Modelling the decline in coronary heart disease deaths in England and
http://www.100md.com
《英国医生杂志》
1 Department of Public Health, Dokuz Eylul University School of Medicine, 35340 Izmir, Turkey, 2 International Health Group, Liverpool School of Tropical Medicine, Liverpool L3 5QA, 3 Division of Public Health, University of Liverpool, Liverpool L69 3GB
Correspondence to: B Unal belgin.unal@deu.edu.tr or belgina@liv.ac.uk
Objective To investigate whether population based primary prevention (risk factor reduction in apparently healthy people) might be more powerful than current government initiatives favouring risk factor reduction in patients with coronary heart disease (CHD) (secondary prevention).
Design, setting, and participants The IMPACT model was used to synthesise data for England and Wales describing CHD patient numbers, uptake of specific treatments, trends in major cardiovascular risk factors, and the mortality benefits of these specific risk factor changes in healthy people and in CHD patients.
Results Between 1981 and 2000, CHD mortality rates fell by 54%, resulting in 68 230 fewer deaths in 2000. Overall smoking prevalence declined by 35% between 1981 and 2000, resulting in approximately 29 715 (minimum estimate 20 035, maximum estimate 44 675) fewer deaths attributable to smoking cessation: approximately 5035 in known CHD patients and approximately 24 680 in healthy people. Population total cholesterol concentrations fell by 4.2%, resulting in approximately 5770 fewer deaths attributable to dietary changes (1205 in CHD patients and 4565 in healthy people) plus 2135 fewer deaths attributable to statin treatment (1990 in CHD patients, 145 in people without CHD). Mean population blood pressure fell by 7.7%, resulting in approximately 5870 fewer deaths attributable to secular falls in blood pressure (520 in CHD patients and 5345 in healthy people) plus approximately 1890 fewer deaths attributable to antihypertensive treatments in people without CHD. Approximately 45 370 fewer deaths were thus attributable to reductions in the three major risk factors in the population: some 36 625 (81%) in people without recognised CHD and 8745 (19%) in CHD patients.
Conclusions Compared with secondary prevention, primary prevention achieved a fourfold larger reduction in deaths. Future CHD policies should prioritise population-wide tobacco control and healthier diets.
Coronary heart disease (CHD) remains the largest cause of death in the United States, Europe, and Australasia.1 However, since the 1980s, CHD mortality rates have halved in Britain and in many industrialised countries.1 Studies in the US, Europe, and New Zealand consistently suggest that 50-75% of the falls in cardiac deaths can be attributed to population-wide improvements in the major risk factors, particularly smoking, cholesterol, and blood pressure.2–5 Modern cardiological treatments for known CHD patients, such as thrombolysis, aspirin, angiotensin converting enzyme inhibitors, statins, and coronary artery bypass surgery, generally explain the remaining 25-50% of the fall in mortality.2–5
Risk factor reduction should thus be a central component of all CHD policies. However, disagreement continues about whether to prioritise risk factor reduction across the whole population, explicitly including all apparently healthy people (primary prevention), or mainly to target CHD patients (secondary prevention). Current funding in the US6 and the United Kingdom clearly favours secondary prevention. This reflects four perceived limitations of primary prevention as an "evidence based" intervention. Firstly, a much quoted Cochrane metaanalysis of 10 intervention studies in primary care that used counselling or education to modify more than one cardiovascular risk factor in adults found only modest changes in risk factors and no effect on mortality.7 Secondly, although confident about prescribing drugs, some clinicians may feel uncomfortable in a health promotion role, perhaps lacking the confidence or skills to influence complex behaviours such as diet or smoking.8 Thirdly, the very long time scales apparently involved may be a deterrent.9 Fourthly, the numbers needed to treat to prevent one event are substantial, often fivefold higher than those for targeting CHD patients.10
In truth, both primary and secondary prevention interventions are probably necessary to maximise population health.11 Quantifying their relative contributions is clearly important but is difficult to do with disease registers or population cohorts.12 Researchers have therefore used models to quantify the potential contribution of risk factor reductions before and after CHD is diagnosed in an individual. For example, use of the CHD policy model suggested that approximately 25% of the decline in CHD deaths in the US between 1980 and 1990 was explained by primary prevention and slightly more (29%) was explained by risk factor reductions in patients with CHD.2
A better understanding of the relative contributions of primary prevention and secondary prevention to the recent falls in deaths from CHD is clearly essential, in order to inform future CHD policy options in Britain and elsewhere.10 We have therefore used the only validated and comprehensive CHD model available in the UK.4 We analysed the decrease in CHD mortality in England and Wales between 1981 and 2000 to estimate the proportions attributable to changes in major cardiovascular risk factors in apparently healthy people (primary prevention) and in patients with CHD (secondary prevention).
Methods
IMPACT CHD model
The cell based IMPACT CHD mortality model, previously validated in Scotland,3 New Zealand,5 and Beijing,13 has been described elsewhere.3 5 14 Briefly, we used the model to synthesise data for the adult population of England and Wales—35.5 million people aged between 25 and 84—describing numbers of CHD patients, uptake of specific treatments, trends in major cardiovascular risk factors in apparently healthy people in populations and in specific patient groups, and the effectiveness (mortality benefits) of the reductions in specific risk factors in people with and without recognised CHD.4
Data sources
Sources of data included national surveys, official statistics, clinical audits, controlled trials, and meta-analyses. These are detailed on our website.15
Primary prevention: risk factor trends and mortality benefits in the general population
For risk factor changes, the model uses regression () coefficients obtained from large meta-analyses, cohort studies, and MONICA analyses (appendix 10 on website).4 15 Each coefficient quantifies the independent relation between population change in a specific CHD risk factor (such as smoking, cholesterol, or blood pressure) and the consequent percentage change in population mortality from CHD. We then estimated the subsequent reduction in the number of deaths produced by the decrease in each major risk factor as the product of three variables: the number of CHD deaths observed in the base year (1981), the relative reduction in that risk factor, and the coefficient, each stratified by age and sex.4 15
To estimate the impact of the population-wide reduction in cholesterol due to dietary change, we subtracted the estimated effect of statins for primary prevention from the overall number of deaths prevented or postponed in the population due to change in mean cholesterol concentration. We explicitly considered demographic change by using age and sex specific population CHD mortality and CHD patient numbers for 1981 and for 2000.4
Secondary prevention: risk factor trends and mortality benefits in CHD patients
We then estimated the mortality benefit attributable to reductions in each major risk factor (smoking, total cholesterol, and blood pressure) in each group of CHD patients as the number of deaths prevented or postponed.4 We categorised CHD patients according to disease groups: acute myocardial infarction, survivors of myocardial infarction, revascularisation patients, and patients with unstable angina, chronic angina, and chronic heart failure. We did not consider the impact of changes in risk factors in patients with an initial acute myocardial infarction or unstable angina, because both are transient states. To avoid double counting, we firstly made adjustments for overlaps between different treatment groups by subtracting the overlapping subgroup from the main group, as detailed in appendix 8 on the website.4 15
We based age and sex specific smoking cessation rates on local surveys and audits. We initially assumed that age and sex specific changes in cholesterol attributable to diet and changes in blood pressure attributable to population secular trends would mirror the changes seen in the general population. We then used rigorous sensitivity analyses to test the effect of much smaller (–50%) and much larger (+50%) changes.
Statins and other treatments
The model aimed to include all medical and surgical treatments provided in 2000. This included statins as primary prevention (in people without recognised CHD) and as secondary prevention (in CHD patients). We calculated the absolute reduction in mortality by using the relative reduction in mortality reported in the most recent meta-analysis15 applied to the age specific case fatality rate observed in unselected patient cohorts. The effect of all other "secondary prevention" drugs (aspirin, blockers, and angiotensin converting enzyme inhibitors) has been previously reported and was explicitly excluded from this analysis.4 We did not consider over the counter statins, as these only became available in 2003.
We estimated the number of deaths prevented or postponed for specific age and sex groups. We used survival benefit over a one year time interval throughout.
Sensitivity analyses
Because of the uncertainties surrounding some values, we did a multiway sensitivity analysis using the analysis of extremes method.16 Illustrative examples are shown in appendix 7 on the website.15
Apportioning deaths prevented or postponed between primary and secondary prevention
We then estimated the deaths prevented or postponed in apparently healthy people as the deaths prevented or postponed in the entire population minus the deaths prevented or postponed in each CHD patient group. Illustrative examples are given in the results section.
Results
Fall in CHD mortality between 1981 and 2000
Between 1981 and 2000, age specific CHD mortality in England and Wales fell by 62% in men and 45% in women aged 25-84. This resulted in 68 230 fewer deaths in 2000, compared with the 1981 baseline.4
Medical and surgical treatments together prevented or postponed approximately 25 805 deaths (minimum estimate 17 110, maximum estimate 49 040). This represented 42% of the total decrease in CHD deaths estimated by the model.4
Approximately 58% of the fall in mortality was attributable to reductions in the risk factors—mainly smoking, cholesterol, and blood pressure.4 Changes in the three major cardiovascular risk factors together produced a best estimate of 45 370 (29 570-76 835) fewer deaths. In contrast, adverse trends in diabetes, obesity, and physical activity together generated approximately 7645 (5395-10 730) additional deaths.4
Risk factor reductions in the general population and in CHD patients
Overall smoking prevalence fell by 35% between 1981 and 2000. This resulted in approximately 29 715 (20 035-44 675) fewer deaths. Approximately 5035 (17%; 3100-8255) fewer deaths resulted from smoking cessation in CHD patients, leaving the remainder—approximately 24 680 (83%; 16 935-36 420)— attributable to reduced smoking prevalence in "healthy people" (table 1).
Table 1 Fall in coronary heart disease mortality attributable to changes in risk factors in people with and without recognised coronary heart disease: England and Wales, 1981-2000
Population total cholesterol concentrations fell by 4.2% between 1981 and 2000, resulting in approximately 7900 (5285-16 695) fewer deaths. Approximately 5770 fewer deaths were attributable to dietary reduction—approximately 1205 (645-2455) in CHD patients, leaving some 4565 (3290-9650) fewer deaths attributable to dietary cholesterol reduction in healthy people. Approximately 2135 (1350-4590) fewer deaths were attributable to statin treatments: 1990 (1305-4180) in CHD patients and 145 (45-410) in healthy people (table 1).
Mean population diastolic blood pressure fell by 7.7% between 1981 and 2000, resulting in approximately 7755 (4250-15 465) fewer deaths. Approximately 520 (285-940) fewer deaths were attributable to the secular fall in blood pressure in CHD patients, leaving some 5345 (3125-11 740) in healthy people, and 1890 (840-2785) fewer deaths were attributable to antihypertensive treatments in around 7.1 million hypertensive people (table 1). 4
All secondary prevention interventions (risk factor reductions in CHD patients) together accounted for approximately 8745 (5335-15 830) fewer deaths (table 1). This represented 19% of the total number of 45 370 deaths prevented or postponed by change in the three major risk factors between 1981 and 2000 (minimum contribution 18.0%, maximum contribution 21.0%).
The remaining reduction in deaths (45 370 minus 8745) could then be attributed to primary prevention in healthy people, which thus accounted for approximately 36 625 (24 235-61 005) fewer deaths (table 1). This 36 625 represented 81% of the total mortality decrease of 45 370 deaths prevented or postponed by change in the three major risk factors between 1981 and 2000 (minimum contribution 53.4%, maximum contribution 79.3%).
Sensitivity analysis comparing primary and secondary prevention: falls in coronary heart disease mortality attributable to changes in risk factors in people with and without recognised coronary heart disease in England and Wales, 1981-2000 (best estimate, with minimum and maximum estimates). CHD=coronary heart disease
Sensitivity analyses
The relative contribution to the overall decline in CHD deaths from primary and secondary prevention for each risk factor was little changed by whether best, minimum, or maximum estimates were considered (figure).
Risk factor reduction benefits in specific groups of CHD patients
In 2000, approximately 30 530 (18 630-54 180) deaths were prevented or postponed in patients with CHD. Some 23 770 (77.9%) were attributable to medical and surgical treatments, and 6760 (22.1%) were attributable to reductions in the three major risk factors. Substantial contributions came from three patient groups: post-myocardial infarction and post-surgical intervention groups, angina in the community, and heart failure (table 2).
Table 2 Fall in coronary heart disease mortality in England and Wales between 1981 and 2000: numbers of deaths prevented or postponed by treatments and by changes in risk factors in people with coronary heart disease, categorised into specific groups
Approximately 1990 (1305-4180) fewer deaths were attributable to statin treatments in CHD patients. The biggest contributions came from statin treatment for patients after acute myocardial infarction (460), revascularisation (675), or heart failure (750) (table 2).
Risk factor reduction benefits by age and sex
Of the 45 370 (29 570-76 835) deaths prevented or postponed by reductions in risk factors, 73.7% occurred in men and 26.3% in women (table 3). The relative contribution from secondary prevention was consistently higher in women (27.3%) than in men (16.4%). The contribution from secondary prevention was relatively consistent across age groups in men, but in women this contribution was higher in the youngest and oldest groups than in those in between (table 3).
Table 3 Numbers of deaths prevented or postponed* by reductions in risk factors: relative contributions from primary prevention and secondary prevention, by age and sex. Values are numbers (percentages)
Discussion
British Heart Foundation Statistics Database. Coronary heart disease statistics, 2005. www.heartstats.org (accessed 12 Jun 2005).
Hunink MG, Goldman L, Tosteson AN, Mittleman MA, Goldman PA, Williams LW, et al. The recent decline in mortality from coronary heart disease, 1980-1990: the effect of secular trends in risk factors and treatment. JAMA 1997;277: 535-42.
Capewell S, Morrison CE, McMurray JJ. Contribution of modern cardiovascular treatment and risk factor changes to the decline in coronary heart disease mortality in Scotland between 1975 and 1994. Heart 1999;81: 380-6.
Unal B, Critchley J, Capewell S. Explaining the decline in coronary heart disease mortality in England and Wales, 1981-2000. Circulation 2004;109: 1101-7.
Capewell S, Beaglehole R, Seddon M, McMurray J. Explaining the decline in coronary heart disease mortality in Auckland, New Zealand between 1982 and 1993. Circulation 2000;102: 1511-6.
US Department of Health and Human Services. Healthy people 2010. Vol 1: Understanding and improving health; Objectives for improving health. Washington, DC: Government Printing Office, 2000.
Ebrahim S, Davey-Smith G. Multiple risk factor interventions for primary prevention of coronary heart disease. Cochrane Database Syst Rev 1999;(2): CD001561.
Bonow RO. Primary prevention of cardiovascular disease: a call to action. Circulation 2002;106: 3140-1.
Law M, Wald N. Why heart disease mortality is low in France: the time lag explanation. BMJ 1999;318: 1471-6.
Boyle R. Meeting the challenge of cardiovascular care in the new National Health Service. Heart 2004;90(suppl 4): iv3-5.
Rose G. The strategy of preventive medicine. Oxford: Oxford University Press, 1992.
Emberson J, Whincup P, Morris R, Walker M, Ebrahim S. Evaluating the impact of population and high-risk strategies for the primary prevention of cardiovascular disease. Eur Heart J 2004;25: 484-91.
Critchley J, Liu J, Zhao D, Wei W, Capewell S. Explaining the increase in coronary heart disease mortality in Beijing between 1984 and 1999. Circulation 2004;110: 1236-44.
Unal B, Critchley JA, Fidan D, Capewell S. Life-years gained from modern cardiological treatments and population risk factor changes in England and Wales, 1981-2000. Am J Public Health 2005;95: 103-8.
Unal B, Critchley J, Capewell S. Appendices for IMPACT CHD mortality model. www.liv.ac.uk/PublicHealth/sc/bua/IMPACT-Model-Appendices.pdf (accessed 22 Jun 2005).
Briggs A, Sculpher M, Buxton M. Uncertainty in the economic evaluation of health care technologies: the role of sensitivity analysis. Health Econ 1994;3: 95-104.
Doll R, Peto R, Boreham J, Sutherland I. Mortality in relation to smoking: 50 years' observations on male British doctors. BMJ 2004;328: 1519.
Critchley J, Capewell S. Mortality risk reduction associated with smoking cessation in patients with coronary heart disease: a systematic review. JAMA 2003;290: 86-97.
Capewell S, MacIntyre K, Stewart S, Chalmers JW, Boyd J, Finlayson A, et al. Age, sex, and social trends in out-of-hospital cardiac deaths in Scotland 1986-95: a retrospective cohort study. Lancet 2001;358: 1213-7.
Department of Health for England. Choosing health: making healthy choices easier. London: Stationery Office, 2004.
Kendall CW, Jenkins DJ. A dietary portfolio: maximal reduction of low-density lipoprotein cholesterol with diet. Curr Atheroscler Rep 2004;6: 492-8.
Vartiainen E, Jousilahti P, Alfthan G. Cardiovascular risk factor changes in Finland, 1972-1997. Int J Epidemiol 2000;29: 49-56.
Dowse GK, Gareeboo H, Alberti KG, Zimmet P, Tuomilehto J, Purran A, et al. Changes in population cholesterol concentrations and other cardiovascular risk factor levels after five years of the non-communicable disease intervention programme in Mauritius. BMJ 1995;311: 1255-9.
California Department of Health, Tobacco Control Section. California tobacco control update. www.dhs.cahwnet.gov/tobacco/documents/TCSupdate.PDF (accessed 27 Jun 2005).(Belgin Unal, associate professor1, Julia)
Correspondence to: B Unal belgin.unal@deu.edu.tr or belgina@liv.ac.uk
Objective To investigate whether population based primary prevention (risk factor reduction in apparently healthy people) might be more powerful than current government initiatives favouring risk factor reduction in patients with coronary heart disease (CHD) (secondary prevention).
Design, setting, and participants The IMPACT model was used to synthesise data for England and Wales describing CHD patient numbers, uptake of specific treatments, trends in major cardiovascular risk factors, and the mortality benefits of these specific risk factor changes in healthy people and in CHD patients.
Results Between 1981 and 2000, CHD mortality rates fell by 54%, resulting in 68 230 fewer deaths in 2000. Overall smoking prevalence declined by 35% between 1981 and 2000, resulting in approximately 29 715 (minimum estimate 20 035, maximum estimate 44 675) fewer deaths attributable to smoking cessation: approximately 5035 in known CHD patients and approximately 24 680 in healthy people. Population total cholesterol concentrations fell by 4.2%, resulting in approximately 5770 fewer deaths attributable to dietary changes (1205 in CHD patients and 4565 in healthy people) plus 2135 fewer deaths attributable to statin treatment (1990 in CHD patients, 145 in people without CHD). Mean population blood pressure fell by 7.7%, resulting in approximately 5870 fewer deaths attributable to secular falls in blood pressure (520 in CHD patients and 5345 in healthy people) plus approximately 1890 fewer deaths attributable to antihypertensive treatments in people without CHD. Approximately 45 370 fewer deaths were thus attributable to reductions in the three major risk factors in the population: some 36 625 (81%) in people without recognised CHD and 8745 (19%) in CHD patients.
Conclusions Compared with secondary prevention, primary prevention achieved a fourfold larger reduction in deaths. Future CHD policies should prioritise population-wide tobacco control and healthier diets.
Coronary heart disease (CHD) remains the largest cause of death in the United States, Europe, and Australasia.1 However, since the 1980s, CHD mortality rates have halved in Britain and in many industrialised countries.1 Studies in the US, Europe, and New Zealand consistently suggest that 50-75% of the falls in cardiac deaths can be attributed to population-wide improvements in the major risk factors, particularly smoking, cholesterol, and blood pressure.2–5 Modern cardiological treatments for known CHD patients, such as thrombolysis, aspirin, angiotensin converting enzyme inhibitors, statins, and coronary artery bypass surgery, generally explain the remaining 25-50% of the fall in mortality.2–5
Risk factor reduction should thus be a central component of all CHD policies. However, disagreement continues about whether to prioritise risk factor reduction across the whole population, explicitly including all apparently healthy people (primary prevention), or mainly to target CHD patients (secondary prevention). Current funding in the US6 and the United Kingdom clearly favours secondary prevention. This reflects four perceived limitations of primary prevention as an "evidence based" intervention. Firstly, a much quoted Cochrane metaanalysis of 10 intervention studies in primary care that used counselling or education to modify more than one cardiovascular risk factor in adults found only modest changes in risk factors and no effect on mortality.7 Secondly, although confident about prescribing drugs, some clinicians may feel uncomfortable in a health promotion role, perhaps lacking the confidence or skills to influence complex behaviours such as diet or smoking.8 Thirdly, the very long time scales apparently involved may be a deterrent.9 Fourthly, the numbers needed to treat to prevent one event are substantial, often fivefold higher than those for targeting CHD patients.10
In truth, both primary and secondary prevention interventions are probably necessary to maximise population health.11 Quantifying their relative contributions is clearly important but is difficult to do with disease registers or population cohorts.12 Researchers have therefore used models to quantify the potential contribution of risk factor reductions before and after CHD is diagnosed in an individual. For example, use of the CHD policy model suggested that approximately 25% of the decline in CHD deaths in the US between 1980 and 1990 was explained by primary prevention and slightly more (29%) was explained by risk factor reductions in patients with CHD.2
A better understanding of the relative contributions of primary prevention and secondary prevention to the recent falls in deaths from CHD is clearly essential, in order to inform future CHD policy options in Britain and elsewhere.10 We have therefore used the only validated and comprehensive CHD model available in the UK.4 We analysed the decrease in CHD mortality in England and Wales between 1981 and 2000 to estimate the proportions attributable to changes in major cardiovascular risk factors in apparently healthy people (primary prevention) and in patients with CHD (secondary prevention).
Methods
IMPACT CHD model
The cell based IMPACT CHD mortality model, previously validated in Scotland,3 New Zealand,5 and Beijing,13 has been described elsewhere.3 5 14 Briefly, we used the model to synthesise data for the adult population of England and Wales—35.5 million people aged between 25 and 84—describing numbers of CHD patients, uptake of specific treatments, trends in major cardiovascular risk factors in apparently healthy people in populations and in specific patient groups, and the effectiveness (mortality benefits) of the reductions in specific risk factors in people with and without recognised CHD.4
Data sources
Sources of data included national surveys, official statistics, clinical audits, controlled trials, and meta-analyses. These are detailed on our website.15
Primary prevention: risk factor trends and mortality benefits in the general population
For risk factor changes, the model uses regression () coefficients obtained from large meta-analyses, cohort studies, and MONICA analyses (appendix 10 on website).4 15 Each coefficient quantifies the independent relation between population change in a specific CHD risk factor (such as smoking, cholesterol, or blood pressure) and the consequent percentage change in population mortality from CHD. We then estimated the subsequent reduction in the number of deaths produced by the decrease in each major risk factor as the product of three variables: the number of CHD deaths observed in the base year (1981), the relative reduction in that risk factor, and the coefficient, each stratified by age and sex.4 15
To estimate the impact of the population-wide reduction in cholesterol due to dietary change, we subtracted the estimated effect of statins for primary prevention from the overall number of deaths prevented or postponed in the population due to change in mean cholesterol concentration. We explicitly considered demographic change by using age and sex specific population CHD mortality and CHD patient numbers for 1981 and for 2000.4
Secondary prevention: risk factor trends and mortality benefits in CHD patients
We then estimated the mortality benefit attributable to reductions in each major risk factor (smoking, total cholesterol, and blood pressure) in each group of CHD patients as the number of deaths prevented or postponed.4 We categorised CHD patients according to disease groups: acute myocardial infarction, survivors of myocardial infarction, revascularisation patients, and patients with unstable angina, chronic angina, and chronic heart failure. We did not consider the impact of changes in risk factors in patients with an initial acute myocardial infarction or unstable angina, because both are transient states. To avoid double counting, we firstly made adjustments for overlaps between different treatment groups by subtracting the overlapping subgroup from the main group, as detailed in appendix 8 on the website.4 15
We based age and sex specific smoking cessation rates on local surveys and audits. We initially assumed that age and sex specific changes in cholesterol attributable to diet and changes in blood pressure attributable to population secular trends would mirror the changes seen in the general population. We then used rigorous sensitivity analyses to test the effect of much smaller (–50%) and much larger (+50%) changes.
Statins and other treatments
The model aimed to include all medical and surgical treatments provided in 2000. This included statins as primary prevention (in people without recognised CHD) and as secondary prevention (in CHD patients). We calculated the absolute reduction in mortality by using the relative reduction in mortality reported in the most recent meta-analysis15 applied to the age specific case fatality rate observed in unselected patient cohorts. The effect of all other "secondary prevention" drugs (aspirin, blockers, and angiotensin converting enzyme inhibitors) has been previously reported and was explicitly excluded from this analysis.4 We did not consider over the counter statins, as these only became available in 2003.
We estimated the number of deaths prevented or postponed for specific age and sex groups. We used survival benefit over a one year time interval throughout.
Sensitivity analyses
Because of the uncertainties surrounding some values, we did a multiway sensitivity analysis using the analysis of extremes method.16 Illustrative examples are shown in appendix 7 on the website.15
Apportioning deaths prevented or postponed between primary and secondary prevention
We then estimated the deaths prevented or postponed in apparently healthy people as the deaths prevented or postponed in the entire population minus the deaths prevented or postponed in each CHD patient group. Illustrative examples are given in the results section.
Results
Fall in CHD mortality between 1981 and 2000
Between 1981 and 2000, age specific CHD mortality in England and Wales fell by 62% in men and 45% in women aged 25-84. This resulted in 68 230 fewer deaths in 2000, compared with the 1981 baseline.4
Medical and surgical treatments together prevented or postponed approximately 25 805 deaths (minimum estimate 17 110, maximum estimate 49 040). This represented 42% of the total decrease in CHD deaths estimated by the model.4
Approximately 58% of the fall in mortality was attributable to reductions in the risk factors—mainly smoking, cholesterol, and blood pressure.4 Changes in the three major cardiovascular risk factors together produced a best estimate of 45 370 (29 570-76 835) fewer deaths. In contrast, adverse trends in diabetes, obesity, and physical activity together generated approximately 7645 (5395-10 730) additional deaths.4
Risk factor reductions in the general population and in CHD patients
Overall smoking prevalence fell by 35% between 1981 and 2000. This resulted in approximately 29 715 (20 035-44 675) fewer deaths. Approximately 5035 (17%; 3100-8255) fewer deaths resulted from smoking cessation in CHD patients, leaving the remainder—approximately 24 680 (83%; 16 935-36 420)— attributable to reduced smoking prevalence in "healthy people" (table 1).
Table 1 Fall in coronary heart disease mortality attributable to changes in risk factors in people with and without recognised coronary heart disease: England and Wales, 1981-2000
Population total cholesterol concentrations fell by 4.2% between 1981 and 2000, resulting in approximately 7900 (5285-16 695) fewer deaths. Approximately 5770 fewer deaths were attributable to dietary reduction—approximately 1205 (645-2455) in CHD patients, leaving some 4565 (3290-9650) fewer deaths attributable to dietary cholesterol reduction in healthy people. Approximately 2135 (1350-4590) fewer deaths were attributable to statin treatments: 1990 (1305-4180) in CHD patients and 145 (45-410) in healthy people (table 1).
Mean population diastolic blood pressure fell by 7.7% between 1981 and 2000, resulting in approximately 7755 (4250-15 465) fewer deaths. Approximately 520 (285-940) fewer deaths were attributable to the secular fall in blood pressure in CHD patients, leaving some 5345 (3125-11 740) in healthy people, and 1890 (840-2785) fewer deaths were attributable to antihypertensive treatments in around 7.1 million hypertensive people (table 1). 4
All secondary prevention interventions (risk factor reductions in CHD patients) together accounted for approximately 8745 (5335-15 830) fewer deaths (table 1). This represented 19% of the total number of 45 370 deaths prevented or postponed by change in the three major risk factors between 1981 and 2000 (minimum contribution 18.0%, maximum contribution 21.0%).
The remaining reduction in deaths (45 370 minus 8745) could then be attributed to primary prevention in healthy people, which thus accounted for approximately 36 625 (24 235-61 005) fewer deaths (table 1). This 36 625 represented 81% of the total mortality decrease of 45 370 deaths prevented or postponed by change in the three major risk factors between 1981 and 2000 (minimum contribution 53.4%, maximum contribution 79.3%).
Sensitivity analysis comparing primary and secondary prevention: falls in coronary heart disease mortality attributable to changes in risk factors in people with and without recognised coronary heart disease in England and Wales, 1981-2000 (best estimate, with minimum and maximum estimates). CHD=coronary heart disease
Sensitivity analyses
The relative contribution to the overall decline in CHD deaths from primary and secondary prevention for each risk factor was little changed by whether best, minimum, or maximum estimates were considered (figure).
Risk factor reduction benefits in specific groups of CHD patients
In 2000, approximately 30 530 (18 630-54 180) deaths were prevented or postponed in patients with CHD. Some 23 770 (77.9%) were attributable to medical and surgical treatments, and 6760 (22.1%) were attributable to reductions in the three major risk factors. Substantial contributions came from three patient groups: post-myocardial infarction and post-surgical intervention groups, angina in the community, and heart failure (table 2).
Table 2 Fall in coronary heart disease mortality in England and Wales between 1981 and 2000: numbers of deaths prevented or postponed by treatments and by changes in risk factors in people with coronary heart disease, categorised into specific groups
Approximately 1990 (1305-4180) fewer deaths were attributable to statin treatments in CHD patients. The biggest contributions came from statin treatment for patients after acute myocardial infarction (460), revascularisation (675), or heart failure (750) (table 2).
Risk factor reduction benefits by age and sex
Of the 45 370 (29 570-76 835) deaths prevented or postponed by reductions in risk factors, 73.7% occurred in men and 26.3% in women (table 3). The relative contribution from secondary prevention was consistently higher in women (27.3%) than in men (16.4%). The contribution from secondary prevention was relatively consistent across age groups in men, but in women this contribution was higher in the youngest and oldest groups than in those in between (table 3).
Table 3 Numbers of deaths prevented or postponed* by reductions in risk factors: relative contributions from primary prevention and secondary prevention, by age and sex. Values are numbers (percentages)
Discussion
British Heart Foundation Statistics Database. Coronary heart disease statistics, 2005. www.heartstats.org (accessed 12 Jun 2005).
Hunink MG, Goldman L, Tosteson AN, Mittleman MA, Goldman PA, Williams LW, et al. The recent decline in mortality from coronary heart disease, 1980-1990: the effect of secular trends in risk factors and treatment. JAMA 1997;277: 535-42.
Capewell S, Morrison CE, McMurray JJ. Contribution of modern cardiovascular treatment and risk factor changes to the decline in coronary heart disease mortality in Scotland between 1975 and 1994. Heart 1999;81: 380-6.
Unal B, Critchley J, Capewell S. Explaining the decline in coronary heart disease mortality in England and Wales, 1981-2000. Circulation 2004;109: 1101-7.
Capewell S, Beaglehole R, Seddon M, McMurray J. Explaining the decline in coronary heart disease mortality in Auckland, New Zealand between 1982 and 1993. Circulation 2000;102: 1511-6.
US Department of Health and Human Services. Healthy people 2010. Vol 1: Understanding and improving health; Objectives for improving health. Washington, DC: Government Printing Office, 2000.
Ebrahim S, Davey-Smith G. Multiple risk factor interventions for primary prevention of coronary heart disease. Cochrane Database Syst Rev 1999;(2): CD001561.
Bonow RO. Primary prevention of cardiovascular disease: a call to action. Circulation 2002;106: 3140-1.
Law M, Wald N. Why heart disease mortality is low in France: the time lag explanation. BMJ 1999;318: 1471-6.
Boyle R. Meeting the challenge of cardiovascular care in the new National Health Service. Heart 2004;90(suppl 4): iv3-5.
Rose G. The strategy of preventive medicine. Oxford: Oxford University Press, 1992.
Emberson J, Whincup P, Morris R, Walker M, Ebrahim S. Evaluating the impact of population and high-risk strategies for the primary prevention of cardiovascular disease. Eur Heart J 2004;25: 484-91.
Critchley J, Liu J, Zhao D, Wei W, Capewell S. Explaining the increase in coronary heart disease mortality in Beijing between 1984 and 1999. Circulation 2004;110: 1236-44.
Unal B, Critchley JA, Fidan D, Capewell S. Life-years gained from modern cardiological treatments and population risk factor changes in England and Wales, 1981-2000. Am J Public Health 2005;95: 103-8.
Unal B, Critchley J, Capewell S. Appendices for IMPACT CHD mortality model. www.liv.ac.uk/PublicHealth/sc/bua/IMPACT-Model-Appendices.pdf (accessed 22 Jun 2005).
Briggs A, Sculpher M, Buxton M. Uncertainty in the economic evaluation of health care technologies: the role of sensitivity analysis. Health Econ 1994;3: 95-104.
Doll R, Peto R, Boreham J, Sutherland I. Mortality in relation to smoking: 50 years' observations on male British doctors. BMJ 2004;328: 1519.
Critchley J, Capewell S. Mortality risk reduction associated with smoking cessation in patients with coronary heart disease: a systematic review. JAMA 2003;290: 86-97.
Capewell S, MacIntyre K, Stewart S, Chalmers JW, Boyd J, Finlayson A, et al. Age, sex, and social trends in out-of-hospital cardiac deaths in Scotland 1986-95: a retrospective cohort study. Lancet 2001;358: 1213-7.
Department of Health for England. Choosing health: making healthy choices easier. London: Stationery Office, 2004.
Kendall CW, Jenkins DJ. A dietary portfolio: maximal reduction of low-density lipoprotein cholesterol with diet. Curr Atheroscler Rep 2004;6: 492-8.
Vartiainen E, Jousilahti P, Alfthan G. Cardiovascular risk factor changes in Finland, 1972-1997. Int J Epidemiol 2000;29: 49-56.
Dowse GK, Gareeboo H, Alberti KG, Zimmet P, Tuomilehto J, Purran A, et al. Changes in population cholesterol concentrations and other cardiovascular risk factor levels after five years of the non-communicable disease intervention programme in Mauritius. BMJ 1995;311: 1255-9.
California Department of Health, Tobacco Control Section. California tobacco control update. www.dhs.cahwnet.gov/tobacco/documents/TCSupdate.PDF (accessed 27 Jun 2005).(Belgin Unal, associate professor1, Julia)