Stroke Mortality Rates in Poland Did Not Decline Between 1984 and 1992
Background and Purpose Stroke mortality has decreased in most industrialized countries in recent decades. In Poland, as in other eastern European countries, mortality rates for stroke remain high.
Methods The Warsaw Stroke Registry (WSR) registered patients in the Mokotów district of Warsaw from 1991 through 1992. The Warsaw Pol-MONICA study registered stroke patients in the North and South Praga regions of Warsaw from 1984 through 1992. Stroke incidence rates, case-fatality rates, and stroke mortality rates were computed based on both studies and compared with published mortality rates based on death certificates. Eight-year trends of stroke incidence, case-fatality rate, and mortality were derived from the Warsaw Pol-MONICA study.
Results The WSR and Warsaw Pol-MONICA studies showed similar incidence rates, mortality rates, and 28-day case-fatality rates for stroke. Mortality rates from the WSR and the Warsaw Pol-MONICA study were similar to rates from death certificate data. Mortality rates in the group aged 35 to 64 years were higher in men (47.5 to 50/100 000 per year) than in women (30/100 000 per year).
Conclusions Two different population-based studies suggest that stroke mortality is high in Poland because of high 28-day case-fatality rates. Stroke mortality failed to decline in Poland in the period 1984 through 1992 because neither case fatality nor stroke incidence declined in this period.
Mortality rates for cerebrovascular disease vary considerably by country.1 2 3 Eastern European countries have high stroke mortality rates.4 Furthermore, unlike western European countries, eastern European countries have shown either no decline or an increase in stroke mortality rates during the period 1970 through 1985.5 6 Poland experienced a rise in mortality rates for cardiovascular diseases from 1970 through 1980.7 However, separate mortality data for stroke during that period are limited. Polish stroke studies have shown disparate trends. A WHO report based on death certificates showed increasing stroke mortality rates in Poland for the years 1970 to 1985.8 A community-based registry using medical records from Poznan showed a decrease in stroke incidence during the period 1977 to 1985.9 The Warsaw Pol-MONICA study has followed acute strokes in an age-truncated population (35 to 64 years) in the districts of South and North Praga of Warsaw since 1984.7 10 The Warsaw Pol-MONICA study is an arm of the multinational WHO MONICA Project.11 Between 1991 and 1992, the WSR collected data on all strokes in the Upper Mokotów district of Warsaw.12
Both the Warsaw Pol-MONICA and WSR studies have found stroke incidence rates in Poland that are comparable with those in other areas of Europe. However, mortality rates and 28-day case-fatality rates are among the highest in Europe.4 6 13 14 The aim of the present study was to compare stroke incidence rates, stroke mortality rates, and stroke case-fatality rates in the WSR with those in the Warsaw Pol-MONICA study, to compare the findings in these two population-based studies to mortality rates derived from death certificates, and to investigate temporal trends during the period 1984 through 1992 for stroke incidence, stroke mortality, and stroke case fatality.
Subjects and Methods
During 1991 to 1992, two population-based studies of stroke were conducted in different districts of Warsaw. The WSR12 registered FES occurring among permanent residents of the Mokotów region in Warsaw during the period January 1, 1991, through December 31, 1992 (183 199 inhabitants [87 554 men and 95 645 women] as of 1991). The Warsaw Pol-MONICA study7 15 examined FES occurring between January 1, 1984, and December 31, 1992, in permanent residents of the North and South Praga regions of Warsaw (209 023 inhabitants [97 825 men and 111 198 women] as of 1991). Stroke was defined according to WHO criteria as a rapid onset of clinical signs due to a focal or global disturbance of cerebral function, lasting more than 24 hours or leading to death, with no apparent nonvascular cause.2 In the WSR, all patients (excluding those with subarachnoid hemorrhage) were registered prospectively. Institutions surveyed included two acute-care hospitals (Institute of Psychiatry and Neurology) and the Mokotówski Hospital, as well as five outpatient clinics and one nursing home. The majority of stroke patients from the Mokotów region are admitted to the Institute of Psychiatry and Neurology. To increase case ascertainment, the records of military and railway hospitals were checked weekly for stroke patients from the Mokotów district. Additional ascertainment came from a review of all death certificates listing ICD-9 codes 430, 431, 433, 434, or 435.
In Warsaw Pol-MONICA, all patients in the age group of 35 to 64 years with ICD-9 diagnoses of 430, 431, 433, 434, or 435 were included. Strokes were ascertained from three sources: hospital records, outpatient clinic records, and death certificates. In the Pol-MONICA study, records of the municipal hospital and the railway hospital were reviewed, as well as those of seven outpatient clinics. In addition, all death certificates with ICD-9 codes 430 through 438 (excluding 435) were reviewed. When available, medical records of dying patients were reviewed. Cases were registered as a stroke only if a focal neurological deficit could be confirmed. Fatal cases involving sudden loss of consciousness or sudden death without neurological deficit were excluded. All primary-care physicians were surveyed as to their practice patterns; all said that they hospitalized stroke patients in preference to outpatient treatment.
For both the WSR and the Pol-MONICA study, all neurologists and internists from the regional hospitals, clinics, and nursing homes were notified of the study and asked to report all cases of stroke. Patients with transient ischemic attacks were excluded from the study. To make comparisons between the two studies, the WSR data was restricted to patients aged 35 to 64 years of age. Patients with subarachnoid hemorrhage were excluded from the Warsaw Pol-MONICA data. Comparisons between the WSR and Warsaw Pol-MONICA study were based on FEL only. Comparisons with death certificate data were based on all strokes (FES and recurrent). In the Warsaw Pol-MONICA study from 1984 to 1992, 2707 patients in the population aged 35 to 64 years (including 1718 men and 989 women) were registered. During 1991 to 1992, the WSR registered 462 patients with FES. There were 158 FES in subjects aged 35 to 64 years (96 men and 62 women). CT confirmation of stroke was obtained in 68% of the patients from the WSR and 21% of the patients from Pol-MONICA. Under the Polish system of health care, with care rigidly allocated by district, it is likely that the case ascertainment rate for both Pol-MONICA and the WSR was very high. Another factor favoring high case ascertainment was the trend of preference of Polish physicians to hospitalize all stroke patients.
CIs were calculated using Poisson (variation) distributions for the number of events.16 Poisson rates were used to compare stroke mortality and stroke incidence rates. Analysis of trends was performed by simple exponential smoothing analysis.16 17
For statistical analysis, the computer programs Statgraf, Statistica, and CIA were used.
Two population-based studies in different areas of Warsaw, both performed from 1991 through 1992, showed similar rates for stroke mortality, stroke incidence, and stroke case-fatality rates in the population aged 35 to 64 years (Table 1⇓). In the North and South Praga districts of Warsaw, incidence rates of FEL were 123.4/100 000 per year in men and 64.5/100 000 per year in women. In the Upper Mokotów district, stroke incidence rates were 127.6/100 000 per year in men and 81.2/100 000 per year in women. Although stroke incidence rates in men and women aged 35 to 64 years were somewhat lower in the Warsaw Pol-MONICA study, these differences were not statistically significant. In North and South Praga, 28-day case-fatality rates for stroke (38% in men and 47% in women) did not differ significantly from those in the Upper Mokotów district (35% in men and 34% in women). Mortality rates for stroke for persons aged 35 to 64 years in the North and South Praga districts (47.5/100 000 per year in men and 30.2/100 000 per year in women) were similar to those in the Upper Mokotów district (50.5/100 000 per year in men and 30.0/100 000 per year in women.) In both regions, age-adjusted stroke mortality rates were higher for men than women (P<.05).
Stroke mortality rates based on death certificate statistics (all types of strokes are included, FEL and recurrent) were similar (Table 2⇓) to stroke mortality rates due to FES in the Warsaw Pol-MONICA study and the WSR. On the basis of Warsaw Pol-MONICA data, the stroke incidence, stroke mortality, and case-fatality rates did not change significantly from 1984 to 1992 (Figure⇓).
Stroke incidence, stroke mortality, and stroke case-fatality rates were similar in two different districts of Poland. Stroke mortality rates in these two population-based studies were similar to official statistics based on death certificate data.
Stroke incidence rates in the group aged 35 to 64 years (128/100 000 per year [95% CI, 102 to 153] in men and 81/100 000 per year [95% CI, 61 to 101] in women) were not high by European standards.4 14 A concern in any community-based study is that incomplete case ascertainment may lead to an underestimation of stroke incidence. However, the similar results of these studies suggest that they correctly reflect stroke incidence in Poland. The organization of health care in Poland favors complete case ascertainment. In Poland, health care is rigidly allotted to certain regions termed “healthcare units.” Residents of each healthcare unit are assigned to predesignated doctors and health centers. Patients who suffer strokes in other cities are subsequently transferred to the hospital serving the healthcare unit of their residence. In Poland, stroke patients are routinely hospitalized in neurological centers and less often in nonneurological centers. In the WSR, 76% of the stroke patients were treated in a neurological department belonging to their catchment area, 11% were treated in nonneurological departments, and 5% were managed as outpatients. The 8% identified by death certificate were mainly patients who sustained a stroke out of the area of their residence and died before they could be transported back to a hospital in their catchment area.12 A possible contributor to the unexpectedly low stroke incidence rates in Poland is the high prevalence of cardiac disease. Some patients die from ischemic heart disease before they reach the age at which they would have suffered a stroke.12 Recent reports suggested that an increase in stroke incidence between 1980 and 1994 in the United States might reflect better survival from ischemic heart disease18 19 and better detection of stroke with CT.20
Although stroke incidence in Poland is comparable with that of other European countries, mortality rates are high. During the study period 1984 through 1992, stroke mortality rates failed to decline in Poland. Declines in stroke mortality observed in many other countries reflect improvements in stroke case-fatality rates rather than declines in stroke incidence. Declining case-fatality rates probably reflect both improved control of stroke risk factors and improved acute-stroke management.2 21 Improved control of risk factors could lead to reductions in stroke incidence or stroke case-fatality rates. Better treatment of hypertension, improved metabolic control of diabetes, and antithrombotic therapy in patients at high risk for embolic strokes may reduce the incidence of stroke and also reduce the severity of disease once it occurs.22 Improved management of stroke patients in specialized units may improve functional outcome and reduce case-fatality rates.23 Declining case fatality seems to be the major (and sometimes the only) factor underlying declining stroke mortality in western European countries.14 22 24 In Poland, 28-day case-fatality rates remained high during the study period (1984 to 1992). Because case-fatality rates are high in both the Warsaw Pol-MONICA study and the WSR, high case-fatality rates are probably not due to lack of case ascertainment. Since case-fatality rates and stroke incidence did not decline in Poland, stroke mortality remains high. In Poland, medical comorbidity, as in other eastern European countries,5 is high. High medical comorbidity, high stroke severity, and differences in medical management may all contribute to high 28-day case-fatality rates.25 In the Warsaw Pol-MONICA Study, a high proportion of cardiovascular patients presented with previously undetected hypertension (47.4% of the men and 27.6% of the women). Furthermore, even after detection, hypertension often was not treated (58.9% of men and 46.6% of women went untreated).10
If Poland follows the pattern of western European countries with declining stroke mortality rates, declines in stroke mortality will depend on improvements in stroke survival rather than declines in stroke incidence. The unacceptably high stroke mortality in Poland reflects very high case-fatality rates. Better control of medical comorbidity and stroke risk factors may lead to improved case-fatality rates by reducing stroke severity and by reducing the risk of death due to medical complications. Further improvements in case-fatality rates may depend on improved management of acute-stroke patients.
Selected Abbreviations and Acronyms
|ICD-9||=||International Classification of Diseases, 9th Revision|
|Pol-MONICA||=||Multinational Monitoring of Trends and Determinants in Cardiovascular Disease (Poland)|
|WHO||=||World Health Organization|
|WSR||=||Warsaw Stroke Registry|
The Warsaw Stroke Registry was supported by a grant from the Maria Sklodowska-Curie Joint Fund. The Warsaw Pol-MONICA study was supported by a Polish Government grant, contract M. 6 of the State Committee for Scientific Research, and contract No. 0253/54/92/02.
Reprint requests to Daniel B. Hier, MD, Department of Neurology (M/C 796), 912 S Wood St, University of Illinois at Chicago, Chicago, IL 60612-7330.
- Received October 10, 1996.
- Revision received December 23, 1996.
- Accepted January 28, 1997.
- Copyright © 1997 by American Heart Association
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