Original ArticleComorbidities in relation to fatality of first myocardial infarction
Introduction
Although fatality from coronary heart disease (CHD) is declining in various populations [1], [2], [3], [4], 25%–35% of those who suffer a coronary event still die within 28 days [1], [2], [3], with the vast majority of cases occurring outside of the hospital [1], [3], [4], [5]. Our knowledge concerning determinants of death from myocardial infarction (MI) is presently limited, although the presence of comorbidity (usually defined as a medical condition existing simultaneously with, and independent of, another medical conditions), is likely to be a risk factor for dying during the acute phase following an MI [6]. Previous studies that took both in- and out-of-hospital deaths into consideration, which may be referred to as population-based studies, focused on selected comorbidities, such as diabetes [4], [7], [8], [9], [10], hypertension [7], [9], [10], [11], [12], hyperlipidemia [7], [12], arrhythmias [4], [13] and angina [4], [13] and arrived at different conclusions regarding the associations of such conditions with MI fatality. Previous hospitalizations due to severe and/or multiple comorbidities may be especially associated with MI fatality. However, no population-based study has yet assessed how the number of previous hospitalizations is related to MI fatality, nor presented a comprehensive overview of earlier diagnoses in individuals who have suffered a fatal coronary event. In addition, only a few earlier investigations in this area have had access to registers documenting diagnoses in connection with previous hospitalizations in combination with questionnaires covering diseases that usually do not require admission to hospital [7], [9], [11], [13].
The overriding aim here was to improve our understanding of how presence of comorbidities may influence fatality from a first MI in the general adult population. Specifically, we explored (1) the association between the number of hospitalizations during a 10-year period prior to the MI and death within 7 days afterwards, (2) which comorbidities are most prevalent among cases of fatal MI, and how these are associated with such fatality, and (3) whether autopsy findings on individuals whose first MI was fatal indicate the presence of co-morbidities other than those identified from other data. This investigation was based on cases of MI identified in connection with the Stockholm Heart Epidemiology Program (SHEEP) performed between 1992 and 1994 – a period during which approximately 70% of all deaths from MI among 45–70-year-old residents in Stockholm were confirmed by autopsy [7]. Information on comorbidities was available from questionnaires, as well as national registers. In addition, autopsy reports provided a unique source of data concerning pathological findings associated with fatal first MI.
Section snippets
Study population
This study is based on material from the Stockholm Heart Epidemiology Program (SHEEP) which was designed to increase our knowledge concerning the influence of various risk factors on the occurrence of and prognosis for MI among male and female Swedish citizens 45–70 years old and residing in Stockholm County. MI was defined with the following criteria: (i) certain symptoms according to anamnesis, (ii) specified changes in serum activity of the creatinine kinase and lactose dehydrogenase, (iii)
Questionnaire data
Non-fatal cases filled in a questionnaire containing a general question concerning any pharmacological treatment during the week preceding the MI and, if so, the purpose for. In addition, these individuals were asked about the occurrence of angina, heart failure, stroke, intermittent claudication, diabetes, hypertension and/or hyperlipidemia at any time before the index event. This questionnaire also encompassed lifestyle, height, weight, psychosocial environment, occupational-related exposures
Ethical statement
The SHEEP study was approved by the Ethical Committee at Karolinska Institutet (91:259). Additional approval for extraction of data from national registers and autopsy reports was granted by the Regional Ethical Review Board in Stockholm (2013/1731–31/1). All participants provided their informed oral consent before being enrolled; at the time the study was initiated (1992) forms for written consent were generally not used.
Results
In comparison to the non-fatal cases, our 7-day fatal cases were on the average about 2 years older, had a lower mean BMI, included a higher proportion of women (35% versus 31%), and included a higher proportion of individuals with low disposable income (Table 1). Other characteristics of these cases, such as factors related to life style factors and family history of cardiovascular disease, have been reported previously [7].
Fatal cases were more often hospitalized repeatedly prior to their MI (
Discussion
In our inception cohort of 45–70-year-olds who suffered a first MI, the number of previous hospitalizations was associated with fatality after adjustment for age, sex and low disposable income, an association not observed in previous studies. The number of hospitalizations might reflect the extent of damage to organs important for survival in the acute phase of a MI, the severity of the underlying disease, and/or the potential deleterious effects of various treatments. This number might also
Conclusions
Our present observations indicate that individuals who have been repeatedly hospitalized prior to their first MI have less chance to survive this event. Furthermore, our explorative approach identified a large number of specific comorbidities associated with MI fatality, i.e., subgroups of individuals with a history of such diseases may be particularly vulnerable if they suffer a MI. Increased scientific insight into this area may promote preventive action towards vulnerable groups as well as,
Sources of funding
The SHEEP study was supported by grants from the Swedish Council for Work Life and Social Research, and the Stockholm County Council. Financial support for this research was also received from the Swedish Heart and Lung Foundation to Dr. Leander (2015–0562). The funding agencies were not involved in the design of the study or the collection, the analysis and interpretation of data.
Conflict of interests: none.
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