HRV measures were significantly lower and depression rating scores were significantly higher in patients with major depression than those of healthy comparison patients (Table 3).
The aim of this study is to highlight the issue of HRV in physically healthy patients with major depression by comparing their HRV measures (point-wise correlation dimension PD2) with those of mentally healthy post-MI patients and physically and mentally healthy comparison subjects. It was found that PD2 measures (an estimate of the RR interval) in patients with major depression were comparable with those of post-MI patients, that is, no significant difference between HRV measures of both groups (t=0.62 and 0.76, P=0.55 and 0.47) (Table 1). On the contrary, HRV measures showed significantly lower values when comparing major depression groups with healthy comparison individuals. These significantly lower measures were also shown when comparing post-MI patients with the healthy individuals. Surprisingly, these results emphasize that patients with major depression were indistinguishable from post-MI patients regarding measures of HRV. As it has not been established whether lowered HRV is a part of the mechanism of increased post-MI mortality or is merely a marker of poor prognosis, it is suggested that lowered HRV is not a simple reflection of the sympathetic overdrive and/or vagal withdrawal owing to poor ventricular performance, but that it also reflects depressed vagal activity, which has a strong association with the pathogenesis of ventricular arrhythmias and sudden cardiac death 19. Lowered HRV can be considered a powerful predictor of mortality and of arrhythmic complications in patients following MI 19,20. Cardiac autonomic imbalance is also represented in patients having major depressive disorder and who are well known not to be experiencing any physical diseases, including any heart problems 14,21. Studies investigated the possible higher risk for cardiac mortality and morbidity in patients either having major depression alone or heart disease 22. In most of these studies, lowered HRV was one of the most powerful indicators of this increased risk 21,22.
Depressed patients in this study were already on treatment. Those on the SSRIs were only included in the study to avoid the heterogeneity of the sample and also because SSRIs are the commonly used antidepressants nowadays. Tricyclic antidepressants were excluded because of potential cardiotoxic effects. We optimized the treatment regimen for each patient for 3 months in both major depression groups (groups I-A and I-B). Group I-B patients were assigned to a physical exercise program in addition to the antidepressant medication during the 3-month period. After the 3 months, we found that Montogomry–Asperg Depression Rating Scale depression scores were significantly lower than baseline scores for both groups (I-A and I-B t=11.3 and 14.6, respectively, P=0.000). Moreover, HRV measures were nearly normalized in group I-B (on medication and physical exercise), that is, significantly lower PD2 measures after 3 months when compared with baseline scores (t=7.61 P=0.000). On the contrary, group I-A (on medication only) showed no significant changes in HRV measure after 3 months when compared with baseline scores (t=2.2, P=0.54). This was in spite of the significant improvement in depression scores. SSRIs have been presumed to have minimal effects on the ANS. Paroxetine, which has some anticholinergic activity, might affect HRV measures. However, many studies have demonstrated that therapeutic doses of SSRIs (including paroxetine) given to depressed patients do not alter HRV measures 15,23.
Exercise training is reported to decrease cardiovascular mortality and sudden cardiac death. Regular exercise training is also thought to be capable of modifying the autonomic balance, improving vagal sensitivity, and modifying sympathetic response, leading to an increased overall responsiveness to autonomic modulation 13,24,25. Moreover, exercise training in post-MI patients was found to reduce the incidence of cardiac mortality and morbidity, but this should be done very tentatively under the supervision of a professional cardiorehabilitation specialist 26.
Large prospective longitudinal studies are needed to determine the sensitivity, specificity, and predictive values of HRV in the identification of individuals at risk for subsequent morbid and mortal events.
Recognition of those problems led the European Society of Cardiology and the North American Society of Pacing and Electrophysiology to constitute a task force charged with the responsibility of developing appropriate standards. The specific goals of this task force were to standardize nomenclature and develop definitions of terms, specify standard methods of measurement, define physiological and pathophysiological correlates, describe currently appropriate clinical applications, and identify areas of future research.
The authors of this research would like to express the greatest gratitude to Professor Dr. Ayman M. El-Said, professor of cardiology, Tanta Faculty of Medicine, for his participation in recruiting patients of the research (post-MI) and for his valuable help in the HRV procedures.
There are no conflicts of interest.
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