Original articlesDifferences in Heart Rate Variability Between Cardioinhibitory and Vasodepressor Responses to Head-Up Tilt Table Testing
Introduction
Syncope is defined as a sudden temporary loss of consciousness associated with a loss of postural tone with spontaneous recovery 1, 2. Neurally mediated syncope is the term used to refer to syncope that results from reflex mechanisms associated with inappropriate vasodilatation and/or bradycardia. Head-up tilt (HUT) testing has assumed an important role in evaluating patients with unexplained syncope 3, 4. Patients with a positive response can be classified into mixed, cardioinhibitory, and vasodepressor categories (5).
Currently, these responses are believed to have a common pathophysiological mechanism. Head-up tilt leads to pooling of venous blood in the lower limbs, resulting in decreased venous return. The normal compensatory response to head-up posture is reflex tachycardia, more forceful contraction of the left ventricle, and vasoconstriction. However, in individuals with neurally mediated syncope, this forceful ventricular contraction in the setting of a relatively empty cavity may activate the cardiac mechanoreceptors. An afferent pathway consisting of unmyelinated left ventricular vagal C fibers transmits signals to specific central nervous system sites. This reduces the efferent sympathetic tone and results in reflex hypotension and/or bradycardia (Bezold-Jarisch reflex) 6, 7, 8.
However, provocation of syncope with HUT testing after heart transplantation has raised questions about this mechanism, because no evidence of reinnervation has been found in these patients 9, 10. This suggests the existence of a peripheral element in the pathophysiology of neurally mediated syncope. Based on the central role of the autonomic nervous system in the genesis of neurally mediated syncope, heart rate variability analysis has been used to explore the cardiac autonomic tone in response to head-upright tilt 11, 12, 13 in normal subjects, HUT results in a significant increase of the low frequency power spectrum in addition to withdrawal of the high frequency or parasympathetic tone. Controversial results have been obtained with heart rate variability analysis in neurally mediated syncope. Heart rate variability has been found to be decreased in normal adults (14) and elderly people (15), while other investigators have found increased parasympathetic activity 16, 17. We hypothesized that the response of the autonomic nervous system to head-up tilt is different in patients showing cardioinhibitory and vasodepressor responses. We, therefore, used heart rate variability analysis to explore the differential responses of cardiac autonomic tone to HUT in a group of patients with a positive non-pharmacological tilt-table test.
Section snippets
Materials and Methods
Twenty-four consecutive patients with a history of ≥2 episodes of syncope were included in the study. Patients were sent from the Outpatient Clinic to the National Institute of Cardiology Electrophysiology Department for additional evaluation. The study group consisted of 14 male and 10 female patients aged 10 to 62 years. All had a positive response during a non-pharmacological HUT test, manifesting different types of syncope during the tilt test. The group showing a mixed response included
Results
Table 1 shows the distribution of age and gender of patients manifesting different types of syncope during the tilt test. The patients in the CI and MX groups were significantly younger than those in the VD group (p <0.001). The mean time syncope the occurred during the tilt test was 12 ± 9 min and was similar in all groups.
Discussion
The classic theory of the pathophysiology of syncope relates bradycardia and hypotension to the afferent stimulation of the parasympathetic nervous system. However, syncope can be induced in patients with heart transplantation without autonomic innervation; therefore, alternative mechanisms have been postulated.
There are few reports on heart rate variability in neurally mediated syncope, and the results have been discrepant (19). Pagani et al. (14) assessed heart rate variability in healthy
Conclusions
The present study provides new findings and supports previous observations in the study of patients with neurally mediated syncope, showing the existence of two main types of autonomic behavior: one in the cardioinhibitory and mixed response groups with predominant parasympathetic activity, and the other in the vasodepressor group, with predominantly sympathetic activity. This suggests that there are different pathophysiological mechanisms involved in neurally mediated syncope that may be
Acknowledgements
The authors wish to thank Yolanda Ortega for her help in the preparation of the manuscript.
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On the construct validity of interoceptive accuracy based on heartbeat counting: Cardiovascular determinants of absolute and tilt-induced change scores
2021, Biological PsychologyCitation Excerpt :Head-up tilt induces a central hypovolemic state, causing baroreceptor unloading (Marchi et al., 2016). Baroreceptor reflex circuitries respond to this state with a compensatory increase of central sympathetic (and decrease of parasympathetic) tone, indicated by higher heart rate (HR), and lower high frequency heart rate variability (HRV) (Guzman, Sanchez, Marquez, Hermosillo, & Cardenas, 1999; Lipsitz, Mietus, Moody, & Goldberger, 1990), as well as increased epinephrine and norepinephrine release (Laszlo, Rossler, & Hinghofer-Szalkay, 2001). Vice versa, head-down-tilt is associated with a central hypervolemic state, baroreceptor loading, and, therefore, with decreased sympathetic (and increased parasympathetic) tone, indicated by higher high frequency HRV (Chouchou et al., 2020; Weise, London, Guerin, Pannier, & Elghozi, 1995), as well as by reduced muscle nerve sympathetic activity (Fu, Sugiyama, Kamiya, & Mano, 2000; Nagaya, Wada, Nakamitsu, Sagawa, & Shiraki, 1995).
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2020, Nutrition, Metabolism and Cardiovascular DiseasesCitation Excerpt :VVS subjects can be divided three hemodynamic subtypes including vasodepressor type, cardioinhibitory type and mixed type according to the blood pressure and HR, each of them has different hemodynamic changes and neuromodulatory mechanisms. Cardioinhibitory type and mixed type are mainly characterized by increased vagus nerve tension, while vasodepressive type is characterized by decreased sympathetic nerve activity [23]. In the present study, our results showed that no differences in CK and CK-MB among the three subtypes, suggesting that CK or CK-MB could not be used as a basis for the differentiation of VVS subtypes.
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2016, International Journal of CardiologyCitation Excerpt :In Zygmunt's study [26], children with neurocardiogenic syncope had significantly lower values of rMSSD and pNN50, and higher LF and lower HF values in comparison to healthy children, indicating that children with neurocardiogenic syncope had alterations in basal autonomic balance. Another study suggested patients with vasodepressor response to HUTT showed higher LF/HF ratio and lower PNN50 and rMSSD compared to patients with cardioinhibitory and mixed responses, demonstrating that patients with a vasodepressor response showed predominantly sympathetic activity and subjects with cardioinhibitory response and mixed responses showed higher vagal tone [27]. In a word, children with VVS-V are characterized by high sympathetic activity and low vagal tone.
Neurocardiogenic syncope in chronic atrioventricular block
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