Impaired arterial baroreceptor sensitivity before tilt-induced syncope

Abstract

Autonomic dysfunction seems to play a central role in the pathophysiology of neurocardiogenic syncope (NCS) but conflicting data have recently become available. We evaluated autonomic nervous system (ANS) function (heart rate variability (HRV), systolic blood pressure variability (SBPV) and baroreceptor gain (BRG)) and non-invasive haemodynamics (cardiac output and total peripheral resistance) in patients with neurocardiogenic syncope. Retrospectively, we evaluated 12 NCS patients (positive head-up tilt without pharmacological provocation) in the basal state and at initial tilt, 12 non-NCS patients with tilt-negative syncope and 12 aged-matched normal controls. Prospectively, we evaluated 16 NCS patients to analyse the haemodynamics and ANS activity throughout the tilt test (beginning of tilt and before syncope occurs). HRV and SBPV were accessed by fast Fourier transforms (FFT) and spontaneous BRG by temporal sequences, slope and a index. Modelflow was used to quantify the non-invasive haemodynamics. None of the autonomic and haemodynamic parameters at baseline or in the first 10 min of tilt was different among the respective NCS, non-NCS syncope and normal control groups, except for SBP, which was higher at baseline in controls. Throughout the tilt test in the prospective NCS group, the heart rate increased (88-95 beats x min(-1), P<0.05), systolic blood pressure decreased (123-109 mmHg, P<0.01), and arterial baroreceptor gain was reduced (7.6 to 5.5 ms mmHg(-1), P<0.01) and the absolute high frequency component of HRV (HF HRV) decreased (150-80 ms(-2), P<0.05), before syncope occurred. There was no change in the low frequency component of HRV (LF HRV), SBPV, cardiac output (CO) or total peripheral resistance (TPR). Tilt-induced syncope could not be predicted by non-invasive haemodynamic or autonomic parameters at rest or in the initial minutes of tilt. The decrease in arterial baroreceptor gain could be a precocious expression of the transient autonomic dysfunction that characterizes the occurrence of neurocardiogenic syncope.

Diurnal variation in time to presyncope and associated circulatory changes during a controlled orthostatic challenge

“…Although baseline ␣-index was not different between the two times of day, we observed a clear decline in ␣-index throughout the course of the orthostatic challenge that was significantly faster in the morning. Tilt-induced syncope preceded by reduction in baroreceptor gain (vagal reflex) and parasympathetic tonic drive have been previously reported (13); therefore, we speculate that reduced sympathetic reactivity and accelerated inhibition of reflex cardiac vagal BRS in the morning may be a key mechanism underlying the inability to maintain BP as effectively at this time of day, and consequently, there is an earlier onset of presyncope.…”

Entropy Measures in the Assessment of Heart Rate Variability in Patients with Cardiodepressive Vasovagal Syncope

“…In most of the studies inquiring into vasovagal faints using standard HRV parameters, the baseline characteristics of patients with a history of fainting were used, but various reactions during HUTT did not vary [3][4][5][6][7]. However, some differences were noted if the studied groups were divided according to the type of vasovagal reaction [12,13].…”

“…In most of the studies, standard HRV parameters (time and/or frequency domain) were assessed, but no differences between HUTT(+) and HUTT(-) patients were found [3][4][5][6][7][8]. As respiratory rate and pattern might impact the results of HRV analysis, in some studies, patients were asked to breathe 15 times per min.…”

Caracterização da modulação autonômica cardiovascular nas posições supina e vertical, usando-se a manobra postural passiva, em pacientes com história clínica de síncope neurocardiogênica e indivíduos saudáveis

“…Por outro lado, nesse contexto, vários outros mecanismos fisiopatológicos, particularmente os que se referem aos mecanismos de gatilho da SINC, ainda precisam ser intensamente investigados, em razão das discordâncias relatadas por diferentes autores na literatura (MOSQUEDA-GARCIA et al, 1997;ALBONI, et al, 2001;SHELDON et al, 2006;VAN DIJK and SHELDON 2008;Sheldon et al, 2010;SHELDON, 2013, VALLEJO et al, 2015. Por outro lado, nos pacientes com história sugestiva de SINC, diferentes relatos na literatura têm documentado que o padrão de respostas das variáveis cardiovasculares ao Tilt-test, entre o momento da mudança postural (horizontal à vertical) e o aparecimento da síncope ou pré-sincope, mostra-se muito heterogênio, tanto quando expresso em valores médios, como em variabilidade de pressão arterial e frequência cardíaca; além disso, a metodologia mais adequada a ser usada na aplicação do Tilt-test ainda não é consensual (FREITAS et al, 1999;PICCIRILLO et al, 2004;MADDEN and LOCKHART, 2009;DUPLYAKOV et al, 2011;FORLEO et al, 2013;MEREU et al, 2013;SHINOHARA et al, 2014). A investigação sobre este último aspecto assume grande importância, porque pode permitir ou não a possibilidade de prever-se a ocorrência de síncope no…”

“…Assim, nos estudos usando como ferramenta a VFC documenta-se aumento ou diminuição e outros ausência de alteração da VFC, seja na posição supina ou vertical (LAGI et al, 1996;KOCHIADAKIS et al, 1997;FREITAS et al, 1999;KOUAKAM et al, 1999;BECHIR et al, 2003;PICCIRILLO et al, 2004;LONGIN et al, 2008;DUPLYAKOV et al, 2011;HOLMEGARD et al, 2012;MEREU et al, 2013;SHIM et al, 2014;VALLEJO et al, 2015).…”