The association between total CVD risk and the benefits of prevention
• The magnitude of cardiovascular benefits from preventive interventions is determined mainly by a person’s total CVD risk, rather than by the level of an individual risk factor or how much a risk factor is lowered. This is demonstrated in Fig. 2.1, a meta-analysis of trials of low-density lipoprotein cholesterol (LDL-C) lowering.
Estimating total CVD risk
• Total CVD risk (i.e. the probability of having a CVD event during a defined time period) is determined by the combined effect of all CVD risk factors present.
• People with identical BP levels (or another single risk factor) may have more than tenfold differences in their total CVD risk, depending on the presence or absence of other CVD risk factors, as illustrated in Fig. 2.2.
• CVD risk factors interact, sometime multiplicatively, so it is not possible to estimate a person’s total CVD risk simply by summing risk factors.
• Total CVD risk is typically estimated using a two-step process. First, people with evidence of pre-existing CVD or end-organ damage are classified at very high risk. For the remainder, total CVD risk is usually estimated using a chart or computer program derived from mathematical risk algorithms that are based on studies that have followed people after measuring their CVD risk factor profiles.
• A wide range of risk charts and computer algorithms are available for estimating total CVD risk (e.g. Systematic COronary Risk Estimation (SCORE)).
• The European Joint Societies Task Force on Cardiovascular Disease Prevention in Clinical Practice state that ‘the higher the risk the greater the benefits from preventive efforts’.
• The Task Force uses four priority groups (see Table 2.1) to classify people according to their estimated risk. Those at highest risk gain most from risk factor management.
• Each of the common risk reduction interventions (smoking cessation, lipid lowering, BP lowering, antiplatelet therapies) is estimated to reduce the total CVD risk by 15–30% over about 5 years, while a combination of at least three of these interventions is likely to reduce risk by over 50%.
• Therefore after categorizing a person according to their total CVD risk, it is possible to estimate the approximate number of people with a similar risk who would need to be treated to prevent one CVD event over a defined time period.
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