Heart rate variability and the outcome of head-up tilt in syncopal children

Heart Rate Variability in Unexplained Syncope Patients Versus Healthy Controls: A Comparative Study

Background Syncope or fainting is the sudden and transient loss of consciousness. This could lead to an increase in mortality due to sudden cardiac death or comorbidity in these patients. Heart rate variability (HRV) is a noninvasive bedside procedure for assessing the cardiovascular autonomic function. There may be an abnormal alteration in the HRV parameters in syncope patients. This can be used for looking into cardiovascular autonomic changes in syncope. This would help in early diagnosis and intervention. Objective The aim of this present study was to compare the HRV parameters between unexplained syncope patients and age-matched healthy controls and to find a correlation between HRV parameters and cardiovascular parameters like pulse and mean blood pressure. Materials and methods A five-minute continuous electrocardiogram (ECG) was recorded and HRV analysis was done by ADInstruments' PowerLab (Oxford, United Kingdom) for 25 cases and 25 controls. Results The mean standard deviation of the RR interval (SDRR) in milliseconds was found to be significantly lower in the cases (21.93 ± 3.53) as compared to controls (71.27 ± 27.40). The mean value of the low-frequency to high-frequency ratio (LF/HF) was significantly higher in cases (1.43 ± 0.40) as compared to controls (0.98 ± 1.07). However, there was no significant correlation between the pulse, blood pressure, and HRV measures. Conclusion The findings suggest a sympathetic predominance in the cases of unexplained syncope as compared to the controls.

The preponderance of initial orthostatic hypotension in postural tachycardia syndrome

Reduced systolic/diastolic blood pressure (BP) by >40/20 mmHg defines initial orthostatic hypotension (IOH). Rapid resolution of hypotension and lightheadedness follows, but tachycardia may be prolonged. We aimed to examine IOH in controls and patients with postural tachycardia syndrome (POTS) using indices of spontaneous fluctuations of heart rate (HR) and systolic BP as measures of cardiac baroreflex differences. We recruited otherwise healthy IOH patients without POTS (n = 20, 16 ± 3 yr), healthy volunteers (n = 32, 17 ± 3 yr), and POTS patients (n = 39, 17 ± 4 yr). Subjects were instrumented for electrocardiography and beat-to-beat BP. After 10 min supine, subjects stood for 5 min. Following supine recovery, subjects underwent 70° head-up tilt for 10 min to test for POTS. BP, HR, and time, referenced to standing, were measured at events during standing: minimum BP, BP recovery, peak HR, HR minimum, and steady state. Baseline HR and BP were higher in POTS compared with healthy groups. IOH occurred in 13% of controls and 51% of POTS patients. The BP minimum was lower in POTS. Parasympathetic modulation of cardiac baroreflex was decreased in all POTS and control-IOH subjects. Sympathetic indices were increased. Events following BP minimum occurred progressively later in all POTS and control-IOH subjects compared with non-IOH controls. IOH is more frequent in POTS than in controls with a lower minimum BP. POTS has markedly reduced heart rate variability and baroreflex, indicating reduced HR buffering of BP. POTS-IOH and control-IOH subjects had similar peak HR despite decreased minimum BP in POTS. IOH data indicate modest parasympathetic and cardiovagal baroreflex deficits in control-IOH subjects. Parasympathetic deficits are more severe in all POTS patients.NEW & NOTEWORTHY Significant initial orthostatic hypotension (IOH) occurs in ~50% of postural tachycardia syndrome (POTS) patients and 13% of controls. Heart rate and blood pressure recovery are prolonged in IOH sustaining lightheadedness; IOH is more prevalent and severe in POTS. Altered cerebral blood flow and cardiorespiratory regulation are more prevalent in POTS. Altered heart rate variability and baroreflex gain may cause nearly instantaneous lightheadedness in POTS. IOH alone fails to confer a strong probability of POTS.

An insight into the autonomic and haemodynamic mechanisms underlying reflex syncope in children and adolescents: a multiparametric analysis

Around 15% of children and adolescents experience at least one episode of syncope until adulthood. Excluding cardiac disease, the majority of syncopes are of reflex origin and benign in nature. In this situation, a tilt test is conducted to reproduce symptoms and to evaluate cardiovascular adaptations to orthostatism, but its mechanisms are not yet well defined. Here, we investigated haemodynamics and autonomic activity during tilt in young patients. Patients (n=113) with unexplained syncope were enrolled. Tilt followed a standard protocol without provocative agents. A positive response (fainters) was defined as a sudden development of syncope or presyncope associated with hypotension, bradycardia, or both. Haemodynamic parameters, autonomic activity, and baroreflex sensibility were evaluated. Data were analysed on baseline; immediately after tilting; on tilt adaptation; before fainting or before tilt-down for non-fainters; and on tilt-down. A total of 45 patients experienced syncope after a mean time of 18 minutes. During tilting up, fainters showed lower blood pressure and peripheral resistance values, which decreased progressively with time together with baroreflex sensibility. Sympathetic tone increased massively along time till syncope. No changes in cardiac output and heart rate were observed. Results show a strong effort of the autonomic nervous system to adapt to orthostatic stress through different magnitudes of sympathetic output, which was maximal before syncope without apparent modifications of parasympathetic tone. These changes suggest an imbalance between both branches of the autonomic nervous system, not enabling a time-progressive adaptation and leading the subject to faint.

Orthostatic tolerance is difficult to predict in recurrent syncope patients

OBJECTIVES

We tested the hypothesis that detailed anthropometric and hemodynamic measurements predict orthostatic tolerance in neurally mediated syncope patients. In addition, we tested whether orthostatic tolerance is related to syncope frequency in real life.

BACKGROUND

Earlier studies in patients with neurally mediated syncope suggested that orthostatic heart rate and blood pressure responses predict the tilt table responses with high sensitivity and specificity.

METHODS

We analyzed data from 157 consecutive patients (n = 100 exploratory cohort, n = 57 confirmatory cohort) with recurrent syncope in whom orthostatic tolerance was quantified as the time to (pre)syncope during head-up tilt testing combined with lower body negative pressure. We measured heart rate, brachial blood pressure, cardiac stroke volume, heart rate and blood pressure variability, and spontaneous baroreflex sensitivity supine and early during head-up tilt.

RESULTS

The orthostatic heart rate increase showed the strongest correlation with orthostatic tolerance. The best multivariate model including age, supine diastolic blood pressure, supine blood pressure variability, as well as tilt-induced changes in diastolic blood pressure and heart rate explained no more that 40% of the variability in orthostatic tolerance. The model failed to predict orthostatic tolerance in the confirmatory cohort. Frequency or number of free-living syncopal episodes were only weakly related to orthostatic tolerance.

CONCLUSIONS

In patients with neurally mediated syncope, orthostatic tolerance in the clinical laboratory is difficult to predict with a wide range of anthropometric and cardiovascular measurements and correlates poorly with syncope occurrence in real life.

The autonomic nervous system dysregulation in response to orthostatic stress in children with neurocardiogenic syncope

Neurocardiogenic syncope is a common disorder, which is considered as a benign condition. However, sudden loss of conscience and muscle tone causes anxiety among the family members due to its similarity to sudden death. Autonomic nervous system dysregulation is thought to be responsible in the aetiology. Heart rate variability is used for assessment of autonomic nervous system.We evaluated 24 children between 6 and 18 years (mean plus or minus standard deviation is equal to 12.5 plus or minus 3.28, with neurocardiogenic syncope and 10 healthy controls, mean plus or minus standard deviation is equal to 12.48 plus or minus 3.27) by using 24 hour Holter monitorisation and head-up tilt test. Heart rate variability analysis was performed using the Holter recordings obtained both during head-up tilt test and throughout the day.Our results revealed that, there is no significant difference between the study and the control groups in terms of the mean heart rate and all indices of the heart rate variability (p > 0.05). However, during the first 5 minutes of the head-up tilt test, standard deviation of all RR intervals and root mean square of successive differences were significantly lower in the syncope group compared with the control group, 42.17 plus or minus 12.56 versus 60.10 plus or minus 33.10 and 21.26 plus or minus 8.87 versus 36.80 plus or minus 31.03; p-values 0.02 and 0.03, respectively.In conclusion; autonomic functions in children with neurocardiogenic syncope are similar to healthy children. However, sympathetic hyperactivation occurs during the early phase of orthostatic stress in children with neurocardiogenic syncope comparing to healthy controls. Parasympathetic innervation is not sufficient in compensation of this sympathetic hyperactivation. Management strategy in neurocardiogenic syncope should be based on these pathophysiologic mechanisms.

Autonomic nervous system function in infants and adolescents: impact of autonomic tests on heart rate variability

Measurement of heart rate variability (HRV) shows information on the functional state of the autonomic nervous system (ANS). In adults there are standardized autonomic tests and well-established ranges of normal values, which is not the case in children. The aim of the present study was (1) to introduce an ANS test battery, especially for children and adolescents; (2) to establish normative HRV parameters; and (3) to determine the impact of ANS tests on HRV parameters compared with baseline measurements. We investigated 100 healthy children and adolescents between 6 and 15 years old. We subdivided the investigated group into a group of children (5-11 years old) and adolescents (12-15 years old) and measured HRV by time and frequency domain parameters during baseline, rhythmic breathing, Valsalva test, active standing, tilt-table testing, and handgrip test. The normative HRV data are presented by means, SDs, medians, and percentiles. The results described refer to baseline values for each HRV parameter separately to demonstrate the influence of age on HRV parameters. The study results present not only first normative HRV data for an autonomic test battery especially adapted to children and adolescents, but they also quantify the autonomic changes induced by test procedures compared with baseline measurements.

Precursors of syncope in linear and non-linear parameters of heart rate variability during pediatric head-up tilt test

The aim of this study was to identify precursors of neurocardiogenic syncope (NCS) in ECG parameters of children and adolescents who undergo head-up tilt testing (HUTT). Established linear and non-linear parameters of heart rate variability (HRV) were calculated minute-by-minute in 44 young patients with an NCS history (age 7-20 years, 22 female, 22 male, positive HUTT) and 34 age-matched healthy controls (age 7-20 years, 17 female, 17 male, negative HUTT) during 60 degrees HUTT. The influence of age and gender on the response to tilting was studied using the Wilcoxon rank sum test. We also assessed the predictive power of individual features with respect to HUTT outcome within three temporal windows (0-2 min after tilt; 2-5 min after tilt, and 5-2 min before tilt-back) by means of receiver operating characteristics analysis. Our results indicate that prediction of HUTT outcome should be restricted to subjects in or after puberty. In this group, descriptors based on co-occurrence or joint-recurrence analysis in recurrence plots showed promising predictive power (up to 86% sensitivity and 90% specificity, area under the curve 0.91). Time-domain parameters (standard deviation of differences for successive RR intervals) reached 75% sensitivity and 80% specificity. We conclude that HRV analysis within the first 5 min after tilting provides significant information on HUTT outcome and may be useful in conjunction with more sophisticated classification strategies for shortening HUTT duration in subjects after puberty.

Autonomic function in children and adolescents with neurocardiogenic syncope

BACKGROUND

This study aimed to clarify whether children with neurocardiogenic syncope (NCS) differ from healthy control subjects in baseline heart rate variability (HRV) and in their response to orthostatic stress induced by active standing and tilt table.

METHODS

This study analyzed the difference between 55 children with a history of NCS or presyncopal symptoms (PS) and healthy control subjects. Measurements included short-term HRV during resting position, tilt table testing, and active standing. Time and frequency domain HRV parameters were computed.

RESULTS

Both the NCS and PS children differed significantly from healthy control subjects during resting position. During tilt table testing, nearly all NCS and PS subjects differed significantly from the control group in calculated HRV parameters. Moreover, for the low-frequency power and total power, the confidence intervals did not overlap.

CONCLUSIONS

The findings suggest that chronic autonomic differences exist between healthy children and patients with NCS and PS. These changes could be detected even by short-term HRV recordings. The tilt table maneuver provoked the most prominent differences between the groups. Low-frequency power and total power during tilt table testing helps to detect children with NCS.

Spectral and time-domain analyses of heart-rate variability during head-upright tilt-table testing in children with neurally mediated syncope

Neurocardiac syncope (NS) is a common cause of syncope in children. The mechanism, though related to abnormalities in autonomic function, has not been fully elucidated, particularly in pediatric patients. This study assessed the heart-rate variability (HRV) response to head-upright tilt-table test (HUT) in children with NS and normal volunteers. Spectral and time-domain analysis of HRV was used to assess changes in autonomic function in 27 children (9 male, mean age 12.3 +/- 1.6 years) with a history of at least one episode of syncope and positive passive HUT and 27 age-matched normal volunteers with negative passive HUT before and during postural tilt and to attempt to relate such changes to specific types of hemodynamic response to tilt. Frequency-domain measurements of the high-(HF) and low-(LF) frequency bands and the ratio LF/HF were derived from Holter recordings and computed by fast Fourier analysis for 5-min intervals. Time-domain measurements of the SDNN, SDNNI, SDANN, RMSSD, and triangular index were derived from 24-h Holter recordings. There were no significant differences between clinical characteristics, time-domain, and basal frequency domain parameters of the groups. Mean values of LF and LF/HF ratio was increased and HF was decreased significantly in response to tilt in both patient and control groups. Mean values of LF and LF/HF ratio were higher and HF was lower compared to controls immediately after tilt. LF and LF/HF ratio showed a statistically significant decrease and a significant increase in HF during syncope in patients. The three subgroups of patients had similar patterns of changes in autonomic activity. The results of this study show that although the basal autonomic function was similar to that of the control group, patients with NS have a different pattern of response to the HUT. In our study, patients with NS demonstrated an exaggerated response to the HUT. This exaggerated response may be the factor that activates the pathological reflexes of NS. The pathological mechanism leading to NS appears to be independent of the specific type of hemodynamic response to HUT.

Orthostatic decrease in cardiac chaos during the head-up tilt test in patients with vasovagal syncope

BACKGROUND

Autonomic dysfunction contributes to orthostatic intolerance in vasovagal syncope (VVS), but as it has not been identified by spectral analysis of heart rate variability (HRV) in previous studies, the present hypothesis was that nonlinear analysis of HRV would identify the orthostatic intolerance in VVS.

METHODS AND RESULTS

Twenty-six patients with VVS and 14 matched controls were subjected to 80-degree head-up tilt test (positive: 13 patients; negative: 13 patients and 14 controls). There were no differences in the orthostatic changes in the indices of spectral analyses of HRV among the 3 groups. The Lyapunov exponent (LE) was calculated from 200 consecutive RR-intervals to investigate chaotic behavior, and cardiac chaos was defined as the incidence of the presence of a positive finite LE. Orthostatic decreases in cardiac chaos were observed in the VVS patients (both the positive and negative groups), although there was no orthostatic decrease in the control group (ANOVA: p = 0.008). The receiver-operator characteristic curve indicated that cardiac chaos during the tilt identified VVS regardless of the results of the tilt (p < 0.001, sensitivity: 85.7%, specificity: 96.2%).

CONCLUSIONS

The decrease in cardiac chaos during the tilt test was specific to patients with VVS, even if their response to the test was negative.

Role of vagal control in vasovagal syncope

The vasovagal reaction is thought to be caused by sympathetic withdrawal and vagal augmentation. While measurements of muscle sympathetic nerve activity support sympathetic withdrawal in tilt induced syncope, the results of previous attempts to quantify vagal control using spectral analyses of heart rate variability (HRV) remain controversial. The sampling period used in the HRV studies is related to the discordant results. In the present study, HRV was computed every second using wavelet transformation to clarify the role of vagal control in tilt induced syncope during the 80-degree head-up tilt test (positive: 10 patients with vasovagal syncope; negative: 10 patients with vasovagal syncope, and 10 control subjects). Autonomic modulations were assessed using the absolute power of the low frequency (LF) (0.04-0.15 Hz) and high frequency (HF) (0.15-2.00 Hz) oscillatory components of R-R variability. Although the LF did not change during the tilt procedure, a decrease in the systolic arterial pressure (SAP) and increases in the R-R interval and HF were observed for the last 30 seconds before the tilt induced syncope in the tilt-positive group. Analyzing the hemodynamic measurements and spectral indices for the last 5 minutes preceding the tilt induced syncope, the study found that the SAP, R-R interval, and HF changed simultaneously during the 30-second period immediately before the tilt induced syncope. Further, the HF was positively correlated with the R-R interval and negatively correlated with the SAP. In conclusion, continuous spectral analysis of the R-R interval demonstrated increased vagal influence on the heart in tilt induced syncope.

Heart rate variability in healthy newborn infants

In adults and older children, heart rate variability (HRV) is frequently used to study autonomic function noninvasively. Normal values of HRV in newborn infants, however, are not widely available. This problem may be partially attributed to the lack of standardization of different methods. This study assessed HRV in normal newborn infants using 24-hour Holter monitoring. From 1997 to 2000, we prospectively evaluated frequency- (spectral analysis), geometric-, and time-domain indexes of HRV in normal term infants. Ninety-six asymptomatic infants who were <72 hours old were studied. Frequency-domain parameters (power in the high, low, very low, ultra low, and total frequency domains), a geometric parameter (HRV triangular index), and time-domain parameters (SDNN, SDANN, SDNNi, r-MSSD, s-NN50) are reported as means +/- SD, medians, and 5th and 95th percentiles to establish the normative values for newborns. A high degree of correlation (r > or = 0.85, p <0.0001) was noted among the 3 vagal tone dependent parameters, such as high-frequency power (frequency domain), r-MSSD, and s-NN50 (time domain). Our study supports the use of vagal dependent time-domain parameters like r-MSSD and sNN50 as surrogates for high-frequency power in newborns. Because the data are reported as means +/- SD, medians, and 5th and 95th percentiles, their use facilitates the study of parasympathetic and sympathetic activity in comparable populations.

Evaluation and treatment of pediatric patients with neurocardiogenic syncope

Neurocardiogenic syncope is the most common form of syncope in children. The most widely accepted mechanism of its etiology is a vigorous contraction of the heart due to relative hypovolemia leading to stimulation of C-fibers and sympathetic withdrawal. Episodes usually occur with an upright position and are preceded by a typical prodrome. A classic history is paramount to the diagnosis. Tilt testing aids in the diagnosis in certain cases. The cornerstone of therapy is maintaining adequate hydration and avoiding situations that may lead to harm with syncopal events. Beta blockers, fludrocortisone, alpha adrenergic agents and disopyramide are commonly used to prevent syncope. Seratonin reuptake inhibitors, pacing with rate drop algorithms and tilt training are relatively new in the armamentarium of therapy.

Decreased entropy of symbolic heart rate dynamics during daily activity as a predictor of positive head-up tilt test in patients with alleged neurocardiogenic syncope

Entropy measures of RR interval variability during daily activity over a 24h period were compared in 30 patients with a positive head-up tilt (HUT) test and 30 patients with a negative HUT test who had a history of alleged neurocardiogenic syncope. Two different entropies, approximate entropy (ApEn) and entropy of symbolic dynamics (SymEn), were employed. In patients showing a positive HUT test, the entropies were significantly decreased when compared with the patients with a negative HUT test. In addition, SymEn in the patients with a negative HUT test was significantly lower than in the normal controls. Discriminant analysis using SymEn could correctly identify 89.3% (520/582) of the 1 h RR interval data of the patients with a positive HUT test regardless of the time of day. Baseline entropies of heart rate dynamics during daily activity were found to be significantly lower in patients with alleged neurocardiogenic syncope and a positive HUT test than in those with the same history but with a negative HUT test. The decreased entropy of symbolic heart rate dynamics may be of predictive value of a positive HUT test in patients with alleged neurocardiogenic syncope.

Prediction of the oculocardiac reflex from pre-operative linear and nonlinear heart rate dynamics in children

This study was aimed to determine whether pre-operatively measured linear and nonlinear analysis of heart rate variability might predict the occurrence of the oculocardiac reflex (OCR) or other arrhythmia during strabismus surgery in children (n = 185, mean (SD) age = 8.09 (3.31) years). We compared time- and frequency-domain, and nonlinear dynamic indices of pre-operatively measured RR interval data between the OCR-positive group (maximum heart rate decrement = 20 beat.min-1 during the traction of extraocular muscle, n = 54), OCR-negative group (< 20 beat x min(-1), n = 78) and arrhythmia-positive group (all other arrhythmias; n = 53). pNN50, rMSSD, high-frequency power and nonlinear prediction error were significantly lower in the OCR-positive and arrhythmia-positive groups than in the OCR-negative group. Discriminant analysis using these indices could correctly identify 39/54 (72.2%) OCR-positive patients. Some pre-operatively measured indices of linear and nonlinear heart rate variability, especially when used in combination, are valuable for predicting significant bradycardia during strabismus surgery in children.

Patterns of orthostatic intolerance: the orthostatic tachycardia syndrome and adolescent chronic fatigue

OBJECTIVES

To describe the orthostatic tachycardia syndrome (OTS) in adolescents, similarities to and differences from chronic fatigue syndrome (CFS), and patterns of orthostatic intolerance during head-up tilt (HUT).

STUDY DESIGN

Using electrocardiography and arterial tonometry, we investigated the heart rate and blood pressure responses during HUT in 20 adolescents with OTS compared with 25 adolescents with CFS, 13 healthy control subjects, and 20 patients with simple faint.

RESULTS

Of the control subjects, 4 of 13 experienced typical vasovagal faints with an abrupt fall in blood pressure and heart rate, and 14 of 20 patients with simple faint experienced similar HUT responses. All patients with CFS (25/25) experienced severe orthostatic symptoms with syncope in 2 of 25, early orthostatic tachycardia during HUT in 16 of 23 (13/16 hypotensive), and delayed orthostatic tachycardia in 7 of 23 (6/7 hypotensive). Acrocyanosis and edema occurred in 18 of 25. Early orthostatic tachycardia occurred in 10 of 20 patients with OTS. Of these, 9 of 10 were hypotensive, but hypotension was delayed in 4 of 9. Delayed tachycardia occurred in 10 of 20 (all hypotensive). Acrocyanosis and edema occurred in most patients with CFS, fewer patients with OTS, and in one patient with simple faint. Orthostatic symptoms were similar but more severe in patients with CFS compared with patients with OTS.

CONCLUSIONS

Symptoms and patterns of orthostatic heart rate and blood pressure change in OTS overlap strongly with those of CFS. Orthostatic intolerance in OTS may represent an attenuated form of chronic fatigue pathophysiology.

Age-related changes of cardiac parasympathetic modulation after vasovagal syncope

The time-domain analysis of 24-hour electrocardiographic recordings showed that vagal modulation of heart rate is reduced within 48 hours from vasovagal syncope. However, patients with recent vasovagal syncope can be differentiated from healthy subjects only up to the age of 40 years with this analysis, because this parasympathetic modulation physiologically decreases with increasing age.

Orthostatic intolerance in adolescent chronic fatigue syndrome

OBJECTIVES

To demonstrate the association between orthostatic intolerance and the chronic fatigue syndrome (CFS) in adolescents and to delineate the form that orthostatic intolerance takes in these children.

STUDY DESIGN

We investigated the heart rate and blood pressure (BP) responses to head-up tilt (HUT) in 26 adolescents aged 11 to 19 years with CFS compared with responses in adolescents referred for the evaluation of simple faint and to responses in 13 normal healthy control children of similar age.

RESULTS

A total of 4/13 of the controls and 18/26 simple faint patients experienced typical faints with an abrupt decrease in BP and heart rate associated with loss of consciousness. One CFS patient had a normal HUT. A total of 25/26 CFS patients experienced severe orthostatic symptoms associated with syncope in 7/25, orthostatic tachycardia with hypotension in 15/25, and orthostatic tachycardia without significant hypotension in 3/25. Acrocyanosis, cool extremities, and edema indicated venous pooling in 18/25. None of the control or simple faint patients experienced comparable acral or tachycardic findings.

CONCLUSIONS

We conclude that chronic fatigue syndrome is highly related to orthostatic intolerance in adolescents. The orthostatic intolerance of CFS often has heart rate and BP responses similar to responses in the syndrome of orthostatic tachycardia suggesting that a partial autonomic defect may contribute to symptomatology in these patients.

Heart rate variability during head-up tilt testing in patients with suspected neurally mediated syncope

The relation between heart rate variability (HRV) and outcome of head-up tilt testing (HUT) in patients with neurally mediated syncope (NMS) was studied in 30 patients with presumed NMS (33 +/- 13 years) and in 11 age-matched controls. After 15 minutes of baseline supine observation, patients were tilted to 60 degrees for 45 minutes or until syncope occurred. HRV parameters included RR intervals, standard deviation of normal-to-normal RR intervals (SDNN), and root mean square successive differences (RMSSD). HRV analysis was performed during 5-minute intervals in the supine position immediately after onset of HUT and before syncope or after 30-35 minutes of tilt in patients without syncope. Syncope occurred after a mean tilt duration of 32 minutes in 14 (47%) of 30 patients with presumed NMS, whereas all controls had an uneventful HUT. In the supine position, RR intervals and RMSSD were comparable among HUT-positive patients, HUT-negative patients, and controls (RR intervals: 799 +/- 92, 854 +/- 137, and 818 +/- 128 ms, P = NS; RMSSD: 43 +/- 40, 36 +/- 34, and 53 +/- 42 ms, P = NS). Baseline SDNN was also comparable in HUT-positive patients versus HUT-negative patients with presumed NMS (50 +/- 26 vs 52 +/- 20 ms, P = NS). Within 5 minutes preceding syncope or after 30-35 minutes of tilt, RR intervals and RMSSD were shorter in HUT-positive patients compared to HUT-negative patients, or to controls (RR intervals: 606 +/- 86 vs 710 +/- 117 and 739 +/- 123 ms, P < 0.05; RMSSD: 12 +/- 5 vs 23 +/- 19 and 40 +/- 32 ms, P < 0.05). Thus, HRV analysis in the baseline supine position was not a predictor of HUT outcome in patients with suspected NMS. Syncope during HUT seemed to be preceded by increased sympathetic activity manifested by an increase in heart rate and by a decreased parasympathetic tone manifested by a decrease in RMSSD measured for 5 minutes before the event, in comparison with HUT-negative patients and with controls.

Neurally mediated hypotension and autonomic dysfunction measured by heart rate variability during head-up tilt testing in children with chronic fatigue syndrome

Recent investigations suggest a role for neurally mediated hypotension (NMH) in the symptomatology of chronic fatigue syndrome (CFS) in adults. Our previous observations in children with NMH and syncope (S) unrelated to CFS indicate that the modulation of sympathetic and parasympathetic tone measured by indices of heart rate variability (HRV) is abnormal in children who faint during head-up tilt (HUT). In order to determine the effects of autonomic tone on HUT in children with CFS we performed measurements of HRV during HUT in 16 patients aged 11-19 with CFS. Data were compared to 26 patients evaluated for syncope and with 13 normal control subjects. After 30 minutes supine, patients were tilted to 80 degrees for 40 minutes or until syncope occurred. Time domain indices included RR interval, SDNN, RMSSD, and pNN50. An autoregressive model was used to calculate power spectra. LFP (.04-.15 Hz), HFP (.15-.40Hz), and TP (.01-.40Hz). Data were obtained supine (baseline) and after HUT. Thirteen CFS patients fainted (CFS+, 5/13 pure vasodepressor syncope) and three patients did not (CFS-). Sixteen syncope patients fainted (S+, all mixed vasodepressor-cardioinhibitory) and 10 did not (S-). Four control patients fainted (Control+, all mixed vasodepressor-cardioinhibitory) and nine did not (Control-). Baseline indices of HRV were not different between Control+ and S+, and between Control- and S-, but were depressed in S+ compared to S-. HRV indices were strikingly decreased in CFS patients compared to all other groups. With tilt, SDNN, RMSSD, and pNN50 and spectral indices decreased in all groups, remaining much depressed in CFS compared to S or control subjects. With HUT, sympathovagal indices (LFP/HFP, nLFP, and nHFP) were relatively unchanged in CFS, which contrasts with the increase in nLFP with HUT in all other groups. With syncope RMSSD, SDNN, LFP, TP, and HFP increased in S+ (and Control+), suggesting enhanced vagal heart rate regulation. These increases were not observed in CFS+ patients. CFS is associated with NMH during HUT in children. All indices of HRV are markedly depressed in CFS patients, even when compared with already low HRV in S+ or Control+ patients. Sympathovagal balance does not shift toward enhanced sympathetic modulation of heart rate with HUT and there is blunting in the overall HRV response with syncope during HUT. Taken together these data may indicate autonomic impairment in patients with CFS.

[Diagnosis and treatment of vasovagal syncope in the child and adolescent]

Recurrent unexplained syncope is a common and often frustrating clinical problem in paediatrics. Over the last decade, head upright tilt table testing has emerged as an important diagnostic method for the identification of patients whose syncope is likely to be neurocardiogenic in origin. At the same time, tilt table testing, by providing syncopal episodes in a controlled setting, has allowed for a greater understanding of their physiopathology. Treatment strategies remain controversial but beta-blocker therapy appears to be very efficient.