Calculating CVD risk
The Scottish Intercollegiate Guidelines Network (SIGN) has recently updated its evidence-based guidance for the prevention of cardiovascular disease?(CVD). SIGN 97: Risk estimation and the prevention of cardiovascular disease was published in February.1 As most GPs will be aware, there is already a robust set of guidelines addressing this issue: The Joint British Societies' guidelines on prevention of cardiovascular disease in clinical practice (JBS2, published in December 2005).2
SIGN 97 has followed the lead of JBS2 to address prevention in CVD rather than just coronary heart disease. Both recommend formal cardiovascular risk assessment for all individuals aged 40 and above. They also suggest risk assessment on younger individuals with a strong family history of premature CVD. Those who have had a cardiovascular event or have diabetes are already deemed high risk.
The first significant difference between the guidelines is the method used to calculate cardiovascular risk.
JBS2 utilises risk charts based around the Framingham dataset, which uses age, sex, smoking status, blood pressure and total cholesterol to HDL ratio to assign a risk score. Additional risk score adjustment is advised for ethnicity and family history.
SIGN recommends a computer programme as opposed to risk charts. The risk calculation utilises the ASSIGN scoring system, which is based on the Scottish Heart Health Extended Cohort, a series of population studies commenced in the 1980s/1990s and followed up until 2005.
The fundamental difference compared with the Framingham dataset is that social deprivation and family history are included in the initial ASSIGN risk calculation. This has the advantage of circumventing one of the key problems with the Framingham dataset: that it tends to underestimate risk in populations with a high prevalence of deprivation, mixed ethnicity and a strong family history of premature CVD. The threshold for intervention in individuals without established CVD or diabetes remains at 20 per cent.
The other key difference between the guidelines is the recommendation in SIGN 97 to continue to adopt a treatment target of 5mmol/l for total cholesterol, rather than the more aggressive optimal target of 4mmol/l in JBS2. It was felt that, until further studies on mortality, safety and cost effectiveness were available, the lower target could not be supported. The SIGN guidance also suggests a total cholesterol of ?8mmol/l as the threshold for intervention in individuals with an isolated risk factor of hyperlipidaemia, rather than the total cholesterol to HDL ratio of ?6 in JBS2.
SIGN 97 puts more emphasis on depression and social isolation as risk factors for CVD than JBS2, and includes a chapter devoted to psychological problems. Also of note is the recommendation to consider the use of cognitive behaviour therapy to increase physical function and improve mood in patients with CVD.
Many other areas in SIGN 97 are in line with previous guidance. The advice on diet, physical activity, smoking and alcohol covers much of the same ground as JBS2, and aspirin 75mg od and simvastatin 40mg od are recommended for all individuals with established CVD or a 10-year cardiovascular risk >20 per cent.
The SIGN recommendations for blood pressure are in line with those in JBS2, with targets of <140/85mmHg for individuals with established CVD and those with a 10-year cardiovascular risk >20 per cent, or 130/80mmHg for individuals with established CVD who also have diabetes and/or renal disease and/or evidence of target organ damage. Both guidelines recommend the A/CD antihypertensive treatment algorithms.
The SIGN guidance comes at a time when primary care teams will be aware of the proposed changes to the QOF, which are likely to include risk assessment as a clinical domain by the end of 2008. In that sense the guidance is timely, but SIGN 97 also serves to reinforce JBS2 with well structured and clearly presented guidance.Author
Dr Peter Savill
BSc MB BS PGDipCard
GPSI Cardiology, Southampton