Genetic Determinants of Heart Rate Variation and Cardiovascular Diseases

Abstract

Additional information is available at the end of the chapter http://dx.doi.org/10.5772/53642 . IntroductionHeart rate HR is a variable parameter that rapidly adjusts to changing hemodynamic demands Fig. . HR is determined by several mechanisms. First, chronotropic regulation of the heart occurs through spontaneous and periodic depolarization of sino-atrial SA pacemaker cells. The activity of the SA node is modulated by the autonomic nervous system, intrinsic cardiac nervous system, baroreflexes, and respiration. Second, the sympathetic nervous system SNS stimulates postganglionic sympathetic nerve fibers and triggers norepinephrine release in the SA node that results in an increase in HR. Third, the parasympathetic nervous system PNS also plays a significant role in regulation of HR. Parasympathetic vagal nerve endings release acetylcholine, which binds to muscarinic cholinergic receptors on pacemaker cells, causing opening of potassium channels, hyperpolarization of the membrane, and, consequently, a decrease in HR. Fourth, humoral and mechanical signals have an effect on HR and its variability. Mechanoreceptors in the atrium respond to stretch occurs during respiration and change HR without neural input [ ]. Βhanges in blood pressure ΑP impact HR via baroreceptor reflexes. In response to high ΑP, stretch-sensitive receptors in the carotid sinus and aortic arch send action potentials via the vagus and glossopharyngeal nerves to the solitary tract nucleus NTS of the brainstem. The NTS affects the ventrolateral medulla is causing an inhibition of sympathetic drive and activates the PNS by triggering the nucleus ambiguous. The result is a decrease in HR and ΑP. In response to hypotension, the baroreceptor reflex works in the opposite direction, leading to an increase in sympathetic drive and decrease in vagal tone, which raises HR and ΑP. Mechanical signals also lead to respiratory sinus arrhythmia -increased in HR during inhalation and decreased HR during exhalation. This normal physiologic phenomenon involves an © 2013 Korshunov et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.increase in intrathoracic volume during inspiration that results in an increase in HR by activation of SNS and a decrease in parasympathetic tone. The integrated spectral power of high frequency HF, > . Hz HR variability HRV is used as an index of the level of parasympathetic activity. Low frequency LF, . -. Hz power of HRV reflects both sympathetic and parasympathetic activity and the LF/HF ratio is an indicator of sympatho-vagal balance [ ]. Αody temperature plays a relatively minor role in HRV. It has been shown that hypothermia is associated with bradycardia decrease in HR and fever associates with tachycardia increase in HR in neonates [ ]. However, the contribution of baseline HR to HRV i...