Genetics of vasovagal syncope

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.

Genetic Analysis of Cardiac Syncope-Related Genes in Korean Patients with Recurrent Neurally Mediated Syncope

Neurally mediated syncope (NMS) is a common clinical problem. The underlying genetic factors of NMS remain controversial. We hypothesized that cardiac syncope-related genes may contribute to NMS in patients with previous frequent syncopal episodes and/or a family history of syncope. A total of 54 consecutive patients diagnosed with NMS were prospectively enrolled between 2013 and 2016. Inclusion criteria were more than five syncopal episodes with a family history of syncope (n = 17) or more than five syncopal episodes with no family history of syncope (n = 37). Ninety-eight cardiac syncope-related genes (channelopathy: 43 genes, cardiomyopathy: 50 genes, primary pulmonary hypertension: 5 genes) were screened by exome sequencing. All identified variants were classified according to the standards and guidelines by the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Of the 54 patients, 17 patients (31.5%) had a family history of syncope. Two patients (3.7%) had pathogenic and likely pathogenic variants (PV/LPV) in cardiac syncope-related genes TTN and MYH7. We investigated genetic variation in patients with frequent NMS with a positive family history of syncope in Korea. PV/LPVs in genes related to cardiomyopathy were associated with recurrent NMS in Korean patients. Closer follow-up of these patients might be needed.

Predictor of Syncopal Recurrence in Children With Vasovagal Syncope Treated With Metoprolol

Objective

To explore the predictors for syncopal recurrence in a pediatric population with vasovagal syncope (VVS) treated with metoprolol.

Study Design

This study was conducted retrospectively among children suffering from VVS with or without syncopal recurrence. Data on the detailed medical history and auxiliary examinations were obtained from the electronic medical records. The risk factors for syncopal recurrence were studied by cox regression analyses and the corresponding best cutoff values were determined using receiver operating characteristic analysis. Kaplan-Meier curves were plotted to determine the trends of the syncopal recurrence-free survival rate.

Results

Forty-two consecutive VVS children were enrolled in the study. At the end of a median follow-up duration of 9.0 (4.8, 19.1) months, 12 patients (29%) experienced ≥1 syncopal episode. Cox regression analyses revealed that the number of previous syncopal episodes before treatment was a risk factor for syncopal recurrence (hazard ratio = 1.027, 95% confidence interval 1.009 - 1.045, P = 0.003). Moreover, 4 previous syncopal episodes were certified as the best cutoff value, and the Kaplan-Meier curves showed that the syncopal recurrence-free survival rate over time in patients with > 4 previous syncopal episodes was significantly lower than that in patients with ≤4 episodes (P = 0.019 at the log-rank test).

Conclusion

In a pediatric population with VVS while on the treatment of metoprolol, the number of previous syncopal episodes before treatment played a significant role in predicting syncopal recurrence.

Association of Polymorphisms in Endothelin-1 and Endothelin Receptor A Genes With Vasovagal Syncope

The endothelin system may play a role in the pathogenesis of vasovagal syncope (VVS) because it is implicated in blood pressure regulation. We hypothesized that endothelin-related genetic polymorphisms might modulate susceptibility to VVS. This study aimed to evaluate the possible influence of endothelin-1 (EDN1) and endothelin receptor A (EDNRA) gene variants on the occurrence of tilt-induced VVS and autonomic nervous system activity during the head-up tilt test (HUT). Results were expressed as mean ± SEM. In 254 patients with recurrent syncope (age 45.33±1.22 years, 94 males, 160 females), heart rate variability (HRV) was measured during HUT. EDN1 rs5370 G>T and EDNRA rs5333 T>C gene polymorphisms were assessed using high-resolution melting analysis. There was no statistically significant association between polymorphisms EDN1 rs5370 and EDNRA rs5333 and positivity of HUT or hemodynamic types of VVS. Patients with GT or TT genotypes at the rs5370 locus of the EDN1 had significantly higher values of high-frequency (HF) and the standard deviation of the average NN intervals at the time of the syncope, and they tended to have lower low-frequency (LF) and LF/HF ratio when compared to homozygotes (GG). No statistically significant differences were found in HRV parameters concerning the EDNRA rs5333 genotypes. Our findings suggest the potential role of EDN1 rs5370 variants in regulating autonomic nervous activity and pathogenesis of VVS.

Towards Understanding the Genetic Nature of Vasovagal Syncope

Syncope, defined as a transient loss of consciousness caused by transient global cerebral hypoperfusion, affects 30-40% of humans during their lifetime. Vasovagal syncope (VVS) is the most common cause of syncope, the etiology of which is still unclear. This review summarizes data on the genetics of VVS, describing the inheritance pattern of the disorder, candidate gene association studies and genome-wide studies. According to this evidence, VVS is a complex disorder, which can be caused by the interplay between genetic factors, whose contribution varies from monogenic Mendelian inheritance to polygenic inherited predisposition, and external factors affecting the monogenic (resulting in incomplete penetrance) and polygenic syncope types.

Genetic markers of vasovagal syncope

Vasovagal syncope may have a genetic predisposition. It has a high prevalence in some families, and children of a fainting parent are more likely to faint than those without a parent who faints. Having two fainting parents or a fainting twin increases the likelihood even further. Several genotypes appear to associate with the phenotype of positive tilt tests, but the control subjects are usually those who faint and have negative tilt tests. Twin studies, highly focused genome-wide association studies, and copy number variation studies all suggest there are loci in the genome that associate with vasovagal syncope, although the specific genes, pathways, and proteins are unknown. A recent multigenerational kindred candidate gene study identified 3 genes that associate with vasovagal syncope. The best evidence to date is for central signaling genes involving serotonin and dopamine. Genome-wide association studies to date have not yet been helpful. Our understanding of the genetic correlates of vasovagal syncope leaves ample opportunity for future work.

SCN8A heterozygous variants are associated with anoxic-epileptic seizures

Anoxic-epileptic seizures (AES) are rare outcomes of common childhood reflex anoxic syncope that trigger a true epileptic seizure. The term AES was coined by Stephenson in 1983, to differentiate these events from convulsive syncopes and the more common reflex anoxic syncopes. A genetic susceptibility for AES has been postulated; but, its molecular basis has up to now been elusive. We report here two illustrative cases and show the association of de novo SCN8A variants and AES. One of them had focal or generalized seizures and autonomic symptoms triggered by orthostatism; the second had breath-holding spells triggered by pain or exercise leading to tonic-clonic seizures; both had repeatedly normal EEGs and a family history of reflex syncope. The data of three additional AES patients further suggest, for the first time, a link between SCN8A pathogenic variants and AES. The neurodevelopment of four patients was abnormal. Four of the five SCN8A mutations observed here were previously described in patients with seizure disorders. Seizures responded particularly well to sodium channel blockers. Our observation enriches the spectrum of seizures linked with SCN8A pathogenic variants.

The Search for the Genes of Vasovagal Syncope

Only humans faint, and not all do so. Syncope tends to recur, and the predisposition to syncope can persist over many decades. Observations such as these have suggested that there may be a genetic predisposition to vasovagal syncope. It seems to have a high prevalence in some families; having a parent who faints increases the likelihood of an offspring fainting, and this is increased even further if both biological parents faint. Numerous studies have correlated a number of genotypes with positive tilt tests. However, the control subjects are usually those who faint, but have negative tilt tests, making the conclusions about association with the clinical phenotype less certain. Twin studies, highly focused genome-wide association studies, and gene duplicate studies all suggest there are sites in the genome that associate with vasovagal syncope, although the specific genes, pathways, and proteins are unknown. A recent large, candidate gene study of kindreds with high, multigenerational prevalence of the vasovagal syncope identified 3 genes that associate with vasovagal syncope. Our understanding of the genetic correlates of vasovagal syncope is in its infancy, with much to be understood.

Remote Limb Ischemic Preconditioning Attenuates Cerebrovascular Depression During Sinusoidal Galvanic Vestibular Stimulation via α1-Adrenoceptor-Protein Kinase Cε-Endothelial NO Synthase Pathway in Rats

BACKGROUND

Vasovagal syncope (VVS) is characterized by hypotension and bradycardia followed by lowering of cerebral blood flow. Remote limb ischemic preconditioning (RIPC) is well documented to provide cardio- and neuroprotection as well as to improve cerebral blood flow. We hypothesized that RIPC will provide protection against VVS-induced hypotension, bradycardia, and cerebral hypoperfusion. Second, because endothelial nitric oxide synthase has been reported as a mediator of cerebral blood flow control, we hypothesized that the mechanism by which RIPC primes the vasculature against VVS is via the α1-adrenoceptor-protein kinase Cε-endothelial nitric oxide synthase pathway.

METHODS AND RESULTS

We utilized sinusoidal galvanic vestibular stimulation in rats as a model of VVS. RIPC attenuated the lowerings of mean arterial pressure, heart rate, and cerebral blood flow caused by sinusoidal galvanic vestibular stimulation, as well as improving behavior during, and recovery after, stimulation. RIPC induced elevated serum norepinephrine, increased expression of brain α1-adrenoceptors, and reduced brain expression of norepinephrine transporter 1. Antagonizing adrenoceptors and norepinephrine transporter 1 prevented RIPC protection of cerebral perfusion during sinusoidal galvanic vestibular stimulation.

CONCLUSIONS

Taken together, this study indicates that RIPC may be a potential therapy that can prevent VVS pathophysiology, decrease syncopal episodes, and reduce the injuries associated with syncopal falls. Furthermore, the α1-adrenoceptor-protein kinase Cε-endothelial nitric oxide synthase pathway may be a therapeutic target for regulating changes in cerebral blood flow.

The management of vasovagal syncope

Vasovagal syncope, or the "common faint", is the most common cause of syncope. Although it is considered a benign condition, there is a significant economic burden and significant impact on quality of life in patients with recurrent syncope, particularly in older adults. Typical vasovagal syncope usually occurs in young adults, and can often be diagnosed on the basis of history, in the absence of structural heart disease. Atypical vasovagal syncope, which is more common in older adults, can be more difficult to diagnose, however. In atypical vasovagal syncope, there is often a short or absent prodrome, and amnesia for loss of consciousness is common and it can, therefore, often be misdiagnosed, for example as falls. A more standardized approach to the diagnosis and management of patients presenting with syncope or unexplained falls is required, and it is anticipated that the number of Syncope Units will increase. Treatment of vasovagal syncope is largely conservative; however, medical or device therapy may be required when syncope is severe and refractory to conservative treatment, as there is significant impact on quality of life and it can be associated with injury. The aim of this article is to provide an overview of the diagnosis and management of vasovagal syncope.

Genome-Wide Association Study of Copy Number Variations in Patients with Familial Neurocardiogenic Syncope

Neurocardiogenic syncope (NCS) is the most frequent type of syncope characterized by a self-limited episode of systemic hypotension. In this study, we conducted the first genome-wide association study testing copy number variations for association with NCS. Study population consisted of 107 consecutive patients with recurrent syncope and positive head-up tilt table testing. Four families with NCS were selected for CNV analysis. Affymetrix GeneChip(®) SNP 6.0 array was used for CNV analysis. Data and statistical analysis were performed with Affymetrix genotyping console 4.0 and GraphPad Prism v6. Positive family history of NCS was present in 19.6 % (n = 21) in our study population (n = 107). Twenty-six CNV regions were found to be significantly altered in families with NCS (P < 0.05). Several CNVs were identified in families with NCS. Further studies comprising wider study population are required to determine the effect of these variations on NCS development.

Slower lower limb blood pooling in young women with orthostatic intolerance

NEW FINDINGS

What is the central question of this study? Orthostatic stress is mostly caused by venous blood pooling in the lower limbs. Venous distension elicits sympathetic responses, and increased distension speed enhances the cardiovascular response. We examine whether lower limb blood pooling rate during lower body negative pressure is linked to orthostatic intolerance. What is the main finding and its importance? A similar amount of blood was pooled in the lower limb, but at a slower rate in women who developed signs of orthostatic intolerance. The difference in blood pooling rate increased with orthostatic stress and was most prominent at a presyncope-inducing level of lower body negative pressure. The findings have implications for the pathophysiology as well as treatment of orthostatic intolerance. Vasovagal syncope is common in young women, but its aetiology remains elusive. Orthostatic stress-induced lower limb blood pooling is linked with central hypovolaemia and baroreceptor unloading. Venous distension in the arm elicits a sympathetic response, which is enhanced with more rapid distension. Our aim was to study both the amount and the speed of lower limb pooling during orthostatic stress and its effects on compensatory mechanisms to maintain cardiovascular homeostasis in women with orthostatic intolerance. Twenty-seven healthy women, aged 20-27 years, were subjected to a lower body negative pressure (LBNP) of 11-44 mmHg. Five women developed symptoms of vasovagal syncope (orthostatic intolerant) and were compared with the remaining women, who tolerated LBNP well (orthostatic tolerant). Lower limb blood pooling, blood flow and compensatory mobilization of venous capacitance blood were measured. Lower body negative pressure induced equal lower limb blood pooling in both groups, but at a slower rate in orthostatic intolerant women (e.g. time to 50% of total blood pooling, orthostatic intolerant 44 ± 7 s and orthostatic tolerant 26 ± 2 s; P < 0.001). At presyncope-inducing LBNP, the mobilization of venous capacitance blood was both reduced (P < 0.05) and much slower in orthostatic intolerant women (P = 0.0007). Orthostatic intolerant women elicited blunted arterial vasoconstriction at low-grade LBNP, activating only cardiopulmonary baroreceptors, while orthostatic tolerant women responded with apparent vasoconstriction (P < 0.0001). In conclusion, slower lower limb blood pooling could contribute to orthostatic intolerance in women. Mobilization of venous capacitance blood from the peripheral to the central circulation was both slower and decreased; furthermore, reduced cardiopulmonary baroreceptor sensitivity was found in women who developed orthostatic intolerance. Further studies including women who experience syncope in daily life are needed.

Prolonged ventricular asystole: a rare adverse effect of hydrocodone use

Patient: Female, 56

Final Diagnosis: Ventricular asystole

Symptoms: Dizziness, headache, near-syncope, weakness

Medication: —

Clinical Procedure: —

Specialty: Cardiology