There is not enough evidence for switching to lifetime CV risk
We should be measuring in quality of life years, argues Dr Tom Marshall - after all, isn’t that how the patient judges lifetime risk for cardiovascular disease?
Recently, the Joint British Societies decided to ditch 10-year cardiovascular risk prediction in favour of a lifetime cardiovascular risk calculator, based on the QRisk Lifetime score. Proponents of a lifetime risk score argue that it will allow much earlier preventative intervention in younger patients who fall below conventional 10-year high-risk thresholds because of their age.
But I am concerned it will not identify many more people who are at immediate risk and could lead to over treatment of others. There are several counter intuitive points about the lifetime cardiovascular risk calculator.
Someone at the age of 60 years has a lower risk than a 30-year-old with the same characteristics. That’s because if we start from the premise that about 40% of people get cardiovascular disease at some point in their life, the longer you survive without it then the lower your chance of getting it. The lifetime risk calculator can give the impression that everybody is at a high risk and that younger people are at even higher risk – but that’s only true in this counter-intuitive way.
Harder to understand
But what the score is actually telling you, is your probability of ever getting cardiovascular disease in your life, which depends on how much life you have left – the immediate risk increases as you get older.
For example, if you have 10 years left to live, you’ve got a high chance of getting it in the next 10 years of your life.
By the same token, if the remainder of your life is 70 years then you haven’t got much chance of getting it in the next 10 years (but as you get older you have an increasing risk, and you’ve got a high risk of getting it in the last 10). It is complicated, and you have to interpret this to figure out what it is telling you.
It is less intuitive than using something that tells you what your risk is in the next five or 10 years. For example if I tell you that your risk of dying is 50% from some particular cause, that may be true over your lifetime. But if you’re 18 and you’re a smoker, your risk of dying in the next 10 years from smoking, for instance, is almost zero. That may explain why young people don’t think much about healthy behaviours, because risks a long way off don’t often concern us as much as ‘near’ ones.
Lower thresholds for treatment
I am concerned that using a lifetime score may increase the number of people being offered treatment when the benefits of that treatment won’t actually happen until quite a lot later in their lives.
For example, if you’re at risk of heart disease but most of that risk happens when you’re over 60 then the preventative activities should happen when you’re over 60 because that’s when you’ll actually get some benefit from it, whereas taking treatments between the ages of 30 and 60 will be of very little benefit to you.
We’ve got no evidence to suggest that taking treatments between 30 and 60 will reduce your risk after the age of 60. If we really want to make sense of this approach we should be determining what the benefits are in terms of the Quality of Life Years gained in relation to the years of treatment you would have to take – that is what the patient is interested in. If you tell me I can get most of this benefit by starting treatment 10 years later, then why should start it now?
Data from the Official of National Statistics showed 88% of deaths from cardiovascular disease take place in people over the age of 65, and 95% of cardiovascular disease deaths take place in people over the age of 55 (ONS, Deaths registered in England and Wales 2011). And the truth is that many of the high-risk people without established cardiovascular disease, most of whom are older, are not on treatment.
Saying we need to catch a whole extra bunch of people who are not really at high risk until 10 or 20 years’ time and treat them, when we haven’t even treated the people who are at high risk today, strikes me as having our priorities wrong. There are people around today who are at high risk who are not yet on treatment and could benefit in the next five years. Aren’t they more needy than people who you could treat for 20 years in the hope that it will give them some benefit in 20 years’ time?
The lifetime approach suggests we’ll start trying to treat people earlier and earlier for less and less benefit and at the same time there are older people who are still not being treated.
If your aim is to get more and more people on treatment irrespective of the benefits then this would be a logical thing to do, but if your aim is to prevent as much heart disease as possible within the available resources then this is not the way to go.
Dr Tom Marshall is a qualified GP and senior lecturer in public health.