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Hospitalization Rates for Ischemic
Heart Disease -- United States, 1970-1986
Ischemic heart disease (IHD) is the leading cause of death in the
United States. Of all chronic diseases, it contributes the most to
the
health-care burden, including hospitalizations (1). This report
describes national trends in hospitalization rates by sex from 1970
through 1986 for IHD and its component diagnoses.
The annual number of hospitalizations was determined from the
first-listed diagnosis in the National Hospital Discharge Survey
(NHDS)
(2) of CDC's National Center for Health Statistics (NCHS).* NCHS
obtains these data from a multistage, stratified cluster sample of
nonfederal short-stay hospitals in the 50 states and the District
of
Columbia. The NHDS collects approximately 200,000 records per year.
Each year, 8800-11,600 patients in the sample were hospitalized
with a
first-listed diagnosis of IHD. Population estimates were determined
from data provided by the Bureau of the Census (5) and
Demo-Detail**
(6).
The general category of IHD includes all hospitalized persons with
a
first-listed diagnosis of 410 through 414 under both ICDA-8 and
ICD-9-CM (3,4). This grouping was subdivided for further analysis
as
follows: acute myocardial infarction (acute MI, ICDA-8 and
ICD-9-CM:
410); other acute and subacute forms of IHD (other acute IHD,
ICDA-8
and ICD-9-CM: 411); chronic IHD (ICDA-8: 412; ICD-9-CM: 412, 414);
and
angina pectoris (ICD-8 and ICD-9-CM: 413).
From 1978 to 1979, hospitalization rates for IHD declined by 98
hospitalizations per 100,000 men (9.5% change) and 113
hospitalizations
per 100,000 women (15% change) (Figure 1). These declines--the
largest
single yearly change from 1970 through 1986--coincided with the
discontinuation of ICDA-8 and the adoption of ICD-9-CM. As a result
of
the change in coding systems, many cases that would have been
assigned
codes 410-414 in ICDA-8 were assigned to ICD-9-CM codes 402
(hypertensive heart disease) and 429.2 (cardiovascular disease,
unspecified) (7).
Among men, hospitalization rates per 100,000 ranged from a low of
784
in 1970 to a high of 1066 in 1986; among women, rates ranged from a
low
of 570 in 1970 to a high of 718 in 1986. If the decrease from 1978
to
1979 is disregarded, the number of hospitalizations per 100,000 men
for
IHD increased an average of 25 per year from 1970 through 1986.
Similarly, the number per 100,000 women for IHD increased an
average of
17 per year from 1970 through 1986. The one exception to these
trends
occurred among men from 1983 to 1984, when the rate declined 39 per
100,000.
From 1970 through 1978, the male-to-female ratio of hospitalization
rates was 1.4. The sex ratio of hospitalizations for men was even
higher from 1979 through 1986, when it was 1.5.
The changes in hospitalization rates from 1970 through 1986 for IHD
obscured important differences among component diseases, in the
ratio
and difference of hospitalization rates between men and women, and
in
the pattern of changes over time (Figure 2).
The sex ratio for hospitalization rates varied considerably among
the
components of IHD and between ICD code periods. Among the component
ICD
codes of IHD, hospitalization rates for acute MI and chronic IHD
were
much greater for males than females, a characteristic of IHD as a
whole. By contrast, other acute IHD and angina pectoris showed
small
differences in hospitalization rates by sex. Differences between
sexes
were greater for acute MI, other acute IHD, and angina pectoris
from
1970 through 1978 than they were from 1979 through 1986; however,
for
chronic IHD, these differences were greater during 1979-1986.
Excluding changes in 1978-1979 and 1982-1983, rates for acute MI
showed
small average yearly increases from 1970 through 1986 of 5
hospitalizations per 100,000 men and 3 per 100,000 women. Since
1983,
acute MI hospitalization rates have increased slightly among both
men
and women despite a decrease in overall hospitalization rates (8).
Beginning in 1985, acute MI replaced chronic IHD as the most common
primary diagnosis among persons hospitalized for IHD.
Rates for chronic IHD among both men and women increased through
1976,
remained relatively unchanged through 1981, and declined sharply
thereafter. From 1981 through 1986, rates declined 40% among men
and
50% among women.
Rates for other acute IHD among both men and women were steady
through
1982, after which they increased. From 1983 through 1986,
hospitalization rates increased 227% among men and 213% among
women.
For women in 1986, only acute MI exceeded other acute IHD as a
first-listed diagnosis among the components of IHD.
Finally, angina pectoris showed very small but consistent average
increases of 5 hospitalizations per year from 1970 through 1986.
Although angina pectoris remains the least frequent diagnosis among
the
IHDs reviewed here, its rate has increased 266% among men and 439%
among women over this period (disregarding the change in coding
between
1978 and 1979).
Reported by: Office of Surveillance and Analysis, Center for
Chronic
Disease Prevention and Health Promotion; Hospital Care Statistics
Br,
Div of Health Care Statistics, National Center for Health
Statistics,
CDC. Editorial Note
Editorial Note: Hospitalization rates reflect a variety of
influences and often do not correspond to incidence or mortality
rates
in magnitude or trend (10).
Sex differentials in hospitalization rates for acute MI and chronic
IHD
are consistent with the incidence and mortality of IHD in general.
By
contrast, the data show few or no sex differentials in
hospitalization
rates for other acute IHD and angina pectoris. The lack of a sex
differential for these conditions may reflect health-care use
differences between men and women for conditions less
life-threatening
than acute MI, thereby obscuring a real difference in incidence.
Although IHD-associated mortality declined by 20% between 1968 and
1986
(11), hospitalization rates for IHD have increased overall since
1970.
The introduction of a prospective payment system based on diagnosis
related groups (DRGs) may have influenced hospitalization rates
after
1983 (12). Changes in hospital use patterns as well as substantial
progress in medical technology increased hospitalization rates for
IHD
while IHD mortality has declined dramatically (13). Finally,
improved
survival from bypass surgery among patients with stenosis of the
left
main coronary artery may have resulted in increased admissions of
patients suspected to be at risk for coronary events or advanced
disease (14-16).
The continued increasing hospitalization rate for acute MI and the
decreasing rate for chronic IHD after 1983 may be related to DRGs.
If
diagnoses are recorded to maximize hospital reimbursement, then
greater
specification of diagnosis might be expected. A large decrease in
the
DRG for atherosclerosis (age greater than 69 years and/or
complications
or comorbidity) may be associated with increases in three related
groups (17). However, a change in coding practices probably does
not
entirely explain the trends observed for hospitalization for IHD.
In the absence of an overall surveillance system for IHD incidence,
it
is unclear to what extent mortality declines represent a true
decrease
in risk and/or improvements in medical care. The observed increase
in
hospitalization for acute IHD may be a manifestation of improving
care
or may be related to other features of the health-care system. The
ultimate answer, which requires further investigation, will have
important policy implications for cardiovascular disease prevention
and
control.
References
Chronic Disease Planning Group, CDC. Positioning for prevention:
an
analytical framework and background document for chronic disease
activities. Atlanta, Georgia: US Department of Health and Human
Services, Public Health Service, 1986.
2.National Center for Health Statistics. National Hospital
Discharge
Survey (machine-readable data files). Hyattsville, Maryland: US
Department of Health and Human Services, Public Health Service,
1970-1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986.
3.National Center for Health Statistics. International
classification
of diseases, adapted for use in the United States. Eighth revision.
Washington, DC: US Department of Health, Education, and Welfare,
Public
Health Service, 1968; PHS publication no. 1693.
4.Health Care Financing Administration. The international
classification of diseases. Ninth revision: clinical modification.
2nd
ed. Washington, DC: US Department of Health and Human Services,
Public
Health Service, 1980; DHHS publication no. (PHS)80-1260.
5.Bureau of the Census. 1970-1980 intercensal population estimates
by
race, sex, and age (machine-readable data files). Washington, DC:
US
Department of Commerce, Bureau of the Census, nd.
6.Irwin R. 1980-1986 intercensal population estimates by race, sex,
and
age (machine- readable data file). Alexandria, Virginia:
Demo-Detail,
1987.
7.Duggar BC, Lewis WF. Comparability of diagnostic data: coded by
the
eighth and ninth revisions of the International Classification of
Diseases. Hyattsville, Maryland: US Department of Health and Human
Services, Public Health Service, 1987; DHHS publication no.
(PHS)87-1378. (Vital and health statistics; series 2, no. 104).
8.National Center for Health Statistics. 1987 summary: National
Hospital Discharge Survey. Hyattsville, Maryland: US Department of
Health and Human Services, Public Health Service, 1988; DHHS
publication no. (PHS)88-1250. (Advance data from vital and health
statistics; no. 159).
9.National Center for Health Statistics, Graves EJ. Utilization of
short-stay hospitals, United States, 1982: annual summary.
Hyattsville,
Maryland: US Department of Health and Human Services, Public Health
Service, 1984:50; DHHS publication no. (PHS)84-1739. (Vital and
health
statistics; series 13, no. 78).
10.CDC. Hospital discharge rates for four major cancers--United
States,
1970-1986. MMWR 1988;37:585-8.
11.Stern MP. The recent decline in ischemic heart disease
mortality.
Ann Intern Med 1979; 91:630-40.
12.McCarthy CM. DRGs--five years later. N Engl J Med
198;318:1683-6.
13.Feinleib M, Havlik RJ, Thom TJ. The changing pattern of ischemic
heart disease. J Car- diovasc Med 1982;7:139-145,148.
14.Mock MB, Ringqvist I, Fisher LD, et al. Survival of medically
treated patients in the Coronary Artery Surgery Study (CASS)
registry.
Circulation 1982;66:562-8.
15.Takaro T, Hultgren HN, Lipton MJ, Detre KM, Participants in the
Study Group. The VA Cooperative Randomized Study of Surgery for
Coronary Arterial Occlusive Disease. II. Subgroup with significant
left
main lesions. Circulation 1976;54(suppl III):III-107-17.
16.Killip T, Passamani E, Davis K, CASS Principal Investigators and
their Associates. Coronary Artery Surgery Study (CASS): a
randomized
trial of coronary bypass surgery--Eight years follow-up and
survival in
patients with reduced ejection fraction. Circulation 1985;72(suppl
V):V102-9.
17.Cohen BB, Pokras R, Meads MS, Krushat WM. How will
diagnosis-related
groups affect epidemiologic research? Am J Epidemiol 1987;126:1-9.
*Diagnoses for 1970-1978 are based on the International
Classification
of Diseases (ICD), Eighth Revision, Adapted (ICDA-8) (3); those for
1979-1986, on the ICD, Ninth Revision, Clinical Modification
(ICD-9-CM)
(4).
**This file contains midyear estimates of the population by race,
sex,
and age for 1980-1986. Use of trade names is for identification
only
and does not imply endorsement by the Public Health Service or the
U.S.
Department of Health and Human Services.
***As of 1982, NCHS coded acute MI as a first-listed diagnosis
whenever
it appeared on a hospitalization record with other circulatory
diseases
and was other than the first entry (9). Thus, the striking increase
from 1981 to 1982 in hospitalization rates for acute MI among both
men
and women resulted from a change in editing procedure by NCHS.
Because
the original first diagnosis was probably a circulatory condition,
the
decrease for chronic IHD from 1981 to 1982 also may have been
caused by
this change.
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