Spectral analysis of heart rate in vasovagal syncope: the autonomic nervous system in vasovagal syncope

Preliminary Observations on the Effect of Amitriptyline Treatment in Preventing Syncope Recurrence in Patients with Vasovagel Syncope

PURPOSE

Vasovagal syncope is a common and challenging problem that may result in injury and causes substantial anxiety among patients and their relatives. However, treatment of vasovagal syncope with standard pharmacologic approaches is not satisfactory. The aim of this study is to investigate the effect of amitriptyline, a tricyclic antidepressant drug, by using its anticholinergic effects in preventing syncopal episodes in patients with vasovagal syncope.

METHODS

In this study, 74 patients (mean age 24 +/- 1.9 years, 26 male) with a history of recurrent syncope and baseline positive head-up tilt table test (syncope or presyncope) were included. Oral amitriptyline treatment was given to all patients, with a starting dose of 10 mg once a day. Head-up tilt table test was performed in all patients 4 weeks after the treatment started. Patients were followed up clinically for 6 months.

RESULTS

After 4 weeks, during head-up tilt table test in 69 patients (93%), syncope or presyncope was not seen and test was assumed as negative. At the end of the 6th month, 67 patients (91%) were free of symptoms. Only two patients (0.3%) did not tolerate amitriptyline due to side effects.

CONCLUSIONS

Oral amitriptyline can be used in the prevention of recurrent episodes of vasovagal syncope safely. However, randomized controlled studies are essential to assess the real effectiveness of this therapy.

Effect of posture on heart rate variability spectral measures in children and young adults with heart disease

BACKGROUND

Reduction of heart rate variability as a consequence of heart disease and postural change has been well documented. However, the data on the effect of postural change in pediatric patients are incomplete and the effect is not fully understood. The aim of the study was to investigate effect of postural change on heart rate variability in relation to the extent of severity of heart disease.

METHODS

The dependence of heart rate variability on posture in 41 children and young adults (8-20 years) with heart disease has been investigated and compared with control. Short-term electrocardiograms (ECGs) were assessed in supine rest and active standing, and spectral measures of heart rate variability were determined.

RESULTS

Two types of response to the change of supine to standing posture were determined in both healthy and diseased subjects. In majority of subjects, the increased heart rate induced by standing was accompanied by a decrease in high-frequency power. However, in about 30% of all subjects, increased heart rate during standing was accompanied by an increased high-frequency power. Independently of posture and disease, high-frequency and low-frequency power were positively correlated. In subjects characterized by a reduction of heart rate variability in standing, the high-frequency power in both postures is reduced in diseased subjects compared to control.

CONCLUSIONS

These results demonstrate that in this age range, the response to posture is not unique because of the difference in high-frequency power, which implies a variety of vagal modulations of heart rate.

Sympathovagal imbalance in pediatric patients with neurocardiogenic syncope during asymptomatic time periods

The pathophysiology of neurocardiogenic syncope (NCS) is only poorly understood. Several studies indicate that NCS is associated with an imbalance of the autonomic nervous system (ANS). We hypothesized that pediatric patients with NCS exhibit alterations of the neurovegetative status also during asymptomatic time periods. To test this hypothesis the non-invasive method of Heart Rate Variability (HRV)-Analysis was used.

METHOD

Holter records (12 channel, 180 Hz; obtained during an asymptomatic 24-hour period) of 32 patients (18 male, 14 female, mean age 14.6 yrs) with a history of syncope and a positive Head-Up tilt (HUT) were compared to the recordings of 33 healthy control subjects (19 male, 14 female, mean age 13.5 yrs) with negative history of syncope and HUT. Time domain and frequency domain features were calculated. Analysis segments were divided in different signal duration groups (1, 3, 6, 24 hours).

RESULTS

For all time scales the standard deviation of wavelet coefficients yields the best discrimination properties. Analysis of the total time duration (24h) shows only moderate discrimination (sensitivity 84%, specificity 45%) between patient and controls. However, analysis of 3 and 6 hour segments (starting and 6 a.m.) showed significant discrimination: sigma wave scale 13 (6-9 a.m.) sensitivity 78%, specificity 71%., sigma wave scale 11 (6-12 a.m.) sensitivity 84%, specificity 61%. The best combination of two parameters is denoted by SDNN and sigma wave scale 11 (6-12 a.m.) with sensitivity 70%, specificity 75%.

CONCLUSION

The results indicate that during an asymptomatic 24-hour-period patients with NCS exhibit an imbalance of the ANS especially in the morning (6-12 a.m.). The findings suggest a time-dependent increased sympathetic or reduced vagal activity in pediatric patients with NCS. Patients could benefit from a time-adjusted medical therapy with beta-blocking agents.

Noninvasive detection of sympathetic neurocirculatory failure

In sympathetic neurocirculatory failure (SNF), reflexive sympathetically mediated cardiovascular stimulation does not compensate for decreased cardiac filling. This explains orthostatic hypotension in chronic primary autonomic failure (CPAF). During phase 2 of the Valsalva maneuver (phase 2_L), blood pressure increases from its peak. During phase 4, blood pressure normally "overshoots" the baseline. Because these changes depend on sympathetically mediated cardiovascular stimulation, a progressive decrease in pressure during phase 2 and absence of the overshoot in phase 4 may indicate SNF. Moreover, because beat-to-beat blood pressure can be measured noninvasively using a photoplethysmographic or tonometric device, evaluating reflexive pressure responses might enable noninvasive diagnosis of SNF. This study assessed the relative frequencies of abnormal phase 2_L and phase 4 blood pressure in patients with CPAF and orthostatic hypotension and whether noninvasive measurement of beat-to-beat blood pressure can be used to diagnose SNF in patients. Twenty patients with chronic primary autonomic failure and orthostatic hypotension and 50 comparison patients, including several with CPAF but lacking orthostatic hypotension, underwent arterial pressure monitoring during performance of the Valsalva maneuver. Of the 20 patients with CPAF and orthostatic hypotension, all had an abnormal phase 2_L or phase 4 pressure response (sensitivity 100%), whereas only 3 of the 50 comparison patients had an abnormal response in either phase (specificity 94%). Seventeen patients with CPAF and orthostatic hypotension had abnormal responses in both phases (sensitivity 85%), but none of the comparison patients had such findings in both phases (specificity 100%). Of 13 patients in whom beat-to-beat blood pressure was recorded simultaneously invasively and noninvasively, all had abnormal blood pressure responses during phase 2_L and phase 4, whereas none of 29 comparison patients had such symptoms. Detection of abnormal blood pressure responses during phase 2_L or phase 4 of the Valsalva maneuver is a highly sensitive test for SNF. Abnormal pressure during these phases appears to identify SNF specifically. Noninvasive measurements can detect both of these abnormalities.

Autonomic control of heart rate variability in vasovagal syncope: a study of the nighttime period in 24-hour recordings

Patients experiencing vasovagal syncope have been claimed to show reduced vagal tone over 24-hour electrocardiography recordings. Assessment of sympathovagal balance in the absence of external stimuli, i.e., nighttime electrocardiography monitoring, might help to clarify if increased sympathetic activity is present in these patients. Heart rate variability was examined at nighttime in 40 patients with recurrent episodes of vasovagal syncope within the last 2 years (22 men; mean age, 37 years) and 20 comparable healthy volunteers. Time domain parameters (pNN50 [proportion of successive RR intervals difference >50 ms in %] and rMSSD [root-mean-square successive difference of RR intervals in ms]), indexes of vagal tone, and frequency domain parameters, expressing the overall heart rate variability, vagal (high frequency [HF]) and sympathetic (low frequency [LF]) activity, and autonomic balance (LF/HF ratio) were compared between groups by Mann-Whitney test. Significant (p<0.05) reduction of heart rate variability and vagal tone (pNN50 and rMSSD) were found for patients with vasovagal syncope, together with increased sympathetic activity (increased LF/HF ratio). These findings could open new insights in the pathogenesis of vasovagal syncope because of the shift of the autonomic balance toward sympathetic activation near the syncopal episode.

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.

Autonomic control of vasovagal syncope

In the pathophysiological study of vasovagal syncope, the nature of the interaction between baroreceptor sensitivity (BS), sympathetic withdrawal, and parasympathetic activity has yet to be ascertained. Altered BS may predispose toward abnormal sympathetic and parasympathetic responses to orthostasis, causing hypotension that may progress to syncope if there is sympathetic withdrawal. To examine this hypothesis, we monitored blood pressure (BP), heart rate (HR), BS, forearm blood flow, and muscle nerve sympathetic activity (MNSA) continuously in 18 vasovagal patients during 60 degrees head-up tilt, syncope, and recovery. Results were compared with those of 17 patients who were able to tolerate tilt for 45 min. During early tilt, BP was maintained in both groups by an increase in HR and MNSA from baseline (P < 0.01), but BS decreased more in the syncopal group (P < 0.05). At the start of presyncope (mean 2.7 +/- 0.2 min before syncope and 15.2 +/- 12 min after tilt), when BP fell, HR and sympathetic activity remained increased from baseline (P < 0.01). Thereafter, BP and HR correlated directly with sympathetic activity and regressed in linear fashion until syncope (P < 0.001), whereas BS increased to baseline. At syncope, BP, HR, and sympathetic activity fell below baseline (P < 0.01, P < 0.05, and P < 0.01, respectively), but BS did not increase. During recovery, sympathetic activity increased to baseline and BS increased (P < 0.05), whereas HR and BP remained low (P < 0.01 and P < 0.05, respectively). The mechanism for the initiation of hypotension during presyncope remains unknown, but BS may contribute. Vasodilatation and bradycardia during presyncope appear to be more closely related to withdrawal of sympathetic activity than to increased parasympathetic cardiac activity.

Review article: heart rate and blood pressure control in vasovagal syncope

Vasovagal syncope is characterized by transient failure of usually reliable physiologic mechanisms responsible for maintaining both systemic arterial pressure and cerebral blood flow. Two circulatory phenomena are almost universally present: systemic arterial vasodilation and bradycardia. A third phenomenon, cerebrovascular constriction, has also been described but its contribution to the faint is less well established. The neural reflex pathways responsible for triggering the circulatory changes in the vasovagal faint are incompletely understood, but have recently been the subject of renewed interest. In part, this interest probably stems from the frequency with which vasovagal symptoms are now recognized to be the cause of fainting spells. Additionally, however, there is an increasingly recognized need to develop treatment strategies for those affected patients in whom recurrent vasovagal symptoms are particularly troublesome. It is the goal of this discussion to focus on those aspects of circulatory control, and in particular on potential interactions among certain neural and humoral systems, which may contribute to the inappropriate physiologic responses associated with the vasovagal faint.

Vagal control of heart rate variability in vasovagal syncope: studies based on 24-h electrocardiogram recordings

The autonomic nervous system has an important role in the pathophysiology of vasovagal syncope. The purpose of this investigation was to evaluate to what extent the autonomic system is involved in the mechanism of fainting and to characterize the profile of heart rate variability of individuals who are prone to undergo a critical event. Thirty patients (mean age 41 years) with vasovagal syncope and 15 comparable controls were monitored by 24-h electrocardiography. Heart rate variability was analysed over the whole 24 h and during the daytime and night-time using time domain parameters (average of heart periods, RR; standard deviation of heart periods, SDNN; standard deviation of the average of RR intervals over all the 5-min segments of the entire recording, SDANN; percentage of the total number of all RR intervals of pairs of adjacent RR intervals differing more than 50 ms over the entire recording, pNN50; the square root of the sum of the square of differences between adjacent RR intervals, rMSSD), as indicated by the Task Force for Clinical Use of Standard Measurements of Heart Rate Variability. These parameters explore the influence of the autonomic nervous system on sinus node function and provide information about the vagal control to the heart. Among these parameters, pNN50 and rMSSD were significantly reduced in individuals with vasovagal syncope when compared with controls, over each time period considered. The two parameters are related to high-frequency oscillations in the frequency domain and to the vagal influence of the heart. These results indicate that the vagal tone to the heart is altered in subjects who suffer from vasovagal syncope. The results of this study provide an insight into the pathophysiological mechanism of fainting and may offer another means of evaluating patients with syncope.

Sympathetic and baroreceptor reflex function in neurally mediated syncope evoked by tilt

The pathophysiology of neurally mediated syncope is poorly understood. It has been widely assumed that excessive sympathetic activation in a setting of left ventricular hypovolemia stimulates ventricular afferents that trigger hypotension and bradycardia. We tested this hypothesis by determining if excessive sympathetic activation precedes development of neurally mediated syncope, and if this correlates with alterations in baroreflex function. We studied the changes in intraarterial blood pressure (BP), heart rate (HR), central venous pressure (CVP), muscle sympathetic nerve activity (MSNA), and plasma catecholamines evoked by upright tilt in recurrent neurally mediated syncope patients (SYN, 5+/-1 episodes/mo, n = 14), age- and sex-matched controls (CON, n = 23), and in healthy subjects who consistently experienced syncope during tilt (FS+, n = 20). Baroreflex responses were evaluated from changes in HR, BP, and MSNA that were obtained after infusions of phenylephrine and sodium nitroprusside. Compared to CON, patients with SYN had blunted increases in MSNA at low tilt levels, followed by a progressive decrease and ultimately complete disappearance of MSNA with syncope. SYN patients also had attenuation of norepinephrine increases and lower baroreflex slope sensitivity, both during tilt and after pharmacologic testing. FS+ subjects had the largest decrease in CVP with tilt and had significant increases in MSNA and heart rate baroreflex slopes. These data challenge the view that excessive generalized sympathetic activation is the precursor of the hemodynamic abnormality underlying recurrent neurally mediated syncope.

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

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.

Autonomic control of asystolic vasovagal syncope

A 30 year old woman with a lifelong history of severe, recurrent, vasovagal syncope became asystolic for 30 seconds after 37 minutes of 60 degrees head-up tilt. During early tilt, sympathetic activity, heart rate, left ventricular contractility, and cardiac output increased. Mean blood pressure was initially maintained. Presyncope was associated with maximal contractility and bradycardia despite sustained sympathetic activity. Subsequently, asystole occurred associated with complete withdrawal of muscle nerve sympathetic activity. In asystolic vasovagal reactions, presyncope may be triggered by increased left ventricular contractility and is associated with increased levels of parasympathetic and sympathetic activity. Asystole and peripheral vasodilatation may be caused by sudden and complete withdrawal of the increased sympathetic activity.