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(Stroke. 2004;35:420.)
© 2004 American Heart Association, Inc.
Original Contributions |
From the University Hospital of Kuopio, Brain Research and Rehabilitation Center Neuron, Kuopio (J.S.); Department of Epidemiology and Health Promotion, KTL (National Public Health Institute), Helsinki (K.K., M.M., J.T., C.S., J.T., V.S.); Raisio Regional Hospital, University of Turku, Turku (P.I.-R.); Turku City Hospital, Turku (M.K.); and University of Turku, Department of Geriatrics, Turku (A.L), Finland.
Correspondence to Professor Juhani Sivenius, Kuopio University Hospital, PO Box 1627, FIN-70211 Kuopio, Finland. E-mail juhani.sivenius{at}fimnet.fi
| Abstract |
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Methods The population-based FINSTROKE register recorded 5650 new strokes among persons 25 to 74 years of age in 2 geographical areas of Finland: 2770 in the Kuopio area (east central Finland) and 2880 in Turku (southwestern Finland). Of these, 3065 were men and 2585 were women.
Results The rates of acute stroke events fell during the whole study period in both men and women. In both FINSTROKE areas combined, the average annual decline in the age-standardized incidence of first stroke events was 2.0% (95% confidence interval [CI], -2.8 to -1.2; P<0.001) among men and 1.7% (95% CI, -2.6 to -0.8; P<0.001) among women. The decline in the incidence of ischemic stroke was even steeper, 2.9%/y (95% CI, -4.9 to -1.1; P<0.001) among men and 3.1%/y (95% CI, -5.0 to -1.1; P<0.001) among women, whereas the incidence of intracerebral hemorrhage and subarachnoid hemorrhage did not change. Mortality from all stroke events declined in the FINSTROKE areas by 3.7%/y (95% CI, -5.3 to -2.0; P<0.001) among men and by 4.1%/y (95% CI, -5.9 to -2.4; P<0.001) among women. The 28-day case fatality of all stroke events also tended to decline, but the decline was of borderline statistical significance only (P=0.07 among men, P=0.05 among women).
Conclusions Incidence and mortality of stroke events declined significantly in these 2 register areas in Finland during the 15-year period of 1983 to 1997.
Key Words: epidemiology Finland incidence mortality stroke
| Introduction |
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The World Health Organization Monitoring Trends and Determinants in Cardiovascular Disease (WHO MONICA) stroke study was launched in the early 1980s to monitor stroke occurrence in populations around the world.15,16 To meet this challenge in Finland, the Finnish MONICA (FINMONICA) stroke register was set up in 3 distinct geographical areas.17 Ten-year trends in stroke events in the FINMONICA study showed that both the incidence and case fatality of stroke declined.13,14 After the end of the FINMONICA period, stroke registration was continued for an additional 5 years, ie, until 1997, in the framework of the FINSTROKE project. The aim of the present study was to analyze the incidence, mortality, and case fatality trends in stroke for the whole registration period from 1983 to 1997 and in stroke subtypes for the 10-year period of 1988 to 1997.
| Materials and Methods |
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The diagnosis of stroke was based, as specified in the WHO MONICA protocol, on clinical signs lasting >24 hours, except in cases of sudden death or if the development of symptoms was interrupted by surgical intervention. All suspected acute strokes were registered and classified as "definite stroke," "not stroke," or "unclassifiable." This final category was restricted, with few exceptions, to fatal events occurring before arrival at hospital and when no autopsy was performed. All hospital admission and discharge diagnoses, as well as cerebrovascular deaths, were routinely checked as source data, and all suspected stroke cases were entered and validated for stroke classification.
Acute stroke events in patients with no previous history of stroke were coded as first (incident) events. All subsequent attacks occurring after 28 days from onset were registered as recurrent strokes; if they occurred within 28 days, they were considered to belong to the same event. Twenty-eight days from the onset was also the cut point used to define fatal stroke. If the subject was alive 28 days from the date of symptom onset, the event was considered nonfatal. We also present routine mortality data for the whole country derived directly from the National Causes of Death Register, in which the numerators for the annual mortality rates are the subjects who died of stroke (International Classification of Diseases [ICD] codes I60 through I69 as the underlying cause of death in the death certificate) during that year regardless of the date of stroke onset.
In Finland, the 8th revision of the ICD was used until 1986; the 9th revision, from 1987 on; and the 10th revision, from 1996 on. The WHO MONICA protocol recommended that, if possible, the codes for specific stroke subcategories should be confirmed by examinations. For subarachnoid hemorrhage (SAH), necropsy, CT scan, or bloody cerebrospinal fluid was required to corroborate the diagnosis; for intracerebral hemorrhage (ICH), the diagnosis had to be confirmed by CT scan, MRI, or necropsy. If it was impossible to assign a definite stroke event to 1 of these categories, the code "unspecified stroke" was used. In this analysis, unspecified stroke and unclassifiable cases were combined with the ischemic stroke group. In the 25- to 64-year-old group, 1.4% of patients had unspecified or unclassifiable stroke; in the 65- to 74-year group, 5% of patients had that classification. The proportions did not vary through years among fatal or nonfatal or incident or recurrent events.
Because the specific imaging investigations, CT and MRI, were often not available in the beginning of our study period, we present the 15-year trends for all strokes combined and the type-specific trends for the 10-year period of 1988 to 1997. CT was performed in 1983 for 22% of men and 27% of women; after that, the CT rate rapidly rose annually until it stabilized at 90% by 1993. The combination of CT, MRI, and autopsy approached 100% at the end of the study period.
The Finnish Population Register provided us with the population data for calculation of the rates. Segis European standard population was used for direct age standardization of the rates.5 The 28-day case fatality was age standardized by use of weights derived from the combined age distribution of myocardial infarction and stroke patients in the WHO MONICA Project.17 We assumed Poisson distribution for the annual number of events to calculate 95% confidence intervals (CIs) for the rates. A log-linear model was used to estimate incidence and mortality trends, thus obtaining the CI for the trends from the standard error of the regression coefficient. To increase precision, estimates from the log-linear model are presented in the text as the rates for the first and last years of the study period.
| Results |
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The incidence of ischemic stroke (Figure 2) declined particularly steeply in the Kuopio register area; it fell during the 10-year period of 1988 to 1997 by 5.2%/y in both men and women (P<0.001). The rates fell from 289 to 182 per 100 000 in men and from 158 to 99 per 100 000 in women. In Turku, these trends were rather flat and nonsignificant. The trends in ICH and SAH remained stable in both areas and in both sexes during the 10-year period (Figure 3).
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Mortality from stroke declined significantly from 1983 to 1997 in both areas and in both sexes (Figure 4). The mortality rate in the entire FINSTROKE register population fell from 85 to 51 per 100 000 in men (-3.7%/y; P<0.001) and from 50 to 30 per 100 000 in women (-4.1%/y; P<0.001). It decreased in the Kuopio area by 49% in men and 46% in women (86 to 44 per 100 000 and 54 to 29 per 100 000, respectively) and in Turku by 33% in men and 42% in women (from 79 to 53 per 100 000 and from 50 to 29 per 100 000, respectively). Compared with stroke mortality statistics for all of Finland from the official mortality statistics, the trends are very similar, but the mortality rates in the official mortality statistics were slightly higher than those in the FINSTROKE register (Figure 4).
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The 28-day case fatality of all stroke events also tended to decrease in both areas and in both sexes. In the entire FINSTROKE population, it decreased in men from 21.7% to 18.2% (P=0.07) and in women from 22.2% to 19.2% (P=0.05) during the 15-year period of 1983 to 1997. The case fatality of ischemic stroke remained stable and similar in men and women,
11%, during the 10-year period of 1988 to 1997. There was a slightly diminishing trend for case fatality of SAH and ICH in men, whereas the case fatality of ICH decreased significantly in women, from 55.2% to 32.6% (P<0.01).
| Discussion |
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Previous reports from the Unites States,8 Europe,6,7 Russia,18 and New Zealand5 have shown little change in stroke incidence (or event) rates during the last decades. However, a marked decrease was seen in northern Europe (Denmark,10 Finland,11 and northern Sweden9) and in Australia,19 and an increase was seen in Estonia,20 Lund-Orup,21 and the Malmö and Örebro areas22 in southern and central Sweden. No decline in mortality was observed in Warsaw, Poland.23 In Shanghai, China, virtually no decline in stroke incidence occurred, but a clear decline in stroke mortality was reported.24 In general, stroke mortality increased in eastern Europe in the second half of the 1980s and the early 1990s.16,25
In the present study, the major emphasis was on the trends in incidence and mortality of stroke and its subgroups over time. In the past, stroke mortality in Finland was the highest in western Europe and one of the highest in the world.26,27 Furthermore, Finland has had one of the highest reported incidences of stroke in the world.28,29 The 10-year results of the FINMONICA stroke study13 showed a highly significant downward trend in both the incidence and mortality of stroke. This study reports a continuing decline in the incidence rate of all stroke events, incidence rate of ischemic stroke, and mortality from stroke but no decline in the corresponding rates of hemorrhagic strokes. The 28-day case fatality of all stroke events also tended to decline, although the decline did not quite reach statistical significance. Our data suggested that the decline was seen mainly in the case fatality of hemorrhagic strokes, whereas the case fatality of ischemic strokes did not change.
A major reason for the decline in stroke incidence and mortality during these 15 years is that the cardiovascular risk factor levels, which used to be very unfavorable in Finland, have improved considerably. Systematic work to lower the risk factors for cardiovascular diseases started in the early 1970s with the North Karelia Project and rapidly expanded to cover the whole country.30,31 The main aim was to change the type of fat used, to lower sodium intake, and to increase vegetable and fruit consumption. Furthermore, it encouraged people to monitor their blood pressure values and to strive for better blood pressure control. These campaigns also included smoking cessation programs. Simultaneously, a comprehensive risk factor monitoring system was developed that included regular population surveys every 5 years. During 1972 to 1997, major changes took place in diets and in blood pressure and serum cholesterol levels. The lipid profile of both hypertensive and normotensive population improved significantly from 1982 to 1997.32 Hypertension care also improved during these years.33 Of the 4 main risk factors (high blood pressure, elevated blood lipids, smoking, and obesity), the only one that has not been reduced by these health-promoting campaigns is obesity. The prevalence of obesity continues to increase among men and women in Finland.34
Another reason for the declining trends in incidence and mortality of stroke is the improved prevention of stroke and other cardiovascular disease by antithrombotic therapy. The use of acetylsalicylic acid has increased in Finland and in other Western countries.35 Acetylsalicylic acid has often been prescribed to patients with symptoms of transient ischemic attack to prevent a cerebral infarction, but perhaps more importantly, it has been prescribed to patients with coronary artery disease who are at increased risk of stroke.
In conclusion, both the incidence and mortality of stroke continued to decline until 1997 in both sexes in these 2 areas of Finland. Primary prevention and better control of cardiovascular risk factor levels in the population are the most likely reasons for this favorable development.
| Acknowledgments |
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Received August 19, 2002; revision received October 2, 2003; accepted October 9, 2003.
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