Abstract
Background:
Revascularization practices with respect to asymptomatic carotid stenosis (ACAS) are known to vary widely among proceduralists. In addition, regional market competition has been previously shown to drive more aggressive practices in a number of surgical procedures. The aim of our study was to examine the association of regional market competition with revascularization thresholds for ACAS.
Methods:
All patients undergoing carotid revascularization in the Vascular Quality Initiative carotid endarterectomy and stenting databases (2016–2020) were included. High-grade carotid stenosis was defined as ≥80%. We calculated the Herfindahl-Hirschman Index (HHI; a measure of physician market competition) for each U.S region as defined by the U.S Department of Health and Human Services. Logistic regression was used to examine the association of degree of carotid stenosis at revascularization with HHI stratified by symptomatology, adjusting for age, sex, race, insurance, and revascularization modality.
Results:
Of 92,243 carotid interventions, 57,094 (61.9%) were performed for ACAS and 35,149 (38.1%) were performed for symptomatic carotid stenosis (SCAS). ACAS patients undergoing revascularization for moderate-grade stenosis were significantly less likely to be aspirin (85.6% vs. 86.3%), clopidogrel (41.3% vs. 45.1%), dual anti-platelet therapy (35.9% vs. 39.2%) and systemic anticoagulants (10.9 vs. 11.7%) compared to high-grade stenosis (all P < 0.05). Multivariable analysis demonstrated that decreased local market competition was independently associated with a lower odds of revascularization for moderate versus high-grade ACAS (odds ratio OR: 0.99 per 10 point increase in HHI, 95% confidence interval CI: 0.98–0.99). There was no association of local market competition with degree of carotid stenosis at time of revascularization among patients with SCAS (OR: 1.00 per 10 point increase in HHI, 95% CI: 0.99–1.00). Among ACAS patients, patients with moderate-grade stenosis had a higher odds ratio of in-hospital stroke or death compared to patients with high-grade stenosis (OR: 1.22, 95% CI 1.03–1.45). This association was not redemonstrated in the SCAS group (OR: 0.92, 95% CI: 0.80–1.06).
Conclusions:
Increased local market competition is associated with a lower threshold for revascularization of ACAS. There is no association between regional market competition and revascularization threshold for SCAS. These findings, combined with the significantly increased risk of perioperative stroke/death among moderate-grade ACAS patients, suggest that competition among proceduralists may result in a higher tolerance for increased operative risk in patients who might otherwise be reasonable candidates for surveillance.
INTRODUCTION
The stroke prevention benefits of carotid revascularization for asymptomatic carotid stenosis (ACAS) > 60% were established in a series of landmark trials completed in the 1990s.1,2 With subsequent improvements in statin, antiplatelet and hypertensive therapy, as well as the advent of adjunctive techniques for carotid revascularization such as transfemoral carotid and transcarotid artery stenting, the landscape of carotid occlusive disease management has changed significantly in the past 2 decades.3,4 Some experts now advocate for surveillance alone for all asymptomatic carotid lesions regardless of degree of stenosis,5 and there are currently several major trials underway seeking to establish updated management guidelines for ACAS in the context of new therapies.6,7 However, societal guidelines for ACAS revascularization still consistently recommend revascularization for ACAS >60%.8,9 Consequently, there is a substantial controversy surrounding the contemporary management of asymptomatic carotid artery stenosis (ACAS).
Previous research has demonstrated that increased market competition can influence surgeons to behave more aggressively with respect to elective procedures. Elevated local market competition has been associated with the repair of abdominal aortic aneurysms at smaller, sub-threshold diameters10 as well as the transplantation of lower quality renal allo-grafts.11 This is thought to result from physician concern that patients in high competition areas will seek procedural intervention from other available physicians, resulting in tolerance of greater risk on behalf of the proceduralist.11
Given the multitude of proceduralists able to provide carotid revascularization, as well as controversy surrounding the appropriate management of ACAS, we hypothesized that local market competition may be a driver in ACAS revascularization. The aim of this study was to examine the association of regional market competition with revascularization thresholds for ACAS. We also sought to describe the association of regional market competition with revascularization thresholds for symptomatic carotid artery stenosis, which should not vary as revascularization for carotid stenosis is indicated for most patients with symptomatic disease.8
METHODS
Study Design
This is a retrospective cross-sectional study using data from the Society for Vascular Surgery Vascular Quality Initiative (VQI) database.12 The VQI is a database that collects preoperative risk factors, intraprocedural variables and postoperative outcomes for several distinct vascular procedures, including carotid endarterectomy (CEA), and carotid artery stenting, the latter of which includes both transfemoral carotid artery stenting (TF-CAS) and transcarotid artery revascularization (TCAR). The VQI accrues data from >780 participating centers, both community and academic. The VQI datasets are made up of procedure-specific variables and grant a high- level of granularity with regards to individual patient symptomatology and various preoperative imaging modalities, allowing patients to be stratified by both symptomatic status as well as degree of stenosis.
The primary study population was defined by querying the VQI CEA and CAS procedure databases from January 1, 2016 to December 1, 2020 to identify all patients who underwent carotid artery revascularization for carotid artery stenosis between 50–99%. Patients with missing data on symptomatic indication (N = 4,269), degree of stenosis (N = 5,038) and laterality (N = 179) were excluded from the analysis, as were patients with <50% stenosis (N = 950), 100% stenosis (N = 1,377), or those undergoing CAS procedures performed as part of intracranial treatment (N = 810). Patients with documented prior symptoms of stroke or TIA ipsilateral to the carotid intervention were designated as having symptomatic carotid artery stenosis (SCAS).
The Institutional Review Board at the Johns Hopkins University School of Medicine approved this study and waived informed consent requirements given that this was a retrospective analysis of a de-identified data source.
Defining Market Competition
Location of center was used to calculate the Herfindahl-Hirschman Index (HHI). The HHI is a measure of local market competition and is calculated as the sum of squares of the market share for each firm participating in the market. Market share was quantified by calculating the proportion of all procedures performed within a region for each provider. The sum of squares of each provider’s market share in a region is the HHI for the region. For example, if a region had 100 procedures performed where one provider did 50, one did 30, and one did 20, the HHI in this case is 502+302+202 = 3,800. The resulting value ranges from 0 to 10,000, where higher HHI reflects less market competition and lower HHI reflects higher market competition.10,13 The highest level of granularity that we were able to obtain from the VQI was state level location data for participating centers; thus, individual centers were organized into US regions based on the United States Department of Health and Human Services regions, which are used as geographically meaningful regions of healthcare delivery within the United States.14
Study Outcomes
The primary outcome of this study was regional proportion of revascularization for moderate-grade (50% to <80%) versus high-grade (≥80%) carotid artery stenosis. Secondary outcomes included in-hospital outcomes of perioperative stroke, death, and composite stroke/death. Given the differences in management strategies for asymptomatic versus symptomatic carotid artery stenosis, we stratified all analyses by symptom status.
Statistical Analysis
We described the study cohort, anatomic characteristics and postoperative outcomes using descriptive statistics. For the primary analysis, we compared outcomes for the moderate-versus high-grade ACAS groups using univariate analysis, including χ2, Student’s t-tests, and Wilcoxon rank-sum testing for categorical and continuous variables, as appropriate. We performed multivariable logistic regression to assess the association of market competition (defined by unweighted regional HHI) with revascularization of moderate-grade (versus high-grade) carotid stenosis for patients with ACAS and SCAS separately, accounting for multiple patient and physician factors including center region. Multivariable logistic regression was also used to examine the association of market competition with in-hospital stroke and death, stratified by symptom status. HHI was included in both models as a continuous variable with an arbitrary binning of base 10 to report the effect size as an outcomes predictor.10 Covariates included in all models were selected by a combination of a priori variables based on clinical meaning, as well as covariates that were found to be statistically significant differences in bivariate analysis, with exclusion of collinear variables.
All statistical analyses were performed using Stata Version 15.1 (StataCorp LP, College Station TX). All values were two-tailed and reported as statistically significant at a level of α ≤ 0.05. Despite the large size of the dataset this threshold was chosen to be consistent with past interrogations of the VQI database10,15–18
RESULTS
Study Cohort
Overall, 92,243 carotid revascularization procedures were performed for carotid stenosis during the study period (Table I). Of these, 57,094 (61.9%) were performed for ACAS and 35,149 (38.1%) were performed for SCAS.
Table I.
Baseline demographics, comorbidities and anatomic characteristics of patients undergoing carotid revascularization, stratified by symptomatology and degree of stenosis
| Asymptomatic | Symptomatic | |||||
|---|---|---|---|---|---|---|
| Patient characteristics | 50 to <80% | ≥80% | P-value | 50 to <80% | ≥80% | P-value |
| N | 19,352 (33.9%) | 37,742 (66.1%) | 14,788 (42.1%) | 20,361 (57.9%) | ||
| Age, years (median, IQR) | 72 (66, 77) | 72 (65, 77) | 0.75 | 72 (65, 79) | 71 (64, 78) | < 0.001 |
| Female | 7,948 (41.1%) | 14,424 (38.2%) | < 0.001 | 5,579 (37.7%) | 7,671 (37.7%) | 0.92 |
| Race | ||||||
| Native Am. | 42 (0.2%) | 102 (0.3%) | 0.004 | 37 (0.3%) | 73 (0.4%) | 0.28 |
| Asian | 181 (0.9%) | 396 (1.0%) | 154 (1.0%) | 213 (1.0%) | ||
| Black | 799 (4.1%) | 1,580 (4.2%) | 855 (5.8%) | 1,210 (5.9%) | ||
| P. Islander | 29 (0.1%) | 26 (0.1%) | 9 (0.1%) | 12 (0.1%) | ||
| White | 17,653 (91.2%) | 34,226 (90.7%) | 13,222 (89.4%) | 18,065 (88.7%) | ||
| Other | 608 (3.1%) | 1,342 (3.6%) | 490 (3.3%) | 748 (3.7%) | ||
| Ethnicity | ||||||
| Hispanic | 606 (3.1%) | 1,270 (3.4%) | 0.11 | 550 (3.7%) | 782 (3.8%) | 0.79 |
| BMI (median, IQR) | 27.9 (24.7, 31.6) | 27.9 (24.7, 31.6) | 0.38 | 27.8 (24.6, 31.6) | 27.8 (24.5, 31.6) | 0.99 |
| Insured | 18,582 (96.0%) | 36,160 (95.8%) | 0.23 | 13,936 (94.2%) | 18,990 (93.3%) | < 0.001 |
| Smoking history | ||||||
| Never | 3,927 (20.3%) | 7,006 (18.6%) | 0.002 | 2,458 (16.6%) | 2,668 (13.1%) | < 0.001 |
| Prior | 8,258 (42.7%) | 14,490 (38.4%) | 4,147 (28.0%) | 4,721 (23.2%) | ||
| Current | 3,628 (18.7%) | 6,940 (18.4%) | 1,941 (13.1%) | 3,020 (14.8%) | ||
| Comorbidities | ||||||
| HTN | 17,487 (90.4%) | 34,219 (90.7%) | 0.24 | 13,172 (89.1%) | 18,132 (89.1%) | 0.95 |
| Diabetes | 6,467 (33.4%) | 12,348 (32.7%) | 0.092 | 4,846 (32.8%) | 6,461 (31.7%) | 0.040 |
| CAD | 6,566 (33.9%) | 13,372 (35.4%) | < 0.001 | 4,908 (33.2%) | 6,851 (33.6%) | 0.37 |
| CHF | 2,565 (13.3%) | 5,123 (13.6%) | 0.29 | 2,010 (13.6%) | 2,912 (14.3%) | 0.058 |
| COPD | 4,693 (24.3%) | 9,154 (24.3%) | 0.99 | 3,566 (24.1%) | 5,144 (25.3%) | 0.014 |
| ESRD | 212 (1.1%) | 462 (1.2%) | 0.29 | 181 (1.2%) | 260 (1.3%) | 0.099 |
| Domicile | ||||||
| Home | 19,187 (99.1%) | 37,397 (99.1%) | 0.71 | 14,444 (97.7%) | 19,884 (97.7%) | 0.74 |
| Facility | 138 (0.7%) | 274 (0.7%) | 314 (2.1%) | 423 (2.1%) | ||
| Homeless | 16 (0.1%) | 24 (0.1%) | 15 (0.1%) | 26 (0.1%) | ||
| ASA class | ||||||
| ≤3 | 15,420 (79.6%) | 29,801 (78.9%) | 0.004 | 10,705 (72.4%) | 14,790 (72.6%) | < 0.001 |
| >3 | 3,781 (19.5%) | 7,672 (20.3%) | 3,819 (25.9%) | 5,128 (25.2%) | ||
| Preop medications | ||||||
| Aspirin | 16,569 (85.6%) | 32,575 (86.3%) | 0.024 | 12,718 (86.0%) | 17,516 (86.0%) | 0.95 |
| P2Y12 | 8,000 (41.3%) | 17,013 (45.1%) | < 0.001 | 8,823 (59.7%) | 12,405 (60.9%) | 0.017 |
| DAPT | 6,939 (35.9%) | 14,780 (39.2%) | < 0.001 | 7,826 (52.9%) | 11,135 (54.7%) | 0.001 |
| Statin | 16,566 (85.6%) | 32,353 (85.7%) | 0.70 | 12,895 (87.2%) | 17,383 (85.4%) | < 0.001 |
| Anticoagulation | 2,103 (10.9%) | 4,412 (11.7%) | 0.003 | 2,029 (13.7%) | 2,679 (13.2%) | 0.13 |
| Laterality, right | 9,525 (49.2%) | 19,288 (51.1%) | < 0.001 | 7,240 (49.0%) | 10,335 (50.8%) | < 0.001 |
| Modality | ||||||
| CEA | 15,813 (81.7%) | 28,436 (75.3%) | < 0.001 | 8,546 (57.8%) | 10,409 (51.1%) | < 0.001 |
| TF-CAS | 1,295 (6.7%) | 2,932 (7.8%) | 3,201 (21.6%) | 5,463 (26.8%) | ||
| TCAR | 2,244 (11.6%) | 6,374 (16.9%) | 3,041 (20.6%) | 4,489 (22.0%) | ||
| Prior revascularization | ||||||
| CEA | 1,096 (5.7%) | 2,895 (7.7%) | < 0.001 | 1,238 (8.4%) | 2,240 (11.0%) | < 0.001 |
| CAS | 502 (2.6%) | 1,108 (2.9%) | 0.020 | 476 (3.2%) | 743 (3.6%) | 0.030 |
| Contralateral disease | ||||||
| 50–79% | 16,252 (84.0%) | 29,702 (78.7%) | < 0.001 | 12,675 (85.7%) | 16,044 (78.8%) | < 0.001 |
| 80–99% | 763 (3.9%) | 3,855 (10.2%) | 696 (4.7%) | 2,130 (10.5%) | ||
| Occluded | 1,053 (5.4%) | 2,020 (5.4%) | 730 (4.9%) | 1,169 (5.7%) | ||
| High risk anatomy | 2,297 (11.9%) | 5,588 (14.8%) | < 0.001 | 2,656 (18.0%) | 4,934 (24.2%) | < 0.001 |
| HHS Region | ||||||
| 1 | 1,365 (7.1%) | 3,312 (8.8%) | < 0.001 | 1,327 (9.0%) | 1,850 (9.1%) | < 0.001 |
| 2 | 1,122 (5.8%) | 2,226 (5.9%) | 819 (5.5%) | 1,077 (5.3%) | ||
| 3 | 3,168 (16.4%) | 6,396 (16.9%) | 2,110 (14.3%) | 3,080 (15.1%) | ||
| 4 | 4,280 (22.1%) | 8,270 (21.9%) | 3,005 (20.3%) | 4,280 (21.0%) | ||
| 5 | 4,448 (23.0%) | 7,133 (18.9%) | 2,959 (20.0%) | 3,923 (19.3%) | ||
| 6 | 1,220 (6.3%) | 3,261 (8.6%) | 1,207 (8.2%) | 1,650 (8.1%) | ||
| 7 | 843 (4.4%) | 1,069 (2.8%) | 801 (5.4%) | 886 (4.4%) | ||
| 8 | 368 (1.9%) | 543 (1.4%) | 206 (1.4%) | 256 (1.3%) | ||
| 9 | 843 (4.4%) | 1,828 (4.8%) | 645 (4.4%) | 863 (4.2%) | ||
| 10 | 811 (4.2%) | 1,602 (4.2%) | 910 (6.2%) | 1,199 (5.9%) | ||
Bolded values are statistically significant.
HTN, hypertension; CAD, coronary artery disease; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; ESRD, end stage renal disease; P2Y12, P2Y12 inhibitors; DAPT, dual antiplatelet therapy.
Among patients with ACAS, 37,742 (66.1%) of carotid revascularizations were performed for high-grade stenosis. Patients with ACAS undergoing carotid revascularization for moderate-grade stenosis were more frequently female, white, and never smokers, and less frequently had coronary artery disease compared to patients with ACAS undergoing carotid revascularization for high-grade stenosis (all, P < 0.05; Table I). ACAS patients undergoing revascularization for moderate-grade stenosis were less likely to be on preoperative ASA, P2Y12, dual antiplatelet therapy, and systemic anticoagulation (all, P < 0.05). ACAS patients with moderate stenosis less frequently had high-risk anatomy, and more frequently received CEA (81.7% vs. 75.3%) than ACAS patients with high-grade stenosis (both P < 0.001).
Among patients with SCAS, 20,361 (57.9%) of carotid revascularizations were performed for high-grade stenosis. Patients with SCAS undergoing carotid revascularization for moderate stenosis were slightly younger and more frequently had insurance, were never smokers, and had diabetes (all, P < 0.05; Table I). SCAS patients undergoing revascularization for moderate-grade stenosis were less likely to be on preoperative P2Y12 or dual antiplatelet therapy, and more likely to be on a statin (all, P < 0.05). SCAS patients with moderate-grade stenosis less frequently had high-risk anatomy, and more frequently received CEA (57.8% vs. 51.1%) than SCAS patients with high-grade stenosis (both P < 0.001).
Association of Market Competition with Revascularization for Moderate-versus High-Grade Carotid Artery Stenosis.
The highest market competition for carotid revascularization procedures existed in the Atlanta and Chicago regions (Regions 4 and 5, both HHI 41) and the lowest market competition was located in the Rocky Mountains (Region 8, Denver, HHI 366) (Fig. 1). There was wide variation in the proportion of ACAS revascularization procedures performed for moderate-grade stenosis across US regions, ranging from 27% to 44% (Fig. 1A). There was less variability in the proportion of SCAS revascularization procedures performed for moderate-grade stenosis across US regions, which ranged from 41% to 47% (Fig. 1B).
Fig. 1.
Proportion of carotid revascularizations performed by HHS region for moderate-grade (50–80%) stenosis in (A) asymptomatic and (B) symptomatic carotid stenosis. Regions of the United States are shaded by degree of physician competition as defined by the Herfindahl-Hirschman Index (HHI), where lower numbers indicate increased market competition (darkest shades) and higher numbers indicated decreased market competition (lightest shades); of note, Regions 4 (Atlanta) and 5 (Chicago) have equivalent competition; the border between these regions is the Ohio River, with Kentucky in Region 4.
Adjusting for patient characteristics, region, and operative approach, lower market competition was associated with lower odds of intervention for moderate-grade versus high-grade ACAS (OR 0.99, per 10 point increase in HHI, 95% CI 0.98–0.99), while there was not a statistically significant association between market competition and odds of intervention for moderate-grade versus high-grade SCAS (Table II). In other words, higher market competition was associated with higher odds of intervention for moderate-grade (versus high-grade) stenosis in asymptomatic but not symptomatic disease.
Table II.
Multivariable analysis (OR, 95% CI) assessing the association of market competition (HHI) with revascularization for moderate-grade (versus high-grade) carotid stenosis, stratified by symptomatology and adjusted for region
| Asymptomatic | Symptomatic | |||
|---|---|---|---|---|
| Patient characteristics | OR | 95% CI | OR | 95% CI |
| HHI (per 10 point increase) | 0.99 | 0.98–0.99 | 1.00 | 0.99–1.00 |
| Age (per year increase) | 1.00 | 0.99–1.00 | 1.01 | 1.01–1.01 |
| Female sex (versus male) | 1.11 | 1.07–1.15 | 1.00 | 0.96–1.05 |
| White race (versus other) | 1.07 | 1.01–1.14 | 1.06 | 0.98–1.14 |
| Right side (versus left) | 0.92 | 0.89–0.96 | 0.93 | 0.89–0.97 |
| Approach (ref CEA) | ||||
| CAS | 0.79 | 0.73–0.85 | 0.69 | 0.65–0.93 |
| TCAR | 0.62 | 0.59–0.66 | 0.75 | 0.71–0.80 |
| Comorbidities | ||||
| Diabetes | 1.04 | 1.00–1.08 | 1.06 | 1.01–1.11 |
| CAD | 1.01 | 0.98–1.05 | 1.01 | 0.96–1.06 |
| COPD | 0.99 | 0.95–1.03 | 0.96 | 0.91–1.01 |
| Preop meds | ||||
| Aspirin | 0.96 | 0.91–1.01 | 0.99 | 0.93–1.05 |
| P2Y12 | 0.97 | 0.93–1.01 | 1.05 | 1.00–1.11 |
| Statin | 1.02 | 0.97–1.08 | 1.17 | 1.09–1.25 |
| Anticoagulation | 0.91 | 0.86–0.97 | 1.04 | 0.97–1.11 |
Bolded values are statistically significant.
HTN, hypertension; CAD, coronary artery disease; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; P2Y12, P2Y12 inhibitors.
Association of Degree of Stenosis with In-Hospital Outcomes
Examining unadjusted in-hospital outcomes stratified by symptomatology and degree of stenosis (Table III) demonstrated no significant difference in in-hospital mortality for moderate-grade versus high-grade ACAS patients (0.3% vs. 0.2%, P = 0.19). However, there was a significantly increased frequency of in-hospital stroke (1.0% vs. 0.8%) and composite stroke/death (1.2% vs. 1.0%) for moderate-grade ACAS patients (both, P < 0.03).
Table III.
Crude in-hospital outcomes following carotid revascularization, stratified by symptomatology and degree of stenosis.
| Asymptomatic | Symptomatic | |||||
|---|---|---|---|---|---|---|
| In-hospital outcome | 50 to <80% | ≥80% | P-value | 50 to <80% | ≥80% | P-value |
| Mortality | 54 (0.3%) | 84 (0.2%) | 0.19 | 79 (0.5%) | 161 (0.8%) | 0.004 |
| Stroke | 197 (1.0%) | 313 (0.8%) | 0.023 | 320 (2.2%) | 424 (2.1%) | 0.60 |
| Composite stroke/death | 231 (1.2%) | 374 (1.0%) | 0.025 | 363 (2.5%) | 540 (2.7%) | 0.25 |
Bolded values are statistically significant.
For patients with SCAS, those with moderate-grade stenosis had a lower frequency of in-hospital mortality compared with high-grade stenosis (0.5% vs. 0.8%, P < 0.01), but there was no difference in in-hospital stroke (2.2% vs. 2.1%) or composite stroke/death (2.5% vs. 2.7%; both P > 0.05).
After adjusting for baseline differences between groups, there was no association of HHI with in-hospital stroke/death in ACAS (OR: 1.02 per 10-point increase in HHI, 95% CI: 0.99–1.04) or SCAS patients (OR: 1.01 per 10-point increase in HHI, 95% CI: 0.99–1.03). Among the ACAS patients, degree of stenosis was independently associated with in-hospital stroke/death, with moderate-grade patients demonstrating a significantly higher odds stroke/death compared to high-grade patients (OR: 1.22, 95% CI 1.03–1.45). This association was not redemonstrated in the SCAS group (OR: 0.92, 95% CI: 0.80–1.06, Table IV).
Table IV.
Multivariable analysis (OR, 95% CI) assessing the association of market competition (HHI) with in-hospital stroke/death following carotid artery revascularization, stratified by symptomatology and adjusted for region.
| Asymptomatic | Symptomatic | |||
|---|---|---|---|---|
| Patient characteristics | OR | 95% CI | OR | 95% CI |
| HHI (per 10 point increase) | 1.02 | 0.99–1.04 | 1.01 | 0.99–1.03 |
| Moderate grade stenosis (versus high) | 1.22 | 1.03–1.45 | 0.92 | 0.80–1.06 |
| Age (per year increase) | 1.02 | 1.01–1.03 | 1.03 | 1.02–1.04 |
| Female sex (versus male) | 1.14 | 0.96–1.35 | 1.05 | 0.91–1.21 |
| White race (versus other) | 0.75 | 0.57–0.98 | 0.68 | 0.56–0.82 |
| Right side (versus left) | 0.80 | 0.68–0.95 | 0.79 | 0.69–0.91 |
| Approach (ref CEA) | ||||
| CAS | 1.34 | 0.96–1.88 | 1.94 | 1.64–2.30 |
| TCAR | 1.43 | 1.11–1.85 | 1.23 | 1.01–1.50 |
| Comorbidities | ||||
| Diabetes | 1.27 | 1.07–1.51 | 1.13 | 0.98–1.31 |
| CAD | 1.28 | 1.07–1.53 | 1.23 | 1.06–1.43 |
| COPD | 1.34 | 1.12–1.61 | 0.91 | 0.77–1.08 |
| Preop meds | ||||
| Aspirin | 0.72 | 0.58–0.90 | 0.80 | 0.66–0.96 |
| P2Y12 | 0.63 | 0.51–0.76 | 0.72 | 0.61–0.84 |
| Statin | 0.74 | 0.59–0.92 | 0.95 | 0.78–1.15 |
| Anticoagulation | 0.76 | 0.57–0.99 | 0.86 | 0.70–1.06 |
Bolded values are statistically significant.
HTN, hypertension; CAD, coronary artery disease; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; P2Y12, P2Y12 inhibitors.
DISCUSSION
The decision to revascularize patients with moderate-grade ACAS is a highly individualized one, with many patient- and proceduralist factors likely playing a role. Overall, the data presented here suggest that market competition among proceduralists factors at least in part into the decision to offer revascularization in this controversial patient population. Taken in conjunction with the inferior crude and adjusted perioperative outcomes demonstrated in moderate-grade compared to high-grade ACAS patients, our results imply that physicians practicing in regions with more competition may have a higher tolerance for increased operative risk when deciding to perform a carotid revascularization on patients with ACAS. Likewise, the relatively low use of preoperative antiplatelet drugs among patients with moderate-grade ACAS may suggest a missed opportunity to implement best medical therapy in affected patients.
Prior studies have suggested that more market competition may drive proceduralists to have a lower threshold to offer patients elective procedures,10,11 sometimes at the detriment of the patient.11 These data are consistent with our current findings in ACAS revascularization; for every 10 point increase in HHI (signifying decreased market competition), patients were 1% less likely to undergo carotid revascularization for moderate-grade ACAS. As expected, there was no relationship between HHI and degree of stenosis with revascularization in SCAS patients, consistent with the nonelective, urgent nature of this procedure. Because the revascularization of ACAS is largely elective, our findings suggest that providers in a high competition market may be forgoing surveillance out of concern for losing a patient to a competing proceduralist with a lower revascularization threshold, thus resulting in higher ACAS revascularization rates overall.
To our knowledge, this is the first study suggesting that moderate-grade ACAS patients have inferior perioperative outcomes compared to high-grade ACAS patients. While this study is retrospective in nature, the observation is concerning both given the large volume of revascularization procedures performed yearly in the United States for ACAS and as well as controversy surrounding the contemporary risk profile of intervening on ACAS. Certainly, not all moderate-grade ACAS lesions are created equally, and a small but significant subset of them will result in an embolic event and potentially disabling stroke.19 Certain plaque characteristics on imaging have been investigated in an attempt to identify ACAS patients who will glean the most benefit from revascularization.7,19,20 However, overall stroke rates attributable to carotid stenosis are decreasing nationwide,21 and best medical therapy with an antiplatelet agent and a statin is gaining traction as an acceptable treatment strategy for ACAS.9,22 Surprisingly, we found a small but statistically significant lower use of preoperative antiplatelet therapy in patients with moderate-compared to high-grade ACAS. Given the higher risk of perioperative stroke/death in moderate-grade compared to high-grade ACAS patients that we report, this suggests that there may be a missed opportunity to implement medical therapy and surveillance in this patient subgroup.
Unexplained regional differences in serious adverse perioperative outcomes such as stroke and death in carotid revascularization have been previously identified within national databases,23,24 including the VQI.23 Most of these observations attributed to unexplained regional variations in patient selection.25 While we did not identify an independent association between U.S region and the composite stroke/death endpoint in either ACAS or SCAS patients, we did note significant regional differences in the odds of ACAS revascularization for moderate-grade disease. Ultimately, our results demonstrate that physician market competition is significant driver of ACAS revascularization patterns, although it is only one of several factors contributing to regional differences in ACAS management, some of which remain undefined.
More than half of the patients in this study (61.9%) were asymptomatic at the time of revascularization, similar to other VQI-based studies of carotid revascularization.24,25 Queries of other nationally-based registries such as the National Inpatient Sample26 and Medicare enrollment database27 have demonstrated that up to 85–92% of all captured carotid revascularizations in the United States are performed for ACAS. However, most claims-based databases are unable to distinguish the degree of stenosis, and symptom status is often inaccurate. Our study demonstrates that more than one-third of procedures for ACAS are performed on patients with only moderate-grade stenosis, suggesting that, depending on the outcomes of ongoing randomized trials on this topic, a relatively large number of carotid revascularization procedures performed in the US may no longer be indicated. Notably, more than 80% of ACAS procedures for moderate-grade stenosis received CEA, which is consistent with the Medicare reimbursement rules surrounding TF-CAS and TCAR.28
The limitations of this study are largely those inherent to retrospective, registry based studies, which are limited by the scope, granularity and accuracy of the input data. Using the VQI database limits both the input data as well as the competition data to only those centers who participate in VQI, by definition excluding some centers that may be competing in a given region. The study population is overwhelmingly of white race and largely male, limiting the generalizability of these results to a more demographically diverse population. The appropriateness of the behavioral trends identified here cannot be fully assessed without a better understanding of plaque morphology, change in stenosis over time, and ultimately the results from ongoing contemporary trials in asymptomatic disease such as CREST-26 and ACST-2.5 Strengths of this analysis include its large sample size, examination of trends across all major modalities of carotid revascularization (CEA, TF-CAS, and TCAR) and use of a procedure-specific registry data that provides a multitude of relevant pre-procedure information such as imaging results, anatomic risk factors, medical comorbidities and preoperative medications. To our knowledge, this is the first examination of the effects of market competition on carotid revascularization practices.
CONCLUSIONS
Increased market competition is associated with a higher odds of revascularization for moderate-grade (50% to <80%) versus high-grade (≥80%) ACAS. An identical analysis in symptomatic patients undergoing carotid revascularization demonstrated no influence of market competition on revascularization threshold. These findings suggest that market competition may influence more aggressive behavior with respect to revascularization of ACAS in patients who may otherwise be good candidates for surveillance. Taken in context with the small but significant increases in adverse perioperative outcomes demonstrated for moderate-grade ACAS patients, these results should encourage critical reflection by proceduralists about factors motivating the decision to offer revascularization to patients with ACAS <80%. Based on current guidelines, these variations in practice cannot be classified as “overtreatment.” At a minimum, there is room for improvement in ensuring patients with ACAS and SCAS are on best medical therapy prior to revascularization. The results of CREST-2 and other ongoing trials designed to assess best management of ACAS will be critical to assessing the appropriateness of these behavior trends, and to direct future research in this area.
Conflicts of interest:
The authors declare that they have no conflicts of interest or relevant financial relationships to disclose. This work did not receive specific grant funding from any public or private institution or individual.
Footnotes
Prepared for the 2022 Vascular and Endovascular Surgical Society Winter Meeting, Snowmass, CO.
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