Low socioeconomic status (SES) is associated with an

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1 Relationship of Socioeconomic Status to the Incidence and Prehospital, 28-Day, and 1-Year Mortality Rates of Acute Coronary Events in the FINMONICA Myocardial Infarction Register Study Veikko Salomaa, MD, PhD; Matti Niemelä, MD; Heikki Miettinen, MD, PhD; Matti Ketonen, MD, PhD; Pirjo Immonen-Räihä, MD, PhD; Seppo Koskinen, MD, PhD; Markku Mähönen, MD, PhD; Seppo Lehto, MD, PhD; Tapio Vuorenmaa, MD, PhD; Pertti Palomäki, MD, PhD; Harri Mustaniemi, MD, PhD; Esko Kaarsalo, MD, PhD; Matti Arstila, MD, PhD; Jorma Torppa, MSc; Kari Kuulasmaa, PhD; Pekka Puska, MD, PhD; Kalevi Pyörälä, MD, PhD; Jaakko Tuomilehto, MD, PhD Background Low socioeconomic status (SES) is associated with increased coronary heart disease mortality rates. There are, however, very little data on the relation of SES to the incidence, recurrence, and prognosis of myocardial infarction (MI) events. Methods and Results The FINMONICA MI Register recorded detailed information on all MI events among men and women aged 35 to 64 years in 3 areas of Finland during the period of 1983 to We carried out a record linkage of the MI register data with files of Statistics Finland to obtain information on indicators of SES, such as taxable income and education, for each individual who is registered. In the analyses, income was grouped into 3 categories (low, middle, and high), and education was grouped into 2 categories (basic and secondary or higher). Among men with their first MI event (n 6485), the adjusted incidence rate ratios were 1.67 (95% CI 1.57 to 1.78) and 1.84 (95% CI 1.73 to 1.95) in the low- and middle-income categories compared with the high-income category. For 28-day mortality rates, the corresponding rate ratios were 3.18 (95% CI 2.82 to 3.58) and 2.33 (95% CI 2.03 to 2.68). Significant differentials were observed for prehospital mortality rates, and they remained similar up to 1 year after the MI. Findings among the women were consistent with those among the men. Conclusions The excess coronary heart disease mortality and morbidity rates among persons with low SES are considerable in Finland. To bring the mortality rates of low- and middle-ses groups down to the level of that of the high-ses group constitutes a major public health challenge. (Circulation. 2000;101: ) Key Words: infarction coronary disease heart diseases socioeconomic status Low socioeconomic status (SES) is associated with an increased risk of coronary heart disease (CHD) death. The reduction in socioeconomic health differentials has been an important goal of health policy in many countries, including Finland. 1 The existing information in this field is, however, of a rather general nature, often based on routine mortality statistics or on the use of surrogate indicators of SES, such as the mean income or education level of the area of residence. 2,3 More precise data on the relation of SES to the incidence, mortality rates, and prognosis of acute coronary events are needed to achieve a reduction in excess CHD deaths among the lower-ses groups. Finland is a Nordic country with a governmentsubsidized health care system and a strong emphasis on egalitarian health care and welfare policies. 1 During the past 25 years, CHD mortality rates in Finland have declined by 60%. 4,5 This decline has been in large part due to improved risk factor levels and primary prevention, but especially lately, improved treatment and secondary prevention have contributed markedly. 5,6 Despite the remarkable general improvement, the socioeconomic differentials in CHD mortality rates have not narrowed. In fact, some studies have suggested that the gap between the socioeconomic groups may be widening. 7 Received August 31, 1999; revision received November 5, 1999; accepted November 19, From the KTL-National Public Health Institute (V.S., S.K., M.M., J. Torppa, K.K., P. Puska, J. Tuomilehto), Helsinki, Finland; Loimaa Regional Hospital (M.N., E.K.), Loimaa, Finland; Department of Medicine (H.M., S.L., P. Palomäki, K.P.), University of Kuopio, Kuopio, Finland; North Karelia Central Hospital (M.K., H.M.), Joensuu, Finland; Heart and Stroke Center (P.I-R.), Turku, Finland; and Department of Medicine (T.V., M.A.), University of Turku, Turku, Finland. Correspondence to Veikko Salomaa, KTL-National Public Health Institute, Department of Epidemiology and Health Promotion, Mannerheimintie 166, FIN Helsinki, Finland. veikko.salomaa@ktl.fi 2000 American Heart Association, Inc. Circulation is available at

2 1914 Circulation April 25, 2000 The FINMONICA Myocardial Infarction (MI) Register Study has provided detailed information on the incidence, mortality rates, and treatment of acute MI events in Finland. 5,8 We carried out a record linkage of the MI register data with several indicators of SES, such as taxable income and education, that were obtained from the files of Statistics Finland. This database provided us with a method of examining the relation of SES to the incidence and prehospital, 28-day, and 1-year mortality rates of acute MI events during 1983 to Methods Data for the present analyses originate from the FINMONICA MI Register Study, which is the Finnish contribution to the WHO MONICA Project (Multinational Monitoring of Trends and Determinants of Cardiovascular Disease 9,10 ). Registration methods and the main findings of the FINMONICA MI Register Study have been published. 5,8 The 10-year study period covered the years of 1983 to Monitored areas were the provinces of North Karelia and Kuopio in eastern Finland and the Turku/Loimaa area in southwestern Finland. Populations of the study areas remained stable during the study period, but annual population counts were obtained from Statistics Finland. In the middle of the registration period, 1988, the combined populations of these 3 areas within the age range of 35 to 64 years were men and women. Each event that was suspected of being a coronary-related death or nonfatal MI that occurred among residents of the study areas was evaluated for registration. The main sources for case finding were hospital admission diagnoses and death certificates of the area. At the National Public Health Institute, the data were further crosschecked with the National Causes-of-Death Register and the National Hospital Discharge Register for completeness. Suspected coronary events were classified on the basis of symptoms, serial Minnesota Codes of ECGs, cardiac enzymes, and, in fatal cases, autopsy findings and history of CHD. Fatal definite and fatal possible MIs as well as nonfatal definite and nonfatal possible MIs (according to the criteria used in the FINMONICA MI Register Study) were included in the present study. The diagnostic criteria for these events have been published. 10,11 In the analyses of the present report, the main emphasis was on first-ever coronary events. Recurrent events were analyzed in relation to education only, because earlier MIs may have had an influence on the income level and SES of the patient. The term incidence refers to first coronary events without any evidence of a clinically recognized previous event in the patient s history. Recurrent events refer to such coronary events where the patient has a history of 1 previous MIs. Death was examined at 3 time points: (1) before reaching the hospital (prehospital deaths) or, in case of recurrent events, deaths 1 day since the beginning of symptoms; (2) at 28 days since the beginning of symptoms; and (3) at 365 days since the beginning of symptoms. Prehospital and 1-day deaths, as well as the 28-day survival rates, were recorded in the FINMONICA MI Register, but the 1-year survival status was obtained through record linkage with the MI register data with the National Causes-of-Death Register. Data on SES were obtained through record linkage with the MI register data with files of Statistics Finland on the basis of personal identification number, which is unique to every resident of Finland. Taxable income and education level for each individual were available for the years 1980, 1985, and The closest records of personal income and education level before the first MI event were used as indicators of SES. For statistical analyses, the income data were grouped into 3 categories: low, middle, and high. Cutoff limits of the income categories were adjusted as necessary for the 1985 and 1990 data to take into account inflation and to keep the relative size of each category constant during the entire 10-year study period. On average, 26.2% of men belonged in the low-income group, 31.9% belonged in the middle-income group, and 41.9% belonged in the high-income group. Among women, the corresponding proportions were 38.9%, 21.4%, and 39.7%. was used as a 2-level TABLE 1. Number of All First (Incident) MI Events and First Events That Were Fatal at Different Time Points After the Infarction and Their Distribution by Taxable and Among and Aged 35 to 64 Years in the FINMONICA MI Register Study During 1983 to 1992 Incident Events, Prehospital, 0 to 28-d, 0 to 365-d, Low 2429 (37.5) 823 (50.6) 1063 (49.5) 1183 (49.3) Middle 2630 (40.6) 573 (35.2) 771 (35.9) 872 (36.4) High 1426 (22.0) 231 (14.2) 312 (14.5) 343 (14.3) Basic 4856 (74.9) 1313 (80.7) 1724 (80.3) 1922 (80.2) Secondary 1629 (25.1) 314 (19.3) 422 (19.7) 476 (19.8) or higher Low 1275 (65.0) 178 (70.0) 321 (72.0) 375 (72.3) Middle 357 (18.2) 45 (17.7) 71 (15.9) 84 (16.2) High 310 (15.8) 31 (12.2) 54 (12.1) 59 (11.4) Basic 1563 (79.7) 220 (86.6) 382 (85.7) 442 (85.3) Secondary or higher 379 (19.3) 34 (13.4) 64 (14.3) 76 (14.7) There were a total of 6485 incident events among men and 1942 events among women. variable: basic, corresponding to 9 years of education, and secondary or higher, corresponding to 10 years of full-time education. Similar data on the income and education distributions in the populations of the study areas were obtained as well and were used as the denominators in the analyses. Interpolation was used to obtain annual population counts for each income group for the interval years between 1980, 1985, and Statistical Analysis The relationship of the SES indicators to MI incidence and coronary mortality rates was similar in all 3 study areas, so the data were pooled for the analyses. Incidence and mortality rates were expressed per inhabitants of the same socioeconomic group per year and age-standardized to the world standard population. 12 The trends in event rates in different education groups were determined with the use of Poisson regression analysis with the natural logarithm of age-standardized rate as a dependent variable and the year as an independent variable. 10 Poisson regression analysis was also used to compute rate ratios and 95% CIs of first MI events in the low- and middle-income categories compared with the high-income category and in the basic education category compared with the secondary or higher education category. The statistical analyses were carried out with the use of software from SAS Institute. 13 Results Of the 8445 first (incident) MI events, 2592 (30.7%) were fatal within 28 days. Among men, 22% of all first events and 14% of fatal first events occurred in the high-income group, whereas 38% of all first events and approximately half of fatal first events occurred in the low-income group (Table 1). Among women, 16% of all first events and 12% of fatal first events occurred in the high-income group, whereas 65%

3 Salomaa et al Socioeconomic Status and CHD Events 1915 Trends in age-standardized incidence and 28-day mortality rates from incident MI events (per inhabitants) by education level among men (top) and women (bottom) aged 35 to 64 years. Among men, incidence declined by 3.4% per year (95% CI 2.3% to 4.5%, P ) in persons with basic education and by 5.2% ( 3.8% to 6.6%, P ) in persons with secondary or higher education. Corresponding declines in 28-day mortality rates were 3.3% ( 1.5% to 5.1%, P ) and 3.7% ( 1.0% to 6.4%, P 0.009). Among women, annual average declines in incidence were 2.9% ( 0.8% to 5.0%, P 0.007) and 3.3% ( 0.3% to 6.3%, P 0.03). In 28-day mortality rates, corresponding declines were 1.7% (2.5% to 5.9%, P 0.42) and 6.1% (1.1% to 13.3%, P 0.10). Trend estimates are adjusted for study area and urban/rural residence. of all first events and 70% of fatal first events occurred in the low-income group. Considerable declines during the 10-year study period were observed in the incidence and 28-day mortality rates in both persons with basic education and persons with secondary or higher education (Figure). Among men, the declines were parallel in the 2 education groups, and no narrowing of the gap was seen between the groups. Among women, the data suggested a steeper decline in 28-day mortality rates among persons with a better education, but the 95% CIs were wide. Regarding incidence, the main difference was observed between the high- and middle-income groups, whereas regarding mortality rates, differences were observed both between the high- and middle-income groups and between the middle- and low-income groups at all 3 time points that were examined (Table 2). Differences between the 2 education groups were smaller than were differences between the 2 extremes of the 3 income groups. Nevertheless, persons with only a basic education had markedly higher incidence and mortality rates for first MI events than did persons with a secondary or higher education (Table 2). Nonfatal incident events also differed by SES; for example, among men, the rates for events that were nonfatal at day 28 were 369, 496, and 283 per persons for the low-, middle-, and high-income categories, respectively. In the attack and mortality rates of recurrent MI events, relative differences between the education groups were approximately similar to the differences in incident events (Table 3). Among men, the adjusted incidence rate ratio showed 1.84 and 1.67 times higher incidence rates in the middle- and low-income categories, respectively, than in the high-income category (Table 4). The adjusted mortality rate ratio showed 2.3 times higher mortality rates in the middle-income category and 3 times higher mortality rates in the lowincome category compared with the high-income category. Differences between the 2 education levels were again somewhat smaller than those between the 2 extremes of the 3 income groups, but the pattern was consistent in the sense that larger differences were observed for mortality rates than for incidence. The pattern of findings remained similar among women. with a low income or only a basic education had a 1.52 and 1.65 times higher adjusted incidence, respectively, and a 2 times higher adjusted mortality rate at each time point that was examined than did women with a middle or high income or with a secondary or higher education. Discussion The present study demonstrated 3 times higher mortality rates from first MI events in the lowest-income group than in the highest-income group. This excess mortality rate was in part due to the higher incidence and in part due to the higher number of prehospital deaths among the lowest-income group. Among patients who reached the hospital alive, the differences between the income groups remained consistent during the subsequent year. Interestingly, a significant difference in mortality rates from first MI events was also observed between persons with middle-class income and those with a high income. A corresponding observation has been reported concerning the relationship between the income level and more global health indicators in Finland; the prevalence of limiting longstanding illness and poor self-rated health was found to be clearly higher in the second income quintile than in the first (highest) income quintile. 14 These findings suggest that absolute material deprivation or economic hardship may not play a crucial role in the causation of health differences between income groups. Several studies in Finland and elsewhere have previously shown higher CHD mortality rates in lower-ses groups. 7,15 17 A strength of the present study is, however, the detailed nature of the FINMONICA MI register data, which allowed us to separately analyze first and recurrent MI events and to obtain new information on the timing of death since the beginning of symptoms up to 1 year after the onset of the

4 1916 Circulation April 25, 2000 TABLE 2. Age-Standardized Rates of All First MI Events (Incidence) and First Events That Were Fatal at Different Time Points After the Infarction by Taxable and Among and Aged 35 to 64 Years in the FINMONICA MI Register Study During 1983 to 1992 Prehospital 0 to 28-d 0 to 365-d Incidence Low 648 ( ) 221 ( ) 279 ( ) 310 ( ) Middle 697 ( ) 150 ( ) 201 ( ) 228 ( ) High 370 ( ) 63 (54 72) 87 (76 97) 96 (85 107) Basic 636 ( ) 169 ( ) 219 ( ) 244 ( ) Secondary or higher 420 ( ) 82 (73 92) 113 ( ) 128 ( ) Low 177 ( ) 27 (22 31) 45 (40 51) 52 (46 58) Middle 155 ( ) 19 (14 25) 31 (24 38) 37 (29 45) High 86 (76 96) 8 (5 11) 16 (12 21) 18 (13 22) Basic 165 ( ) 25 (21 28) 41 (36 45) 47 (42 52) Secondary or higher 99 (89 109) 9 (6 11) 17 (12 21) 20 (15 24) Rates are expressed per inhabitants per year with 95% CIs in parentheses. There were a total of 6485 events among men and 1942 events among women. event. Consistent with our results, the Scottish MONICA Study reported a higher prehospital mortality rate in lower- SES groups. 18 The magnitude of the differences is not comparable, however, because of the different methods used to classify the SES groups. Another strength of the present study is that we had the opportunity for record linkage of the MI register data with taxable income and education level for each individual. It leads to less misclassification than the use of surrogate markers of SES and therefore gives a more correct picture on socioeconomic health differentials. It has been shown that a better characterization of SES leads to the demonstration of mortality differentials that are considerably wider than those obtained when less precise measures are used. 19 We did not, however, have information on family income, which may be a source of some misclassification among women. In Finland, this may be less of a problem compared with many other countries, because a high proportion of Finnish women have their own careers and own income. More importantly, the data on education are also unbiased among women. Another potential source of concern is that a person may have had a low income due to angina pectoris, which in turn makes him or her more prone to experience MI or CHD death. The fact that we specifically investigated first-ever MI events made such a bias unlikely. Furthermore, the education level of an adult does not change as a consequence of illness and, accordingly, is also free of this possibility of bias. Interestingly, the pattern of SES differences was similar for recurrent MI events as for first events. Persons who have TABLE 3. Age-Standardized Attack Rates of All Recurrent MI Events and Recurrent Events That Were Fatal at Different Time Points After the Infarction by Among and Aged 35 to 64 Years in the FINMONICA MI Register Study During 1983 to 1992 Category All Recurrent Events at 24-h at 0 to 28-d at 0 to 365-d Basic 425 ( ) 125 ( ) 157 ( ) 190 ( ) Secondary or higher 275 ( ) 78 (68 88) 100 (89 111) 119 ( ) Basic 75 (69 81) 13 (11 15) 19 (16 22) 24 (21 27) Secondary or higher 44 (37 51) 8 (5 11) 9 (6 12) 11 (8 14) Rates are expressed per inhabitants per year with 95% CI in parentheses. There were a total of 4401 recurrent events among men and 898 events among women.

5 Salomaa et al Socioeconomic Status and CHD Events 1917 TABLE 4. Adjusted and Age-Standardized Rate Ratios of First MI Events (Incidence) and First Events That Were Fatal at Different Time Points After the Infarction by Taxable and Among and Aged 35 to 64 Years in the FINMONICA MI Register Study During 1983 to 1992 Prehospital at 0 to 28-d at 0 to 365-d Incidence Low 1.67 ( ) 3.39 ( ) 3.18 ( ) 3.18 ( ) Middle 1.84 ( ) 2.33 ( ) 2.30 ( ) 2.34 ( ) High Basic 1.48 ( ) 2.00 ( ) 1.92 ( ) 1.87 ( ) Secondary or higher Low 1.52 ( ) 2.09 ( ) 2.17 ( ) 2.15 ( ) Middle or high Basic 1.65 ( ) 2.81 ( ) 2.43 ( ) 2.34 ( ) Secondary or higher Rate ratios are adjusted for study area and urban or rural residence with 95% CIs in parentheses. Because of small numbers, the middle- and high-income categories were combined among women. survived a MI should have regular contacts with health care professionals for treatment and secondary prevention. It would be important to find out whether these contacts have reduced the SES differences in the risk of a recurrent event. Unfortunately, the incidence rate of recurrent events, expressed with population used as the denominator, does not allow direct inferences to be made regarding the recurrence risk by SES. Our data showed, however, that there were more nonfatal first events in the lower-ses group than in the higher-ses group. The higher rate of recurrent events in the lower-ses groups is therefore in part explained by the higher prevalence of first MI survivors in those groups compared with the higher-ses groups. The difference in recurrent events was quite substantial, however, and therefore it seems likely that there also were SES differences in the risk of recurrence among survivors of a first MI. This interpretation is supported by other reports in the literature, which have shown poorer survival and functional recovery rates after MI in patients from lower-ses groups Reasons for the differences between the SES groups in CHD mortality rates are complex and insufficiently known. Because a big difference was observed in the prehospital mortality rates for first MIs, it can be assumed that a large part of the difference is due to the SES differences in the main risk factors of CHD. Previous literature has shown considerable differences between the SES groups in the levels of cholesterol, blood pressure, and smoking in both Finland and elsewhere It has been repeatedly reported, however, that differences in these classic risk factors do not fully explain the difference in CHD mortality rates between the SES groups. 24,27,28 Thus, it is possible that differences in the treatment of chronic CHD, such as the use of -blockers and acetylsalicylic acid and the availability of revascularization procedures, also contributed. An additional explanation for the SES differences in CHD mortality and morbidity rates may be the hypothesis on fetal origins of cardiovascular disease. 29,30 This hypothesis suggests that children with a low birth weight have a tendency later in life to respond adversely to cardiovascular risk factors (in particular, overweight) and that they therefore have an increased risk of CHD. Because a low birth weight is more common in children of families with low SES, it is possible that the adverse effects of low SES on CHD risk begin very early in life and are cumulative during the life span. For this and other reasons, such as measurement repeatability, it is not surprising that the SES differences in CHD mortality rates are only in part explained by risk factor levels that are measured at middle age. In Finland, almost all acute MIs are treated in public hospitals, where treatment can be obtained for a nominal fee. This fee is fixed and does not depend on the examinations performed or treatments given. Also, the costs of medications for certain chronic diseases such as CHD are strongly subsidized. Therefore, there have been no major economic obstacles to obtaining hospital care or medications. A notable exception was, however, access to revascularization procedures. In the 1980s, the capacity to perform these operations in public hospitals was insufficient, and the costs in private hospitals may have been too high for some patients. Although there is good evidence that access to coronary artery bypass graft surgery was not equal among different SES groups in the 1980s, 31 this is likely to explain only a small fraction of the difference in CHD mortality rates. A reduction in the socioeconomic inequalities in cardiovascular health is not easy, but it is not impossible, at least in

6 1918 Circulation April 25, 2000 principle. Finland is ethnically and genetically a homogeneous society, and it is unlikely that there are unchangeable biologic differences among the different income and education groups. Scientific studies, such as the present one, are needed to generate more detailed understanding on the origins of the SES differences. This information can then be used to more precisely direct the prevention and treatment efforts. If the CHD mortality rates of the low- and middle- SES groups could be brought down to the level of the high-ses group, this would constitute a major public health improvement. Acknowledgments The FINMONICA Study was supported by the Finnish Academy and the Finnish Foundation for Cardiovascular Research. References 1. Helsinki Ministry of Social Affairs and Health. Health for All by the Year 2000: The Finnish National Strategy, 2nd ed. Helsinki, Finland: Ministry of Social Affairs and Health; Valkonen T. 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