Pathophysiology of reflex syncope: A review

Cardiac Geometry and Function in Patients with Reflex Syncope

Reflex syncope (RS) is the most prevalent form of syncope, yet its pathophysiology and clinical presentation are not well understood. Despite controversy, the 'ventricular theory' remains the most plausible hypothesis to explain RS in susceptible patients. Certain assumptions regarding the geometry and function of the heart are essential in supporting this theory. Given these considerations, the goal of this review was to try to integrate data on heart morphology and function in a phenotype of a patient susceptible to RS. Previous research suggests that a small left ventricle and atria, in addition to a normo- or hypercontractile myocardium, predispose to more syncopal events. These findings have been confirmed in different subsets of patients, including those with small heart and chronic fatigue syndrome, highlighting common pathophysiologic pathways in these subgroups of population. Heart geometry and function seem to play a role in different treatment strategies for RS patients, including the administration of medications, pacing, and possibly cardioneural ablation. In addition, parameters related to the geometry of the heart chambers and of the electrical activation of the heart seem to have predictive value for syncope recurrence. These parameters could be included in the future and improve the accuracy of predictive models for RS.

Effectiveness analysis of deceleration capacity and traditional heart rate variability in diagnosing vasovagal syncope

Background

Vasovagal syncope (VVS) is a prevalent medical condition with a lack of efficient methods for its detection.

Aim

This study aimed to explore an objective clinical indicator in diagnosing VVS.

Methods

The retrospective analysis involved clinical data of 243 syncope patients from 1 June 2020 to 31 July 2023. Among them, 108 patients had a negative result in the tilt test (TTT), while the remaining 135 patients had a positive result in the TTT. Relevant statistical methods were utilized to examine the correlation between VVS and different indicators of heart rate variability.

Results

After screening, 354 patients being considered for VVS were evaluated, resulting in a final sample size of 243. Sex, age, deceleration capacity (DC), and standard deviation of all normal-to-normal intervals (SDNNs) were the variables that showed statistical significance between the TTT(-) group and the TTT(+) group. Independent risk factors identified by multivariate logistic regression were DC [odds ratio (OR) 1.710, 95% confidence interval (CI) 1.388-2.106, P < 0.001] and SDNN (OR 1.033, 95% CI 1.018-1.049, P < 0.001). Comparing the groups, receiver operating characteristic analysis revealed a notable distinction in both DC and SDNN [the respective areas under the curve were 0.789 (95% CI 0.730-0.848) and 0.702 (95% CI 0.637-0.767); the cutoff values were 7.15 and 131.42; P < 0.001, respectively].

Conclusion

In summary, DC can function as an impartial and easily accessible clinical marker for differentiating VVS. A value exceeding 7.15 ms might suggest a higher likelihood of syncope.

Normal baseline cardiac autonomic function and increased pupillary parasympathetic tone in patients with vasovagal syncope

It is controversial whether people with vasovagal syncope (VVS) have abnormal autonomic responses at baseline and whether specific diagnostic manoeuvres have a diagnostic value. We investigated whether the pupillary light reflex and cardiac autonomic tests can be used to identify autonomic dysfunction in volunteers with a medical history of VVS. The study groups included 128 healthy volunteers, of whom 31 reported a history of typical VVS. The right pupil was evaluated using an automated, commercial infra-red pupillometer under strict conditions. In addition to miosis and mydriasis kinetics, pupil diameters were measured. Heart rate variability at rest and heart rate changes to standing were quantified with high-resolution electrocardiography and designated software. The demographic and clinical characteristics of both groups were statistically similar. Average constriction velocity (ACV) was significantly higher in VVS patients following a univariate analysis (3.83 ± 0.59 vs. 3.56 ± 0.73 mm/s, p = 0.042) and after correcting for potential confounders (p = 0.049). All other pupillometric and heart rate indices were comparable between groups. Patients with a history of VVS depict pupillary parasympathetic overactivity in response to light stimuli, manifested as increased ACV. The prognostic implications of this finding and the significance of using this simple clinical tool to identify patients who are at risk for developing frequent episodes of VVS or physical injuries following a syncope merits further study.

Vasovagal syncope: An overview of pathophysiological mechanisms

Syncope is a short-term transient loss of consciousness, characterized by rapid onset and complete spontaneous recovery. According to the 2018 European Society of Cardiology guidelines, three different types of syncope have been identified. However, all forms of syncope share a common final pathophysiological event, global cerebral hypoperfusion, which results from the inability of the circulatory system to maintain blood pressure at the level required to efficiently supply blood to the brain. The vasovagal syncope (VVS) is the most common form of syncope. Although, VVS is generally harmless, its frequent occurrence can negatively affect quality of life and increase the risk of adverse events. The pathophysiological mechanisms underlying VVS remain obscure. The multifaceted nature of VVS presents a veritable challenge to understanding this condition and developing preventative strategies. Thus, the aim of this review was to discuss the factors contributing to the pathogenesis of VVS and provide guidance for future research.

Syncope with autonomic dysfunction assessed with the Thai-COMPASS 31 questionnaire

Introduction

Alteration of autonomic function is the main pathophysiology of most types of syncope, including syncope due to orthostatic hypotension and neurally mediated syncope or reflex syncope. The aim of this study was to investigate the difference in autonomic dysfunction assessed between each type of syncope and to evaluate the association between the severity of autonomic dysfunction and the recurrence of syncope.

Methodology

Three hundred and six participants, including 195 syncope and 109 healthy control participants, were recruited to this retrospective cohort study. Autonomic function was initially assessed by the Thai version of the Composite Autonomic Symptom Score 31 (COMPASS 31), a self-administered questionnaire.

Result

According to one hundred and ninety-five syncope participants, twenty-three participants had syncope due to orthostatic hypotension, 61 had reflex syncope, 79 had presyncope, and 32 had unclassified syncope. Participants in the syncope due to orthostatic hypotension and reflex syncope groups had significantly higher COMPASS 31 scores than the control and presyncope groups, of which the syncope due to orthostatic hypotension group had the highest score. The cutoff score of 32.9 for COMPASS 31 had a sensitivity of 50.0% and a specificity of 81.9% to predict the recurrence of syncope.

Conclusion

The degree of autonomic dysfunction, which was assessed by COMPASS 31, could vary depending on the syncope type. The COMPASS 31, which is an easy-to-use self-administered questionnaire utilized for the assessment of autonomic symptoms and function, was a helpful tool for classifying some types of syncope and predicting the recurrence of syncope, which could lead to appropriate further management.

The Role of Adenosine and Its Degradation Enzymes - Adenosinedeaminase and Adenosinekinase in Pathogenesis of Vasovagal Syncope

INTRODUCTION

Adenosine is mediator regulating physiological and pathological processes in organism. It probably plays a role in pathogenesis of vasovagal syncopes (VVS), too. Adenosine, its receptors and degradation enzymes- adenosinedeaminase (ADA) and adenosinekinase (ADK), are called the adenosinergic system.

AIM

We aimed to evaluate serum levels of adenosine, ADA and ADK in patients with tilt-induced VVS and compare them to tlit-negative controls. Secondary aim was to compare the levels between the types of VVS and correlate them with hemodynamic parameters.

SUBJECTS AND METHODS

Altogether 132 individuals were involved in this study (age 39,88±15,64 years, 51 males). All patients underwent head up tilt test (HUTT) in differential diagnosis of syncope. Blood sampling was performed before and after HUTT. Baseline and stimulated serum levels of adenosine, ADA and ADK were evaluated by ELISA method.

RESULTS

HUTT was positive in 91 patients (HUTT+), 41 individuals were negative (HUTT-). HUTT+ patients had higher baseline and stimulated adenosine levels, when compared to HUTT- population. The rise in adenosine was higher in HUTT+ group. On the other hand, the increase of ADA was significantly higher in HUTT- subjects. Among HUTT+ group, the highest adenosine was found during vasodepressoric VVS.

CONCLUSION

Adenosinergic system may play role in pathogenesis of VVS. Patients with VVS have higher adenosine levels, that may be caused by attenuated degradation. Adenosine seems to be involved predominantly in vasodepressoric type of VVS. Further research evaluating complex function of adenosinergic system in these patients is needed.

Long-Term COVID 19 Sequelae in Adolescents: the Overlap with Orthostatic Intolerance and ME/CFS

Purpose of Review

To discuss emerging understandings of adolescent long COVID or post-COVID-19 conditions, including proposed clinical definitions, common symptoms, epidemiology, overlaps with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and orthostatic intolerance, and preliminary guidance on management.

Recent Findings

The recent World Health Organization clinical case definition of post-COVID-19 condition requires a history of probable or confirmed SARS-CoV-2 infection, with symptoms starting within 3 months of the onset of COVID-19. Symptoms must last for at least 2 months and cannot be explained by an alternative diagnosis. Common symptoms of the post-COVID-19 condition include, but are not limited to, fatigue, shortness of breath, and cognitive dysfunction. These symptoms generally have an impact on everyday functioning. The incidence of prolonged symptoms following SARS-CoV-2 infection has proven challenging to define, but it is now clear that those with relatively mild initial infections, without severe initial respiratory disease or end-organ injury, can still develop chronic impairments, with symptoms that overlap with conditions like ME/CFS (profound fatigue, unrefreshing sleep, post-exertional malaise, cognitive dysfunction, and orthostatic intolerance).

Summary

We do not yet have a clear understanding of the mechanisms by which individuals develop post-COVID-19 conditions. There may be several distinct types of long COVID that require different treatments. At this point, there is no single pharmacologic agent to effectively treat all symptoms. Because some presentations of post-COVID-19 conditions mimic disorders such as ME/CFS, treatment guidelines for this and related conditions can be helpful for managing post-COVID-19 symptoms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40124-022-00261-4.

Management strategies for vasovagal syncope

Vasovagal syncope (VVS) (or neurocardiogenic syncope) is a common clinical condition that is challenging to both physicians and patients alike. Severe episodes of recurrent syncope can result in physical injury as well as psychological distress. This article provides a brief overview of current management strategies and a detailed overview of therapeutic modalities such as closed loop stimulation (CLS) and cardioneuroablation (CNA).

Prospective analysis of syncope/pre-syncope in a tertiary paediatric orthopaedic fracture outpatient clinic

BACKGROUND

The incidence of vasovagal syncope (VVS) precipitated by medical procedures such as blood donation is quoted as between 0.13% and 4.17%. Vasovagal events have been observed to occur following cast removal at our paediatric orthopaedic clinic; however, there is no available information in the existing literature regarding incidence or risk factors. This study aims to identify the incidence and demographic traits of patients experiencing syncopal events following cast removal.

METHODS

Over a 12-month period, paediatric patients experiencing a syncopal or pre-syncopal event during an outpatient appointment for cast removal were prospectively enrolled into the study. Basic demographic data were recorded, as well as injury and procedure details and a description of the event. Statistical analysis as well as calculation of incidence of vasovagal events were performed.

RESULTS

A total of 6078 patients presented for cast removal in the 12-month period. Twenty syncopal or pre-syncopal events were recorded. Incidence was calculated as 0.32%. Mean patient age was 10.8 years. Male : female ratio was 2.3:1. Mean body mass index (BMI) was 20.08, with a trend for higher prevalence of males under the 50th BMI percentile-for-age. The mean time post-injury was 31.4 days. Ninety-five percent of patients were being treated for an upper limb injury and 30% had injuries that had been treated surgically. There were no associated secondary complications or injuries.

CONCLUSIONS

Incidence of VVS following cast removal is comparable to the values quoted in literature for other medical procedures. Demographic data of our cohort suggested that those who experienced VVS were predominantly young males of lower-than-average BMI.

"Complex" Vasovagal Syncope: A Zebra Among Horses

Background: Vasovagal syncope (VVS) occurs due to cerebral hypoperfusion from a fall in blood pressure, with accompanying bradycardia in most cases. Seizure and/or asystole may accompany VVS, though their prediction within the VVS cohort remains elusive.

Objective: To further characterize VVS and to find predictive features of “complex” VVS (defined as VVS associated with seizures and/or asystole).

Methods: We reviewed medical records of all patients who were referred for orthostatic intolerance and had a definite VVS during the head-up tilt table testing (HUTT). The following variables were recorded: cardiovascular indices during HUTT, autonomic testing results, and semiology of asystole and/or seizure when present. Simple frequency and correlation analysis were performed using the ANOVA.

Results: A total of 78 independent VVS were recorded in 60 patients of which 24% were not preceded by presyncope. Vasodepressor (45%) and mixed (38%) VVS were the most prevalent types. Eighteen (23%) were complex VVS; five had an associated seizure (SySz), nine were accompanied by asystole (SyAs), and four had both (SySzAs). Males were significantly more likely to have complex VVS. Mean asystole duration was somewhat longer in the SyAsSz group. The severity of bradycardia significantly correlated with complex VVS and was a predictor of SySz. Autonomic abnormalities were frequent but did not distinguish the two VVS subgroups. Seizures had multiple distinguishing features from those typically associated with epileptic seizures.

Conclusions: The underlying pathophysiologic mechanisms of complex VVS remain unclear, but the severity of cerebral hypoperfusion due to bradycardia likely plays a key role in seizure generation.

Neurohormones in the Pathophysiology of Vasovagal Syncope in Adults

Vasovagal syncope (VVS) is the most common cause of syncope across all age groups. Nonetheless, despite its clinical importance and considerable research effort over many years, the pathophysiology of VVS remains incompletely understood. In this regard, numerous studies have been undertaken in an attempt to improve insight into the evolution of VVS episodes and many of these studies have examined neurohormonal changes that occur during the progression of VVS events primarily using the head-up tilt table testing model. In this regard, the most consistent finding is a marked increase in epinephrine (Epi) spillover into the circulation beginning at an early stage as VVS evolves. Reported alterations of circulating norepinephrine (NE), on the other hand, have been more variable. Plasma concentrations of other vasoactive agents have been reported to exhibit more variable changes during a VVS event, and for the most part change somewhat later, but in some instances the changes are quite marked. The neurohormones that have drawn the most attention include arginine vasopressin [AVP], adrenomedullin, to a lesser extent brain and atrial natriuretic peptides (BNP, ANP), opioids, endothelin-1 (ET-1) and serotonin. However, whether some or all of these diverse agents contribute directly to VVS pathophysiology or are principally a compensatory response to an evolving hemodynamic crisis is as yet uncertain. The goal of this communication is to summarize key reported neurohumoral findings in VVS, and endeavor to ascertain how they may contribute to observed hemodynamic alterations during VVS.

Is there any link between vitamin D deficiency and vasovagal syncope?

BACKGROUND

This study aimed to investigate serum 25[OH]D levels between patients with vasovagal syncope (VVS) diagnosed with head-up tilt table test (HUTT) and age-matched healthy people.

METHODS

The study included 75 consecutive patients (32.3 ± 10.7 years), who presented with syncope and underwent HUTT and 52 healthy controls (32.9 ± 14.1 years). HUTT patients were divided into two groups according to whether there was syncope response to the test. Patients underwent cardiac, psychiatric, and neurological investigation. Serum 25[OH]D levels were measured by chemiluminescent microparticle immunoassay method.

RESULTS

There was no difference between the two groups in terms of age, gender, body mass index (BMI), echocardiographic findings (P > .05). Mean serum 25[OH]D (24.5 ± 6.3 vs 20.1 ± 8.8 ng/mL, P = .003) and vitamin B12 levels (436.4 ± 199.2 vs 363.1 ± 107.6 pg/mL, P = .009) was lower in syncope patients when compared to the control group. In correlation analyses, syncope was shown as correlated with the vitamin D (r = -264, P = .003) and vitamin B12 levels (r = -233, P = .009). But, multivariate regression analyses showed that only vitamin D increased risk of syncope [OR: 0.946, 95% CI (0.901-0.994)]. There was no difference in terms of age, gender, BMI, echocardiographic findings between the in HUTT positive (n = 45) and negative groups (n = 29). Only vitamin D level was significantly lower in HUTT positive group (17.5 ± 7.7 vs 24.4 ± 9.1 ng/mL, P = .002). There was no difference among in the vasovagal subgroups in terms of vitamin D level and other features.

CONCLUSION

Vitamin D and B12 levels were reasonably low in syncope patients, but especially low Vitamin D levels were associated with VVS diagnosed in HUTT.

Late-onset multiple acyl-CoA dehydrogenase deficiency with cardiac syncope: A case report

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an uncommon autosomal recessive disorder of mitochondrial fatty acid beta-oxidation. Syncope is a transient loss of consciousness due to acute global cerebral hypoperfusion. Late-onset MADD with syncope has not been reported previously.

CASE SUMMARY

We report a 17-year-old girl with exercise intolerance and muscle weakness. She felt palpitation and shortness of breath after short bouts of exercise. She also suffered from a transient loss of consciousness many times. Muscle biopsy showed lipid storage. Genetic mutation analysis indicated a compound heterozygous mutation c.250G > A (p.A84T) and c.872T > G (p.V291G) in the ETFDH gene. The results of Holter electrocardiogram monitoring showed supraventricular tachycardia when the patient experienced a loss of consciousness. After treatment with riboflavin and carnitine, muscle weakness and palpitation symptoms improved rapidly. No loss of consciousness occurred, and the Holter electrocardiogram monitoring was normal.

CONCLUSION

Late-onset MADD with supraventricular tachycardia can cause cardiac syncope. Carnitine and riboflavin supplement were beneficial for treating the late-onset MADD with cardiac syncope. Attention should be paid to the prevention of cardiac syncope when diagnosing late-onset MADD.

Swallow (deglutition) syncope: An evaluation of swallowing-induced heart rate and hemodynamic changes in affected patients and control subjects

BACKGROUND

Syncope triggered by swallowing is a well-known but uncommon condition that has been the focus of case reports but is otherwise largely unstudied. To better understand swallow syncope we examined heart rate (HR) and blood pressure (BP) changes during swallowing in clinically suspected swallow syncope patients and asymptomatic control subjects.

METHODS

The study population comprised four individuals with a history suggesting swallow syncope (three men, 53 ± 14.9 years) and 15 (nine men, 46 ± 17.1 years, P = NS vs patients) asymptomatic volunteer control subjects. Studies in all individuals comprised noninvasive beat-to-beat HR and BP measurement during swallowing 150 mL of cold liquid while standing. Additional tests in swallow syncope patients included: active standing, Valsalva maneuver, carotid sinus massage (CSM), and head-up tilt (HUT).

RESULTS

Swallowing resulted in a greater decrease of both HR (-22 ± 22.1 vs -3 ± 11.7 beats/minute [bpm]; P = 0.045) and BP (-22 ± 17.4 vs - 2 ± 11.8; P = 0.036) in swallow syncope patients than in controls. Further, in swallow syncope patients the time to lowest HR and BP differed (9 ± 5.5 vs 19 ± 7.2 seconds; P = 0.02), suggesting that both cardioinhibitory (CI) and vasodepressor (VD) mechanisms are present but operate independently. Other autonomic studies were normal in swallow syncope patients except for CSM pause more than 3 seconds in two patients.

CONCLUSION

Swallow syncope is associated with transient and temporally independent CI and VD features, consistent with reflex syncope. Potentially, a swallowing test during autonomic evaluation may be useful to unmask relative magnitudes of CI and VD responses, thereby facilitating treatment strategy decisions.