SIGN 97: Risk estimation and the prevention of cardiovascular disease

Guideline Index Page | SIGN Methodology

1 Introduction

1.1 The need for a guideline

Coronary heart disease (CHD) will directly affect the majority of the Scottish population at some point in their life. In 2003 around one per 300 were newly diagnosed with some form of CHD in Scotland.1 The incidence of CHD is higher amongst men, the elderly and in deprived areas of Scotland. The annual prevalence rates in 2005 were 4.2% in men and 3.0% in women, although this underestimates the true scale of the disease as it only records patients treated in hospital.2

Recent estimates of disease incidence show that rates are falling and, although the reasons for this decline are complex, improvements in diet and a reduction in smoking rates are significant factors.

There has been an increasing recognition that it is no longer sufficient to predict the risk of vascular disease only in terms of CHD as this underestimates the risk of stroke. All cardiovascular disease (CVD) should be considered as a spectrum of disorder including coronary artery disease, cerebrovascular disease and peripheral arterial disease and the guideline has been extended to include the prevention of other forms of cardiovascular disease. A recent meta-analysis of randomised controlled trials (RCTs) shows that statins are effective in the primary and secondary prevention not only of CHD events and coronary revascularisation, but also of strokes and combined major vascular events.3

Cardiovascular disease has a multifactorial aetiology with a number of potentially modifiable risk factors. The classical Framingham risk factors, age, sex, cigarette smoking, blood pressure, total cholesterol and high density lipoprotein (HDL) cholesterol have proved consistent risk factors in every population studied. Various ethnic groups may display differences in population baseline risk.4 Scotland's minority ethnic population is small, but growing. At the 2001 census around 2% of the country's five million people were from minority ethnic backgrounds.5

Of particular relevance to the Scottish context, are the effects of socioeconomic status on the risk of developing cardiovascular disease. The incidence and mortality rates from acute myocardial infarction in those aged under 65 are higher in deprived areas than in more affluent areas.6-9

Recognising cardiovascular disease as a continuum challenges the traditional concepts of primary and secondary prevention, with healthcare professionals adopting a "high-risk" approach to prevention.10 In fact, most CVD cases occur in the large number of individuals at lower levels of absolute risk.11 High risk approaches have been facilitated both by the availability of scoring systems to estimate absolute risk (rather than the traditional use of single risk factors) and by the advent of several treatments, principally statins and blood pressure reducing drugs, which produce marked and apparently independent reductions in CVD risk in high risk subjects.12

The guideline has attempted to devise effective strategies for the reduction of CVD that take a combined approach using both "high risk" and a population approach.

1.2 Remit of the guideline

This guideline deals with both primary prevention, defined as the potential for intervention prior to the disease presenting through a specified event, and secondary prevention, defined as the potential for intervention after an event has occurred. The guideline group have tried to consider cardiovascular disease as a continuum from the pre-clinical to the end stage disease, potentially offering different opportunities to intervene, both prior to, and after an event, so creating the potential to alter the outcome of the disease process. The group believes that it is more relevant to consider an individual in terms of whether they have a high or low risk of CVD rather than in terms of primary or secondary prevention.

1.3 Risk estimation

For many health professionals the calculation of absolute cardiovascular risk is the starting point for the development of CHD prevention strategies.

1.3.1 Definitions

"Absolute risk" is also known as "total risk" or "global risk". This risk is defined as the percentage chance of an individual developing a CVD event over a given period of time, eg a ten year risk of 15%. "Relative risk" refers to the risk of someone developing a CVD event who has risk factors compared to an individual of the same age and sex who does not.

1.3.2 Risk scores

Risk scores cannot predict absolute risk. They are extremely useful in assessing or estimating risk and in prioritising treatment on an equitable basis.

In Scotland absolute CVD risk is usually calculated from electronic decision support tools based on the US Framingham heart study.13 Framingham risk equations have been validated in different populations.14

A large systematic review of cardiovascular risk assessment in primary prevention has shown that the performance of Framingham risk scores vary considerably between populations and that accuracy relates to the background risk of the population to which it has been applied.15 There is general agreement that Framingham overpredicts absolute risk in populations with low observed CHD mortality and underpredicts in populations, such as the socially deprived, with high CHD mortality.15

The accuracy of Framingham cardiovascular risk assessments is limited by the exclusion of certain risk factors including obesity, physical inactivity, family history of cardiovascular disease and social status. Work done using the Scottish MIDSPAN data suggests that the exclusion of social deprivation in the estimation of cardiovascular risk results in a serious underestimation of absolute risk.16

Based on these findings SIGN has commissioned work to incorporate risk coefficients, accounting for both family history and social deprivation in a new risk scoring system (see section 2.3.4).17,18

1.4 Statement of intent

This guideline is not intended to be construed or to serve as a standard of care. Standards of care are determined on the basis of all clinical data available for an individual case and are subject to change as scientific knowledge and technology advance and patterns of care evolve. Adherence to guideline recommendations will not ensure a successful outcome in every case, nor should they be construed as including all proper methods of care or excluding other acceptable methods of care aimed at the same results. The ultimate judgement must be made by the appropriate healthcare professional(s) responsible for clinical decisions regarding a particular clinical procedure or treatment plan. This judgement should only be arrived at following discussion of the options with the patient, covering the diagnostic and treatment choices available. It is advised, however, that significant departures from the national guideline or any local guidelines derived from it should be fully documented in the patient's case notes at the time the relevant decision is taken.

1.4.1 Patient version

A patient version of this guideline is available from the SIGN website,

1.4.2 Additional advice to nhsscotland from NHS Quality Improvement Scotland and the Scottish Medicines Consortium

NHS QIS processes multiple technology appraisals (MTAs) for NHSScotland that have been produced by the National Institute for Health and Clinical Excellence (NICE) in England and Wales.

The Scottish Medicines Consortium (SMC) provides advice to NHS Boards and their Area Drug and Therapeutics Committees about the status of all newly licensed medicines and any major new indications for established products.

SMC advice and NHS QIS validated NICE MTAs relevant to this guideline are summarised in the section on implementation.

1.5 Review and updating

This guideline was issued in 2007 and will be considered for review in three years. Any updates to the guideline in the interim period will be noted on the SIGN website:

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Guideline Index Page | SIGN Methodology

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