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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

  1. 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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