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Objective: To estimate the number of coronary events that could be prevented in Australia each year by the use of preventive and therapeutic strategies targeted to subgroups of the population based on their levels of risk and need. Patrick McElduff Centre for Clinical Epidemiology and Biostatistics, University of Newcastle, New South Wales Annette J. Dobson Department of Social and Preventive Medicine, University of Queensland Methods: Estimates of risk reduction from the published literature, prevalence estimates of elevated risk factor levels from the 1995 National Health Survey and treatment levels from the Australian collaborating centres in the World Health Organizationâs MONICA Project were used to calculate numbers of coronary events preventable among men and women aged 35-79 years in Australia. Konrad Jamrozik and Michael S.T. Hobbs Department of Public Health, University of Western Australia Results: Approximately 14,000 coronary events could be avoided each year if the mean level of cholesterol in the population was reduced by 0.5 mmol/L, smoking prevalence was halved and prevalence of physical inactivity was reduced to 25%. This represents a reduction in coronary events of about 40%. Even with less optimistic targets, a reduction of 20% could be attained, while the achievement of some internationally recommended targets could lead to almost 50% reduction. In the short term, aggressive medical treatment of people with elevated levels of risk factors and established coronary disease offers the greatest opportunity for reducing coronary events. Conclusion: A comprehensive approach to reduce levels of behavioural and biological risk factors and improve the use of effective treatment could lead to a large reduction in coronary event rates. In the long term, primary prevention â especially to reduce smoking, lower cholesterol levels and increase exercise â has the potential to reduce the population levels of risk and hence contain the national cost of coronary disease. (Aust N Z J Public Health 2001; 25: 24-30) here has been a continuous decline in mortality from coronary heart disease (CHD) in Australia since the late 1960s. However, rates of coronary events (i.e. coronary deaths and non-fatal myocardial infarctions) in Australia are still twice as high as those in some other countries.1,2 It has been consistently shown by large cohort studies that the risk of a coronary event increases with increasing blood pressure, with increasing levels of cholesterol and with cigarette smoking.3,4 Recent evidence from randomised controlled trials has shown that reducing cholesterol or reducing blood pressure will cause a reduction in coronary events.5,6 It has also been shown that ex-smokers who have quit smoking for more than five years have a similar risk of a coronary event as people who have never smoked.7 Using estimates from the published literature on the benefits of modification of risk factors and improvements in medical care, we calculate the potential reduction in coronary events that could be achieved by the implementation of preventive and therapeutic strategies targeted at specific groups in the community. treatment for three mutually exclusive subgroups of the population, defined by different levels of risk: Group I â people who have never been told they have hypertension, hypercholesterolaemia or CHD; Group II â people with no history of CHD but with a history of hypertension or hypercholesterolaemia; Group III â people with a history of symptomatic, clinically evident CHD. A further reduction in fatal events can be achieved by improved treatment for people who have a coronary event. The number of coronary events that could be prevented in each group was calculated by multiplying the estimated percentage reduction in event rates, due to the prevention and treatment in that group, by the number of events that occurred in the 1994/95 financial year. The number of deaths that could be prevented during acute coronary events was calculated by multiplying the estimated percentage reduction in the risk of death, due to improved treatment, by the number of coronary deaths that actually occur. Number of people at risk and number of coronary events in Australia All estimates were calculated separately for men and women in each of the 10-year age groups from 35-44 to 65-74 and those Methods We estimated the benefit of reducing risk factors and increasing the use of medical Submitted: May 2000 Revision requested: November 2000 Accepted: December 2000 Correspondence to: Patrick McElduff, Centre for Clinical Epidemiology and Biostatistics, David Maddison Building, University of Newcastle, Callaghan, New South Wales 2308. Fax: (02) 4923 6148; e-mail: patrickm@mail.newcastle.edu.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2001 VOL. 25 NO. 1 Major Causes of Death Control of heart disease in Australia Table 1: Estimated reduction in risk of a major coronary event, or death during acute episode due to a reduction in a risk factor or use of medical therapy and expected time to realise the full reduction. Biological stage of CHD Risk factor/ treatment Smoking11 Developed risk factor but not CHD 67% lower risk for never smokers aged <65 years (compared with smokers); 40% lower risk for never smokers aged â¥65 years Ex-smokers have the same level of risk as never smokers after five years of quitting7 Population strategy: Ã=0.0302 High risk strategy: 14% reduction in risk â Reduction in blood pressure is maintained for 2-3 years and the reduction in CHD persisted for at least five years Population strategy: Ã=0.3052 High risk strategy: 34% reduction in risk â Reduction was evident within two years and persisted for at least five years 35â55% No randomised controlled trials have been conducted â as estimates are based on cohort studies and no time frame is available N/A Acute episode Established CHD N/A 67% lower risk for never smokers aged <65 years; 40% lower risk for never smokers aged â¥65 years Blood pressure5 N/A High risk strategy: 14% reduction in risk Cholesterol6 N/A High risk strategy: 30% reduction in risk Physical inactivity12,13 N/A 20% reduction in total mortality Reduction occurred within 2-3 years 19% reduction in vascular events Benefit was consistent for trials with treatment longer than one month (mean length = 27 months) 23% reduction in total mortality Trials ranged from 6 to 24 months 23% N/A Similar to treatment with CABG 68% LMDd; 42% 3 vessel; 23% 2 vessel Benefit was evident after about two years and persisted for more than 10 years Aspirin14 21% Beta-blockers15,16,17 ACEa inhibitors18 Streptokinase19 PTCAb 20 CABGc 21 N/A N/A N/A N/A N/A 15% 6% 18% â â Notes: (a) ACE = Angiotensin-converting enzyme. (b) PTCA = percutaneous transluminal coronary agioplasty. (c) CABG = coronary artery bypass grafting. (d) LMD = left mean disease. aged 75-79 years (the results have been aggregated in the tables). The prevalence of hypertension, hypercholesterolaemia and CHD, and hence the proportions of people in Groups I, II and III, were obtained from self-report data from the 1995 National Health Survey (NHS). These were multiplied by the number of people in the Australian population in 1994 to obtain the number of people in each group.8 Numbers of non-fatal myocardial infarctions (MIs) were approximated by the number of non-fatal hospital separations with principal diagnosis code 410 from the International Classification of Diseases â 9th Revision (ICD9-CM) and length of hospital stay greater than two days during the 1994/95 financial year (Australian Institute of Health and Welfare national morbidity database). The numbers of coronary deaths were those in 1994 coded to ICD9-CM rubrics 410-414 by the Australian Bureau of Statistics.9 We used data from the registers of coronary events established by the Perth and Newcastle MONICA centres to estimate the proportion of the non-fatal MIs and coronary deaths that occurred in each of the risk groups.10 2001 VOL. 25 NO. 1 Levels of risk factors and use of treatment in the Australian population The prevalence of cigarette smoking, hypercholesterolaemia, hypertension and physical inactivity was estimated from the 1995 NHS. Respondents were deemed to be physically inactive if they reported they had not walked for sport, recreation or fitness, or performed moderate or vigorous exercise in the two weeks prior to the interview. Surveys of risk factors conducted in Perth and Newcastle in 1994 provided data on mean levels of blood pressure and cholesterol. The NHS was also used to estimate the prevalence of treatment in the community. However, data from the MONICA Centres in Perth and Newcastle were used to estimate the use of treatment in hospital during MI. Estimates from the Newcastle centre for the age group 65-69 were used for the people aged 70-79 years. Risk reduction associated with reducing risk factors and using treatment The benefit associated with improving risk factor levels in the population and the benefit associated with using various forms AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH McElduff et al. Article Table 2: Percentages of the population, and of coronary deaths, non-fatal myocardial infarctions and total coronary events in groups defined by age, sex and medical history. Population Risk groupa Population (%) 30.9 7.7 1.3 4.7 3.1 1.7 31.6 7.0 0.6 5.2 4.8 1.2 8,000,450 Coronary deaths (%) 4.6 7.4 6.2 8.3 21.3 16.8 1.2 2.1 1.8 5.4 13.9 11.0 16,839 Non-fatal myocardial infarctions (%) 10.1 20.3 7.8 6.3 15.4 10.2 2.4 5.1 2.1 4.0 9.8 6.5 20,258 Total coronary events (%) 7.6 14.5 7.1 7.2 18.1 13.2 1.9 3.7 1.9 4.6 11.7 8.5 37,097 Men, 35-64 years Ia IIb IIIc I II III I II III I II III Men, 65-79 years Women, 35-64 years Women, 65-79 years Total Notes: (a) Group I â people who have never been told they have hypertension, hypercholesterolaemia or CHD. (b) Group II âpeople who have a history of hypertension or hypercholesterolaemia but not CHD. (c) Group III â those with a history of CHD. Percentages may not add to 100 due to rounding. of medical treatment were obtained from the latest reviews or meta-analyses. The size of the benefits and the estimated time to fully realise the benefits are shown in Table 1. Targets for improved levels of risk factors and treatments Using three distinct sets of targets, we estimate the benefits of prevention and treatment strategies that are assumed to be fully used and effective. The âAustralianâ set of targets include a primary prevention strategy designed to reduce the risk of CHD among people in group I. The national goal in Australia was to reduce the prevalence of physical inactivity to 25% by 2000.22 For other risk factors, the targets were to reduce cigarette smoking by 50%, reduce the mean level of diastolic blood pressure by 4 mmHg and reduce the mean level of serum cholesterol by 0.5 mmol/L. The reductions in blood pressure and cholesterol were targeted for people in group I and for those in groups II and III not receiving treatment for hypertension or hypercholesterolaemia. For groups II and III we set targets to reduce the proportion of untreated hypertensives by 50% and also to reduce the proportion of individuals with untreated hypercholesterolaemia by 50%. For medical therapy, the targets were for all eligible people to be effectively treated. We assumed that 80% of patients with symptomatic CHD (Group III) are eligible for aspirin and 50% for beta blockers and ACE inhibitors. From estimates of the prevalence of three vessel disease and left main artery disease we assumed that 60% of Group III would be eligible for coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA).23 The âinternationalâ set of targets is based on the current recommendations for the management of patients in Britain and the United States.24,25 In each of these countries recommendations for the management of people without established CHD are based on the Framingham risk equations, which estimate an individualâs risk of a coronary event within the next 10 years. In Britain the guidelines recommend that patients with an absolute risk of CHD of more than 15% have intensive lifestyle interventions and, where appropriate, drug treatment for hypertension and hypercholesterolaemia. Patients with an absolute risk of more than 30% should be considered for treatment with aspirin, antihypertensives and cholesterol-lowering drugs (statins). For patients with established CHD it is recommended that they stop smoking, increase aerobic exercise, reduce systolic blood pressure to below 140 mmHg and total cholesterol to less than 5.0 mmol/L. It is also recommended that all patients with established CHD are treated with aspirin, cholesterol-lowering agents and beta-blockers and, for patients with symptoms of heart failure or persistent left ventricular systolic dysfunction, ACE inhibitors. Based on these recommendations, the âinternationalâ set of targets are: ⢠Among patients in Group II, use drug therapy to treat all patients with hypertension or hypercholesterolaemia, reduce the mean level of untreated blood pressure by 10mmHg and reduce the mean level of untreated cholesterol by 1 mmol/L. ⢠For patients in Groups II and III, reduce the prevalence of smoking and physical inactivity to zero. ⢠Treat Group III patients with aspirin, statins and beta-blockers and treat 50% of patients in group III with ACE inhibitors. The same levels of CABG and PTCA are used as in the âAustralianâ set of targets. The modest set of targets is intended to achieve reductions in levels of risk factors that are half of those aimed for in the âAustralianâ targets. Also, the goal for increased use of effective drug treatment is equal to half of the increase required to achieve full treatment levels in all eligible people. 2001 VOL. 25 NO. 1 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Major Causes of Death Control of heart disease in Australia Table 3: Total risk reduction (percentage) and percentages of the coronary deaths, non-fatal myocardial infarctions and total coronary events that could be prevented each year in groups defined by age, sex and medical history if the âAustralianâ targets for risk reduction were achieved. Population Risk group Total risk reduction (%) 42.6 37.3 48.5 2.2 33.0 27.3 44.2 3.2 37.7 35.4 56.9 6.0 33.8 29.0 48.5 5.0 7,642 Coronary deaths (%) 2.0 2.7 3.0 0.4 2.7 5.8 7.5 1.3 0.5 0.7 1.0 0.3 1.8 4.0 5.4 1.5 41.0 13,894 Non-fatal myocardial infarctions (%) Total coronary events (%) Men, 35-64 years Ia IIb IIIc Acute I II III Acute I II III Acute I II III Acute 6,852 Men, 65-79 years Women, 35-64 years Women, 65-79 years Events prevented Total number of events prevented Notes: (a) Group I â people who have never been told they have hypertension, hypercholesterolaemia or CHD. (b) Group II âpeople who have a history of hypertension or hypercholesterolaemia but not CHD. (c) Group III â those with a history of CHD. Percentages may not add to 100 due to rounding. In the acute phase, full utilisation of medical treatment was assumed to mean that 100% of patients with acute MI who reach hospital alive would receive aspirin, 80% ACE inhibitors, and 50% beta-blockers and fibrinolytic therapy.26,27 The method used to estimate the percentage reduction in coronary event rates in given in the Appendix. strategies were fully implemented and effective are shown in Table 4. Irrespective of which set of targets were used, the greatest reduction in coronary events would be achieved if the mean level of serum cholesterol in the general population was reduced. Reducing smoking and reducing the level of physical inactivity in the community would also lead to substantial reductions in the number of coronary events. Results The percentages of the population and the distribution of coronary events by sex, age and the three risk groups are shown in Table 2. Overall, Group I (people with no history of hypertension, hypercholesterolaemia or CHD) comprised 72% of the population and had 21% of the coronary events; Group II represented 23% of the population and experienced 48% of events; while Group III, who were only 5% of the population, had 31% of the events. Table 3 shows the estimated percentage reductions and the distributions of deaths and non-fatal MIs that could be prevented each year if all the strategies in the âAustralianâ targets were applied. Reduction of risk factors in asymptomatic individuals with hypertension or hypercholesterolaemia, and intensive follow-up care and attention to risk factors in those with symptomatic CHD show most promise for reducing mortality and morbidity, at least in the short term. The estimated percentage reductions and the number of coronary events that could be prevented each year if individual 2001 VOL. 25 NO. 1 Discussion Our calculations indicate that both incidence and mortality related to major coronary events could be reduced by a further 40% in Australia if national targets were achieved. Evidence suggests much of the gain in outcomes would be accrued within five years of achieving changes in risk factor and treatment levels and most of the gain is achievable within 10 years. For the present, a comprehensive approach to both behavioural and biological risk factors in asymptomatic individuals with known hypertension or hypercholesterolaemia appears to have greater potential to reduce major coronary events than does a true primary preventive strategy. However, important gains might be made sooner through systematic application of proven treatments to patients with clinically evident CHD, especially those over the age of 65 years. Nevertheless, attention to smoking, exercise, diet and weight has the advantages of simplicity and wide applicability, and effective primary prevention would reduce the size of the groups at elevated risk in both the short and longer terms. In AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH McElduff et al. Article Table 4: Number of coronary events that could be prevented each year among men and women aged 35-79 years in groups I, II and III if the three sets of targets were achieved. Risk factor subject to modification or treatment strategy Number (percentage) of events prevented by the implementation of individual preventive and treatment strategies Modest targetsa Smoking Physical Inactivity Cholesterol â Populationb â Treatmentc Blood pressure â Population â Treatment Aspirin ACE inhibitors Beta-blockers CABG/PTCA 1,383 1,730 2,421 537 1,119 100 390 308 298 899 (3.7) (4.7) (6.5) (1.4) (3.0) (0.3) (1.1) (0.7) (0.8) (2.4) (22.1) âAustralianâ targets 2,763 1,633 4,661 1,075 2,177 197 779 616 600 1,797 13,894 (7.4) (7.1) (12.6) (2.9) (5.9) (0.5) (2.1) (1.7) (1.6) (4.8) (37.5) âInternationalâ targets 3,939 5,396 6,590 4,601 2925 397 1,255 616 2,007 1,797 17,771 (10.6) (14.5) (17.7) (12.4) (7.9) (1.1) (3.4) (1.7) (5.4) (4.8) (47.9) Total (i.e. by the implementation of all preventive 8,183 and treatment strategies simultaneously) Notes: (a) Modest targets are half those of the âAustralianâ targets. (b) The population strategy assumes that the benefit of reducing the mean level of cholesterol (or blood pressure) is attained by all people in groups I, II and III who will not receive a cholesterol-lowering agent (or a antihypertensive agent). (c) The treatment strategy is the estimated benefit associated with increasing the level of cholesterol-lowering agents (or antihypertensive agents) among people with raised cholesterol (or blood pressure). addition, an effective primary prevention strategy would reduce the risk in those individuals with undiagnosed hypertension or hypercholesterolaemia without the need for screening. Patients with symptomatic CHD form an important target group in terms both of changing lifestyles and systematic application of proven medical and surgical interventions. Gains can be made by increasing the use of CABG and PTCA in these patients, but this is a relatively expensive and short-term option from a population perspective. The potential for reducing CHD is even greater if the âinternationalâ targets were to be achieved. These targets may be overly optimistic and focus on treatment rather than primary prevention to reduce the incidence of CHD. The third set of targets are far more modest and seem attainable over a short period of time. They are only half as ambitious as the âAustralianâ targets but they could still achieve a significant reduction in the rate of CHD. Once reached, the modest targets would put us in a better position to aim for the other targets. Australia has low levels of case fatality from acute MI compared with other countries and people in Australia who suffer an MI and reach hospital alive are already likely to be treated with drugs that have been shown to improve survival.28 Thus, the potential reductions in mortality from CHD that might be achieved by modifying the management of acute MI are more modest than those estimated for primary and secondary prevention. Limitations The total number of coronary events that we identify as being potentially avoidable by the specified changes in levels of risk factors and treatments should be considered âball parkâ estimates. The population was divided into categories defined by history of CHD, hypertension or hypercholesterolaemia using self-reported data from the NHS. Estimates of the mean levels of cholesterol and blood pressure were obtained from surveys of risk factors conducted in Newcastle and Perth in 1994. Predictions of the benefit of reducing levels of risk factors or increasing the use of medical therapy were obtained from the latest reviews and other estimates used were also the âbestâ available. However, these figures are all estimates and may not accurately represent the conditions that exist throughout Australia today. Except in the case of smoking, all benefits associated with reducing the levels of risk factors and increasing medical treatment are assumed to be the same for men and women and for all age groups. Meta analyses of clinical trials show that the relative benefit of lowering cholesterol and blood pressure is similar for men and women and similar for all people aged less than 80 years.6,29 For the other factors considered, there is insufficient evidence in the medical literature to provide good estimates of effect for each age and sex group separately. In the absence of agespecific figures the best available estimates have been used. We have also assumed that the relative reduction in risk associated with each intervention is independent of the other interventions. For the risk factors considered in this report this assumption is likely to be true.4 It is also likely to be true for the treatments considered for use during acute episodes of CHD.26 There are other potential biases that could affect the accuracy of the estimates calculated in this report. First, the effectiveness of medical treatments based on published overviews may over-estimate or under-estimate their true potential impact. Inclusion criteria for randomised controlled trials may make participants in them unrepresentative of the entire population. Data from reviews may be outdated because of new 2001 VOL. 25 NO. 1 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Major Causes of Death Control of heart disease in Australia âstate-of-the artâ treatments that may have greater benefits than used in these calculations, such as stents with angioplasty. Second, we have assumed that optimum doses are being administered to each person under pharmacological treatment now. Additional gains may be made by ensuring that each individual actually does receive the optimum dose of treatment. Finally, in practice it may not be possible to achieve all of the predicted impact because of issues related to compliance and behavioural change. Cardiovascular disease accounted for 8% of all admissions to hospitals in Australia in 1994/5 and more than a third of these were for CHD. Drugs for treating cardiovascular disease make up approximately 22% of all prescriptions and 30% of all costs of prescriptions subsidised by the Pharmaceutical Benefits Scheme (with expenditure on some of the most expensive and widely used drugs growing most rapidly).30 Effective prevention of CHD therefore stands to bring substantial savings in overall expenditure on health care in Australia. Conclusion We conclude that further major reductions in mortality and morbidity from CHD can be achieved relatively inexpensively in Australia through reducing the mean level of cholesterol and blood pressure in the general population, reducing the prevalence of smoking and increasing physical activity in people with and without established CHD, and by fully using aspirin in people with a history of CHD.
Australian and New Zealand Journal of Public Health – Wiley
Published: Feb 1, 2001
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