(Stroke. 1995;26:1724-1728.)
© 1995 American Heart Association, Inc.
Articles |
Epidemiology of Carotid Endarterectomy and Cerebral Arteriography in the United States
From the Centers for Disease Control and Prevention, Hyattsville, Md.
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Abstract |
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 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
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Background and Purpose Results of North American and European trials of carotid endarterectomy published in 1991 may have affected the frequency of the procedure in the United States. Therefore, data from a national survey of hospital discharges were examined to determine whether rates of carotid endarterectomy and arteriography increased after 1991 and whether race and sex variations in rates have persisted.
Methods Data from the National Hospital Discharge Survey were examined for the years 1980 through 1993. Estimated numbers of procedures performed in nonfederal US hospitals were used to compute rates per 100 000 population by year, age, race, and sex.
Results In persons aged 65 years and over, the rate of carotid endarterectomy increased rapidly between 1980 and 1983 with a slight further increase through 1985. A marked fall in the rate occurred between 1985 and 1988, followed by a plateau and a sharp upturn in 1992. After 1985, there was a steady decline in the rate of cerebral arteriography procedures in hospital. No reliable data were available on outpatient cerebral arteriography. Throughout the period, whites had estimated rates of carotid endarterectomy procedures over four times higher than blacks. Whites also had higher rates of cerebral arteriography, but the disparity was not as great as for endarterectomy. Rates of carotid endarterectomy were 60% higher in men than women, but rates of cerebral arteriography were only 9% higher in men than women.
Conclusions Rates of carotid endarterectomy increased sharply after the 1991 publication of trial results. Marked racial disparities in the use of this procedure persist and require further evaluation.
Key Words: blacks • carotid endarterectomy • cerebral angiography • clinical trials • women
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Despite long-term declines in death rates, stroke remains the third leading cause of death and the leading cause of serious disability in the United States.1 It is also a major contributor to healthcare costs. Hospitalization rates have not declined appreciably. Between 1970 and 1990, the percentage of patients hospitalized for stroke who were treated with surgical or diagnostic procedures increased from 15% to 57%.2 Results of NASCET and a European trial of CE showing benefits in symptomatic patients with severe carotid stenosis, which were published in 1991, may be expected to increase the frequency of that procedure in the United States.3 4 Furthermore, the repeated publication of studies documenting race- and sex-related disparities in the use of CE and other cardiovascular surgery over the past decade might also affect the relative rates of procedures in blacks compared with whites.5 6 7 8 Therefore, data from a national survey of hospital discharges were examined to describe patterns and trends in CE and arteriography by age, race, and sex in the United States from 1980 through 1993.
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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The NHDS produces estimates of numbers of patients discharged from nonfederal hospitals located in the 50 states and the District of Columbia.9 10 11 Eligible hospitals include those licensed facilities with at least six beds where the average length of stay for all patients was less than 30 days. Hospital discharges are selected for abstracting by a multistage sampling procedure. From more than 6000 hospitals, a sample of more than 500 was selected, of which more than 400 consented to participate and met eligibility criteria (exact numbers varied by year). Within hospitals, the daily listing sheet of discharges was the frame from which discharges were sampled randomly. For hospitals that provided data in electronic format, sampling was automated. Since discharges were sampled, an individual patient might appear more than once in the sample. Probabilities of selection at each stage of sampling were known, so that estimates of national statistics were obtained. Either hospital staffs or representatives of the NCHS performed the sample selection and transcribed information from the hospital record face sheet to abstract forms or extracted data from computer tapes. In 1988, a new sample design was put in operation, which may affect comparisons with earlier years.11
NCHS staff coded up to seven diagnoses and four procedures according to the ICD-9-CM.9 10 12 Discharges were enumerated with the following all-listed procedures: endarterectomy of carotid artery (ICD-9-CM 38.12) and arteriography of cerebral arteries using contrast material (ICD-9-CM 88.41). To obtain more reliable estimates given the relatively small numbers of cases in the sample, the average of data from 3 or more years was used in some analyses. The civilian resident population was used to compute discharge rates. Race was not stated on a substantial proportion of records (eg, about 12% of the records in 1988 through 1990); furthermore, the sample contained too few blacks with these procedures to permit computation of reliable discharge numbers or rates for each race by age and sex. An approximation of the variance of estimates using methods described previously is provided.9 For estimates from the NHDS of 50 000 and 100 000 with approximate relative standard errors of 10% and 7.6%, respectively, differences of approximately 13 000 and 21 000, respectively, are statistically significant at the P=.05 level.9
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Results |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Fig 1
shows the rate per 100 000 civilian
population of CE procedures by age in 1980 through 1993. In persons
aged 65 years and over, the rate of operation increased rapidly between
1980 and 1983 with a slight further increase through 1985. A marked
fall in the rate occurred between 1985 and 1988, followed by a plateau
and a sharp upturn in 1992. Similar but less pronounced trends were
seen at ages 45 to 64 years. Data from the NASCET and European CE
trials showing benefits of the procedure in symptomatic
patients with severe carotid stenosis were published in
mid-1991.
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The Table shows the estimated number of CE procedures
performed in the United States in 1980 through 1993. The number
increased steadily from 1980 until 1985, reaching a peak of 107 000.
Thereafter, the number declined until 1991. A marked increase in the
number of procedures was seen in 1992, with no further increase in
1993, when 89 000 procedures were performed. The relative standard
errors of 1992 and 1993 estimates are approximately 7.5%.
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Fig 2 shows the rate of cerebral arteriography
procedures performed in hospital by age in 1980 through 1993. In
persons aged 65 years and over, there was a marked increase in the rate
from 1980 through 1985, similar to that seen for CE. After 1985, there
was a steady decline in the rate of procedures, with no important
change between 1991 and 1992, and a further decline in 1993 at ages 65
years and over. Similar but less marked changes were seen at ages 45 to
64. The number of cerebral arteriography procedures in 1993 (96 000;
approximate relative standard error, 7.3%) was less than the number in
1980 (Table
). No reliable data were available on cerebral arteriography
procedures performed in outpatient settings.
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Throughout the period, whites had estimated rates of CE procedures much
higher than blacks (Fig 3). At the beginning and end of
the period, rates were over four times higher in whites than in blacks.
In the mid-1980s, rates were seven times higher in whites than blacks.
Whites also had higher rates of cerebral arteriography, but the
disparity was not as great as for endarterectomy
(Fig 4). Rates in whites were over 50% higher than
those in blacks before 1988 and 20% higher in 1988 through 1992.
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Fig 5 shows rates of both procedures in men and women
aged 45 years and over in 1991. Rates of CE were 60% higher in men
than women, but rates of cerebral arteriography were only 9% higher in
men than women.
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Marked fluctuations in the rates of CE and cerebral arteriography have occurred since 1980. A marked rise before 1985 was followed by an equally striking decline. A sharp increase in the number and rate of endarterectomy procedures in 1992 is consistent with an effect on medical practice of the publication in mid-1991 of the results of two major trials of CE, which supported continued use of the procedure.3 4 This higher rate was essentially unchanged in 1993 and was still considerably below the rates of 1983 through 1985. Unfortunately, the present data do not permit a determination as to whether the increase occurred only in the subset of patients for whom the procedure was recommended, namely symptomatic patients with severe carotid stenosis. A US Veterans Affairs study found that only 1 in 27 patients referred for evaluation of cerebral ischemia fit the criteria for surgical intervention.13 Major disparities between blacks and whites in the use of CE and cerebral arteriography were documented through 1992. Some disparity was also suggested for women.
NASCET collaborators speculated that the publishing of results of North American and European trials in 1991 might increase the frequency of CE in the United States.3 4 US hospitalization data presented here suggest that this indeed occurred. NASCET found significantly reduced risk of major stroke and death in patients with recent transient ischemic attack or nondisabling stroke and ipsilateral severe carotid stenosis (70% to 99%) among those randomized to surgery compared with medical care. Both groups received antiplatelet therapy. The European trial showed no benefit for patients with mild stenosis (0% to 29%) but a clear benefit for symptomatic patients with 70% to 99% stenosis.4 A US Veterans Affairs trial was terminated because of NASCET and European trial results; however, a significant benefit of CE was nevertheless demonstrated in symptomatic men with ipsilateral carotid stenosis >50%.13 Definitive data were still lacking pending completion of further trials for patients with moderate carotid stenosis (30% to 69%) and for asymptomatic stenosis. Thus, in 1992 and 1993 recommendations were that surgery is indicated only for the subset of patients with recent cerebrovascular symptoms and ipsilateral severe carotid stenosis.3 However, in 1994 the National Institute of Neurological Disorders and Stroke issued a clinical alert announcing interim results of the Asymptomatic Carotid Atherosclerosis Study of a statistically significant relative risk reduction of 55% for stroke or death in patients with asymptomatic carotid stenosis greater than 60% reduction in diameter.14 Therefore, further increases in rates of endarterectomy may be expected.
The reversal of a long-term upward trend in rates of endarterectomy in 1985 through 1986 was attributed to a number of publications in 1985 through 1986 questioning the indications for the procedures.15 The introduction of prospective payment for Medicare patients and diagnosis related groups in 1983 through 1986 could also have had some impact. The role of utilization review in the decline between 1985 and 1988 is also worthy of study. The decline in rates of cerebral arteriography in hospitals since 1985 was likely due in part to the shift of substantial numbers of procedures from the inpatient to the outpatient setting16 and to increasing use of noninvasive techniques such as duplex ultrasonography in lieu of arteriography, as well as to the above factors. Although specific ICD-9-CM codes for such procedures were lacking in the years studied, the estimated number of inpatient procedures coded as diagnostic ultrasound of the head and neck (ICD-9-CM 88.71) increased from 54 000 in 1985 to 131 000 in 1992.
Fluctuations in the rates of endarterectomy did not appear related to trends in overall cerebrovascular disease death rates or hospitalization rates. Death rates have declined throughout the period.1 2 6 7 17 Hospitalization rates increased between 1970 and 1985, falling thereafter.1 2 6 17
Despite declining mortality rates through 1991, US blacks have higher stroke mortality rates than whites under age 85 years.6 7 17 The excess mortality in blacks is similar for cerebral infarction and cerebral hemorrhage.18 Blacks have also been found to have higher incidence and prevalence rates of stroke and higher hospital case-fatality rates than whites.7 These patterns are in striking contrast to those for CE reported here.
A number of studies reviewed elsewhere have reported an increased
occurrence of intracranial compared with extracranial occlusions of
cerebral arteries in series of patients having cerebral arteriography
and a lower occurrence of transient ischemic attacks in blacks
compared with whites.7 Blacks may have a greater
occurrence of small-vessel disease intracranially than whites. These
findings indicate a prevalence of surgically treatable carotid
stenosis in blacks that is lower than might be expected from
stroke mortality data. However, given the much higher stroke incidence
and mortality in blacks, it remains to be determined how much greater
the absolute prevalence of carotid stenosis in the population
is in whites than blacks, especially among women. Few population-based
data are available.7 19 20 Data were reported from a
population sample that included a relatively small number of blacks
aged 65 years and over studied by B-mode ultrasound.21 22
Comparing blacks with whites, carotid stenosis 
50% was 40%
more prevalent in white than black men and twice as prevalent in white
than black women, differences which did not attain statistical
significance.22 However, the excess was much less than the
four to seven times white excess in CE rates (Fig 3). Furthermore, at
ages 45 to 64 years, the thickness of the carotid wall (an indicator of
arteriosclerosis) at three sites was greater in
blacks than whites.23
A recent study of US veterans with symptomatic cerebrovascular disease indicated that age, access to care, socioeconomic status, comorbidity, and geographic region did not explain the lower likelihood of black than white patients of undergoing cerebral arteriography (adjusted risk ratio, 0.47) or endarterectomy (adjusted risk ratio, 0.28).5 In a series of patients having carotid endarterectomies in North Carolina, blacks were underrepresented.24 Only 3% of randomized patients in NASCET were black.20 Racial disparities in the use of coronary bypass surgery have been well documented; these are not explained by coronary anatomy or disease severity.8 25 Further studies incorporating ultrasound and arteriographic findings are needed to determine the basis of the disparity and the possible need for intervention.
Limitations of NHDS data for the study of patterns and trends in cardiovascular procedures have been discussed elsewhere and include possible inaccuracies in listing and coding of procedures.6 8 In recent years, substantial numbers of cerebral arteriography procedures were probably performed in outpatient settings.16 Unfortunately, the NHDS had no information on outpatient procedures, and the National Hospital Ambulatory Medical Survey of 1992 and 1993 did not have a sufficient sample size to provide a reliable estimate for cerebral arteriography.26 Thus, trends in total numbers of cerebral arteriography procedures cannot be accurately assessed in more recent years (after 1985). Furthermore, the NHDS sample was not large enough to provide reliable estimates of perioperative death rates.
A limitation for analyses by race is the substantial number of
discharges with race not stated (13% of discharges with CE in 1992).
An unpublished study indicates that for the period 1988 through 1992
this affected estimates for whites to a greater extent than estimates
for blacks, resulting in a possible slight underestimate of the number
and rate of procedures in whites (shown in Fig 3, J. Kozak, NCHS,
unpublished data, Who is Missing? Race Data from the National
Hospital Discharge Survey, presented at the American
Public Health Association Annual Scientific Sessions, November
2, 1994). Thus the racial disparity in procedures may be, if anything,
even greater than that shown. This problem is not limited to this
survey, since data on race were missing for 9% of procedures in a
study in which the medical records of Medicare patients were
abstracted.27
Continued monitoring of trends in CE and cerebral arteriography will be useful in assessment of the impact of clinical trials, studies of appropriateness of technology use, and effects of changes in the healthcare system on the use of these procedures. Studies using clinical, noninvasive, and arteriographic databases are needed to establish whether the lower utilization of CE in blacks than whites is due to a lower prevalence of severe carotid stenosis in blacks than whites, to less frequent surgery in black than white patients with equivalent degrees of carotid stenosis, or both. Further studies using B-mode ultrasonography of the external carotid arteries in larger population samples may help to establish the prevalence of early arteriosclerotic changes and severe carotid stenosis in blacks compared with whites.
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Selected Abbreviations and Acronyms |
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Footnotes |
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Reprint requests to R.F. Gillum, MD, Centers for Disease Control and Prevention, National Center for Health Statistics, 6525 Belcrest Rd, Hyattsville, MD 20782.
Received April 4, 1995; revision received May 16, 1995; accepted June 12, 1995.
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References |
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