GPs should keep to their current approach to estimating CHD or CVD risk until better methods are available, says Dr Alan Begg
Measuring the absolute risk profile of patients in general practice is an important element in the prevention of CHD. In patients without clinical evidence of cardiovascular disease, measurement of risk can help inform decisions on initiating therapeutic prevention in line with national clinical guidelines.
The Sheffield Table, the New Zealand guidelines and the Joint British Societies Coronary Risk Prediction Chart are the most widely used risk assessment tools in the UK. The 1999 edition of the last, which estimates the 10-year risk of a CHD event, has been used in British guidelines and was recently updated to measure CVD risk.
The 2004 British Hypertension Society guidelines recommend that patients with cholesterol >=3.5 mmol/l and a 10-year CVD risk of 20% should be considered for statin therapy. Those with a sustained raised systolic blood pressure of 140-159mmHg and/or diastolic blood pressure of 90-99 mmHg and a 10-year CVD risk >=20% should be given drug therapy.1
All three risk assessment methods use the Framingham Risk Equation, developed from the North American Framingham Heart Study and the Framingham Offspring Study. The authors have cautioned about applying their data to other populations, and although it is recognised as an imperfect way to predict risk, it has been validated in populations in the United States, Northern Europe, Western Australia and New Zealand. It has been shown to predict CHD events in British studies, including the absolute risk of future events in men taking part in the West of Scotland Coronary Prevention Study. The Joint British Societies charts published in the BNF clearly state when they should not be used and in which groups they may underestimate risk.
However, a recent study showed that the Framingham risk function overestimated absolute CHD risk in the British Regional Heart Study cohort of men aged 40-59 years who were initially free of CHD.2 This has also been seen in other European studies.
This overestimation may result from the elapse of time since the baseline Framingham study, declining trends in cardiovascular mortality, differences between populations and the effect of preventative measures. Concern has been expressed that the logistic equation derived from the British Regional Heart Study may be out of step with other risk functions for British populations because the cohort is unrepresentative.
GPs should continue with their current approach to estimating risk. The previous threshold of 30% for the use of statins was chosen for economic reasons and to ensure that priority was given to those at highest risk, although evidence justifies initiating statin therapy at a CHD threshold of 15% (CVD risk of 20%).
Those tempted to use the Framingham recalibration suggested by the recent study should exercise care, although this is a possible future approach.2 It has not been externally validated and assumes a constant ratio across age, sex and regional populations and did not examine stroke risk.
Confidence in the accuracy of risk assessment methods that take into account the changing epidemiology of CHD is vital. For the future we require methods that are more accurate in predicting events than those currently available.
The new SCORE charts, which form the basis of the 2003 European guidelines on cardiovascular disease prevention in clinical practice, give the absolute 10-year risk of developing a fatal cardiovascular event.3 Although these charts have documented qualifiers they take into account the variation in cardiovascular mortality across European populations. The SCORE project has made it possible to produce risk charts tailored for individual countries.
- Williams B, Poulter NR, Brown MJ et al. Guidelines for the management of hypertension: report of the fourth working party of the British Hypertension Society, 2004 - BHS IV. J Hum Hypertens 2004; 18: 139-85.
- Brindle P, Emberson J, Lampe F et al. Predictive accuracy of the Framingham coronary risk score in British men: prospective cohort study. Br Med J 2003; 327: 1267-70.
- Conroy RM, Pyorala K, Fitzgerald AP et al. Estimation of ten-year risk of fatal cardiovascular disease in Europe: the SCORE project. Eur Heart J 2003; 24: 987-1003.