (29.9)8 740 (26.2)
       Urban county, KT210 237 (39.6)2 754 (36.6)12 991 (39.0)
       Rural county, KT34 787 (18.5)1 366 (18.2)6 153 (18.5)
       Sparsely populated county, KT44 200 (16.3)1 107 (14.7)5 307 (15.9)
      Distance from residency to hospital
       Linear distance – km11.26 (5.39–21.93)12.63 (5.71–26.02)11.52 (5.45–22.78)
       Driving time – min16.39 (8.95–27.85)18.35 (9.93–31.75)16.72 (9.17–28.85)
      Location of hospital
       Administratively independent city, KT111 723 (45.4)4 318 (57.5)16 041 (48.1)
       Urban county, KT27 224 (28.0)1 661 (22.1)8 885 (26.6)
       Rural county, KT33 295 (12.8)748 (10.0)4 043 (12.1)
       Sparsely populated county, KT43 454 (13.4)716 (9.5)4 170 (12.5)
      Data are presented as n (%) or median (first – third quartile). CEA = carotid endarterectomy; CAS = carotid artery stenting; KT = settlement structure type of district according to the Federal Institute for Building, Urban and Regional Research.
      Directly standardised with European standard population 2013.
      Figure 1
      Figure 1Flowchart for inclusion of patients treated by carotid endarterectomy (CEA) or carotid artery stenting (CAS) from 2005 to 2016 in Germany. Patients who underwent combinations of CEA/CAS, whose sex or residency was unknown, or whose residency was outside Germany were excluded from analyses.

      Hospital incidence time course between 2005 and 2016

      For CEA, hospital incidences were assessed between 2005 and 2016. The median age standardised annual hospital incidence over this time frame was 67.2 per 100 000 inhabitants (Fig. 2). In 2005, the hospital incidence amounted to 67.7 per 100 000 inhabitants, reached a maximum in 2009, and thereafter declined to 59.7 per 100 000 inhabitants in 2016.
      Figure 2
      Figure 2Age standardised incidence of carotid endarterectomy (CEA) and carotid artery stenting (CAS) procedures between 2005 and 2016 in Germany. Directly standardised with European standard population 2013.
      For CAS, data were available for the years 2010 through 2016. The median age standardised annual hospital incidence was 16.3 per 100 000 inhabitants. The incidence declined from 17.3 per 100 000 inhabitants in 2010 to 15.1 per 100 000 inhabitants in 2013 and thereafter increased to 17.1 per 100 000 inhabitants in 2016.

      Current carotid artery disease treatment and outcomes

      Data on the current management of carotid artery disease were retrieved for the year 2016 (Table 2). A total of 33 340 patients were treated, with 25 824 and 7 516 patients undergoing CEA and CAS, respectively. CEA procedures were performed in hospitals with a median annual caseload of 21, while the median caseload of centres offering CAS was 40.
      Table 2Management, treatment, and outcomes of patients treated by carotid endarterectomy (CEA) or carotid artery stenting (CAS) in Germany in 2016
      CEA (n = 25 824)CAS (n = 7 516)Total (n = 33 340)
      Hospital volume21 (8–48)40 (18–68)24 (10–53)
      Type of admission
       Scheduled admission16 660 (64.5)3 869 (51.8)20 529 (61.6)
       Emergency7 010 (27.1)2 867 (38.1)9 877 (29.6)
       Transferred from other hospital
      Containing a limited number of missing values because of data protection regulations.
      2 154 (8.3)780 (10.4)2 934 (8.8)
      Documented complications
       Acute myocardial infarction368 (1.4)135 (1.8)503 (1.5)
       Cardiopulmonary resuscitation239 (0.9)66 (0.9)305 (0.9)
      Treatment on ICU6 226 (24.1)1 006 (13.4)7 232 (21.7)
      Treatment on stroke unit731 (2.8)614 (8.2)1 345 (4.0)
      Prolonged ventilation1 031 (4.0)756 (10.1)1 787 (5.4)
      Duration of ventilation – min51 (16–190)57 (16–205)53 (16–197)
      Length of stay – days7 (5–11)5 (3–11)
      Mortality315 (1.2)298 (4.0)613 (1.8)
      Sex
       Male221 (1.3)179 (3.5)400 (1.8)
       Female94 (1.1)119 (5.1)213 (2.0)
      Hospital volume
      Based on data from 2012 to 2016.
       1st quartile64 / 3 884 (1.7)25 / 955 (2.8)89 / 4 839 (1.8)
       2nd quartile173 / 16 789 (1.0)59 / 2 314 (2.6)232 / 19 103 (1.2)
       3rd quartile360 / 33 806 (1.1)209 / 7 024 (3.0)569 / 40 830 (1.4)
       4th quartile846 / 77 932 (1.1)707 / 23 416 (3.0)1 553 / 101 348 (1.5)
      Data are presented as n (%) or median (first – third quartile). CEA = carotid endarterectomy; CAS = carotid artery stenting; ICU = intensive care unit.
      Containing a limited number of missing values because of data protection regulations.
      Based on data from 2012 to 2016.
      The proportion of emergency admissions was lower among CEA patients (27.1% vs. 38.1%).
      Regarding peri-operative complications, CEA patients had a lower rate of myocardial infarction (1.4% vs. 1.8%) and a lower mortality (1.2% vs. 4.0%) than CAS patients. Among CEA patients, mortality tended to be higher in men (1.3% vs. 1.1%), whereas female CAS patients had higher mortalities (5.1% vs. 3.5%) than their male counterparts.

      Annual caseload and distribution of care

      Hospitals were categorised into quartiles according to their annual caseload. The resulting hospital volume groups were characterised by 1–13, 14–34, 35–65, and > 65 CEA procedures, and 1–3, 4–8, 8–23, and > 23 CAS procedures per year, respectively.
      Over the five year period (2012–2016), 132 411 patients underwent CEA (Table 3). The majority (58.9%) of patients were treated in high volume (4th quartile) centres.
      Table 3Hospital level characteristics and outcomes depending on their annual carotid endarterectomy (CEA) caseload between 2012 – 2016
      Annual hospital CEA caseload
      1st quartile (1 – 13)2nd quartile (14 – 34)3rd quartile (35 – 65)4th quartile (> 65)Total
      Patients
      Row percentages.
      n
      3 884 (2.9)16 789 (12.7)33 806 (25.5)77 932 (58.9)132 411 (100)
      Hospitals
      Row percentages.
       2012136 (23.7)149 (26.0)144 (25.1)144 (25.1)573 (100)
       2013143 (24.7)152 (26.2)138 (23.8)147 (25.3)580 (100)
       2014156 (26.9)139 (24.0)143 (24.7)150 (25.9)580 (100)
       2015141 (24.0)146 (24.8)146 (24.8)140 (23.8)588 (100)
       2016147 (25.7)155 (27.1)141 (24.6)138 (24.1)573 (100)
      Location of hospital
       Administratively independent city, KT1214 (29.6)221 (29.8)225 (31.6)375 (52.2)1035 (35.8)
       Urban county, KT2244 (33.7)230 (31.0)217 (30.5)207 (28.8)898 (31.0)
       Rural county, KT3160 (22.1)151 (20.4)109 (15.3)71 (9.9)491 (17.0)
       Sparsely populated county, KT4102 (14.1)139 (18.8)160 (22.5)65 (9.0)466 (16.1)
      Patient collective in hospital
       Age – y72.5 (68.5–76)72.5 (70.5–74.0)72 (71.0–73.5)72 (71.0–73.0)72 (71.0–74.0)
       Elixhauser Score
      Median of the medians of each hospital with first and third quartile.
      6 (2–10)5 (2–7)5 (2–6)4 (2–5)5 (2–7)
       Men – %
      Median of the shares of each hospital in % with first and third quartile.
      0.67 (0.05–0.91)0.68 (0.6–0.75)0.69 (0.64–0.74)0.68 (0.64–0.71)0.68 (0.62–0.75)
       Linear distance – km
      Median of the medians of each hospital with first and third quartile.
      9.19 (5.55–14.93)9.69 (6.85–13.62)10.76 (7.38–14.81)11.67 (7.96–17.0)10.4 (6.97–14.95)
      Mortality64 (1.7)173 (1.0)360 (1.1)846 (1.1)1443 (1.1)
      Peri-operative myocardial infarction40 (1.0)160 (1.0)268 (0.8)703 (0.9)1171 (0.9)
      Data are presented as n (%) or median (first – third quartile). KT = settlement structure type of district according to the Federal Institute for Building, Urban and Regional Research.
      Row percentages.
      Median of the medians of each hospital with first and third quartile.
      Median of the shares of each hospital in % with first and third quartile.
      Overall mortality was 1.1%, with similarly low rates in 2nd through 4th quartile hospitals and the highest rate (1.7%) in 1st quartile centres.
      Between 2012 and 2016, 33 709 patients underwent CAS in Germany (Table 4). The majority of CAS procedures (69.5%) were performed in high volume centres. Most such centres offering CAS were situated in administratively independent cities (62.4%).
      Table 4Hospital level characteristics and outcomes depending on their annual carotid artery stenting (CAS) caseload between 2012 – 2016
      Annual hospital CAS caseload
      1st quartile (1 – 3)2nd quartile (4 – 8)3rd quartile (8 – 23)4th quartile (> 23)Total
      Patients
      Row percentages.
      955 (2.8)2 314 (6.9)7 024 (20.8)23 416 (69.5)33 709 (100)
      Hospitals
      Row percentages.
       2012108 (27.6)81 (20.7)108 (27.6)95 (24.2)392 (100)
       2013113 (29.5)83 (21.7)99 (25.8)88 (23.0)383 (100)
       2014100 (26.1)84 (21.9)97 (25.3)95 (24.8)383 (100)
       2015112 (29.8)84 (22.3)90 (23.9)100 (26.6)376 (100)
       2016107 (27.7)75 (19.4)97 (25.1)112 (29.0)386 (100)
      Location of hospital
       Administratively independent city, KT1183 (33.9)139 (34.2)188 (38.3)306 (62.4)816 (42.3)
       Urban county, KT2187 (34.6)144 (35.4)153 (31.2)95 (19.4)579 (30.0)
       Rural county, KT379 (14.6)61 (15.0)66 (13.4)42 (8.6)248 (12.9)
       Sparsely populated county, KT491 (16.9)62 (15.2)84 (17.1)46 (9.4)283 (14.7)
      Patient collective in hospital
       Age – y69 (63.0–75.0)70.5 (66.5–74.0)71 (67.0–73.0)70 (68.0–72.0)70 (67.0–73.0)
       Elixhauser Score
      Median of the medians of each hospital with first and third quartile.
      5 (0.25–10)5.5 (2.0–9.0)5 (2.0–8.0)6 (3.0–7.0)5 (2.0–8.0)
       Men – %
      Median of the shares of each hospital in % with first and third quartile.
      100 (50–100)75 (57–83)70 (60–80)69 (63–75)71 (60–85)
       Linear distance – km
      Median of the medians of each hospital with first and third quartile.
      10.59 (6.24–18.37)10.49 (6.95–16.29)11.59 (7.33–18.57)12.86 (9.02–19.89)11.4 (7.28–18.35)
      Mortality25 (2.6)59 (2.6)209 (3.0)707 (3.0)1 000 (3.0)
      Peri-procedural myocardial infarction4 (0.4)18 (0.8)77 (1.1)269 (1.2)368 (1.1)
      Data are presented as n (%) or median (first – third quartile). KT = settlement structure type of district according to the Federal Institute for Building, Urban and Regional Research.
      Row percentages.
      Median of the medians of each hospital with first and third quartile.
      Median of the shares of each hospital in % with first and third quartile.
      CAS patients treated at centres performing more than seven procedures annually (3rd and 4th quartiles) had mortality rates of 3%, whereas those treated in 1st and 2nd quartile hospitals had mortalities of 2.6%.
      Table S2 details caseload distributions for CEA and CAS within German hospitals. Between 2012 and 2016, patients underwent CEA or CAS in Germany in a mean of 638 hospitals. Among those, 37 institutions ranged within the 4th quartile for both CEA and CAS, whereas 12 hospitals performed only low numbers of CEA (1–13) and CAS (1–3). There were 251 institutions performing CEA, but no CAS procedures. In contrast, 58 hospitals offered CAS without performing any CEA.
      The Lorenz curve in Fig. S1 illustrates the more non-homogeneous distribution of care for CAS compared with CEA.
      Additional analysis was performed to detect differences in outcomes of institutions offering both CEA and CAS, or only one of these therapeutic options (Table S3). This demonstrated mortality was highest in centres offering only CAS (3.2%), followed by those offering both CEA and CAS (1.6%), and then those performing only CEA (0.8%).

      Hypothetical effects of minimum caseload requirements

      To estimate the effect of a potential introduction of statutory minimum caseload requirements on patients’ accessibility to care, the percentage of the German population was plotted against the distance from home to treating hospital for different minimum caseload scenarios (Fig. 3). When compared with CAS, the graphs for CEA illustrating different minimum caseload scenarios run closer, demonstrating smaller effects on care accessibility.
      Figure 3
      Figure 3Hospital accessibility for (A) carotid endarterectomy (CEA) and (B) carotid artery stenting (CAS) in relation to hypothetical minimum hospital caseloads in 2016 in Germany. The dashed line indicates 75%.

      Discussion

      The principal finding of the present study was that centres performing CEA are distributed more homogeneously across Germany compared with those offering CAS. Therefore, with respect to accessibility of care, the introduction of minimum caseload requirements would have a higher impact on CAS than CEA. Subordinate findings were a declining incidence of revascularisation procedures to treat carotid artery disease and lower complication rates in patients who underwent CEA compared with CAS.

      Distribution of care to treat carotid artery disease in Germany

      The present analysis revealed 251 hospitals performing CEA but no CAS procedures, while 58 hospitals performed CAS without offering CEA. Mortality was highest in centres performing only CAS. Although this study disrespects potential co-operation between centres, this observation points out two major issues with a potentially negative effect on quality of care. First, because of lower peri-operative complication rates, current evidence suggests CEA to be the standard of care for most carotid artery stenoses.
      • Naylor A.R.
      • Ricco J.B.
      • de Borst G.J.
      • Debus S.
      • de Haro J.
      • Halliday A.
      • et al.
      Management of atherosclerotic carotid and vertebral artery disease: 2017 Clinical Practice Guidelines of the European Society for Vascular Surgery (ESVS).
      ,
      • Eckstein H.H.
      • Kuhnl A.
      • Berkefeld J.
      • Lawall H.
      • Storck M.
      • Sander D.
      Clinical practice guideline: diagnosis, treatment and follow-up in extracranial carotid stenosis.
      However, certain risk groups of patients might benefit when treated with CAS rather than CEA. Therefore, centres offering one of these therapeutic options will not be able to treat all patient groups with the lowest possible peri-operative risk. Bearing in mind the possibility of confounding, this observation might be true particularly for institutions performing CAS only (Table S3). Furthermore, it is doubtful that hospitals performing only one treatment option have routine multidisciplinary team meetings to discuss treatment strategies (as recommended in international guidelines).
      • Naylor A.R.
      • Ricco J.B.
      • de Borst G.J.
      • Debus S.
      • de Haro J.
      • Halliday A.
      • et al.
      Management of atherosclerotic carotid and vertebral artery disease: 2017 Clinical Practice Guidelines of the European Society for Vascular Surgery (ESVS).
      ,
      • Eckstein H.H.
      • Kuhnl A.
      • Berkefeld J.
      • Lawall H.
      • Storck M.
      • Sander D.
      Clinical practice guideline: diagnosis, treatment and follow-up in extracranial carotid stenosis.
      Second, vascular access complications following CAS are not infrequent,
      • Tan K.T.
      • Cleveland T.J.
      • Berczi V.
      • McKevitt F.M.
      • Venables G.S.
      • Gaines P.A.
      Timing and frequency of complications after carotid artery stenting: what is the optimal period of observation?.
      underlining the necessity for a vascular surgeon permanently being on site, as recommended in the recently published German-Austrian carotid guidelines.
      • Eckstein H.H.
      • Kuhnl A.
      • Berkefeld J.
      • Lawall H.
      • Storck M.
      • Sander D.
      Clinical practice guideline: diagnosis, treatment and follow-up in extracranial carotid stenosis.
      The high proportion of patients treated by CAS (20.3% between 2012 and 2016) might be traced back to a high proportion of emergency admissions, occasionally requiring mechanical thrombectomy in combination with CAS.

      Hypothetical effects of minimum caseload requirements

      Although the present analysis was not able to account for secondary distribution effects (redistribution of patients to other hospitals after closing of a lower volume department), it provides the first ever estimate of how statutory minimum caseload requirements would affect the German healthcare landscape with respect to carotid artery disease. An increasing centralisation of care inevitably leads to greater travel distances for a certain proportion of the population. With hospitals performing CEA (Fig. 3A) distributed more evenly than those offering CAS (Fig. 3B), a hypothetical restriction of hospitals according to their annual caseloads would have a greater impact on travelling distances to receive CAS compared with CEA. If only those centres performing more than 20 and 10 cases were authorised to offer CEA or CAS, respectively, as recommended by the current German-Austrian carotid guidelines,
      • Eckstein H.H.
      • Kuhnl A.
      • Berkefeld J.
      • Lawall H.
      • Storck M.
      • Sander D.
      Clinical practice guideline: diagnosis, treatment and follow-up in extracranial carotid stenosis.
      75% of the population could reach their care provider after covering 45 km for a CEA procedure, and approximately 70 km for CAS.

      Hospital incidence

      The present study showed a 12% decline in the age standardised hospital incidence for CEA between 2005 and 2016. For CAS, the hospital incidence declined from 2010 to 2013, to rise again until 2016.
      Concordantly, a cross sectional study of the United States Nationwide Inpatient Sample database detected a 41% decrease in the annual incidence of CEA, while the frequency of CAS increased by 250% between 2001 and 2010.
      • Kim L.K.
      • Yang D.C.
      • Swaminathan R.V.
      • Minutello R.M.
      • Okin P.M.
      • Lee M.K.
      • et al.
      Comparison of trends and outcomes of carotid artery stenting and endarterectomy in the United States, 2001 to 2010.
      Notably, CAS incidence reached a plateau after 2006, reflecting the time frame assessed in the present study.
      Presumably, a multifactorial effect, one reason might be a decline in carotid artery disease. An ultrasound study of a vascular prevention cohort revealed a reduction of the proportions of patients with a > 60% and > 80% stenosis by 29.9% and 36.4% between 2002 and 2014.
      • Hackam D.G.
      • Spence J.D.
      Decline in the severity of carotid atherosclerosis and associated risk factors from 2002 to 2014.
      One reason for the decline in carotid artery disease might be the significantly reduced prevalence of tobacco smoking over the past two decades.
      • Zeiher J.
      • Finger J.D.
      • Kuntz B.
      • Hoebel J.
      • Lampert T.
      • Starker A.
      Trends in smoking among adults in Germany: evidence from seven population-based health surveys from 1991-2015.
      Another reason for the lower CEA incidence might be an increasing reluctance to offer CEA, particularly to patients with asymptomatic carotid stenoses. With improved medical therapy, the stroke incidence of purely medically treated patients with carotid artery disease has been declining to around 1.0 per 100 person years.
      • Goldstein L.B.
      Temporal changes in the external validity of clinical trials: asymptomatic carotid artery stenosis.
      The five year results of the ACAS
      Executive Committee for the Asymptomatic Carotid Atherosclerosis Study
      Endarterectomy for asymptomatic carotid artery stenosis.
      and ACST
      • Halliday A.
      • Mansfield A.
      • Marro J.
      • Peto C.
      • Peto R.
      • Potter J.
      • et al.
      Prevention of disabling and fatal strokes by successful carotid endarterectomy in patients without recent neurological symptoms: randomised controlled trial.
      trials were published in 1995 and 2004, possibly affecting subsequent decision making. With the number needed to treat to prevent one stroke being fairly high (17 and 19),
      • Naylor A.R.
      Time to rethink management strategies in asymptomatic carotid artery disease.
      both studies demonstrated only a moderate benefit for CEA in asymptomatic patients.
      Therefore, recent carotid guidelines have included criteria in addition to degree of stenosis, to define patient subgroups benefitting from CEA.
      • Naylor A.R.
      • Ricco J.B.
      • de Borst G.J.
      • Debus S.
      • de Haro J.
      • Halliday A.
      • et al.
      Management of atherosclerotic carotid and vertebral artery disease: 2017 Clinical Practice Guidelines of the European Society for Vascular Surgery (ESVS).
      The declining hospital incidence of CAS between 2010 and 2013 might be traced back to the penultimate ESVS guidelines published in 2009, stating that CAS should only be performed in high volume centres with documented low peri-procedural stroke and death rates or within well conducted clinical trials.
      • Liapis C.D.
      • Bell P.R.
      • Mikhailidis D.
      • Sivenius J.
      • Nicolaides A.
      • Fernandes e Fernandes J.
      • et al.
      ESVS guidelines. Invasive treatment for carotid stenosis: Indications, techniques.
      The increased incidence of CAS after 2013 mirrors a more liberal attitude towards stenting, also expressed by the most recent ESVS guidelines,
      • Naylor A.R.
      • Ricco J.B.
      • de Borst G.J.
      • Debus S.
      • de Haro J.
      • Halliday A.
      • et al.
      Management of atherosclerotic carotid and vertebral artery disease: 2017 Clinical Practice Guidelines of the European Society for Vascular Surgery (ESVS).
      and possibly accounting for a discrete transition of revascularisation strategies towards CAS. However, the increase of CAS procedures after 2013 did not outweigh the overall decline of carotid revascularisations.

      Mortality

      This analysis revealed a lower mortality for patients undergoing CEA compared with those receiving CAS (1.2% vs. 4.0%), which was not shown by a meta-analysis of RCTs.
      • Murad M.H.
      • Shahrour A.
      • Shah N.D.
      • Montori V.M.
      • Ricotta J.J.
      A systematic review and meta-analysis of randomized trials of carotid endarterectomy vs stenting.
      A more recent systematic review and meta-analysis found the peri-operative mortality after CEA to be 0.89% and 0.36% for symptomatic and asymptomatic patients, respectively. The corresponding numbers for CAS were 1.97% and 0.89%.
      • Lokuge K.
      • de Waard D.D.
      • Halliday A.
      • Gray A.
      • Bulbulia R.
      • Mihaylova B.
      Meta-analysis of the procedural risks of carotid endarterectomy and carotid artery stenting over time.
      One reason for the differing results between RCTs and non-randomised studies like the present one might be attributable to selection bias, as high risk patients might be more likely to undergo CAS in real world settings. This is reflected by the higher Elixhauser scores observed in the CAS cohort compared with CEA patients. Furthermore, the present cohort contains an important proportion of emergency patients, who are known to be at higher risk of peri-procedural stroke or death,
      • Knappich C.
      • Kuehnl A.
      • Tsantilas P.
      • Schmid S.
      • Breitkreuz T.
      • Kallmayer M.
      • et al.
      Patient characteristics and in-hospital outcomes of emergency carotid endarterectomy and carotid stenting after stroke in evolution.
      but are almost always excluded from RCTs.
      Regarding sex differences, the present analyses demonstrated similar mortality rates for men and women (1.3% vs. 1.1%) who underwent CEA. This conforms to previously published results, which despite higher combined stroke or death rates,
      • Bond R.
      • Rerkasem K.
      • Cuffe R.
      • Rothwell P.M.
      A systematic review of the associations between age and sex and the operative risks of carotid endarterectomy.
      did not indicate higher mortality rates for women treated by CEA compared with men.
      • Bond R.
      • Rerkasem K.
      • Cuffe R.
      • Rothwell P.M.
      A systematic review of the associations between age and sex and the operative risks of carotid endarterectomy.
      ,
      • Schmid S.
      • Tsantilas P.
      • Knappich C.
      • Kallmayer M.
      • Konig T.
      • Breitkreuz T.
      • et al.
      Risk of inhospital stroke or death is associated with age but not sex in patients treated with carotid endarterectomy for asymptomatic or symptomatic stenosis in routine practice: secondary data analysis of the nationwide German statutory quality assurance database from 2009 to 2014.
      The present study showed exceptionally high mortality for women treated by CAS compared with males (5.1% vs. 3.5%). Although some studies indicate higher peri-interventional stroke or death rates for women,
      • Dansey K.D.
      • Pothof A.B.
      • Zettervall S.L.
      • Swerdlow N.J.
      • Liang P.
      • Schneider J.R.
      • et al.
      Clinical impact of sex on carotid revascularization.
      ,
      • Howard V.J.
      • Lutsep H.L.
      • Mackey A.
      • Demaerschalk B.M.
      • Sam 2nd, A.D.
      • Gonzales N.R.
      • et al.
      Influence of sex on outcomes of stenting versus endarterectomy: a subgroup analysis of the Carotid Revascularization Endarterectomy versus Stenting Trial (CREST).
      with respect to mortality, no sex differences were described.
      • Schmid S.
      • Tsantilas P.
      • Knappich C.
      • Kallmayer M.
      • Breitkreuz T.
      • Zimmermann A.
      • et al.
      Age but not sex is associated with higher risk of in-hospital stroke or death after carotid artery stenting in symptomatic and asymptomatic carotid stenosis.
      ,
      • Jim J.
      • Dillavou E.D.
      • Upchurch Jr., G.R.
      • Osborne N.H.
      • Kenwood C.T.
      • Siami F.S.
      • et al.
      Gender-specific 30-day outcomes after carotid endarterectomy and carotid artery stenting in the Society for Vascular Surgery vascular registry.
      Nevertheless, as demonstrated by analyses of the German quality assurance database, male patients who underwent CAS in an emergency setting to be treated for stroke in evolution, showed a trend towards lower mortality (adj. RR 0.75; CI 0.52–1.08) compared with their female counterparts.
      • Knappich C.
      • Kuehnl A.
      • Tsantilas P.
      • Schmid S.
      • Breitkreuz T.
      • Kallmayer M.
      • et al.
      Patient characteristics and in-hospital outcomes of emergency carotid endarterectomy and carotid stenting after stroke in evolution.
      With deaths after CAS performed in a non-emergency setting shown to be as low as 0.4% and 0.9% for (a)symptomatic patients,
      • Schmid S.
      • Tsantilas P.
      • Knappich C.
      • Kallmayer M.
      • Breitkreuz T.
      • Zimmermann A.
      • et al.
      Age but not sex is associated with higher risk of in-hospital stroke or death after carotid artery stenting in symptomatic and asymptomatic carotid stenosis.
      the high mortality in the present study might be attributable to the high proportion of emergency CAS procedures.
      Looking at mortality in relation to hospital volume, a U shaped distribution was shown for CEA with higher mortality rates specifically for very low, but also for high volume centres. Previous publications demonstrated a rebound of peri-operative stroke or death after CEA for very high volume centres.
      • Kuehnl A.
      • Tsantilas P.
      • Knappich C.
      • Schmid S.
      • Konig T.
      • Breitkreuz T.
      • et al.
      Significant association of annual hospital volume with the risk of inhospital stroke or death following carotid endarterectomy but likely not after carotid stenting: secondary data analysis of the statutory German carotid quality assurance database.
      Possible reasons might be a ceiling effect limiting the effect of routine to a certain annual volume, but also higher risk patients being treated predominantly at high volume centres.
      • Kuehnl A.
      • Tsantilas P.
      • Knappich C.
      • Schmid S.
      • Konig T.
      • Breitkreuz T.
      • et al.
      Significant association of annual hospital volume with the risk of inhospital stroke or death following carotid endarterectomy but likely not after carotid stenting: secondary data analysis of the statutory German carotid quality assurance database.
      ,
      • Trenner M.
      • Kuehnl A.
      • Salvermoser M.
      • Reutersberg B.
      • Geisbuesch S.
      • Schmid V.
      • et al.
      Editor's choice - high annual hospital volume is associated with decreased in hospital mortality and complication rates following treatment of abdominal aortic aneurysms: secondary data analysis of the nationwide German DRG statistics from 2005 to 2013.
      Furthermore, trainees’ learning curves might have the greatest effect on the outcomes of high volume centres, which are more likely to be teaching hospitals. These assumptions might also explain CAS patients’ higher mortality rates if treated at higher volume centres (3rd and 4th quartiles: 3.0%) compared with lower volume centres (1st and 2nd quartiles: 2.6%).

      Limitations

      This study is subject to a number of limitations, which in part have been reported previously.
      • Kuhnl A.
      • Erk A.
      • Trenner M.
      • Salvermoser M.
      • Schmid V.
      • Eckstein H.H.
      Incidence, treatment and mortality in patients with abdominal aortic aneurysms.
      ,
      • Trenner M.
      • Kuehnl A.
      • Reutersberg B.
      • Salvermoser M.
      • Eckstein H.H.
      Nationwide analysis of risk factors for in-hospital mortality in patients undergoing abdominal aortic aneurysm repair.
      ,
      • Trenner M.
      • Kuehnl A.
      • Salvermoser M.
      • Reutersberg B.
      • Geisbuesch S.
      • Schmid V.
      • et al.
      Editor's choice - high annual hospital volume is associated with decreased in hospital mortality and complication rates following treatment of abdominal aortic aneurysms: secondary data analysis of the nationwide German DRG statistics from 2005 to 2013.
      First, the underlying dataset contains administrative data with hospital remuneration as the primary purpose. Despite regular controls by the Medical Review Board of the Statutory Health Insurance Funds, under reporting of comorbidities not affecting hospital remuneration with falsely low comorbidity rates cannot be ruled out. Nevertheless, hospital incidence and death were considered reliable outcomes. As there was no individual patient identifier, double counts cannot be excluded; however, the number of these cases was considered negligible.
      Furthermore, no information was available on specific intra- and peri-procedural factors (e.g. surgical and interventional technique, type of anaesthesia, neuromonitoring, peri-operative medication, diagnostic measures) and on individual surgeon volume.
      Second, follow up is limited to the period of hospital stay.
      Third, the dataset did not allow differentiation of whether a stroke was the initial reason for a patient to undergo CEA or CAS or complicated the intervention in the peri-procedural course. Therefore, peri-operative stroke was not suitable as an outcome measure and volume outcome analyses with respect to peri-operative stroke rates were not feasible. For the same reason, it was not possible to distinguish between symptomatic and asymptomatic carotid artery disease or to assess the time interval between index event and intervention.
      Because of the unrestricted inclusion of a broad variety of patients (e.g. symptomatic and asymptomatic, emergency and non-emergency), and a lack of randomisation to either treatment option or caseload quartile, all outcomes are affected by a multitude of (un)known factors (selection bias), and thereby should be interpreted with caution. Type of admission (i.e. scheduled admission, emergency, and transferred from other hospital) represents an administrative rather than a clinical variable.
      Fourth, coding errors or intentional upcoding cannot be excluded. However, because of the high case numbers, their impact on the whole cohort was considered negligible. Furthermore, adequacy of coding is regularly checked by the Medical Review Board of the Statutory Health Insurance Funds.
      Fifth, only the municipal centre of patients’ residency was considered for accessibility studies. If a patient’s residency was situated in the border zone between two types of districts, reaching a hospital close to the adjacent border might be quicker.
      Sixth, because of data protection restrictions, all estimations on potential effects of hypothetical minimum caseload requirements did not imply potential secondary distribution effects.
      Seventh, because of the heterogeneity of health systems, transferability of results to other European countries remains unclear.

      Conclusions

      A main finding of this full survey was that centres performing CEA are distributed more homogeneously across Germany, than those offering CAS. Therefore, with regards to accessibility of care, statutory minimum caseload requirements presumably would affect CEA less than CAS.
      Presumably because of a decline in carotid artery disease and more restricted use in asymptomatic patients, the hospital incidence for CEA has been declining.

      Acknowledgements

      We would like to thank Melanie Heiliger, Jutta Spindler and Sabine Nemitz from the German Federal Statistical Office for supporting this research.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

      Conflict of interest

      None.

      Funding

      None.

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