Dear Bruce - I have responded to others who have asked about reversibility
-see my response to Toby Lipman:
"Toby - Yes, I am saying that the difference in absolute risk between the
early and late treated hypertensives will be very small and so the NNT very
large. The evidence comes from comparing the effect of treatment in RCTs
compared with the estimated difference in risk in cohort studies. What we
find is that the predicted effect of lonterm differences in risk from
cohort studies is very similar to the actual effects observed in trials."
>In message <C0F01F10DD54D2119CD30060B0680ABC017244A0@exchange_1>, Gary
>Jackson <[log in to unmask]> writes
>>For example, lets take two 35 yr old hypertensive smokers. One we treat
>>with anti-hypertensives, achieving good control. The other we "watchfully
>>wait". Both decline our attempts to stop smoking. Neither became
>>symptomatic. At age 45 we start the 2nd on antihypertensive treatment,
>>achieving like control. My understanding is that at this point their future
>>risks (chance of death/MI etc) are identical? Ie 10 years of presumably
>>extra workload on the heart/blood vessels had no effect on the untreated
>>person? And this means the only point of treating the first for 10 years
>>was the risk reduction you achieved over that 10 year period.
>>
>
>Yes that's the point I was trying to make. Is there evidence to answer
>this question? - and of course if there is a difference in the rate of
>CVD events in patients managed in these two ways say at age 55, then an
>NNT can be calculated. Or is Rod saying that the absolute risk reduction
>will be so small as to make NNT unreasonably high?
>
>Toby
Also in another response:
"As you probably know about 5 years after stopping smoking, a person's cvd
risk is similar to that of a never smoker and after about 10-15 yrs lung
cancer risk is back to never smoking levels. So the same applies to other
cvd risk factors."
With regard to the reversibility being counter-intuitive I don't have any
good answer except that intuitiveness is rather low level of evidence and
the Barker hypothesis remains very much a hypothesis which because of the
type of evidence available, remains very susceptible to serious confounding.
Regarding the benefits of multiple interventions, we just don't have
adequate evidence. It is certainly time for some trials testing multiple
vs single interventions.
Rod
>
>I was interested in your comment that most CVD risk is reversible.
>This seems counter-intuitive in relation to the fetal programming
>literature/the Barker hypothesis and the Whitehall studies which
>found that the classical risk factors only explained a relatively
>small proportion of differences in CVD risk between social groups (in
>that case grades of civil servant).
>
>I have struggled with the problem of trying to work out the effect of
>multiple interventions when there isn't trial data looking at them as
>a whole (eg secondary prevention of IHD trials look at statins, ACE
>inhibitors, beta blockers, aspirin as single interventions although
>there are usually people on other interventions within the trial -
>I'm not aware of there being data to say whether they're additive,
>multiplicative or less than additive).
>
>Is there any data to support the idea of CVD risk being mostly
>reversible or is it predictions from Framingham on the assumption
>that if you reduce cholesterol with a drug then that's the same as if
>it was 'naturally' at the level you achieve with the drug?
>
>Bruce
>
>Bruce Guthrie,
>MRC Training Fellow in Health Services Research,
>Department of General Practice,
>University of Edinburgh,
>20 West Richmond Street,
>Edinburgh EH8 9DX
>Tel 0131 650 9237
>e-mail [log in to unmask]
Dr Rodney Jackson MBChB PhD FAFPHM
Associate Professor of Epidemiology
Head of Department
Dpt of Community Health, School of Medicine
University of Auckland
(Grafton Mews, 52-54 Grafton Rd)
Private Bag 92019, Auckland, New Zealand
Phone: +64 (0)9-3737599 ext 6343
Fax: +64 (0)9-3737503
e-mail: [log in to unmask]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|