We appreciate Hart et al. from the SPAF study examining their cohort
data in order to compare it with our results. One of our findings was
that the small number of diuretic users with lower serum potassium and
atrial fibrillation had a 10-fold greater risk of stroke compared with
those with higher serum potassium without atrial fibrillation. [1] The
SPAF findings do not contradict our findings. They calculate the risk of
stroke for those diuretic users with serum potassium levels less than 4.1
meq/L compared with greater than 4.0 meq/L among participants with atrial
fibrillation. However, in our study the comparison group was those
diuretic users without atrial fibrillation and a serum potassium level
greater than 4.0 meq/L. If we restrict our analysis to those with atrial
fibrillation, there is a relative risk of 4.7 (p=0.026, 95% confidence
interval of 1.2 to 18.2) for a potassium level less than 4.1 compared with
greater than 4.0 after adjustments for covariates. These confidence
intervals overlap with theirs (RR 1.5, p=0.12, 95% confidence interval 0.9
to 2.4), therefore their results are within sampling error of ours.
SPAF study participants were treated with either aspirin or placebo and
were more closely monitored than those in CHS, thereby potentially
decreasing the relative risk by preventing some strokes in those with low
serum potassium.
In the CHS only 21% of those with lower potassium and 20% with higher
potassium levels were using potassium supplements, compared with 43% and
42% in SPAF. The greater use of potassium supplementation in the SPAF
trial may have made it more difficult to detect an effect of low serum
potassium on stroke risk.
Their results also cannot challenge our overall finding of higher
stroke risk associated with lower serum potassium level that we found for
all diuretic users with or without atrial fibrillation. Nor do they
address our finding of higher stroke risk with low dietary potassium
intake among older individuals not taking diuretics. We agree with Hart
et al. that no recommendations can be made with regard to diuretic use
based on these studies however, we question whether diuretics would be
more effective with closer potassium level monitoring and supplementation.
We again encourage further prospective studies or reexamination of prior
cohort studies to corroborate our findings.
References:
1) Green DM, Ropper AH, Kroumal RA, Psaty BM, Burke GL, for The
Cardiovascular Health Study. Serum potassium level and dietary potassium
intake as risk factors for stroke. Neurology 2002;59:314-320.
We appreciate Hart et al. from the SPAF study examining their cohort data in order to compare it with our results. One of our findings was that the small number of diuretic users with lower serum potassium and atrial fibrillation had a 10-fold greater risk of stroke compared with those with higher serum potassium without atrial fibrillation. [1] The SPAF findings do not contradict our findings. They calculate the risk of stroke for those diuretic users with serum potassium levels less than 4.1 meq/L compared with greater than 4.0 meq/L among participants with atrial fibrillation. However, in our study the comparison group was those diuretic users without atrial fibrillation and a serum potassium level greater than 4.0 meq/L. If we restrict our analysis to those with atrial fibrillation, there is a relative risk of 4.7 (p=0.026, 95% confidence interval of 1.2 to 18.2) for a potassium level less than 4.1 compared with greater than 4.0 after adjustments for covariates. These confidence intervals overlap with theirs (RR 1.5, p=0.12, 95% confidence interval 0.9 to 2.4), therefore their results are within sampling error of ours. SPAF study participants were treated with either aspirin or placebo and were more closely monitored than those in CHS, thereby potentially decreasing the relative risk by preventing some strokes in those with low serum potassium.
In the CHS only 21% of those with lower potassium and 20% with higher potassium levels were using potassium supplements, compared with 43% and 42% in SPAF. The greater use of potassium supplementation in the SPAF trial may have made it more difficult to detect an effect of low serum potassium on stroke risk.
Their results also cannot challenge our overall finding of higher stroke risk associated with lower serum potassium level that we found for all diuretic users with or without atrial fibrillation. Nor do they address our finding of higher stroke risk with low dietary potassium intake among older individuals not taking diuretics. We agree with Hart et al. that no recommendations can be made with regard to diuretic use based on these studies however, we question whether diuretics would be more effective with closer potassium level monitoring and supplementation. We again encourage further prospective studies or reexamination of prior cohort studies to corroborate our findings.
References:
1) Green DM, Ropper AH, Kroumal RA, Psaty BM, Burke GL, for The Cardiovascular Health Study. Serum potassium level and dietary potassium intake as risk factors for stroke. Neurology 2002;59:314-320.