1116
Multicenter Review of Preoperative Risk Factors
for Carotid Endarterectomy in Patients
With Ipsilateral Symptoms
Larry B. Goldstein, MD; Douglas C. McCrory, MD; Pamela B. Landsman, MPH;
Gregory P. Samsa, PhD; Marek Ancukiewicz, PhD;
Eugene Z. Oddone, MD; David B. Matchar, MD
Downloaded from http://stroke.ahajournals.org/ by guest on June 15, 2017
Background and Purpose Randomized clinical trials have
shown that carotid endarterectomy decreases the risk of
subsequent stroke in patients with high-grade carotid stenosis
and ipsilateral transient ischemic attack or minor stroke. The
benefit of surgery is highly dependent on surgical risk. We
previously found that patients with ipsilateral hemispheric
symptoms were at greater risk of carotid endarterectomy
complications compared with those who were asymptomatic or
had nonipsilateral symptoms. The goals of the present study
were (1) to identify preoperative clinical factors that may
increase the risk of complications after carotid endarterectomy
in patients with ipsilateral hemispheric symptoms and (2) to
develop a risk index based on this patient-level data.
Methods Records from 1160 carotid endarterectomies performed at 12 academic medical centers composed the primary
data set. Hospital charts for the admission during which
carotid endarterectomy was performed were systematically
reviewed by abstractors using a defined protocol. The present
analysis was carried out on data from the subset of patients
who had carotid endarterectomy for ipsilateral hemispheric
symptoms. Candidate variables were identified based on
univariate Fisher's exact tests or x2 tests. A risk index was then
developed using those variables with a greater than 90%
probability of being associated with adverse outcomes.
Results Of the 697 patients with ipsilateral symptoms, 8.5%
had either stroke, myocardial infarction, or died during the
postoperative period of hospitalization. Those over the age of
75 had a greater risk of myocardial infarction (6.6% versus
2.3%, P= .024) but not of stroke or death (/>> .10). The overall
frequencies of adverse outcomes were also higher in the 5
patients with complete ipsilateral carotid occlusions (40%
versus 8.2%, P<.01), the 28 patients with ipsilateral intraluminal thrombus (17.9% versus 8.1%, P=.01), and the 65
patients with ipsilateral carotid siphon stenosis (13.9% versus
7.9%, P=.10). There were no differences in adverse outcomes
among those with different degrees of ipsilateral stenosis (30%
to 49%, 50% to 69%, and 70% to 99%). Adverse outcome
rates were similar regardless of the type of symptom (transient
ischemic attack, recent ipsilateral minor stroke, remote ipsilateral minor stroke). There were no significant differences in
adverse outcome rates based on sex, race, history of angina,
recent myocardial infarction, congestive heart failure, chronic
obstructive pulmonary disease, hypertension, degree of stenosis of the contralateral carotid artery, or presence of ulceration
in the ipsilateral artery (Fisher's exact tests, P>.10). A count
of variables with greater than 90% probability of being associated with adverse outcomes (age >75 years or angiographic
evidence of ipsilateral carotid occlusion, stenosis in the region
of the carotid siphon, or intraluminal thrombus) was used to
form a simple risk index. "High-risk" patients (one or more
risk factors) had more than two times the risk of complications
compared with "low-risk" patients who had no risk factors
(odds ratio, 2.18; 95% confidence interval, 1.25 to 3.81).
Conclusions Certain preoperative clinical variables may
place patients with ipsilateral symptoms at greater risk of
perioperative complications after carotid endarterectomy. Prospective validation of a simple risk index would provide an
additional method for assessing preoperative risk in endarterectomy candidates. (Stroke. 1994;25:1116-1121.)
Key Words • angiography • carotid endarterectomy •
clinical trials • prognosis • risk factors
T
scribed combined morbidity and mortality rates of 6%
to 20%. 1317 A retrospective survey of all carotid endarterectomies performed at Johns Hopkins Hospital over
a 10-year period found an 8.2% total rate of morbidity
and mortality.18 In a recent review of carotid endarterectomies performed at 12 academic medical centers, we
found that 6.9% of patients had at least one major
complication (death, 1.4%; nonfatal stroke, 3.4%; and
nonfatal myocardial infarction (MI), 2.1%. 19 Individual
patient-level risk factors were identified, and a risk
index was developed and validated. Of these individual
risk factors, one of the most important was a history of
ipsilateral hemispheric symptoms as an indication for
endarterectomy. Of the 1160 reviewed cases, 60% had
ipsilateral symptoms, 28% of patients were asymptomatic, and 12% had nonipsilateral symptoms. The complication rate (stroke, MI, or death) for those with
ipsilateral symptoms was nearly double that of the
remaining patients (8.5% versus 4.5%; * 2 , P<.01). This
he benefit of carotid endarterectomy in comparison to medical therapy alone is highly dependent on surgical risk. 15 Postoperative complication rates higher than the 4% to 6% reported in
randomized trials would eliminate the potential benefit
of the operation. 69 Although several surgical series
report perioperative complication rates of approximately 3%, 1 - 1012 community-based surveys have deReceived February 25, 1994; final revision received March 15,
1994; accepted March 15, 1994.
From the Center for Health Policy Research and Education
(L.B.G., D.C.M., G.P.S., M.A., D.B.M.) and the Divisions of
Neurology (L.B.G.) and General Internal Medicine (D.C.M.,
E.Z.O., D.B.M.), Department of Medicine, Duke University,
Durham, NC; and the Center for Health Services Research in
Primary Care (D.C.M., P.B.L., G.P.S., E.Z.O., D.B.M.) and
Division of Neurology (L.B.G.), Durham Department of Veterans
Affairs Medical Center, Durham, NC.
Correspondence to Larry B. Goldstein, MD, Box 3651, Duke
University Medical Center, Durham, NC 27710.
Goldstein et al Risk of Carotid Endarterectomy for Ipsilateral Symptoms
TABLE 1 .
1117
In-Hospital Complication Rates According to Symptom Status
Ml
Death
Stroke
Any
Symptom
N
%
P
%
P
<%
P
Ipsilateral
697
3.2
.40
5.7
<.OO4
1.6
.50
Other or none
463
2.4
2.2
1.1
C
P
Co
8 .5
<.01
4 .8
Ml indicates myocardial infarction; Any, presence of either Ml, stroke, or death. Univariate probabilities determined by x2 tests.
finding is of importance because, to date, carotid endarterectomy has been shown to be effective only for
those with high-grade stenosis and ipsilateral hemispheric symptoms. The present analysis focuses on this
clinically important subgroup of patients. The goals of
the present study were (1) to identify preoperative
clinical factors that may increase the risk of complication after carotid endarterectomy in patients with ipsilateral hemispheric symptoms and (2) to develop an
independent risk index based on this patient-level data.
Downloaded from http://stroke.ahajournals.org/ by guest on June 15, 2017
Methods
Details of the primary data collection methodology have
been reported previously.19 Briefly, 100 carotid endarterectomies each were selected randomly from all those performed
during the calendar years 1988 through 1990 at 11 of the 12
member hospitals of the Academic Medical Center Consortium (listed in "Acknowledgments"). Because of a lower
operative volume at the twelfth hospital, the 100 procedures
were randomly selected from those performed there during
the calendar years 1987 through 1990. Forty cases were
subsequently excluded from further analysis because the operative procedure was miscoded in administrative records.
Records from the remaining 1160 carotid endarterectomies
constituted the primary data set.
Hospital charts for the admission during which carotid
endarterectomy was performed were systematically reviewed
by abstractors using a defined protocol. Data included patient
demographics, comorbid diseases, neurological symptoms
(type, location, and frequency of symptoms), data from the
radiologists' reading of preoperative carotid angiograms, clinical details from the operative report, and postoperative
complications. In patients with prior ipsilateral stroke, when
sufficient data were available, the preoperative functional
deficit was rated as severe if the patient was totally dependent
on others for care or unable to work, moderate if the patient
had some deficit but was independent or able to work, and
mild if there was no associated disability. Angiographic risk
factors were considered absent unless specifically recorded in
the radiologist's report. Abstracted data forms (along with
xerographic copies of discharge summaries, angiograms, and
operative reports) were reviewed by a study investigator.
Adverse outcomes included postoperative in-hospital strokes,
Mis, and deaths occurring during the hospitalization for
carotid endarterectomy.
Univariate Fisher's exact tests were used to identify potentially important predictors (ie, P<.10). x2 Statistics were used
for comparisons of categorical data as indicated. Logistic
regression modeling was not appropriate because the number
of outcome events was relatively small, and the number of
potential risk factors was relatively large (regression analysis is
unreliable when there are fewer than 10 times as many
outcome events as there are candidate variables).20 A splitsample design for model development and validation was not
feasible because of sample size considerations.21 The final risk
index was obtained by counting the number of risk factors for
each patient. Risk was stratified into "low" and "high" groups
for the outcomes of nonfatal stroke, nonfatal MI, or death.
The odds ratio with 95% confidence interval, positive likelihood ratio, and negative likelihood ratio were calculated.22
Results
An initial analysis of the data failed to reveal any
significant differences in adverse outcomes among the
12 hospitals that constitute the Academic Medical Center Consortium.19 Therefore, hospital-level variables
were not further considered, and the data were collapsed for further analysis.
Table 1 compares the frequencies of perioperative
complications in the 697 patients undergoing carotid
endarterectomy for ipsilateral symptoms with the 463
patients who were either asymptomatic or had nonipsilateral symptoms. None of the patients with prior
ipsilateral stroke for whom sufficient data were available (n=55) were rated as having a severe preoperative
functional deficit. Overall, patients with ipsilateral
symptoms had a higher frequency of in-hospital stroke
but not MI or death. Table 2 gives the frequencies of
adverse outcomes according to each type of presenting
symptom in comparison to the remaining patients with
other types of ipsilateral symptoms (ipsilateral transient
ischemic attack, stroke within 3 weeks of endarterectomy, stroke beyond 3 weeks of endarterectomy, or
evolving stroke). Because there were no significant
differences according to symptom type, the data were
collapsed for further analysis.
Table 3 lists candidate variables with the frequencies
of adverse outcomes and associated univariate probabilities. The only significant medical and demographic
variable was age >75 years. Those patients over the age
of 75 had a greater risk of MI (6.6% versus 2.3%,
P=.O24) but not stroke or death (P>.10). Significant
angiographic variables included complete occlusion, evidence of intraluminal thrombus, and stenosis near the
carotid siphon of the ipsilateral internal carotid artery.
The frequencies of all three adverse outcomes were
higher for the 5 patients with complete ipsilateral
carotid occlusions compared with those without occlusion (MI, 20% versus 3%, Ps.03; stroke, 40% versus
5.5%, F<.001; death, 20% versus 1.5%, P<.001). The
28 patients with ipsilateral intraluminal thrombus had a
higher risk of stroke (14.3% versus 5.4%, P=.O7) but not
MI (7.1% versus 3.0%, P=.22) or death (3.6% versus
1.5%, F=.37). Two of the 28 patients with intraluminal
thrombus had an associated complete carotid occlusion.
The overall adverse experience rate was also higher for
the 65 patients with ipsilateral carotid siphon stenosis
(Table 3), but individual complication rates did not
differ significantly (MI, 6.2% versus 2.9%, f=.14;
stroke, 9.2% versus 5.4%, P=.25; death, 1.5% versus
1.6%, P=1.0). Nonsignificant medical and demographic
variables (P>.10) included sex, race (nonwhite versus
white), history of MI within the previous 6 months,
congestive heart failure, chronic obstructive pulmonary
disease, impairment in activities of daily living prior to
surgery, and any subsequent major operative procedure
(except coronary artery bypass grafting) during the
hospitalization. Nonsignificant angiographic risk factors
included the degree of stenosis of the operated (other
than complete occlusion) or contralateral carotid artery
and the presence of ulceration on arteriogram. There
1118
Stroke Vol 25, No 6 June 1994
TABLE 2.
Presenting Ipsilateral Symptoms and Complication Rates
Ml
Death
Stroke
Any
N
%
P
%
P
%
P
%
P
Yes
509
3.1
1.00
5.7
1.00
1.2
.18
8.5
1.00
No
188
3.2
Symptom
TIA
2.7
5.9
8.5
Stroke <3 weeks
Yes
68
1.5
No
629
3.3
Yes
115
3.5
No
582
3.1
5
20.0
692
3.0
.71
5.9
1.00
5.7
1.5
1.00
1.6
7.4
1.00
8.6
Stroke >3 weeks
.77
5.2
1.00
2.6
.40
1.4
5.8
8.7
.86
8.4
Evolving stroke
Yes
No
.15
20.0
5.6
.26
20.0
1.5
.08
20.0
.36
8.4
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Ml indicates myocardial infarction; TIA, transient ischemic attack; and Any, presence of either Ml, stroke, or death. The
frequencies of adverse outcomes according to each type of presenting symptom in comparison to the remaining patients
with other types of ipsilateral symptoms (ipsilateral TIA, stroke within 3 weeks of endarterectomy, stroke beyond 3 weeks
of endarterectomy, or evolving stroke) are given. The term "evolving stroke" refers to patients with a progressing
neurological deficit. Univariate probabilities were determined by Fisher's exact tests (two-tailed) for in-hospital complications of Ml, stroke, death, or any complication.
was no difference in the frequency of adverse outcomes
when the 551 patients with 70% to 99% ipsilateral
stenosis were compared with the 146 remaining patients
(eg, 5 patients with complete occlusion and 141 patients
with less than 70% ipsilateral carotid stenosis; 8.2%
versus 9.6%, P=.61) or when the 5 patients with complete occlusion were excluded (8.2% versus 8.5%,
F=.9O).
A simple risk index was obtained by counting the
number of risk factors among patients with age >75
years, arteriographic evidence of ipsilateral carotid occlusion, intraluminal thrombus, and siphon stenosis.
The overall risk as indicated by increasing numbers of
univariate risk factors in individual patients was significantly related to adverse outcome. Because of the
relatively small number of patients with more than one
factor, risk was then stratified into low- and high-risk
groups. Low-risk patients were those who had no risk
factors. High-risk patients had one or more risk factors
(Table 4). Based on the dichotomized data, the odds
ratio for postoperative complications in high-risk versus
low-risk patients is 2.18 (95% confidence interval, 1.25
to 3.81) with a positive likelihood ratio of 1.66 and a
negative likelihood ratio of 0.32.
Discussion
The overall complication rate of 8.5% for postoperative nonfatal stroke, nonfatal MI, or death is similar to
prior community-based surveys.13-'s In the present
study, only adverse events occurring during the hospitalization for carotid endarterectomy were considered.
Because the study was retrospective, the definition of
perioperative complications as those occurring within 30
days of the surgical procedure was not used. Also,
unlike community surveys, the present analysis focused
on patients with ipsilateral symptoms undergoing endarterectomy. The observed complication rate is somewhat higher than that reported in recent randomized
controlled trials of patients with ipsilateral symptoms.6"8
However, the present study included nonfatal MI as an
adverse outcome, whereas the perioperative complication rates in these randomized trials included only
stroke or death.
Because of differences in the ways in which outcomes
were tabulated and variables defined, direct comparisons between different studies of the impact of individual potential risk factors on endarterectomy complications are difficult. The high risk of endarterectomy in
patients with ipsilateral occlusion has been noted in
previous reviews and case series.10-"'23-25 In a study
similar to the present work, Fode and coworkers13
carried out a multicenter retrospective review of the
results and complications of endarterectomy performed
in 1981 with 46 institutions contributing 3328 cases.
There was a 6.2% overall risk of perioperative (occurring during hospitalization) stroke or death, 4.2% risk of
nonfatal stroke, and 2.0% risk of death. Excluding 51
patients undergoing surgery for prior major stroke, 2170
patients (66%) had ipsilateral symptoms (assuming that
transient ischemic attack/amaurosis fugax [n = 1744],
minor stroke [n=388], and progressing stroke [n=38]
were ipsilateral). In the present study, 60% of patients
undergoing carotid endarterectomy had ipsilateral
symptoms. Table 5 gives the combined death and nonfatal stroke rates according to symptom type for each
study. The complication rates are virtually identical.
Thus, based on these data, the overall complication
rates of carotid endarterectomy for patients with ipsilateral symptoms have apparently remained stable between 1981 and 1988 through 1990, when the present
data were collected.
Aside from advanced age (>75 years), other potential
risk factors for carotid endarterectomy complications in
the present analysis were identified based on angiographic data. There is currently debate as to the need
for angiographic evaluation of carotid endarterectomy
candidates.26 Proceeding to endarterectomy solely on
the basis of noninvasive studies has been advocated.2728
Although carotid duplex studies may identify intralumi-
Goldstein et al
TABLE 3.
Risk of Carotid Endarterectomy for Ipsilateral Symptoms
1119
Potential Risk Factors
Complication Rate
Factor
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Medical and demographic
Sex
Male
Female
Race
Nonwhite
White
Age, y
<75
>75
Ml within 6 months
Yes
No
CHF
Yes
No
COPD
Yes
No
Impaired activities of daily living prior to surgery
Yes
No
Subsequent procedures
Yes
No
Severe hypertension
Yes
No
Angina
Yes
No
Angiographic
Stenosis of operated artery
No./n
38/441
21/256
8.6
8.2
.89
3/36
56/661
8.3
8.5
1.00
42/560
17/137
7.5
12.4
.09
3/16
56/681
18.8
8.2
.15
5/59
54/638
8.5
8.5
1.00
9/109
50/588
8.3
8.5
1.00
4/66
55/631
6.1
8.7
.64
1/9
58/688
11.1
8.4
.55
21/186
38/511
11.3
7.4
.12
22/229
37/468
9.6
7.9
.47
100%
<100%
2/5
57/692
40.0
8.2
70-99%
50-69%
30-49%
45/551
9/110
3/30
0/1
8.2
8.2
10.0
0
.97
5/48
54/649
10.4
8.3
.61
8/108
13/114
28/358
5/69
7.4
11.4
7.8
7.3
.62
20/213
39/484
9.4
8.1
.55
5/28
54/669
17.9
8.1
.07
9/65
50/632
13.9
7.9
.10
0-29% or not stated
Stenosis of contralateral artery
100%
<100%
70-99%
50-69%
30-49%
0-29% or not stated
Ulcer
Yes
No
Intraluminal thrombus
Yes
No
Siphon stenosis
Yes
No
Ml indicates myocardiai infarction; CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; No., number of
patients with a given complication; and n, total number of patients with or without a factor.
Univariate probabilities were determined by Fisher's exact tests (two-tailed). Complications were the adverse outcomes of stroke,
death, or myocardiai infarction. A factor was considered absent unless noted in the patient's medical record. Severe hypertension was
defined as preoperative blood pressure of greater than 180/110 mm Hg during endarterectomy hospitalization.
1120
Stroke Vol 25, No 6 June 1994
TABLE 4. Risk Index for Patients With Ipsilateral
Symptoms Undergoing Carotid Endarterectomy
Ml, Stroke, or Death
Count
0
6.4% (482)
1
12.2% (197) '
2
18.8% (16)
3
50.0% (2)
P=.0O1
6.4% (482)
13.0% (215)
P=.OO4
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Ml indicates myocardial infarction. The risk index is a simple,
unweighted count of significant (P<.1) factors based on univariate Fisher's exact tests (age >75, ipsilateral carotid occlusion,
siphon stenosis, and intraluminal thrombus as indicated in
preoperative angiographic reports). Numbers in parentheses
indicate the number of patients with the indicated factor count.
Percentages indicate the percent of patients with complications
(postoperative stroke, myocardial infarction, or death). The second column dichotomizes risk based on the presence of none
versus one or more factors. Probabilities are calculated with x2
statistics. Based on the dichotomized data, the odds ratio for
postoperative complications in patients with one or more risk
factors compared with those with no risk factors is 2.18 (95%
confidence interval, 1.25 to 3.81) with positive likelihood ratio of
1.66 and negative likelihood ratio of 0.32.
nal thrombus in some cases,29 the distinction between
complete carotid occlusion and high-grade stenosis can
be difficult,30-31 especially in the setting of contralateral
disease.32 Transcranial Doppler ultrasonography can be
used to evaluate the carotid siphon,33 but interpretation
of the study may be difficult in patients with proximal
stenosis.29 Thus, the data from the present analysis
suggest that careful angiographic evaluation may be
important in helping to better estimate surgical risk in
patients with ipsilateral symptoms irrespective of its role
in defining the degree of carotid stenosis in surgical
candidates.5
Several important caveats should be stressed. First, this
was a retrospective survey with all of its inherent limitations. Unless a factor was noted in the medical record, it
was considered to be absent. This is particularly important
with respect to the angiographic data. Second, variables
were chosen based on univariate tests of significance.
There may be significant intercorrelations among the
selected variables. Because the data were not amenable to
formal regression modeling, we cannot comment on the
independent contributions of the individual variables.
Third, the present risk index has not been validated. In
general, such indices tend to "overfit" the data from which
they were derived. This was the case when our overall
predictive risk index, derived from a randomly selected
portion of the data set, was validated against the remaining patients.19 As expected, we found that the predictive
index lost some statistical significance when it was applied
to the validation data set. Fourth, our original analysis was
designed to provide a method for risk stratification to
adjust for different levels of severity among institutions for
retrospective outcome research. Finally, because this was
not a randomized controlled trial, we cannot determine
how individuals with ipsilateral symptoms at higher risk of
complications would have fared without carotid endarterectomy. From the standpoint of the clinician making
decisions for individual patients, understanding these
points is critical. However, the present data provide tools
for comparative retrospective outcome research and quality assurance. Prospective validation of the present index
would provide an additional means for presurgical risk
assessment in individual patients. In the interim, these
data should be considered when carotid endarterectomy is
recommended.
Acknowledgments
We gratefully acknowledge the support of the Commonwealth Fund, the John A. Hartford Foundation, the American
Medical Association, the Academic Medical Center Consortium, the RAND Corporation, and the Agency for Health
Care Policy and Research, contract no. 282-91-0028.
Member institutions of the Academic Medical Center Consortium include: Alton Ochsner Medical Foundation, New
Orleans, La; Brigham and Women's Hospital, Boston, Mass;
Dartmouth-Hitchcock Medical Center, Lebanon, NH; Duke
University Medical Center, Durham, NC; Johns Hopkins
Hospital, Baltimore, Md; Massachusetts General Hospital,
Boston, Mass; Mayo Clinic Foundation, Rochester, Minn;
TABLE 5. Comparisons of the Impact of Selected Variables on Stroke or Death After Carotid
Endarterectomy Between the Previous Survey by Fode et al 1 3 and the Present Study for
Patients With Ipsilateral Symptoms
Nonfatal Stroke
Qualifying Symptom
N
Death
n (%)
P
n (%)
P
72(4.1)
.44
24(1.4)
.73
Transient ischemic attack
Fode et al
1744
509
25 (4.9)
Fode et al
388
20 (5.2)
Present
183
7 (3.8)
38
6(15.8)
5
0 (00.0)
Present
6(1.2)
Minor stroke
.48
10(2.6)
.78
4 (2.2)
Progressing stroke
Fode et al
Present
.34
2 (5.3)
.22
1 (20.0)
Total
Fode et al
Present
2170
98 (4.5)
697
32 (4.6)
.93
36(1.7)
.88
11 (1.6)
Only comparable variables are included. For study of Fode et al, 13 qualifying symptoms were presumed to
be ipsilateral to the side of carotid endarterectomy. Probabilities were determined by x2 tests.
Goldstein et al
Risk of Carotid Endarterectomy for Ipsilateral Symptoms
New England Medical Center Hospitals, Boston, Mass; UCLA
Medical Center, Los Angeles, Calif; University of Iowa Hospitals and Clinics, Iowa City, Iowa; University of Pennsylvania
Medical Center, Philadelphia, Pa; and University of Rochester
Medical Center, Rochester, NY.
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Stroke. 1994;25:1116-1121
doi: 10.1161/01.STR.25.6.1116
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