Heart rate variability in ageing and hypertrophic cardiomyopathy

Abstract

Heart rate variability (HRV) reflects the interaction between sympathetic and parasympathetic components of the autonomic nervous system. It is an indicator of cardiovascular function in normal and pathophysiological conditions. Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disease caused by a single mutation in one of the sarcomeric protein genes, leading to cardiac hypertrophy and predominantly affecting the interventricular septum. Autonomic dysfunction is common in individuals with HCM and could lead to potentially lifethreatening arrhythmias and sudden cardiac death. There is limited evidence about effects of lifestyle interventions on HRV in individuals with HCM. The present thesis firstly, investigated the effect of age and sex on HRV measures and functional capacity in healthy individuals. Secondly, it assessed HRV measures and cardiometabolic function in individuals with HCM. Finally, it evaluated the effect of a novel home-based lifestyle intervention incorporating physical activity and dietary nitrate supplementation on HRV measures and functional capacity in individuals with HCM. The major findings of this thesis can be summarized as the following three points. Firstly, among several time- and frequency-domain measures of HRV, it appears that the mean RR interval is the only measure influenced by sex. Data showed that there was not any effect of age on HRV measures. Secondly, vagal indices of HRV are increased in individuals with HCM compared to healthy individuals. Thirdly, the lifestyle intervention incorporating physical activity and dietary nitrate supplementation improved parasympathetic measures of HRV and mean arterial blood pressure in individuals with HCM. The research contained in this thesis is important as it improves understanding of the pathophysiology and its malleability with lifestyle intervention in individuals with HCM.