EFFECT OF AGE AND GENDER ON HEART RATE VARIABILITY IN PATIENTS WITH HEART FAILURE.
Objective: To determine the effects of age and gender on heart rate variability in patients with heart failure.
Study Design: Cross sectional analytical study.
Place and Duration of Study: Department of Clinical Cardiac Electrophysiology Armed Forces Institute of Cardiology/National Institute of Heart Diseases, Rawalpindi from April 2013 to August 2013.
Material and Methods: 47 patients with the diagnosis of chronic heart failure of either sex, having age more than 19 years and with left ventricular ejection fraction equal to or 0.05). Age was negatively correlated with all the domains of heart rate variability, however, the correlation was significant only for SDNN and SDANN (p-value < 0.05).
Conclusion: Heart rate variability reduces with advancing age irrespective of the gender reflecting increased likelihood for developing ventricular arrhythmias in the predisposed patients.
Keywords: Autonomic nervous system, Heart rate variability, Heart failure.
There is a fine interaction between sympathetic and parasympathetic activity to sustain a balanced internal environment. Various methods and processes have been developed to detect the function and integrity of the sympathetic and parasympathetic systems1. Unstable autonomic nervous system activity is attributed as a predictor of ventricular tachyarrhythmias which may lead to sudden cardiac death. Heart Rate Variability (HRV) is considered as the most significant, accessible and non-invasive marker to evaluate equilibrium between sympathetic and parasympathetic divisions of autonomic nervous system2. Knowledge of heart rate variability helps in quantifying the autonomic nervous system balance which controls heart rate and rhythm. Variations in HRV are considered as reflection of heart's ability to adapt to rapidly changing internal environment in various physiological and pathological conditions.
Reduced heart rate variability is associated with poor prognosis whereas increased variability is a characteristic of healthy heart3,4. Autonomic nervous system dynamics have been implicated in a wide range of cardiac and non-cardiac disorders5. HRV thus provides remarkable prognostic information in patients with heart diseases1.
It has been documented in various studies that young healthy females have significantly reduced sympathetic activity as compared to young healthy males4. Thus, in a healthy adult, female gender has protective effect against development of coronary heart diseases and arrhythmias6. It has been established in literature that women who are younger than 50 years have higher vagal but lower sympathetic modulations of heart rate than the age-matched men, however these gender-related autonomic differences disappear in the elderly age group2,7,8. It has also been documented in studies that prognosis of heart failure is generally better in women as compared to age the matched men. Also the mortality rate in heart failure increases with advancing age9. In a report from the Framingham Study it has been documented that mortality rate in heart failure increased in both men and women with the advancement of age10.
It has been documented that autonomic nervous system imbalance due to changes in geometry of the failing heart may lead to mechanical distortion of sensory nerve endings11. As a result, there is an abnormal increase in the firing rate at sympathetic nerve endings thus leading to electrical instability by decreasing heart rate variability consequently generating potentially lethal ventricular tachyarrhythmias. Extensive research has been carried out in the past to find out association of age and gender with electrophysiological properties of the heart12,13. Age and gender affect functioning of the heart by modulating autonomic nervous system and ion channels14. However, data regarding their effect on heart rate variability is scant. The current study was planned to investigate the effects of age and gender on heart rate variability in patients with heart failure.
The study will provide a deeper understanding about electrophysiological mechanisms involved in generating heart rate variability and cardiac arrhythmias. The study may also be beneficial in providing knowledge about the age group and gender with reduced heart rate variability as the heart failure patients corresponding to these groups may be at high risk of developing ventricular arrhythmias.
Table-1: Gender differences of heart rate variability indices (N=47).
SDNN (ms)###78.83 +- 37.43###83.25 +- 46.15###0.91
SDANN (ms)###71.00 +- 38.21###75.92 +- 47.72###0.94
SDNNi (ms)###37.14 +- 17.66###35.00 +- 19.40###0.63
RMSSD (ms)###29.91 +- 12.78###30.00 +- 14.85###0.79
pNN50 (%)###9.06 +- 8.34###8.25 +- 8.98###0.51
Table-2: Correlation of age with different indices of heart rate variability (N=47).
MATERIAL AND METHODS
A cross sectional analytical study conducted at Armed Forces Institute of Cardiology/National Institute of Heart Diseases, Rawalpindi (AFIC/NIHD) from April 2013 to August 2013. A formal approval was obtained from Medical Ethics Committee of Army Medical College and Institutional Review Board of AFIC/NIHD before commencement of the study. Written informed consent was also attained from the patients under study. 47 patients with the diagnosis of chronic heart failure were recruited by convenience sampling. Patients from either sex, having age more than 19 years and with left ventricular ejection fraction equal to or 0.05).
Table-2 illustrates correlation of age with different indices of heart rate variability. The r-values show that age was inversely correlated with all the indices of heart rate variability, however the correlation was significant only for SDNN and SDANN (p-value < 0.05).
Results of the current study demonstrate that there was no effect of gender on heart rate variability in patients with heart failure. However, age was negatively correlated with heart rate variability indices and the correlation was significant with SDNN and SDANN. Although it is established that there are gender differences in autonomic nervous system and electrophysiological properties of heart, it seems paradoxical to report that gender does not affect heart rate variability. Current knowledge belief is that pathophysiology of heart rate variability stands on autonomic nervous system and cardiac electrophysiology. This knowledge belief appears to be contradictory with the results of current study.
It seems that genesis of heart rate variability is multifaceted and some more complicated processes must be involved which might have blunted the effect of gender despite variations in the apparently underlying mechanisms. Studies have demonstrated that the effect of gender on heart rate variability disappear in the elderly age group6. Literature has revealed that in age strata [greater than or equal to]60 years there is no difference in HRV measurements between the genders15. The mean age of patients in the current study was 54.68 +- 16.79 years so there was possibility that gender had no impact on the variation in heart rate between males and female patients of our study. As 28 of our patients (60%) had age above 50 years, so this could again be a possible explanation for insignificant difference of heart rate variability indices between the two genders. Voss A and coworkers studied the effect of age and gender on heart rate variability in healthy subjects16.
They reported that heart rate variability was significantly different between males and females with age below 45 years, however the difference vanished in old age groups. Females have vagal predominance as compared to males conferring stability to their heart rhythm. Some studies have reported that this beneficial effect is attributed to the female hormones17. After the age of menopause, due to drop in female hormones this beneficial effect is abolished which may diminish the mechanistic variations underlying heart rate variability. Another possible explanation for insignificant gender difference in heart rate variability could be the relatively small number of female patients in our study as compared to males.
Multiple factors have been implicated in reducing heart rate variability with advancing age. Out of the two divisions of autonomic nervous system, parasympathetic control is predominant over heart and it keeps the heart rate and rhythm under check. Studies have shown that with advancing age parasympathetic control of heart diminishes leading to alterations in autonomic balance.18
New balance is supposed to be in favor of sympathetic dominance which might be the underlying basis of reduced heart rate variability. Voss A and colleagues in two different studies investigated the effect of age on heart rate variability in healthy subjects19,20. They reported that heart rate variability reduces in all the domains with advancing age. The results are similar to our study as we also found diminished heart rate variability in all the domains with increasing age. However, in our study only the two indices SDNN and SDANN were significantly reduced with advancing age. These two indices especially SDNN correlate with overall heart rate variability which corresponds to the total power of spectral analysis. It encompasses high as well as low frequency components of heart rate variability, hence an indicator of overall functioning of the autonomic nervous system activity.
Reduction in SDNN and SDANN reflects attenuation of vagal and heightened sympathetic responses and this setting may lead to initiation of many interlinked processes involved in arrhythmogenesis in the predisposed patients.
Heart rate variability reduces with advancing age irrespective of the gender reflecting increased likelihood for developing ventricular arrhythmias in the predisposed patients. This is a group of patients which needs extra medical care and supervision as ventricular arrhythmias are potentially fatal and may result in sudden cardiac death.
CONFLICT OF INTEREST
This study has no conflict of interest to declare by any author.
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|Publication:||Pakistan Armed Forces Medical Journal|
|Date:||Apr 30, 2016|
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