Pharmacological norepinephrine transporter inhibition for the prevention of vasovagal syncope in young and adult subjects: A systematic review and meta-analysis

Serotonin and vasovagal syncope

PURPOSE

The goal of this manuscript was to review the biological and clinical evidence that serotonin neurotransmission might play an important role in the  physiology and treatment of vasovagal syncope.

METHODS

The authors reviewed PubMed and handsearches of secondary sources for papers related to the Bezold-Jarisch reflex and serotonin, the plausible involvement of the Bezold-Jarisch reflex in vasovagal syncope, and three lines of clinical evidence involving serotonin and the syncope.

RESULTS

The Bezold-Jarisch reflex was first described following the infusion of veratrum alkaloids into animals in the 19th century. The reflex is triggered by serotonin stimulation chemoreceptors and mechanoreceptors in the the left ventricle. The afferent component of the reflex is carried by unmyelinated type C vagal nerve fibers, which results in parasympathetic efferent stimulation that causes bradycardia. The similarity of the combination of hypotension and bradycardia in the Bezold-Jarisch reflex and in vasovagal syncope led to the suggestion that the reflex was the cause of the syndrome.  Three lines of evidence implicate the serotonin 5HT3 receptors in the heart in the reflex. There is genetic and physiologic evidence for the serotonin 5HT1A and 5HT3 receptors and the serotonin reuptake transporter (SERT). Acute blockade of SERT induces vasovagal syncope in humans undergoing head-up tilt table testing, and SERT inhibition reduces hypotension and bradycardia during spinal anaesthesia. Finally, three randomized clinical trials of SERT inhibitors uniformly reported that they significantly reduce the likelihood of vasovagal syncope recurrences.

CONCLUSION

Multiple lines of evidence implicate serotonin neurotransmission in the cause of vasovagal syncope.

Twenty-five years of research on syncope

Over the last 25 years, the Europace journal has greatly contributed to dissemination of research and knowledge in the field of syncope. More than 400 manuscripts have been published in the journal. They undoubtedly improved our understanding of syncope. This symptom is now clearly differentiated from other forms of transient loss of consciousness. The critical role of vasodepression and/or cardioinhibition as final mechanisms of reflex syncope is emphasized. Current diagnostic approach sharply separates between cardiac and autonomic pathways. Physiologic insights have been translated, through rigorously designed clinical trials, into non-pharmacological or pharmacological interventions and interventional therapies. The following manuscript is intended to give the reader the current state of the art of knowledge of syncope by highlighting landmark contributions of the Europace journal.

The Seventh Prevention of Syncope Trial (POST VII)-A randomized clinical trial of atomoxetine for the prevention of vasovagal syncope: Rationale and study design

BACKGROUND

Vasovagal syncope (VVS) is common, recurs, and is associated with markedly reduced quality of life, anxiety, and frequent injuries. The few pharmacological therapies for VVS proven to have a moderate benefit in reducing recurrences are limited to patients without coexisting conditions such as hypertension or heart failure. Although there is some data to suggest Atomoxetine, a norepinephrine reuptake transport inhibitor (NET), may be a promising treatment option, an adequately powered randomized placebo-controlled trial is needed.

STUDY DESIGN

POST VII is a multicenter, randomized, double-blind, placebo-controlled, crossover study that will randomize 180 patients with VVS and at least 2 syncopal spells in the preceding year to a target daily dose of atomoxetine 80 mg daily or to a matching placebo, with an observation period of 6 months in each phase and with a 1-week washout period between phases. The primary end point will be the proportion of patients with at least one syncope recurrence in each arm analyzed with an intention-to-treat approach. The secondary end points include total syncope burden, quality of life, cost, and cost-effectiveness.

POWER CALCULATIONS

Assuming a 33% relative risk reduction in syncope recurrence with atomoxetine, and a dropout rate of 16%, the enrollment of 180 patients will give an 85% power of reaching a positive conclusion about atomoxetine, with P = .05.

CONCLUSIONS

This will be the first adequately powered trial to determine whether atomoxetine is effective in preventing VVS. If proven effective, atomoxetine might become the first-line pharmacological treatment for recurrent VVS.

Effects of Atomoxetine for the Treatment of Neurogenic Orthostatic Hypotension in Patients With Alpha-synucleinopathies: A Systematic Review of Randomized Controlled Trials and a Focus-Group Discussion

BACKGROUND AND PURPOSE

Neurogenic orthostatic hypotension (nOH) is one of the most important nonmotor symptoms in patients with α-synucleinopathies. Atomoxetine is a selective norepinephrine transporter blocker that is a treatment option for nOH. This systematic review and expert focus-group study was designed to obtain evidence from published data and clinical experiences of Korean movement-disorder specialists about the efficacy and safety of atomoxetine for the pharmacological treatment of nOH in patients with α-synucleinopathies.

METHODS

The study comprised a systematic review and a focus-group discussion with clinicians. For the systematic review, multiple comprehensive databases including MEDLINE, Embase, Cochrane Library, CINAHL, PsycInfo, and KoreaMed were searched to retrieve articles that assessed the outcomes of atomoxetine therapy. A focus-group discussion was additionally performed to solicit opinions from experts with experience in managing nOH.

RESULTS

The literature review process yielded only four randomized controlled trials on atomoxetine matching the inclusion criteria. Atomoxetine effectively increased systolic blood pressure and improved OH-related symptoms as monotherapy or in combination with other drugs. Its effects were pronounced in cases with central autonomic failure, including multiple-system atrophy (MSA). Atomoxetine might be a safe monotherapy regarding the risk of supine hypertension.

CONCLUSIONS

Atomoxetine is an effective and safe option for short-term nOH management, which could be more evident in patients with central autonomic dysfunction such as MSA. However, there is a paucity of evidence in the literature, and data from the focus-group discussion were inadequate, and so further investigation is warranted.

Atomoxetine for suppression of vasovagal syncope

OBJECTIVE

Vasovagal syncope (VVS) is a common clinical condition with few effective medical therapies. The study aimed to evaluate the effectiveness of atomoxetine in suppressing syncope in patients with recurrent VVS.

METHODS

This was a retrospective, open-label, observational case series of 12 patients taking atomoxetine for suppression of recurrent vasovagal syncope. We compared syncope frequency in the 1 year before atomoxetine and while subjects were taking atomoxetine. We used novel applications of the Poisson distribution to describe the results as a collection of n = 1 studies.

RESULTS

There were 12 subjects, eight female, with a mean age 47 ± 22 years and a mean Calgary Syncope Symptom Score of 2 (diagnostic of vasovagal syncope). The patients received a mean dose of atomoxetine of 66 ± 16 mg (1.06 ± 0.21 mg/kg). The mean follow-up period was 1.21 ± 1.01 years. While taking atomoxetine, 11/12 patients appeared to improve and 7/12 had no syncope in follow-up (p = 0.0046). The annualized syncope frequency decreased from a median 5.5 (IQR 4, 6.75) syncope per year to 0 (IQR 0, 0.88) syncope per year (p = 0.002, Wilcoxon rank-sum test). According to the Poisson distribution, 7/12 subjects significantly improved with p values of < 0.0001 to 0.0235, 3/12 did not faint but had too brief follow-up times to detect significance, and 2/12 did not improve significantly.

CONCLUSIONS

In this case series, atomoxetine was a promising oral agent for the prevention of vasovagal syncope. The Poisson distribution permits individual patient-level assessment of improvement and detects insufficient follow-up despite apparent improvement.

Current approach to the treatment of vasovagal syncope in adults

Vasovagal syncope (VVS) is the most common cause of transient loss of consciousness. Although not associated with mortality, it causes injuries, reduces quality of life, and is associated with anxiety and depression. The European and North American cardiac societies recently published syncope clinical practice guidelines. Most patients with VVS do well after specialist evaluation, reassurance and education. Adequate hydration, increased salt intake when not contraindicated, and careful withdrawal of diuretics and specific hypotension-inducing drugs are a reasonable initial strategy. Physical counterpressure maneuvers might be helpful but can be of limited efficacy in older patients and those with short or no prodromes. Orthostatic training lacks long term efficacy and is troubled by non-compliance. Yoga might be helpful, although the biomedical mechanism is unknown. Almost a third of VVS patients continue to faint despite these conservative measures. Metoprolol was not helpful in a pivotal randomized clinical trial. Fludrocortisone and midodrine significantly reduce syncope recurrences with tolerable side effects, when titrated to target doses. Pacing therapy with specialized sensors appears promising in carefully selected population who have not responded conservative measures. Cardioneuroablation may be helpful but has not been studied in a formal clinical trial.

Prevention of Blood Donation-related Vasovagal Response by Applied Muscle Tension: a Meta-analysis

Objective

Vasovagal reaction (VVR) is an adverse reaction to blood donation. Applied muscle tension (AMT) has been reported to reduce the probability of VVR during blood donation; however, the results have been controversial. We therefore conducted a meta-analysis to systematically evaluate the effect of AMT in reducing VVR.

Methods

We searched six major databases using “applied muscle tension” and “blood donation-related vasovagal response” as keywords. Relevant articles published in English or Chinese between 1 January 2000 and 30 June 2021 were included in the analysis. The quality of the included articles was evaluated and publication bias was assessed by forest and funnel plots and by Egger's test.

Results

Fifty-one articles were identified, of which six were included according to the pre-defined inclusion and exclusion criteria. A fixed-effects model was adopted for effect size combination and revealed a relative risk of 0.52 (95% confidence interval 0.40 to 0.67). The AMT group was superior to the control in terms of VVR prevention. A funnel plot and Egger's test suggested that the findings were accurate and reliable with low publication bias.

Conclusion

AMT could effectively reduce VVR during blood donation. Further multicenter studies with large sample sizes are needed to confirm these results.

Neurally Mediated Syncope in Children and Adolescents: An Updated Narrative Review

Syncope presents a proportion of up to 25% among children and adolescents and accounts for 0.9% of emergency room visits. Its most frequent aetiology is neurally mediated syncope, which includes vasovagal syncope and orthostatic hypotension. Up to 70% of the paediatric population with reflex syncope is female. There are usually precipitating factors and prodromes. This mini-review will discuss the particularities of the clinical presentation, diagnosis, modified Calgary score, indications and accuracy of the head-up tilt test, classification, and pathophysiology in four sequential phases. Prognostic data and the non-pharmacological and pharmacological approaches will also be reviewed and differences regarding reflex syncope in adults will be discussed.

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).

Atomoxetine as an adjunct to nonpharmacological treatments for preventing vasovagal attacks in patients with recurrent vasovagal syncope: A pilot randomized-controlled trial

BACKGROUND

Despite the reduced quality of life in patients with recurrent vasovagal syncope (VVS), pharmacologic treatment options remain limited. Studies indicate that norepinephrine reuptake inhibition reduces tilt-induced syncope/pre-syncope. This study aimed to evaluate the effects of atomoxetine on syncopal/pre-syncopal episodes in patients with recurrent VVS.

METHODS

In a placebo-controlled trial, we randomized patients with newly diagnosed VVS who experienced ≥3 syncopal episodes in the past three months to receive either atomoxetine (20 mg daily for two weeks followed by 40 mg daily for two weeks) or placebo. The primary endpoint was the combined number of syncopal and pre-syncopal episodes.

RESULTS

Among 843 patients initially screened, 46 were randomized (N = 23 in each group) and reevaluated at one and three months. Compared to placebo, atomoxetine significantly reduced the primary endpoint after three months (P < 0.001). In the atomoxetine arm, the median time to first pre-syncopal episode was 55 days (95% confidence interval (CI): 41.21-68.79), while this was 27 days (95% CI: 14.48-39.52) for the placebo group (P < 0.001). In a subgroup analysis of patients with systolic blood pressure < 110 mmHg, atomoxetine reduced the primary endpoint, and the number of syncopal and pre-syncopal episodes after one and three months. In this subgroup, the median time to first pre-syncopal attack was 56 days in the atomoxetine group as opposed to 9 days in the placebo group.

CONCLUSIONS

In this pilot study, the promising effects of atomoxetine in reducing syncopal/pre-syncopal episodes in recurrent VVS, especially with low blood pressure phenotype, warrant the conduction of future randomized trials.

New insights in diagnostics and therapies in syncope: a novel approach to non-cardiac syncope

This article aims to give advice on how to identify and manage patients with syncope who are at risk of severe outcomes, that is, at risk of trauma, potentially life-threatening episodes or frequent recurrences reducing quality of life. The first step of syncope diagnostic assessment is to identify patients with cardiac syncope, and once established, these patients must receive the adequate mechanism-specific treatment. If cardiac syncope is unlikely, reflex (neurally mediated) syncope and orthostatic hypotension are the most frequent causes of transient loss of consciousness. For these presentations, efficacy of therapy is largely determined by the mechanism of syncope rather than its aetiology or clinical features. The identified mechanism of syncope should be carefully assessed and assigned either to hypotensive or bradycardic phenotype, which will determine the choice of therapy (counteracting hypotension or counteracting bradycardia). The results of recent trials indicate that 'mechanism-specific therapy' is highly effective in preventing recurrences. Established mechanism-specific treatment strategies include withdrawal of hypotensive drugs, applying fludrocortisone and midodrine for the hypotensive phenotype and cardiac pacing in the bradycardic phenotype.

Non-Pharmacological and Pharmacological Management of Cardiac Dysautonomia Syndromes

Vasovagal syncope, postural orthostatic tachycardia syndrome, and inappropriate sinus tachycardia comprise a heterogenous group of common autonomic disorders that are associated with significant symptoms that impair quality of life. Clinical management of these disorders should prioritize conservative non-pharmacological therapies and consider incorporating pharmacological agents for recurrences. The selection and titration of medications may be complicated by the occurrence of potentially overlapping pathophysiological variants, differences in specific clinical presentations, and commonly associated comorbidities. However, with appropriate long-term management and specialist input, most patients note both symptomatic improvement and functional restoration over time.