Author + information
- Axel F. Sigurdsson, MD∗ ()
- ↵∗Department of Cardiology, Landspitali University Hospital, Hringbraut, 101 Reykjavik, Iceland
I read with interest the paper by Savarese et al. (1) reporting the results of a meta-analysis of the benefits of statins in elderly subjects without established cardiovascular (CV) disease. One of the biggest questions facing clinical cardiology today is the decision regarding which individuals to treat with statins in primary prevention. Because statins are not without adverse effects, we have to be sure that the risk of harm does not outweigh the presumed benefits.
In their meta-analysis, Savarese et al. (1) came to the conclusion that statins significantly reduce the incidence of myocardial infarction (MI) and stroke but do not significantly prolong survival in the short-term. They believe their meta-analysis provides “first-time evidence that the benefits of statins on major CV events extends to people ≥65 years without CV disease.”
MI occurred in 2.7% of subjects allocated to receive statins compared with 3.9% of those receiving placebo during a mean follow-up of 3.5 years. This finding corresponds to a relative risk reduction of 39.4%. Stroke was reported in 2.1% of subjects randomized to receive statins compared with 2.8% receiving placebo during the same mean follow-up period. This finding corresponds to a relative risk reduction of 23.8%.
The authors calculated that 24 patients needed to be treated for 1 year to prevent 1 MI and that 42 patients needed to be treated for 1 year to prevent 1 stroke. The authors repeat these numbers in the final section of the paper, where cost/benefit evaluation of statin treatment in elderly subjects is discussed.
It appears that the authors have made an erroneous calculation. The annual MI rate was 1.1%, and the annual rate of stroke was 0.8% in patients allocated to receive placebo. Considering a relative risk reduction of 39.4% and 23.8%, respectively, the absolute risk reduction (ARR) for 1 year is approximately 0.43% for MI and 0.19% for stroke. The number needed to treat (NNT) is the inverse of the ARR: NNT = 100/ARR.
By using data from the paper, I have calculated that the NNT for 1 year to prevent 1 MI and 1 stroke, respectively, may be approximately 10 times higher than that reported by Savarese et al. (1), given that NNT is constant over time. In my opinion, the most appropriate approach would have been to report the NNT for the mean follow-up of 3.5 years, which would have been approximately 83 to prevent 1 MI and 142 to prevent 1 stroke. This is the approach most commonly used in similar studies.
The NNT is very important when assessing the efficacy of statin therapy. It is therefore essential that the authors do a recalculation of their data and report the correct NNT numbers. They may also have to reconsider the main conclusions of their meta-analysis.
- American College of Cardiology Foundation