Response to beta blockers in patients with neurocardiogenic syncope: how to predict beneficial effects

The Role of the Autonomic Nervous System in Vasovagal Syncope

The mechanism of vasovagal syncope (VVS) is multifaceted and involves a delicate balance within the autonomic nervous system (ANS). This review delves into the complex interplay between the ANS and VVS, elucidating the pivotal role that autonomic imbalance plays in the pathophysiology of this condition. Through a comprehensive exploration of the sympathetic and parasympathetic branches of the ANS, this review provides insights into the mechanisms that underlie VVS. In addition, this article discusses established and emerging research on the management of VVS.

Poincaré Plot Can Be a Useful Tool to Select Potential Responders to Metoprolol Therapy in Children with Vasovagal Syncope

Purpose

To explore the value of the longitudinal axis/transverse axis ratio (L/T) of Poincaré plot in selecting children with vasovagal syncope (VVS) who were suitable for metoprolol therapy.

Patients and Methods

Children with VVS hospitalized in Peking University First Hospital between January 2012 and June 2019 and treated with metoprolol were retrospectively included as the training set, and children with VVS hospitalized between July 2019 and December 2020 were included as the validation set. The sex, age at admission, height, weight, body mass index, course of disease, syncope symptom score before metoprolol treatment, treatment duration, supine heart rate (HR), supine systolic pressure, supine diastolic pressure, peak HR during the head-up tilt test (HUTT), changes of HR during HUTT, hemodynamic response during HUTT, left ventricular ejection fraction, left ventricular fractional shortening and the L/T of Poincaré plot were compared between responders and nonresponders in the training set. Logistic regression analysis was conducted to explore predictors. Receiver operating characteristic curve was utilized to determine the value of the predictors for selecting potential responders. Finally, the value of the predictors was further verified.

Results

In the training set including 105 children, the L/T in responders was distinctly higher than that in nonresponders (P < 0.001), and there was no apparent difference between the two groups in other indexes. The L/T was statistically related to the efficacy of metoprolol (P < 0.001). The L/T >2.7 yielded a sensitivity of 88.2% and a specificity of 82.8% for indicating responders to metoprolol. Taking L/T >2.7 to select potential responders in another 43 children with VVS in the validation set, the sensitivity was 96.6%, specificity 71.4%, and accuracy 88.4%.

Conclusion

The L/T of Poincaré plot >2.7 can be a useful tool to select potential responders to metoprolol therapy in children with VVS.

Identifying drug-related attributes to personalise antihypertensive agents: the outcome report of patients receiving metoprolol therapy

Background

Currently, numerous antihypertensive drugs from different pharmacological classes are available; however, blood pressure control is achieved in only less than a third of patients treated for hypertension. Moreover, providing optimal and personalised treatment for hypertension is challenging. Therefore, in this study, we propose a ‘drug-related attributes’ sensitive spectrum. This novel concept can assist clinicians in selecting an optimal antihypertensive drug and improve blood pressure control after examining the attributes of a patient.

Methods

We collected clinical data on attributes related to hypertension and its therapy of inpatients from West China Hospital who received metoprolol therapy and constructed the sensitive spectrum using data-visualisation tools.

Results

Our analysis revealed that haematocrit, haemoglobin, serum creatinine, serum cystatin C, serum urea, age, sex, systolic pressure, diastolic pressure, pulse pressure, and heart rate are metoprolol-related attributes.

Conclusion

Our study showed that all metoprolol-related attributes identified are reasonable and helpful in improving the personalisation of metoprolol therapy. The proposed drug-related attributes spectrum can help personalise antihypertensive medication. Moreover, data-visualisation tools can be effectively used to mine the drug-related attributes sensitive spectrum.

Management of vasovagal syncope

Vasovagal syncope (VVS) is a very common form of fainting. Treatment begins with patient education about the mechanism of fainting, and the non-lethal nature of vasovagal syncope. In this article, we review several non-pharmacological approaches that form the foundation of our current treatments. These include increases in dietary salt and water intake, the use of compression garments, physical counter-maneuvers and tilt-training. When these approaches are inadequate, medications can sometimes be effective. While the evidence base for the pharmacological treatment of VVS is modest, recent trial data have found drugs to be useful in placebo-controlled randomized trials. For select patients, and those patients more refractory to medications, procedural treatments may be an option. In this review, we discuss the current state of evidence for the non-pharmacological and pharmacological treatments for VVS, as well as some novel, emerging therapies for VVS.

High Remission Rates in Vasovagal Syncope: Systematic Review and Meta-Analysis of Observational and Randomized Studies

OBJECTIVES

The aims of this study were to quantify the degree of improvement in vasovagal syncope after assessment and to identify predictive factors.

BACKGROUND

No treatments for vasovagal syncope have been proved effective, but patients in all prospective studies appear to show a reduction in the likelihood of fainting.

METHODS

A systematic review and meta-analysis was performed of studies published from 1993 through 2013. Inclusion criteria were: 1) vasovagal syncope frequency in the preceding 1 to 2 years; and 2) the proportion of subjects with syncope in at least the first follow-up year. Random-effects methods were used.

RESULTS

Of 338 screened studies, 17 were analyzed, with a mean of 112 subjects (range 9 to 511 subjects). In the preceding epoch, 97% of subjects fainted, with 2.6 ± 1.0 syncopal spells per year. In the follow-up year, the proportion of patients with ≥1 syncope recurrence was 677 of 1,912 (35.4%), and in the meta-analysis, the proportion of subjects fainting was only 0.44 (95% confidence interval: 0.41 to 0.46; p < 0.001). Subjects in larger studies were less likely to faint than those in randomized trials (relative risk: 0.35 vs. 0.55; p = 0.004). The probabilities of ≥1 syncope recurrence in the observational versus randomized studies were 0.30 (95% confidence interval: 0.24 to 0.37) and 0.54 (95% confidence interval: 0.46 to 0.62), respectively (p < 0.001). None of the degree of blinding, type of intervention, age, sex, and number of recent faints predicted the probability of syncope recurrence. Heterogeneity was very high in all analyses (I² = 60% to 96%).

CONCLUSIONS

The spontaneous remission rate in highly symptomatic syncope patients is high, and remission occurs in all types of studies. Improvement was more likely in larger and observational studies.

Age-dependence of relative change in circulating epinephrine and norepinephrine concentrations during tilt-induced vasovagal syncope

BACKGROUND

Although vasovagal syncope (VVS) is preceded by a surge of circulating catecholamines (epinephrine [Epi] and norepinephrine [NE]) of adrenal/renal and synaptic origin, prevention of VVS with β-adrenergic blockade has been ineffective except in "older" VVS patients.

OBJECTIVE

We hypothesized that age-related differences of β-blocker effect may be due in part to differences in the relative magnitudes of Epi and NE release during an evolving faint, specifically, greater Epi/NE ratio in younger fainters compared to older patients. To assess this hypothesis, we measured changes in Epi/NE ratios in younger (<40 years) vs older (≥40 years) patients during head-up tilt-table test-induced VVS.

METHODS

The study comprised 29 patients (12 patients ≥40 years [mean 56 ± 10.7 years] and 17 patients <40 years mean 25 ± 5.7 years]) with recurrent suspected VVS in whom 70° head-up tilt testing reproduced symptoms. Arterial Epi and NE concentrations were measured at baseline (supine), 2 minutes of head-up tilt, and syncope.

RESULTS

Baseline Epi and NE concentrations and the Epi/NE ratio did not differ in younger and older groups (Epi: 90 ± 65 pg/mL vs 70 ± 32 pg/mL; NE: 226 ± 122 pg/mL vs 244 ± 183 pg/mL). However, Epi/NE ratio increased to a greater extent in younger fainters during head-up tilt and tended to be greater in younger patients at both 2 minutes (<40: 1.02 ± 1.29 vs ≥40: 0.40 ± 0.27, P = .11) and at symptoms (<40: 2.6 ± 1.26 vs ≥40: 1.6 ± 0.71, P = .03). At symptoms, Epi/NE ratio ≥2.5 was observed in 9 of 17 younger patients vs 1 of 12 older patients (P = .02).

CONCLUSION

Epi/NE ratios tend to be greater in younger fainters, a finding that may account in part for the observation that β-blocker therapy is less effective in reducing VVS susceptibility in younger individuals.

Prevention of Syncope Trial (POST): a randomized, placebo-controlled study of metoprolol in the prevention of vasovagal syncope

BACKGROUND

Previous studies that assessed the effects of beta-blockers in preventing vasovagal syncope provided mixed results. Our goal was to determine whether treatment with metoprolol reduces the risk of syncope in patients with vasovagal syncope.

METHODS AND RESULTS

The multicenter Prevention of Syncope Trial (POST) was a randomized, placebo-controlled, double-blind, trial designed to assess the effects of metoprolol in vasovagal syncope over a 1-year treatment period. Two prespecified analyses included the relationships of age and initial tilt-test results to any benefit from metoprolol. All patients had >2 syncopal spells and a positive tilt test. Randomization was stratified according to ages <42 and > or =42 years. Patients received either metoprolol or matching placebo at highest-tolerated doses from 25 to 200 mg daily. The main outcome measure was the first recurrence of syncope. A total of 208 patients (mean age 42+/-18 years) with a median of 9 syncopal spells over a median of 11 years were randomized, 108 to receive metoprolol and 100 to the placebo group. There were 75 patients with > or =1 recurrence of syncope. The likelihood of recurrent syncope was not significantly different between groups. Neither the age of the patient nor the need for isoproterenol to produce a positive tilt test predicted subsequent significant benefit from metoprolol.

CONCLUSIONS

Metoprolol was not effective in preventing vasovagal syncope in the study population.

Fluoxetine vs. propranolol in the treatment of vasovagal syncope: a prospective, randomized, placebo-controlled study

AIMS

To compare the therapeutic efficacy of placebo, propranolol, and fluoxetine in patients with vasovagal syncope (VVS).

METHODS AND RESULTS

Ninety-six consecutive patients with VVS were randomized to treatment with placebo, propranolol, or fluoxetine and followed-up for 6 months. Before and during treatment, they reported their syncopal and presyncopal episodes and graded their well-being, expressed as the general evaluation of life, general activities, and everyday activities (each scaled from 1 = very good to 5 = very bad). Two patients refused follow-up. Among the remaining 94, no difference between groups was observed regarding the distribution of time of vasovagal events (syncopes or presyncopes) during follow-up (log-rank test). No difference was also observed when syncopes and presyncopes were assessed separately. Eighteen patients discontinued therapy. Among the remaining 76 ('on-treatment' analysis), the mean time to a vasovagal episode (syncope or presyncope) was significantly longer in the fluoxetine group when compared with the two other groups (log-rank test, P < 0.05). A significant difference in favour of fluoxetine was also observed regarding presyncopes. The difference between groups regarding the syncope-free period was not significant. During therapy, patients' well-being was improved (decreased) only in the fluoxetine-group (13.4 +/- 0.7 vs. 15.4 +/- 0.9 before treatment, P < 0.01).

CONCLUSION

Fluoxetine seems to be equivalent to propranolol and placebo in the treatment of VVS. However, it improves patients' well-being and might be more effective in reducing presyncopes and total vasovagal events in some patients with recurrent VVS.

Prognostic value of head-up tilt test with intravenous beta-blocker administration in assessing the efficacy of therapy in patients with vasovagal syncope

BACKGROUND

Although beta-blockers are frequently used in order to prevent the recurrence of vasovagal syncope, the efficacy of this treatment is difficult to determine.

OBJECTIVES

To determine if the result of a tilt test with an intravenously administered beta-blocker can predict the long-term efficacy of beta-blockade.

METHODS

The study group consisted of 62 patients (29 females, mean age 32.8 +/- 12.3 years and 33 males, mean age 35.9 +/- 18.2 years) with at least two syncopal episodes during 6 months preceding the positive tilt test. After the baseline tilt test, propranolol (0.1 mg/kg BW) was administered intravenously and the tilt test was repeated. Beta-blockade was considered effective if the subsequent tilt test proved negative (complete efficacy) or if the time until the occurrence of syncope at the subsequent tilt test was longer compared to the baseline test (partial efficacy). All the patients were put on continuous propranolol treatment and were followed up for a period of 1 year or until the time when syncope recurred.

RESULTS

Intravenously administered propranolol prevented (n = 33) or delayed (n = 18) the occurrence of syncope at the tilt test in 51 patients (82%), while it was found ineffective in the remaining 11 patients (18%). During the 8.6 +/- 6.7 months (range 1-14) of the follow-up period, the syncope recurred in 20 patients (32%), with 13 patients (25%) in the group where intravenously administered propranolol proved effective versus 7 patients (64%) for whom intravenously administered propranolol did not prevent syncope during the tilt test (P < 0.015). The survival analysis with respect to the recurrence of syncope revealed a significant correlation between the results of the tilt test with intravenously administered propranolol and the efficacy of the long-term beta-blocker therapy (P < 0.003). There were no significant differences with respect to the predictive value of the tilt test with propranolol between the patients showing complete and partial propranolol efficacy (ns), while significant differences were observed between these two groups on one hand and the patients in whom intravenously administered propranolol was found ineffective on the other (P < 0.04 and P < 0.002, respectively).

CONCLUSIONS

Intravenous propranolol prevents tilt-induced syncope in a significant percentage of patients. The results of the tilt tests combined with the administration of propranolol predict the efficacy of a continuous propranolol treatment. Both complete and partial propranolol efficacy at tilt test can successfully identify those patients who will benefit from continuous beta blockade.

What is the Optimal Increase in Resting Heart Rate with Low Dose Isoproterenol Infusion for Tilt-Induced Vasovagal Response?

Isoproterenol is widely used as a provocative medium for vasovagal responses during tilt testing. Dose of isoproterenol infusion is generally titrated empirically by increase in resting heart rate before tilt up. To determine the optimal increase in resting heart rate with isoproterenol for tilt-induced vasovagal responses, we studied 97 consecutive patients with unexplained syncope. After the end of a negative baseline tilt (80 degrees for 30 min), the isoproterenol tilt was performed using one of two protocols: two-stage isoproterenol-tilt protocol, with doses of 0.01 and 0.02 microg/kg per min for 10 min each, or one-stage isoproterenol-tilt protocol, with a dose of 1 or 2 microg/min for 10 min. The resting heart rate increase was defined as a percentage increase in the resting heart rate after isoproterenol infusion, compared to the baseline heart rate before the tilt test. In 117 tilt procedures, 28 (93%) of the 30 positive responses occurred with a resting heart rate increase of > or = 21%. With the resting heart rate increase of 60 and 100%, 18 (60%) and 27 (90%) positive responses were observed, respectively. In conclusion, the minimum resting heart rate increase of > or = 21% was required to provoke a vasovagal response during subsequent isoproterenol-tilt (80 degrees for 10 min). Preferably, heart rate should be increased to 60-100% by isoproterenol titration before tilting.

Strategy for the management of vasovagal syncope

The disorders of autonomic control associated with orthostatic intolerance are a diverse group of syndromes that can result in syncope and near-syncope. A basic understanding of the pathophysiology of these disorders is essential to diagnosis and proper treatment. It is especially important to recognise the difference between the effect of prolonged upright posture on a failing autonomic nervous system (a hyposensitive or dysautonomic response) and the vasovagal response (which may be a hypersensitive response). Vasovagal syncope is the most common abnormal response to upright posture and occurs in all age groups. The advent of tilt table testing has helped define a population with an objective finding during provocative testing that has enabled researchers to study the mechanism of vasovagal syncope and to evaluate the efficacy of treatments. In most patients, vasovagal syncope occurs infrequently and only under exceptional circumstances and treatment is not needed. Treatment may be indicated in patients with recurrent syncope or with syncope that has been associated with physical injury or potential occupational hazard. Based on study data, patients with vasovagal syncope can now be risk stratified into a high-risk group likely to have recurrent syncope and a low-risk group. Many patients with vasovagal syncope can be effectively treated with education, reassurance and a simple increase in dietary salt and fluid intake. In others, treatment involves removal or avoidance of agents that predispose to hypotension or dehydration. However, when these measures fail to prevent the recurrence of symptoms, pharmacological therapy is usually recommended. Although many pharmacological agents have been proposed and/or demonstrated to be effective based on nonrandomised clinical trials, there is a remarkable absence of data from large prospective clinical trials. Data from randomised placebo-controlled studies support the efficacy of beta-blockers, midodrine, serotonin reuptake inhibitors and ACE inhibitors. There is also considerable clinical experience and a consensus suggesting that fludrocortisone is effective. Encouraging new data suggest that a programme involving tilt training can effectively prevent vasovagal syncope. For patients with recurrent vasovagal syncope that is refractory to these treatments, implantation of a permanent pacemaker with specialised sensing/pacing algorithms appears to be effective. A number of larger clinical trials are underway which should help further define the efficacy of a number of different treatments for vasovagal syncope.

Epinephrine, vasodilation and hemoconcentration in syncopal, healthy men and women

Healthy young people may become syncopal during standing, head up tilt (HUT) or lower body negative pressure (LBNP). To evaluate why this happens we measured hormonal indices of autonomic activity along with arterial pressure (AP), heart rate (HR), stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR) and measures of plasma volume. Three groups of normal volunteers (n = 56) were studied supine, before and during increasing levels of orthostatic stress: slow onset, low level, lower body negative pressure (LBNP) (Group 1), 70 degrees head up tilt (HUT) (Group 2) or rapid onset, high level, LBNP (Group 3). In all groups, syncopal subjects demonstrated a decline in TPR that paralleled the decline in AP over the last 40 s of orthostatic stress. Ten to twenty seconds after the decline in TPR. HR also started to decline but SV increased, resulting in a net increase of CO during the same period. Plasma volume (PV, calculated from change in hematocrit) declined in both syncopal and nonsyncopal subjects to a level commensurate with the stress, i.e. Group 3 > Group 2 > Group 1. The rate of decline of PV, calculated from the change in PV divided by the time of stress, was greater (p < 0.01) in syncopal than in nonsyncopal subjects. When changes in vasoactive hormones were normalized by time of stress, increases in norepinephrine (p < 0.012, Groups 2 and 3) and epinephrine (p < 0.025, Group 2) were greater and increases in plasma renin activity were smaller (p < 0.05, Group 2) in syncopal than in nonsyncopal subjects. We conclude that the presyncopal decline in blood pressure in otherwise healthy young people resulted from declining peripheral resistance associated with plateauing norepinephrine and plasma renin activity, rising epinephrine and rising blood viscosity. The increased hemoconcentration probably reflects increased rate of venous pooling rather than rate of plasma filtration and, together with cardiovascular effects of imbalances in norepinephrine, epinephrine and plasma renin activity may provide afferent information leading to syncope.

Neurohormonal profile before and after beta-blockade in patients with neurocardiogenic syncope

Our objective was to evaluate the effects of beta-blockers on the neurohormonal profile, particularly vasopressin (VP) release, in vasovagal syncope and to gain further insight on the pathophysiology of this syndrome. Patients (< or =75 years) with no cardiovascular, neurological disorders, or contraindications to the use of isoproterenol or beta-blockers and being explored for unexplained syncope were included. An 80 degrees HUT was performed under identical conditions. After a 25-min period of passive tilt, isoproterenol was infused at a rate of 1-5 microg/mn if required. Two groups matched for age and sex were considered: a HUT-positive and a HUT-negative group. The HUT-positive group was then given beta-blockers, subsequently reassessed, and divided into two subgroups: alpha beta-blocker nonresponder group and a beta-blocker responder group. Blood samples for assays of norepinephrine (NE), epinephrine (E), and VP were taken at baseline and the end of the procedure. In all, 44 subjects entered the study, 22 in each group. The HUT-positive group exhibited an obvious lesser increase in plasma NE and a clear-cut rise in plasma E and VP compared to the HUT-negative group (P < 0.05). Even though no patient in the HUT-positive group reported recurrent symptoms under treatment, the second HUT could distinguish two subgroups: a beta-blocker nonresponder group (n = 12) whose HUT remained positive and a beta-blocker responder group (n = 10) whose HUT was normalized. The time course of plasma E and VP during the second HUT was similar to that for the HUT-positive and HUT-negative groups. In conclusion, the efficacy of beta-blockers is associated not only with a reduction of the sympathoadrenal stimulation seen in vasovagal syncope but also with a lower release of VP suggesting that low-pressure baroreceptors might be involved in VP release.