Differences in heart rate variability between cardioinhibitory and vasodepressor responses to head-up tilt table testing

Factors affecting the syncopal episodes in pediatric vasovagal syncope

OBJECTIVE

To investigate factors that influence the syncopal episodes in pediatric vasovagal syncope (VVS).

METHODS

A retrospective analysis was performed on the clinical data of 2908 children who were diagnosed with VVS for the first time between January 2001 and February 2023. The study examined the linear relationships among age, sex, height, weight, heart rate (HR), blood pressure, hemodynamic type, and head-up tilt test (HUTT) mode in relation to the onset of syncope.

RESULTS

(1) Comparative analysis of intergroup differences revealed statistically significant variations in sex, age, height, weight, HR, systolic blood pressure, hemodynamic classification, and HUTT mode among syncopal episodes groups (P < 0.05); (2) Univariate analysis identified age, female, height, weight, VVS-cardioinhibited type (VVS-CI), VVS-mixed type (VVS-M) as potential risk factors for syncope episodes. Conversely, HR and sublingual nitroglycerin HUTT (SNHUT) emerged as potential protective factors against syncope episodes. (3) Multivariate analysis indicated that the frequency of syncope episodes increased by 0.27/0.02 for each unit increase in age/weight. When females compared to males and VVS-CI and VVS-M compared to VVS-vasoinhibited type (VVS-VI), the frequency of syncope episodes increased by 1.36, 0.53, and 0.66 respectively. Furthermore, SNHUT was associated with a reduction in the number of syncope episodes by 0.34 relative to basic HUTT.

CONCLUSION

Female, age, weight, VVS-CI, and VVS-M were identified as independent risk factors for syncopal episodes, while SNHUT was recognized as an independent protective factor against syncopal episodes.

Potential consequences of cardioneuroablation for vasovagal syncope: A call for appropriately designed, sham-controlled clinical trials

Cardioneuroablation (CNA) is being increasingly used to treat patients with vasovagal syncope (VVS). Bradycardia, in the cardioinhibitory subtype of VVS, results from transient parasympathetic overactivity leading to sinus bradycardia and/or atrioventricular block. By mitigating parasympathetic overactivity, CNA has been shown to improve VVS symptoms in clinical studies with relatively small sample sizes and short follow-up periods (<5 years) at selected centers. However, CNA may potentially tip the autonomic balance to a state of sympathovagal imbalance with attenuation of cardiac parasympathetic activity. A higher heart rate is associated with adverse cardiovascular events and increased mortality in healthy populations without cardiovascular diseases. Chronic sympathovagal imbalance may also affect the pathophysiology of spectra of cardiovascular disorders including atrial and ventricular arrhythmias. This review addresses potential long-term pathophysiological consequences of CNA for VVS.

Research progress on the predictive value of electrocardiographic indicators in the diagnosis and prognosis of children with vasovagal syncope

Neurally mediated syncope (NMS) is a common type of syncope in children in clinical practice, among which vasovagal syncope (VVS) is the most frequent. In recent years, more and more studies have been carried out to assess the diagnosis and prognosis of VVS. The electrocardiographic indicators such as heart rate variability (HRV), QT dispersion (QTd), P-wave dispersion (Pd), ventricular late potentials (VLP), deceleration ability of heart rate (DC), etc., are easy to obtain and inexpensive. With the help of electrocardiographic indicators, the diagnostic procedure and individualized treatment strategies of pediatric VVS can be optimized. This article reviews the value of electrocardiographic indicators in the diagnosis and prognosis of children with VVS.

On the construct validity of interoceptive accuracy based on heartbeat counting: Cardiovascular determinants of absolute and tilt-induced change scores

Interoceptive accuracy (IAcc) as assessed with the heartbeat counting task (IAcc_HBCT) may be affected by a range of factors including (1.) the ability to adequately detect cardiac signals, indicated by IAcc in a heartbeat discrimination task (IAcc_HBDT), (2.) cardiac signal properties, affected by sympathetic and parasympathetic tone, and (3.) non-interoceptive processes, including time estimation accuracy (TEAcc). In the current study we investigated the contribution of these factors to absolute and Δ IAcc_HBCT scores, induced by passive head-up and head-down tilt in 49 healthy individuals. A set of hierarchical regression models showed IAcc_HBDT scores as the strongest and, across different orthostatic (tilt) conditions, most stable (positive) predictor of absolute and Δ IAcc_HBCT scores. Neither indicators of cardiac signal properties (except for HR in head-down-tilt), nor TEAcc predicted absolute or Δ IAcc_HBCT scores. These findings support the convergent and discriminant validity of absolute and Δ IAcc_HBCT scores.

Clinical values of creatine kinase and its isoenzymes in children and adolescents with vasovagal syncope

BACKGROUND AND AIM

Vasovagal syncope (VVS) in children and adolescents is a common disorder. There may be an internal relationship between creatine kinase (CK) and its isoenzymes (CKMB) and syncope. The aim of this study was to evaluate the changes of CK and CKMB in children and adolescents with VVS.

METHODS AND RESULTS

The VVS group included 218 patients (93 male and 125 female). The control group included 129 healthy children (78 male and 51 female). Serum CK and CKMB levels were estimated. We founded ①Serum CK and CK-MB levels decreased in VVS group than that in control group (P < 0.05). ②The CK levels of female were significantly lower than those of male in VVS group (P < 0.05). ③Serum level of CK-MB were in negative correlation with age, height, weight, BMI whereas in positively correlation with HR. ④CK was effected by CK-MB (β = 0.147, P = 0.037) while CK-MB was independently influenced by age (β = -0.203, P = 0.002) and DBP (β = 0.171, P = 0.011). ⑤Both CK and CK-MB significantly influenced on VVS occurrence after adjusting for the effects of gender, age, height, weight, BMI and HR.

CONCLUSION

The serum CK and CKMB levels decrease in children and adolescents with VVS. CK and CK-MB are the independent protective factors with VVS.

Deceleration capacity-a novel measure for autonomic nervous system in patients with vasovagal syncope on tilt-table testing

This study was to investigate the changes of autonomic nerve function and hemodynamics in patients with vasovagal syncope (VVS) during head-up tilt-table testing (HUT). HUT was performed in 68 patients with unexplained syncope and 18 healthy subjects served as control group. According to whether bradycardia, hypotension or both took place during the onset of syncope, the patients were divided during the test into three subgroups: vasodepressor syncope (VD), cardioinhibitory syncope (CI) and mixed syncope (MX) subgroups. Heart rate, blood pressure, heart rate variability (HRV), and deceleration capacity (DC) were continuously analyzed during HUT. For all the subjects with positive responses, the normalized low frequency (LFn) and the LF/HF ratio markedly decreased whereas normalized high frequency (HFn) increased when syncope occurred. Syncopal period also caused more significant increase in the power of the DC in positive groups. These changes were more exaggerated compared to controls. All the patients were indicative of a sympathetic surge in the presence of withdrawal vagal activity before syncope and a sympathetic inhibition with a vagal predominance at the syncopal stage by the frequency-domain analysis of HRV. With the measurements of DC, a decreased vagal tone before syncope stage and a vagal activation at the syncopal stage were observed. The vagal tone was higher in subjects showing cardioinhibitory responses at the syncopal stage. DC may provide an alternative method to understand the autonomic profile of VVS patients.

[Role of the sympathetic nervous system in vasovagal syncope and rationale for beta-blockers and norepinephrine transporter inhibitors]

Vasovagal or neurocardiogenic syncope is a common clinical situation and, as with other entities associated with orthostatic intolerance, the underlying condition is a dysfunction of the autonomic nervous system. This article reviews various aspects of vasovagal syncope, including its relationship with orthostatic intolerance and the role of the autonomic nervous system in it. A brief history of the problem is given, as well as a description of how the names and associated concepts have evolved. The response of the sympathetic system to orthostatic stress, the physiology of the baroreflex system and the neurohumoral changes that occur with standing are analyzed. Evidence is presented of the involvement of the autonomic nervous system, including studies of heart rate variability, microneurography, cardiac innervation, and molecular genetic studies. Finally, we describe different studies on the use of beta-blockers and norepinephrine transporter inhibitors (sibutramine, reboxetine) and the rationality of their use to prevent this type of syncope.

Analysis of Heart Rate Variability Before and During Tilt Test in Patients with Cardioinhibitory Vasovagal Syncope

BACKGROUND

Cardioinhibitory vasovagal response is uncommon during the tilt test (TT). Heart rate variability (HRV) by use of spectral analysis can distinguish patients with that response.

OBJECTIVE

To compare the HRV in patients with cardioinhibitory vasovagal syncope (case group - G1) with that in patients without syncope and with negative response to TT (control group - G2).

METHODS

64 patients were evaluated (mean age, 36.2 years; 35 men) and submitted to TT at 70 degrees, under digital Holter monitoring. The groups were paired for age and sex (G1, 40 patients; G2, 24).

RESULTS

In G1, 21 patients had a type 2A response and 19 had type 2B, with mean TT duration of 20.4 minutes. There was a greater low frequency (LF) component (11,6 versus 4,5 ms2, p=0.001) and a lower low/high frequency ratio in the supine position (3,9 versus 4,5 ms2, p=0.008) in G1, with no difference during TT between the groups. Applying the receiver operating characteristic curve for cardioinhibitory response, the area under the curve was 0.74 for the LF component in the supine position (p = 0.001). The following were observed for the cutoff point of 0.35 ms(2) for the LF component: sensitivity, 97.4%; specificity, 83.3%; positive predictive value, 85.3%; negative predictive value, 96.9%; and positive likelihood ratio, 5.8.

CONCLUSION

HRV in the supine position allowed identifying patients with syncope and cardioinhibitory response with a high negative predictive value and likelihood ratio of 5.8.

Telemetry-derived heart rate variability responses to a physical stressor

Analysis of heart rate variability (HRV) responses to an orthostatic challenge can be used to investigate autonomic control of heart rate, an index of cardiovascular function. HRV is typically assessed using the electrocardiogram (ECG), which can be impractical for use with large population-based studies.

PURPOSE

To assess the validity and reliability of telemetry-derived HRV responses to an orthostatic challenge.

METHODS

Twenty healthy adults (26 + 5 years, 45% male) were tested on three separate mornings. Following 20-min supine rest, R-R intervals were recorded using a telemetric device during three conditions: BASE, TILT and RECOVERY. ECG was simultaneously used on 1 day for validity comparison. Measures of HRV included the following: standard deviation of normal-to-normal intervals (SDNN), the root-mean-square of successive differences (RMSSD) and the low-frequency (LF) and high-frequency (HF) spectral power.

RESULTS

For all parameters, there was excellent agreement between devices for BASE (r = 0·96-0·99), TILT (r = 0·89-1·00) and RECOVERY (r = 0·96-1·00). For the telemetric device, between-day intraclass coefficient values for RMSDD, SDNN and HF were all above the 0·75 criterion for each condition, indicating excellent between-day reliability. For each condition, the reliability coefficient, expressed as a percentage of the mean (RC%), was marginally lower (greater reliability) for RMSDD (RC% 11-13) and SDNN (RC% 10-12) compared to HF (RC% 12-17). However, SDNN did not significantly respond to the orthostatic challenge.

CONCLUSION

Telemetric HRV, particularly RMSDD and HF, can be used to provide a sensitive, valid and reliable assessment of autonomic control of heart rate.

Heart rate variability analysis during head-up tilt test predicts nitroglycerine-induced syncope

Objective

The aim of this study was to determine whether or not heart rate variability (HRV) analysis during the first 20 min of head-up tilt testing could predict whether patients will develop syncope after nitroglycerine administration.

Design

64 patients with previous loss of consciousness underwent head-up tilt testing with the Italian protocol, which involves the administration of nitroglycerine after 20 min of tilt. HRV parameters were analysed from 5 min intervals selected during pretest supine rest (phase 1), the first 5 min (phase 2) and the last 5 min (phase 3) of passive 20 min of tilting, prior to the administration of nitroglycerine. Differences in power (ms²) of the spectral components between the various phases of tilting were calculated for each patient and expressed as Δ.

Results

20 patients (group 1, 9 women, mean age 43.2±24.5 years) had a syncope during tilt testing after nitroglycerine, while the other 44 (group 2, 24 women, mean age 41±20.5 years) did not. In group 1, the HRV spectral parameters high frequency (HF) and total power (TP) had a significant decrement from phases 2 to 3 (p=0.012 and 0.027, respectively), while in group 2 the average HF and TP values did not change. The Δ of spectral parameters between phases 2 and 3 were able to differentiate between the two groups and to predict syncope after nitroglycerine administration (p<0.05).

Conclusions

HRV analysis within the first 20 min of passive tilting demonstrated that patients with nitroglycerine-induced syncope are characterised by a progressive decrement of parasympathetic activity, which does not occur in patients with a negative response to nitroglycerine. If confirmed on a wider population, HRV analysis could replace nitroglycerine administration and shorten the duration of the tilt test.

Baseline heart rate variability in children and adolescents with vasovagal syncope

Purpose

This study aimed to evaluate the autonomic imbalance in syncope by comparing the baseline heart rate variability (HRV) between healthy children and those with vasovagal syncope.

Methods

To characterize the autonomic profile in children experiencing vasovagal syncope, we evaluated the HRV of 23 patients aged 7-18 years and 20 healthy children. These children were divided into preadolescent (<12 years) and adolescent groups. The following time-domain indices were calculated: root mean square of the successive differences (RMSSD); standard deviation of all average R-R intervals (SDNN); and frequency domain indices including high frequency (HF), low frequency (LF), normalized high frequency, normalized low frequency, and low frequency to high frequency ratio (LF/HF).

Results

HRV values were significantly different between healthy children and those with syncope. Student t test indicated significantly higher SNDD values (60.46 ms vs. 37.42 ms, P=0.003) and RMSSD (57.90 ms vs. 26.92 ms, P=0.000) in the patient group than in the control group. In the patient group, RMSSD (80.41 ms vs. 45.89 ms, P=0.015) and normalized HF (61.18 ms vs. 43.19 ms, P=0.022) were significantly higher in adolescents, whereas normalized LF (38.81 ms vs. 56.76 ms, P=0.022) and LF/HF ratio (0.76 vs. 1.89, P=0.041) were significantly lower in adolescents. In contrast, the control group did not have significant differences in HRV values between adolescents and preadolescents.

Conclusion

The results of this study indicated that children with syncope had a decreased sympathetic tone and increased vagal tone compared to healthy children. Additionally, more severe autonomic imbalances possibly occur in adolescents than in preadolescents.

Differences in autonomic balance in patients with cardioinhibitory and vasodepressor type of reflex syncope during head-up tilt test and active standing

OBJECTIVE

To improve the pathophysiological understanding of cardioinhibitory and vasodepressor reflex syncope, by evaluating orthostatic effects on electrical and hemodynamic variables. To unravel the pathogeneses further, we studied these effects during both the passive head-up tilt test and the active standing test.

BACKGROUND

The current knowledge of the compromised autonomic balance in patients with reflex syncope is limited. The orthostatic responses to head-up tilt test in cardioinhibitory and vasodepressor patients differ, suggesting different pathogeneses; however, the more physiological active standing test represents daily life situations better.

METHODS

We included 74 patients; 36 cardioinhibitory and 38 vasodepressor. Patients were compared with respect to vascular hemodynamics and heart rate variability during the change from supine to upright position. Resting electrolytes, brain natriuretic peptide (BNP), pro-atrial natriuretic peptide (pro-ANP), and the C-terminal of pro-vasopressin, copeptin were measured.

RESULTS

Resting systolic blood pressure was higher in cardioinhibitory (117.8 ± 15.7 mmHg) than in vasodepressor patients (109.1 ± 15.3 mmHg, p < 0.001). Changes in heart rate tended to be smaller in cardioinhibitory patients (6.7 ± 9.8 vs. 10.7 ± 8.9 bpm, p = 0.056). Heart rate variability was lower and changed less in cardioinhibitory patients (p < 0.05). Cardioinhibitory patients had higher pro-ANP levels (63.5 ± 18.8 pM) compared to vasodepressor patients (54.2 ± 31.4 pM, p = 0.018). Responses during active standing were attenuated compared to head-up tilt in both groups.

CONCLUSIONS

This study demonstrated that cardioinhibitory patients had higher blood pressure, attenuated hemodynamic responses, and reduced autonomic regulation compared to vasodepressor patients. Furthermore, cardioinhibitory patients showed a sympathetic predominance in their modulation of autonomic responses. Orthostatic responses induced by active standing were modest and did not sufficiently explain potential pathophysiological differences between cardioinhibitory and vasodepressor patients.

Neurocardiogenic syncope in chronic atrioventricular block

We report a 37-year-old man with type I second-degree atrioventricular (AV) block (atypical Wenckebach's periodicity) referred to our department for pacemaker implantation because of an episode of syncope. After exhaustive evaluation, including electrophysiological test, in which Wenckebach's cycles with block within the AV node was demonstrated, syncope was considered to be neurally mediated. Head-up tilt testing with sublingual isosorbide dinitrate was positive. The decrease in atrial rate at the beginning of the vasovagal reaction was not immediately accompanied by a depressed AV node conduction. Only at the moment of syncope did incomplete AV block appear. This observation illustrates (1) a neurally mediated origin of syncope in a patient with chronic AV block, and (2) the different time-course responses of the sinus and AV nodes to autonomic tone.

Predictors of positive head-up tilt test in patients with suspected neurocardiogenic syncope or presyncope

Neurocardiogenic syncope is the most common cause of syncope in patients who present in outpatient clinics. Head-up tilt test (HUT) has been widely used to diagnose neurocardiogenic syncope. However, the HUT does not always produce a positive response in patients with suspected neurocardiogenic syncope. The aim of the present study was to assess the clinical history and characteristics of patients with suspected neurocardiogenic syncope or presyncope who undertook HUT, and to identify prognostic factors of a positive HUT response. During the first phase of HUT, patients were tilted to a 70-degree angle for 30 minutes. If the first phase produced a negative response, the second phase was subsequently performed involving intravenous isoproterenol administration. Of 711 patients, 423 (59.5%) patients showed a positive HUT response. In contrast to previous studies, this study showed that the vasodepressive type (76.6%) was the most common pattern of positive response, and that the rate of positive response during the first phase was low (7.1%). By multivariate analysis, the occurrence of junctional rhythm was found to be a predictor of an impending positive response in HUT (P < 0.001). The shorter time interval between the last episode and HUT was also a predictor of positive response (P = 0.0015). Younger age (P = 0.0003) and a history of physical injury during a syncopal episode (P = 0.019) were found to be associated with a positive response in the first phase of HUT.

[Syncope of unknown origin in patients with permanent auriculoventricular block with an implanted pacemaker. Usefulness of the tilt table test]

Four female patients aged 26 to 71 years, with permanent complete AV heart block and an implanted pacemaker had syncope or presyncope after the pacemaker implantation. As part of the study protocol the tilt table test was done. Neurological disease, arrhythmias, pacemaker syndrome or dysfunction of the stimulation system were ruled out. A head up tilt was performed, isosorbide was used as pharmacological challenge, since the basal test was negative. In three patients this test was positive: in one patient possibly caused by postural orthostatic tachycardia syndrome, and two with neurally mediated syncope. In one patient it was not possible a diagnosis. The head-up tilt test is a useful procedure to identify the etiology of the appearance of syncope or presyncope after a pacemaker implantation in patients with complete and permanent AV block.

Orthostatic hypotension, 2001

Upright posture requires rapid and effective circulatory and neurologic compensations to maintain blood pressure and consciousness. Although it has been recognized over the past 100 years or more that the act of standing may cause hypotension in patients with autonomic dysfunction, only recently several of the pathophysiologic mechanisms resulting in orthostatic intolerance have been discovered. In patients with orthostatic hypotension, failure of reflex vasoconstriction causes pooling of blood in the legs during standing. Not everyone with a postural blood pressure drop requires treatment, nor does everyone with posturally induced symptoms have orthostatic hypotension. This review will discuss current knowledge of a broad, heterogeneous group of disturbances in the autonomic nervous system, each of which is manifested by hypotension, orthostatic intolerance, and often syncope.