With great interest we have read the article by Gehi et al titled 鈥淒epression and Heart Rate Variability in Patients With Stable Coronary Heart Disease.鈥�¹

In this outstanding large study no association was found between depression and heart rate variability (HRV) in patients with stable coronary heart disease. This is surprising because most studies revealed a reduced HRV in depressive syndromes independent of underlying cardiovascular disease.^2-4 The participants of Gehi et al's investigation were considerably older than those in most other studies on this subject. As HRV substantially decreases with increasing age,⁵ this may have led to a less-detectable effect of depression on HRV. Moreover, the large difference in mean age in both strata may not have been sufficiently considered because depressed participants were on average 7 years younger. To our knowledge, no other study investigating HRV in depressed patients with heart disease included participants with such a huge difference in age. The antagonistic effects of age and depression may have additionally confounded the results. Several possible interactions between depression and HRV were tested by analysis of covariance, but this large amount of interactions might have produced multicorrelations and therefore might have 鈥渉idden鈥� the effect of age on HRV. An analysis of covariance solely with age as the covariate would be of great interest.