From the Eastern Vascular Society
Carotid artery stenting: Impact of practitioner
specialty and volume on outcomes and resource
Todd R. Vogel, MD, MPH, Viktor Y. Dombrovskiy, MD, PhD, MPH, Paul B. Haser, MD, and
Alan M. Graham, MD, New Brunswick, NJ
Objectives: A variety of endovascular specialists perform carotid artery stenting (CAS), but little data exist on outcomes
and resource utilization among these specialists. We analyzed differences in outcomes after CAS was performed by
radiologists (RAD), cardiologists (CRD), and vascular surgeons (VAS).
Methods: Secondary data analysis of the 2005-2006 State Inpatient Databases for New Jersey were analyzed. Patients with
elective admission to the hospital who had CAS procedure <2 days after admission were identified. CAS outcomes were
analyzed with respect to practitioner specialty and volume, associated complications, and hospital resource utilization.
Results: We identified 625 CAS cases. CRD performed 378 (60.5%), VAS, 199 (31.8%); and RAD, 48 (7.7%). The overall
stroke rate was 2.72% and by specialty was CRD, 3.17%; VAS, 2.01%, and RAD, 2.08% (P ? .6880). The overall cardiac
complication rate was 2.40% (CRD, 2.12%; VAS, 3.02%; RAD, 2.08%; P ? .7899). Renal and pulmonary complications
were low (0.64% and 0.32%, respectively). Mean hospital length of stay (LOS) in days was significantly shorter for VAS
(1.64 ? 1.40) compared with RAD (2.83 ? 5.15; P ? .0167) and had the same trend compared with CRD (2.14 ? 3.37;
P ? .0649). Intensive care unit (ICU) LOS was shorter for VAS (0.52 ? 0.97) and CRD (0.30 ? 0.71) than for RAD
(2.12 ? 4.48; P < .0001). The mean total hospital cost was significantly greater for RAD ($20,987 ? $26,603) and CRD
($18,182 ? $16,364) than for VAS ($10,000 ? $4947; P ? .0011 and P < .0001, respectively). ICU cost for RAD
($5963 ? $14,551) was also more than for VAS ($864 ? $1514; P < .0001) and CRD ($473 ? $1561; P < .0001).
Medical supply costs were significantly greater for CRD ($8772 ? $9546) than for VAS ($3354 ? $2261; P < .0001)
and RAD ($4964 ? $2595; P ? .0142). Total hospital cost, LOS, and medical supplies were significantly lower for
high-volume practitioners vs low-volume practitioners (P < .0001).
Conclusion: Stroke rates after CAS did not vary significantly among practitioner specialties. Hospital resource utilization
did vary significantly: Vascular surgeons had the lowest utilization of hospital resources for performing CAS. High
practitioner volume was associated with lower hospital resource utilization. Elucidation of factors creating resource
utilization disparities among endovascular practitioners may lead to improved patient outcomes and permit significant
future cost savings for carotid interventions. (J Vasc Surg 2009;49:1166-71.)
increased utilization of health care services and has also
been linked to improved patient outcomes.1,2Carotid end-
arterectomy (CEA) has been established as the gold stan-
dard for the management of carotid disease, and CEA use
has been shown to be influenced by specialty training.3-6At
the same time, a dramatic influx of new technology has
occurred for the treatment of carotid artery disease with the
as noninferior to CEA and is currently performed by mul-
tiple specialties with varied backgrounds and training.7-9
Most CAS procedures are currently performed by car-
diologists, but are also performed by radiologists and vas-
cular surgeons.10Each of these specialties has very different
training processes, credentialing, and experience with pa-
tient care. It is possible that variations in training, back-
ground, and endovascular skill sets may lead to disparate
outcomes. We evaluated CAS procedures performed in
New Jersey and identified practitioners performing these
procedures for the purpose of examining the influence of
physician specialty and volume on outcomes and hospital
resource utilization for CAS.
Data source. Our data were derived from the publicly
available New Jersey State Inpatient Database (NJ SID) for
the years 2005 and 2006, developed as part of the Health-
care Cost and Utilization Project (HCUP) and sponsored
by the Agency for Health Care Research and Quality
(AHRQ).11The NJ SID includes inpatient discharge ab-
stracts from all acute care community hospitals in the state
and contains ?200 various data elements. Among them,
we used for the analysis variables recognizing patient de-
mographics (age, gender, and race), admission type, prin-
cipal and secondary diagnoses, principal and secondary
number of days from admission to procedure, hospital
length of stay (LOS), hospital charges and costs, and Elix-
From the Division of Vascular Surgery, The Surgical Outcomes Research
Group, University of Medicine and Dentistry, New Jersey–Robert Wood
Johnson Medical School.
Competition of interest: none.
Reprint requests: Todd R. Vogel, MD, MPH, UMDNJ–Robert Wood
Johnson Medical School, Division of Vascular Surgery, One Robert
Wood Johnson Pl, MEB-541, New Brunswick, NJ 08903-0019 (e-mail:
Copyright © 2009 by the Society for Vascular Surgery.
hauser comorbidities. We also calculated the Elixhauser
score as a sum of comorbidities presented for each obser-
vation. The HCUP Cost-to-Charge Ratio Files were used
to convert charges to cost from the data.12
The Elixhauser Index13-15was used to identify and
SID data are 29 AHRQ comorbidity measures reported by
Elixhauser et al.14To identify these comorbidities, we used
the Comorbidity Software developed as part of the
HCUP.16The performance of the Elixhauser comorbidity
measures in predicting patient outcomes are well validated
and have been established in the prediction of in-hospital
and 1-year mortality among patients with congestive heart
failure, diabetes mellitus, chronic renal failure, stroke, and
patients undergoing coronary artery bypass grafting.15
Study population. All patients who underwent CAS
?2 days after elective admission to the hospital were ana-
lyzed. To identify these patients, we used the International
Classification of Diseases, Ninth Revision, Clinical Modifi-
cation (ICD-9-CM) procedure code 00.63 in any of eight
procedure positions in the data. Using the information
about the number of days from admission to procedure, we
selected only those cases where CAS was performed ?2
to increase the likelihood that elective cases, without a
preexisting diagnosis of stroke, were selected for the study.
Selecting only elective admissions and a short time to
intervention decreases the likelihood of including patients
with a pre-existing stroke.
To identify complications, we used the following ICD-
9-CM diagnosis codes in the secondary diagnoses posi-
● For stroke: 997.00, 997.01, 997.02, 997.09, 433.11,
434.01, 434.11, and 434.91 (Table I);
● For cardiac complications, including myocardial infarc-
tion: 997.1, 410.00-410.02, 410.10-410.12, 410.20-
410.22, 410.30-410.32, 410.40-410.42, 410.50-410.52,
410.60-410.62, 410.70-410.72, 410.80-410.82, and
● For pulmonary complications: 997.3, 518.4, and
● For renal complications: 997.5.
To identify practitioner specialty, we used a variable in
the NJ SID that identified operating physician. We then
divided practitioners into three groups of physicians who
perform CAS: radiologists, cardiologists, and vascular sur-
of these specialties, and the ICD-9-CM codes for these
procedures were identified as outlined in Table II. We
subsequently analyzed the frequency and distribution of
these procedures among practitioners from the data and
then identified practitioner specialty by procedure types
performed. Physicians had ?80% of the codes in a specialty
before they were classified. The six practitioners not iden-
tified using this approach were excluded from the analysis.
To identify symptomatic patients, we used the follow-
ing ICD-9-CM diagnosis codes: 435 (transient cerebral
ischemia) and all subcodes, 437.1 (other generalized isch-
emic cerebrovascular disease), 781.4 (transient paralysis of
limb), 362.34 (transient arterial occlusion, amaurosis fu-
gax), and 368.12 (transient visual loss).
According to the number of CAS performed by each
practitioner, we classified all operating physicians as high-
volume, middle-volume, and low-volume specialists. The
distribution of practitioners by CAS volume was highly
skewed to the low levels; therefore, stratification by quar-
tiles for the analysis was not used. Providers were ranked in
order of increasing estimated total volume to create cate-
goric variables for volume. Cutoff points were selected that
approximated the experience and credentialing criteria of
the lead-in for the Carotid Revascularization Endarterec-
tomy vs. Stent Trial (CREST) to select a volume number of
Table I. International Classification of Diseases, Ninth
Revision, Clinical Modification (ICD-9-CM) stroke codes
ICD-9 codesDescription of codes
997.01 Central nervous system complication with cerebral
Iatrogenic cerebrovascular infarction or
hemorrhage; postoperative stroke.
Nervous system complication, unspecified.
Other nervous system complications.
Occlusion and stenosis of the carotid artery with
Cerebral thrombosis with infarction.
Cerebral embolism with infarction.
Cerebral artery occlusion, unspecified with
Table II. International Classification of Diseases, Ninth
Revision, Clinical Modification (ICD-9-CM) codes used
to determine specialist
Right heart cardiac catheterization
Left heart cardiac catheterization
Percutaneous nephrostomy with
Other percutaneous procedures
on biliary tract
Injection or infusion of cancer
Transcatheter embolization for
gastric or duodenal bleeding
Resection of vessel with
replacement aorta, abdominal
Resection of vessel with
replacement of other vessels of
head and neck
JOURNAL OF VASCULAR SURGERY
Volume 49, Number 5
Vogel et al 1167
20 as a high-volume specialist.17The techniques used to
develop volume thresholds are consistent with previous
state and national investigations of the volume-outcomes
effect for CEA and other surgical procedures.18,19
The high-volume specialists (?20 CAS procedures)
represented the top 10% of practitioners and accounted for
51% of all CAS procedures. Physicians who performed 10
to 19 CAS were classified as middle-volume (10% practitio-
ners, 19% of CAS procedures), and physicians with ?10
procedures were recognized as low-volume (80% practitio-
ners, 30% of CAS procedures).
Statistical analysis. Analysis of the database and all
statistics was done with SAS 9.1 software (SAS Institute,
Cary, NC). To test the difference between groups, we used
chi-square analysis with calculating odds ratio (OR) and
95% confidence interval (95% CI) for categorical variables,
t test and analysis of variance (ANOVA) for continuous
variables, and test for difference between two independent
proportions when results were presented as percentage. All
means are presented with standard deviations. A value of
P ? .05 was considered significant for all analyses.
We identified 625 cases for CAS, of which cardiologists
performed 378 (60.5%), followed by vascular surgeons
with 199 (31.8%) and radiologists with 48 (7.7%). The
mean age of those who were operated on by vascular
surgeons (71.7 ? 8.98 years) was similar to the age of
patients operated on by cardiologists (72.0 ? 9.51) and
radiologists (71.3 ? 7.9; P ? .8411). However, the mean
Elixhauser score for the cardiologists’ patients (2.3 ? 1.17)
was greater than for those of vascular surgeons (1.8? 1.18;
two groups did not differ significantly.
The overall stroke rate was 2.72% for all CAS per-
formed, with no significant variation among specialties
(cardiologists, 3.17%; vascular surgeons, 2.01%; radiolo-
gists, 2.08%; P ? .6880). The overall cardiac complication
rate after CAS was 2.40%, and we also did not find signifi-
cant differences among physicians (cardiologists, 2.12%;
vascular surgeons, 3.02%; radiologists, 2.08%; P ? .7899).
Renal and pulmonary complications were low in the study
cohort (0.64% and 0.32%, respectively). Of the 625 CAS
patients identified, only 22 (3.52%) were symptomatic.
Because of the low incidence found and concerns about
coding within the data set, subset analysis of symptomatic
patients was not performed. Mean Elixhauser comorbidity
scores were calculated for the three practitioner specialties.
The patients were at 2.27 ? 1.17 for cardiologists, 1.78 ?
1.18 for vascular surgeons, and 1.47 ? 1.35 for radiolo-
gists. The cardiologists had patients with higher comorbid-
ity scores (P ? .001) compared with the other specialties.
Resource utilization differences are summarized in Ta-
ble III. Mean hospital length of stay (LOS) in days was
significantly shorter for vascular surgeons (1.64 ? 1.40)
compared with radiologists (2.83 ? 5.15; P ? .0167) and
had the same trend compared with cardiologists (2.14 ?
3.37; P ? .0649). ICU LOS was also shorter for vascular
surgeons (0.52 ? 0.97) and cardiologists (0.30 ? 0.71)
than for radiologists (2.12 ? 4.48; P ? .0001). Mean total
hospital cost was significantly greater for radiologists
($20,987 ? $26,603) and cardiologists ($18,182 ?
$16,364, P ? .0011) than for vascular surgeons
($10,000 ? $4947; P ? .0001). ICU cost for radiologists
($5963 ? $14,551) was also larger than for vascular sur-
geons ($864 ? $1514; P ? .0001) and cardiologists
($473 ? $1561; P ? .0001). No differences were noted in
the operating room costs among the three specialties.
However, medical supply costs were significantly greater
for cardiologists ($8772 ? $9546) than for vascular sur-
geons ($3354 ? $2261; P ? .0001) and radiologists
($4964 ? $2595; P ? .0142).
A subset analysis of this study failed to demonstrate
significant differences for stroke by volume, although high-
volume specialists appeared to have a lower stroke rate
overall. Physicians who performed 20 to 35 procedures had
a stroke rate of 1.92% compared with the 3.80% (P ?
0.641) stroke rate for those who performed fewer than five
procedures. This did not reach statistical significance and is
likely based on the small sample size and lack of power for
this type of analysis.
Significant differences existed in hospital resource uti-
lization among specialists with different volumes (Table
IV). A similar hospital LOS was found in patients from the
Table III. Hospital resource utilization for patients with carotid artery stenting performed by various specialists
1.64 ? 1.40
0.52 ? 0.97
2.14 ? 3.37
0.30 ? 0.71
2.83 ? 5.15
2.12 ? 4.48
10,000 ? 4947
864 ? 1514
2837 ? 2686
3354 ? 2261
18,182 ? 16,364
473 ? 1561
2781 ? 2489
8772 ? 9546
20,987 ? 26,603
5963 ? 14,551
2461 ? 2276
4964 ? 2595
ICU, Intensive care unit; LOS, length of stay.
aData are presented as the mean ? standard deviation.
JOURNAL OF VASCULAR SURGERY
1168 Vogel et al
high-volume (1.7 ? 1.4 days) and medium-volume (1.7 ?
1.2 days), which was significantly lower than the LOS in
low-volume specialists (2.4 ? 4.1 days; P ? .0182 and P ?
.0422, respectively). Total hospital costs for high-volume
specialists ($13,193 ? $9095) did not differ significantly
from costs for medium-volume specialists ($8442 ? $3983;
P ? .0971) but were significantly lower than for low-
volume specialists ($19,325 ? $19,236; P ? .004 and P ?
.0001, respectively). Similar to total hospital cost, costs of
medical supplies in high- and medium-volume specialists
($4496 ? $5692 and $3060 ? $2372, respectively; P ?
.3056) were significantly lower than in low-volume special-
ists ($8800 ? $9043; P ? .0001 for both).
Multiple trials and registries evaluating CAS and CEA
have demonstrated noninferiority of CAS as well as inferior
results.7,8,20Explanations for these variations in outcomes
for CAS may include differences in practice patterns, expe-
rience or training of the operator, patient selection, and the
learning curve associated with CAS. This study has evalu-
ated the influence of specialty (cardiology, radiology, and
vascular surgery) and procedure volume on outcomes for
CAS in New Jersey.
Within vascular surgery, surgeon volume and special-
ization have been correlated with improved outcomes for
patients undergoing CEA and abdominal aortic aneurysm
repair.6The influence of volume has been further evaluated
for CEA, using population data and statistical modeling,
and a significant volume effect for death has been demon-
strated.21Surgical mortality has varied significantly across
chance alone or differences in case-mix.18Rosenthal et al1
concluded that patients undergoing abdominal aortic an-
eurysm repair performed by a specialized team have signif-
icantly better outcomes than those whose surgery is done
by general surgeons.
Other areas within medicine have also evaluated the
differences between practitioners and their associated out-
comes. Greenfield et al22evaluated resource utilization for
medical specialties for the management of general medical
patients and demonstrated that increased usage was inde-
pendently related to specialty.22Additional analyses have
demonstrated that subspecialists use more resources than
generalists, whereas other authors suggest that practice
organization may also have a significant influence on phy-
sician resource utilization.23,24Although a large body of
research has suggested the importance of specialty training,
the true clinical mechanisms underlying variation in surgi-
cal mortality remain largely unknown.25
This study has demonstrated no significant difference
specialty. Other authors have suggested a significant learn-
ing curve is associated with performing CAS. Mas et al20
referred to the “learning curve” for CAS as a reason for the
inferior results associated with CAS by the Endarterectomy
Versus Angioplasty in Patients With Symptomatic Severe
Carotid Stenosis (EVA-3S) investigators. However, a
subanalysis of that study demonstrated that most of the
strokes in CAS patients occurred with the interventionalists
who had the most experience doing CAS. We did not find
this trend. As well, it has been well established that the risk
associated with CEA varies among surgeons,6,18and it is
likely that CAS has similar risks associated with the opera-
Others have demonstrated the center’s experience is
associated with peri-interventional stroke and death. Theiss
et al26demonstrated that neurologic complications or
death, or both, occurred 1.76 times more often in the first
50 interventions of an institution. Their findings support
for CAS.26As well, the CREST trial found that 94 opera-
tors who had performed ?15 CAS procedures had a
stroke/death rate of 7.1% compared with 3.7% for the nine
operators who had performed ?15 CAS procedures.17
Our analysis was unable to demonstrate a significant
difference for stroke rates based on practitioner volume,
although this finding may be biased by the relatively small
sample size and the rare event of stroke. No differences
were noted for stroke or other complications, but we did
find an association between experience and specialty with
resource utilization for CAS.
Outcomes for CAS were similar for all practitioners,
variation may be predicated on discrepancies in training,
medical background, in-hospital work up, and endovascu-
lar skill sets. Kilaru et al27demonstrated CEA was cost-
saving compared to CAS owing to the higher rate of stroke
with CAS and the high cost of stents. We have demon-
strated that CAS cost can also vary significantly based on
the practitioner. Medical supply costs were significantly
greater for cardiologists compared with the other groups.
Table IV. Hospital resource utilization for patients with carotid artery stenting by specialist volume
High (?20)Medium (10-19) Low (?10)
Hospital LOS, days
1.7 ? 1.41.7 ? 1.22.4 ? 4.1
13,193 ? 9095
4496 ? 5692
8442 ? 3983
3060 ? 2372
19,235 ? 19,236
8800 ? 9043
LOS, Length of stay.
aData are presented as the mean ? standard deviation.
JOURNAL OF VASCULAR SURGERY
Volume 49, Number 5
Vogel et al 1169
Reasons for this may include the number of catheters and
the types of equipment used by cardiologists. Beyond sup-
ply costs, hospital resource utilization also varied by spe-
cialty. Vascular surgeons as a whole had the shortest LOS
after CAS intervention and the lowest ICU costs. Previous
studies looking at specialties in medicine found different
related to specialty.22
It is also possible that the disparities noted for CAS may
be influenced by volume, experience, and credentialing.
Studies of multiple procedures have demonstrated that
surgeons with higher volumes demonstrated consistently
lower mortality and morbidity rates than surgeons with low
volumes.6,28,29It has also been demonstrated that vascular
surgeons with basic catheter and guidewire skills can be-
come credentialed to perform CAS with 10 to 30 proce-
dures.17A subset analysis of this study failed to demon-
but this may be secondary to the sample size and power
required for this type of analysis.
A subset analysis of resource utilization according to
practitioner volume, regardless of specialty, did demon-
strate significant differences in resource utilization between
high- and low-volume practitioners. High-volume practi-
tioners used significantly fewer medical supplies and signif-
icantly less hospital resources overall. These data suggest
that practitioners with greater experience and larger proce-
dural volume may have more efficient use of resources to
streamline and accomplish the same procedure.
Further analysis to elucidate disparities between practi-
tioner specialties was performed. Elixhauser comorbidities
were analyzed on patients treated by the three specialties.
Significant differences in comorbidities were found among
the patients of cardiologists, vascular surgeons, and radiol-
ogists. This analysis indicates that the cardiology cohort
had a greater number of comorbidities, which may explain
variations in greater length of stay but fails to fully elucidate
the medical supply utilization variation of the CAS proce-
To further evaluate higher utilization by cardiologists,
secondary procedures, including cardiac catheterization
and percutaneous transluminal angioplasty, were analyzed.
There was not a significant increase in secondary proce-
dures performed by cardiologists compared with the other
specialties. Cardiac interventions were the lowest in the
vascular surgery group at 1.1% and highest in the cardiol-
ogy group at 5.1%. To discern if secondary cardiac inter-
ventional cases affected our results, we excluded them from
the data set and performed a subset analysis. The new
results were similar to the previous ones, and no significant
changes in utilization were noted. Thus, reasons for varia-
tion among providers with different specialties and volume
still remains unclear.
Limitations for this study include that the NJ SID
database does not contain patients from military hospitals
or Veterans Affairs medical centers. The potential for inclu-
sion bias based on limited coding schemes for the many
clinical entities cannot be entirely excluded nor can con-
founding by indication of the procedures. Classification as
elective vs nonelective was based on the HCUP variable for
Another study limitation is the coding used for the
diagnosis of stroke. The NJ SID is an administrative dis-
charge data set based on billing. The data contained in the
NJ SID and other discharge data sets are limited by the
coding schemes created by AHRQ and ICD-9-CM codes.
It is possible that the definition of stroke and coding may
vary within the data set and may vary between institutions
and hospital coders. We expanded the stroke codes used in
this study with the rational that stroke is an acute diagnosis
of admission, patients were unlikely to carry an acute stroke
codes in their administrative discharge data unless this
event occurred during that hospitalization and likely in
association with a carotid intervention. Our group has
previously reported this methodology for the evaluation of
stroke after carotid interventions.30
Also possible is a type II error in evaluating the rates of
stroke for different practitioners due to the relativity small
sample size for the evaluation of a rare complication. Fi-
nally, we were not able to discern symptomatic patients
within the data set due to coding limitations. We acknowl-
edge that there is a trade-off in using administrative data
compared with smaller cohorts with more refined clinical
information. Both types of studies have drawbacks and
strengths, but we believe that administrative databases pro-
cedures, outcomes, and resource utilization.
Physician specialty did not significantly influence pa-
tient outcomes or complications. We have demonstrated
that hospital resource utilization did vary significantly by
specialty, with vascular surgeons having the lowest utiliza-
tion of hospital resources for CAS. As well, we have dem-
onstrated that high-volume practitioners used significantly
fewer medical supplies and had lower hospital resource
utilization for performing CAS regardless of specialty. The
reasons for these disparities remain unclear, and further
analyses examining possible explanations for these discrep-
ancies may offer future cost savings and increased standard-
ization of CAS.
Conception and design: TV
Analysis and interpretation: TV, VD
Data collection: VD
Writing the article: TV
Critical revision of the article: TV, PH, AG
Final approval of the article: TV
Statistical analysis: TV, VD
Obtained funding: Not applicable
Overall responsibility: TV
JOURNAL OF VASCULAR SURGERY
1170 Vogel et al
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