SIGN 97: Risk estimation and the prevention of cardiovascular disease

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3 Estimating cardiovascular risk

3.1 Assessing risk

Treatment decisions are based on the likelihood that an individual will have a cardiovascular event over a given period of time. Assessment of absolute cardiovascular risk is the starting point for discussions between clinicians and patients who are potentially at significant risk of a cardiovascular event. The prevention of cardiovascular events is the goal of treatment.

This guideline uses many of the risk assessment strategies outlined in JBS2.28 Evidence level 4

The following individuals should have an assessment of cardiovascular risk at least every five years:

The following groups of people should be assumed to be at high risk (a ten year CVD risk≥20% based on clinical history alone) and do not require risk assessment with a scoring system: 28

3.2 Recording risk factor information

Cardiovascular risk is the product of the effect of several risk factors. Individual risk factors can cluster together in significant patterns and tend to have a multiplicative effect on an individual's total cardiovascular risk.35 Measuring any single risk factor will usually not adequately estimate total cardiovascular risk.

3.2.1 Taking a clinical history

The following items of information should be collected routinely when assessing cardiovascular risk.28

Table 2: Items to include in a clinical history for cardiovascular risk assessment

Risk factor Rationale for measurement<.td>
age Cardiovascular risk increases with age.
sex >Other factors being equal, men are at higher risk of a cardiovascular event.
lifetime smoking habit (and number of cigarettes smoked per day) Categorising an individual?s smoking status as current smoker or non-smoker is insufficient for the calculation of accurate CVD risk. A current smoker may have less lifetime exposure to tobacco and less associated cardiovascular damage than an ex-smoker. The CVD risk of an ex-smoker is likely to be intermediate between a current smoker and a lifelong non-smoker.
family history of cardiovascular disease In people with a family history of clinically proven cardiovascular disease (angina, myocardial infarction, transient ischaemic attack, or ischaemic first-degree relative (parent, sibling) before the age of 60 years, the risk of a coronary event is approximately doubled.36 The risk of ischaemic stroke in men with a family history of stroke is slightly less than double that< risk for those without a family history, relative risk, RR,1.89 (95% confidence interval, CI,1.23 to 2.91).37
socioeconomic status For given levels of other risk factors, populations which are more deprived have a higher CVD risk.

3.2.2 Clinical measurements

The following should be measured when assessing cardiovascular risk:28

Table 3: Factors that should be measured for cardiovascular risk assessment

Risk factor Rationale for measurement
blood pressure Systolic blood pressure should be measured according to the British Hypertension Society (BHS) guidelines.38 The mean systolic pressure measured over two separate occasions should be used to calculate risk. In individuals taking antihypertensive medication, the most recently pre-treatment value should be adopted.
weight and waist circumference Individuals with a body mass index (BMI)>30 kg/m2 have a 40-fold increased risk of developing diabetes and a two to three-fold increased risk of CHD39,40 and stroke compared to individuals with a normal BMI (≤25 kg/m2).41 Central obesity, as measured by waist circumference, is a better predictor of cardiovascular risk than BMI.40,42 Central obesity is present if the waist circumference is ≥102 cm in men (≥90 cm in Asian men) and ≥88 cm in women (≥80 cm in Asian women).
total cholesterol and high density lipoprotein cholesterol Total cholesterol (TC) and HDL cholesterol should be measured in a laboratory from a random (non-fasting) sample of blood. In individuals taking lipid lowering medication, the most recently recorded pre-treatment value should be adopted.
glucose In order to screen for diabetes, impaired glucose tolerance or insulin resistance should be measured from the same random (non-fasting) blood sample that is drawn to measure cholesterol levels. A value of ≤6.0 mmol/l indicates a normal level. A value of ≥6.1 mmol/l but ≤7.0 mmol/l requires a repeat measurement on a fasting blood sample. If the value is ≥7.0 mmol/l an oral glucose tolerance test should be performed.
renal function Individuals with chronic kidney disease (CKD) are at significantly increased risk of cardiovascular events.43 To aid the differential diagnosis of CKD, renal function should be estimated from glomerular filtration rate (GFR). A GFR <60 ml/min/1.73m2 is indicative of stage 3 CKD and such individuals should have aggressive risk reduction interventions to reduce their risk of cardiovascular events.

3.3 Using risk assessment Tools

The ASSIGN cardiovascular risk assessment tool allows clinicians to estimate ten year risk of CVD events in asymptomatic individuals with no clinical evidence of cardiovascular disease. The calculation of risk will be via a computer based desktop tool. Computer programs give a more precise estimate of risk than charts, presenting risk as a continuous variable rather than a threshold, such as ≥20%.44

Unless recent pre-treatment risk factor values are available it is generally safest to assume that CVD risk is higher than that predicted by current levels of blood pressure or lipids on treatment.

True CVD risk will be higher than the results indicated by estimation tools in:28

Evidence level 4

In some ethnic minorities risk tools underestimate CVD risk, because they have not been validated in these populations. For example, in people originating from the south Asian subcontinent it is safest to assume that the CVD risk is higher than predicted from most scoring tools (see section 1.1). The ASSIGN risk tool incorporates family history as a risk factor which may account for some or all of the excess CVD risk of individuals from some ethnic minorities.

3.4 How to determine cardiovascular risk

DIndividuals with symptoms of cardiovascular disease or who are over the age of 40 years and have diabetes (type 1 or 2) or familial hypercholesterolaemia should be considered at high risk (≥20% risk over ten years) of cardiovascular events.

DCardiovascular risk should be estimated at least once every five years in adults over the age of 40 years with no history of cardiovascular disease, familial hypercholesterolaemia or diabetes and who are not being treated for blood pressure or lipid reduction.

DAsymptomatic individuals should be considered at high risk if they are assessed as having ≥20% risk of a first cardiovascular event over ten years.

DIndividuals at high cardiovascular risk warrant intervention with lifestyle changes and consideration for drug therapy, to reduce their absolute risk.

[Good practice point] Risk factors should be monitored at least annually in people who are on antihypertensive or lipid lowering therapy.

[Good practice point] Individuals from deprived socioeconomic groups must be regarded as being at higher total cardiovascular risk than indicated by risk estimation tools that do not use social deprivation to calculate total risk.

[Good practice point] Other risk factors not included in the CVD risk prediction should be taken into account in assessing and managing a person?s overall CVD risk. These include: ethnicity, abdominal obesity, impaired glucose tolerance, raised fasting triglyceride and a family history of premature CVD.

Asymptomatic people without established atherosclerotic CVD who have a combination of risk factors which puts them at an estimated multifactorial risk of =20% over ten years should be considered for treatment. Other risk factors which should be taken into account in the overall assessment include: ethnicity, social deprivation, renal disease, abdominal obesity, impaired glucose tolerance, raised fasting triglyceride and a family history of premature CVD. The ASSIGN risk estimation tool takes account of social deprivation and family history.

Some individuals will have extreme values of single risk factors. Although absolute risk takes several risk factors into account, possession of such a 'lighthouse' risk may mandate intervention.38 Single risk factors in this range include total cholesterol ≥8 mmol/l (see section 9.9.2) or elevated blood pressure (systolic BP =160 mm Hg or diastolic BP ≥100 mm Hg, or lesser degrees of hypertension with associated target organ damage (see section 10).28,45 In these cases, whilst treatment is aimed at the lighthouse risk, the reduction of global risk is the ultimate goal. Management of other risk factors is also important, especially where the key risk factor proves refractory. Evidence level 2++, 4

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