European Heart Journal Advance Access originally published online on August 5, 2007
European Heart Journal 2007 28(17):2051-2052; doi:10.1093/eurheartj/ehm323
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Coronary disease surveillance: a public health imperative
Department of Cardiovascular Diseases, Mayo Clinic, 200 First Street, SW, Rochester, MN 55905, USA
Corresponding author. Tel: +1 507 284 0519; fax: +1 507 266 0228. E-mail address: roger.veronique{at}mayo.edu
This editorial refers to ‘Contribution of changes in incidence and mortality to trends in the prevalence of coronary heart disease in the UK: 1996–2005’ by A.R. Davies et al., on page 2142
Footnotes
The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology
Coronary heart disease (CHD) is the leading cause of death in the Western world, thereby constituting an immense public health problem. While CHD mortality declined in the last four decades, the use of age-adjusted rates to describe CHD mortality obscures the fact that the decline largely represents the postponement of CHD deaths until older age. In fact, the burden of CHD is increasing in parallel with the increase in life expectancy.1 As the burden of prevalent CHD is increasing, identifying persons with CHD, measuring its incidence and outcome and how these vary over time and across populations is essential to understand the determinants of the trends in CHD. This in turn is crucial to define the relative contributions of risk factor reduction and therapeutic improvements, which is necessary to design effective interventions to reduce CHD.
The monitoring (otherwise termed surveillance) of CHD requires several conditions. The availability of a defined population is indispensable to generate incidence rates, and valid definitions that actually measure the intended event are essential. The definitions should be standardized to enable reliable data collection and comparisons across studies. The definitions should also be relatively immune to temporal changes so that time trends in the occurrence of CHD can be appraised. Despite their apparent simplicity, these requirements are rarely met.
Indeed, hospital discharges, while constituting an intuitive indicator of the occurrence of CHD, are event based, not person based, and allow for multiple hospitalizations for the same individual to be counted. The diagnoses are not standardized such that they may reflect different entities depending on care delivery patterns, themselves depending on insurance coverage, medical practice habits, etc. As they do not differentiate between first and subsequent admission for a given condition, hospital discharges cannot measure incidence. Finally, shifts in discharge diagnoses related to payment systems further hinder the validity of these sources to measure the burden of a given disease accurately.2
Community surveillance is a comprehensive approach designed to track disease at the community level, and is less costly and more efficient than cohort studies.3 CHD community surveillance typically tracks CHD deaths and myocardial infarction incidence and outcomes, and, in the absence of a global surveillance system, it is essential to monitor CHD trends. Community surveillance programmes share several common methodological features. They are retrospective by design, rely on diagnostic codes for case finding, and potential cases are validated using standardized approaches.
In the USA, selected community surveillance studies that reported on temporal trends include the Atherosclerosis Risk in Communities (ARIC) study,4 the Minnesota Heart Survey (MHS),5 the Olmsted County Study,6 and the Worcester Heart Attack Study.7 Each programme has a different focus, such that they provide complementary information. Collectively, the data from US studies indicate that the incidence of CHD remained largely stable over the past two decades, while mortality declined substantially. These findings suggest that medical care of clinical CHD was the main contributor to the mortality decline. This in turn underscores that the enormous progress made in the clinical care of persons with CHD translated into a reduction in mortality at the population level, but also emphasizes the need for renewed primary prevention strategies.
Outside the USA, the World Health Organization (WHO) MONICA (Multinational MONItoring of trends and determinants in CArdiovascular disease) Project was established in the early 1980s to monitor trends in cardiovascular diseases and to relate these to risk factor changes.8 Its central goal was to explain the trends in cardiovascular disease mortality observed from the 1970s. There were 32 MONICA centres in 21 countries. The population monitored included 10 million men and women, aged 25–64 years. The breadth of populations covered by MONICA is unique and the data exceptionally rich. Under the auspices of MONICA, FINAMI is a population-based registry which was originally the Finnish contribution to the MONICA Project.9 FINAMI evaluates all events compatible with myocardial infarction or CHD death among residents of several geographical areas in Finland, which in 1995 encompassed 82 849 men and 87 360 women aged 35–64 years. Similarly, MONICA Augsburg established a population-based myocardial infarction registry in the Augsburg region of MONICA.10
The data from MONICA8 and FINMONICA9 indicate that, in these populations, the decline in coronary disease mortality is mostly related to the decline in CHD events, thereby pointing to primary prevention as the main source of the decline. In MONICA Augsburg, however, the decrease in CHD mortality occurred while a decline of recurrent CHD events and a reduction in myocardial case fatality were observed, reflecting intensified reperfusion therapy and use of evidence-based medications to treat acute myocardial infarction.10
How can these findings all be reconciled? Importantly, there are notable differences in the age of the populations studied. Indeed, US studies and MONICA Augsburg either have an upper age limit of age 744,5,10 or no upper age limit.6,7 Conversely, the populations evaluated by MONICA and FINMONICA have an upper age limit of 64 years, which does not account for a large segment of the population in which CHD events occur. This is particularly important given the gradual temporal shift of the burden of CHD towards older segments of the population, and underscores the importance of including all age groups in CHD surveillance.
In this context, the study by Davies et al. is of considerable interest.11 This paper examines trends in CHD incidence, prevalence, and mortality in the UK between 1996 and 2005. Three hundred and fourteen general practices across the UK combining a total of 5 million patients contribute to The Health Information Network (THIN), a voluntary registry, which represents 3% of the population of the UK. Subjects 35 years of age and older with no upper age limit were included. Using this resource, Davies et al. identified individuals with diagnostic codes compatible with CHD, to evaluate incidence, prevalence, and mortality. To contextualize this report appropriately, it is important to understand that the ascertainment methodology relies on a voluntary registry, which has inherent limitations. The level of completeness of enrolment of patients within a given practice and within the registry, and the type of patients that might be selected for entry in the registry may lead to selection biases, thereby hindering external validity. Variations in the practices that elected to participate to the registry may also result in bias. The observation period extends from the date of registration in the practice until the date when the patient left the practice, death, or last data collection. As events occurring outside the observation period will unavoidably escape surveillance, the data may not represent true incidence. Finally, while the authors underscore the generalizibility of their findings, only 3% of the population is covered by THIN, a proportion which cannot help but raise questions about the broad applicability of the data. These limitations notwithstanding, these findings, which pertain to a recent time period, are important as they represent a large sample size from a unique data source and provide much needed data on the contemporary burden of CHD. Indeed, the importance of such a study resides less in the external validity of the data than in the ability to examine, simultaneously, in the same population, all determinants of CHD mortality. The results from THIN indicate that, while CHD mortality declined, CHD incidence decreased less than mortality, resulting in an increase in CHD prevalence. These data are thus congruent with the US surveillance data discussed above, which were generated among populations of similar age distribution. Collectively, therefore, these consistent findings should be interpreted as an alarm signal for primary prevention in the Western world. This is particularly urgent given the increasing prevalence of obesity and diabetes, probably not yet fully reflected in published reports.
Effective primary prevention in turn mandates a worldwide reflection on appropriate strategies. Indeed, while THIN did not detect a shift in the burden of CHD towards women and the elderly, other surveillance programmes did.6,7 This indicates that effective prevention strategies should be designed for ageing populations with different psycho-social barriers, which should be recognized and addressed.
Interpreting the Davies study in light of other published reports on populations across the world also points to the importance of integrating findings from individual studies to reach a comprehensive appraisal of the disease burden. This global understanding urgently requires more studies, particularly in diverse populations and different countries. These studies must be designed to generate data that can be formally or informally compared with results of other studies. This will require methodological standardization and, more importantly, the commitment to collaboration and ‘team science’ needed for scientific and public health research.12
Conflict of interest: none declared.
Footnotes
The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology
doi:10.1093/eurheartj/ehm272 
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- Davies AR, Smeeth L, Grundy EMD. Contribution of changes in incidence and mortality to trends in the prevalence of coronary heart disease in the United Kingdom: 1996–2005. Eur Heart J (2007) 28:2142–2147. First published on July 18, 2007, doi:10.1093/eurheartj/ehm272.
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EHJ 2007 28: 2142-2147.[Abstract] [FREE Full Text]
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