What is the optimal age for starting lipid lowering treatment? A mathematical model

Editor- Ulrich et al(1) have bravely attempted to tackle a problem
which has been quietly side-stepped for some time; namely that lipid
lowering does not (as far as we are aware) prevent coronary heart disease,
it merely postpones it. The concept of assessing the value of treatment
in terms of 'event free life years' is a useful one, but using a risk
calculator to estimate potential benefit is fraught with difficulty.

The authors base their calculation on the Framingham equation, in
common with most coronary risk calculators, and have made one particularly
common, but incorrect, assumption regarding age. With the publication of
the Framingham equation, Anderson et al(2) stated that the equation 'may
be used for estimating outcome probabilities over a range of 4 to 12 years
for persons aged 30 to 74 years'. Quoting calculated risks for ages 15 to
94 years is therefore clearly inappropriate. To attempt to recalculate
such risks using a pharmacologically lowered cholesterol is even less
appropriate.

Anderson's statement is also relevant to the notion of a '3% annual
risk' which cannot be reliably predicted by the Framingham equation
directly. The Joint British Guidelines(3) circumvent this by referring to
a '30% 10 year risk', which will in fact identify subjects whose initial
risk is less than 3% p.a. because the risk is higher in the later years.

Finally, it should be remembered that the equation is less reliable
at the extremes of any of the variables included, hence a very high
cholesterol in a young person should stimulate further clinical thought.
Ulrich et al illustrate calculated benefits of treatment for cholesterol
levels of 9 mmol/l and greater. Such individuals require proper
investigation of their dyslipidaema rather than a keyboard exercise to
(badly) estimate cardiovascular risk.

1. Ulrich S, Hingorani A D, Martin J, Vallance P. What is the
optimal age for starting lipid lowering treatment? A mathematical model.
BMJ 2000;320:1134-40.
2. Anderson K M, Odell P M, Wilson P W F, and Kannel W B. Cardiovascular
disease risk profiles. Am Heart J 1991;121:293-8.
3. Wood D et al. Joint British guidelines on prevention of coronary heart
disease in clinical practice. Heart 1998;80(Suppl 2):S1-S29.