Heart Rate Variability and the Outcome of Head-Up Tilt in Syncopal Children

Abstract

Neurocardiogenic syncope may be caused by enhanced sympathetic activity evoking a vasodepressor-cardioinhibitory reflex. Heart rate variability (HRV) methods can be used to assess the modulation of sympathetic and parasympathetic activity. To determine whether HRV measurements are related to the outcome of head-up tilt testing (HUT), we studied 29 syncopal patients aged 7-19 y. After 30 min supine, patients were tilted to 80 degrees for 30 min or until syncope occurred. Sequential beats free from ectopy were analyzed. Time domain indices included SD (SDNN), root mean square successive differences (RMSSD), percent exceeding 50 ms (pNN50). An autoregressive model was used to calculate power spectra. Low frequency power (LFP, 0.05-0.15 Hz), high frequency power (HFP, 0.15-0.40 Hz), and total power (TP, 0.01-0.40 Hz) were compared before and after tilt. Data were obtained supine before tilt (baseline), within 5 min after HUT (early), 5-10 min after HUT (mid), and 15 min after HUT or presyncope (late). Seventeen patients fainted (HUT+), and 12 patients did not (HUT-). Variability indices were different for HUT- and HUT+ at baseline: SDNN was 123 +/- 17 versus 78 +/- 6, RMSSD was 127 +/- 23 versus 64 +/- 6 ms, pNN50 was 51 +/- 6 versus 31 +/- 4, respectively. Spectral data demonstrated decreased HFP and TP in HUT+ (834 +/- 133 and 2855 +/- 420 ms2) versus HUT- (3433 +/- 840 and 7062 +/- 1500). With tilt, SDNN, RMSSD, and pNN50 decreased proportionately in HUT- and HUT+. However, sympathovagal balance, measured by the ratio LFP/HFP and by normalized LFP, was markedly increased in HUT+ (2.2 +/- 0.7 and 0.43 +/- 0.03) compared with HUT- (0.8 +/- 0.2 and 0.31 +/- 0.02) at baseline and differences increased with tilt. With syncope, sympathetic activity decreased, and parasympathetic activity increased. Decreased RR variability with decreased parasympathetic activity and increased indices of sympathovagal balance before HUT predict a positive tilt test in children referred for evaluation of neurocardiogenic syncope.

Cardiac nodal and cardiac autonomic functions in children with vasovagal syncope

“…There are studies evaluating sympathovagal balance in children suffering from syncope by investigating the parameters of heart rate variability (HRV). However, these studies have yielded controversial results [6][7][8][9][10] . D y s f u n c t i o n o f s i n o a t r i a l n o d e a n d atrioventricular node is another rare cause of syncope 3 .…”

On the feasibility of tilt test outcome early prediction using ECG and pressure parameters

“…Power spectrum has been evaluated with parametric (auto-regressive [8,5]) and nonparametric methods (Fast Fourier Transform [7] and Wavelet [14]), yielding equivalent results. Hence, spectral indices were not included in the set of analyzed indices.…”

“…Other studies have analyzed the VVS in terms of the previously mentioned signals [5,[7][8][9]14], but did not focus on early prediction. Nevertheless, some recent studies have pointed out the difficulties that are found when the early prediction results are to be replicated in different patient databases.…”

“…In addition, the patient may feel very uncomfortable when the presyncopal or syncopal symptoms are reproduced. These problems have motivated the search for methods allowing the early prediction of the TTT [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The aim of these methods has often been to obtain a simple measurement, taken from an easily available cardiac signal (such as HR or pressure tachogram) at the beginning of the test, which would be used as a predictive criterion for the final result.…”

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 isso, constitui-se um achado isolado, o de BECHIR, 2003, e LONGIN, 2008(BECHIR et al, 2003LONGIN et al, 2008). O estudo de BECHIR documentou no Pré-Tilt, ser a atividade simpática na posição horizontal, em portadores de síncope, maior do que a encontrada em indivíduos do grupo controle, sugerindo que uma disfunção do balanço autonômico basal também participaria da fisiopatologia dessa síndrome (BECHIR et al, 2003 (LAGI et al, 1996;STEWART et al, 1996;KOCHIADAKIS et al, 1997;FURLAN et al, 1998;JARDINE et al, 1998;KOCHIADAKIS et al, 1998;FREITAS et al, 1999;KOUAKAM et al, 1999;PICCIRILLO et al, 2004;SHIM et al, 2014 KOUAKAM et al, 1999). Esses resultados também corroboram com o estudo de MORILLO, 1994e KOCHIADAKIS, 1997(MORILLO et al, 1994KOCHIADAKIS et al, 1997).…”