Effect of beta blockers on the time to first syncope recurrence in patients after a positive isoproterenol tilt table test

Biomarkers and Hemodynamic Parameters in the Diagnosis and Treatment of Children with Postural Tachycardia Syndrome and Vasovagal Syncope

In children, vasovagal syncope and postural tachycardia syndrome constitute the major types of orthostatic intolerance. The clinical characteristics of postural tachycardia syndrome and vasovagal syncope are similar but their treatments differ. Therefore, their differential diagnosis is important to guide the correct treatment. Therapeutic methods vary in patients with the same diagnosis because of different pathomechanisms. Hence, in patients with vasovagal syncope or postural tachycardia syndrome, routine treatments have an unsatisfactory efficacy. However, biomarkers could increase the therapeutic efficacy significantly, allowing for an accurate and detailed assessment of patients and leading to improved therapeutic effects. In the present review, we aimed to summarize the current state of research into biomarkers for distinguishing the diagnosis of pediatric vasovagal syncope from that of postural tachycardia syndrome. We also discuss the biomarkers that predict treatment outcomes during personalized therapy for each subtype.

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.

Unusual Cases of Syncope in the Pediatric Age Group

Syncope is common in the pediatric population and occurs in up to 15 percent of children prior to the end of adolescence. While the etiology of syncope in children is often benign and the majority of cases can be explained by isolated changes in vasomotor tone, a thorough evaluation is warranted to rule out more serious, life-threatening causes of syncope. Here, we present three atypical cases of syncope: a young judo player with recurrent syncope and dizziness, a teenage boy with syncopal episodes always preceded by stretching, and a child who experienced urticaria before losing consciousness. Herein, we review the pathophysiology, diagnosis, and management of syncope in children and adolescents.

Managing the military patient with syncope

Syncope is a relatively common occurrence in military populations. It is defined as a transient loss of consciousness due to global cerebral hypoperfusion, characterised by a rapid onset, short duration and a spontaneous and complete recovery. While the symptom of syncope is easily elicited, discovering the mechanism can be more problematic and may require a plethora of diagnostic tests. The aim of this paper is to review current evidence pertaining to the classification, investigation and management of syncope, from a military perspective. Emphasis is placed on assisting primary healthcare professionals in the assessment and management of syncope, in the UK and on operations, while providing explicit guidance on risk. The occupational limitations required in safely managing patients with syncope are stressed along with the potential long-term limitations.

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.

Management of vasovagal syncope: 2004

Vasovagal syncope is a common disorder that affects at least 20% of people at some time in their lives. Probably half of these patients faint recurrently; for many this causes physical trauma, a substantial reduction in quality of life, and difficulties with driving, employment and education. The last 15 years have seen striking advances in diagnostic approaches and prognostic understanding. A number of physiological, pharmacological and electrical therapies have been developed and tested to various degrees in patients. These include counterpressure manoeuvres, salt and fluid recommendations, and attempted treatment with fludrocortisone, midodrine, beta-blockers, serotonin reuptake inhibitors, and permanent pacemakers. This review highlights the most important of these advances and suggests strategies for managing this often difficult problem.

Poor diagnostic performance of tilt testing in hypertensive patients with unexplained syncope

Syncope is a common condition. Tilt testing with sublingual nitroglycerin (TT-TNT) provides a test with good specificity and positivity rate in young and old patients. Its use in hypertensive patients with unexplained syncope has not been validated. The aims of this study were to evaluate the positivity rate, specificity and tolerability of TT-TNT in hypertensive patients with unexplained syncope. Five hundred and ten subjects (mean age 55 years) were enrolled, 388 patients with unexplained syncope (73 hypertensive and 315 normotensive) and 122 controls (59 hypertensive and 63 normotensive). All subjects underwent TT-TNT. The responses were classified as positive, negative or exaggerated (aspecific). In hypertensive patients, the usual hypotensive therapy was taken on the day of the test. In hypertensive controls, the positive responses were higher than in normotensives (19% vs 6%, P<0.001). The overall specificity was 81% in hypertensives and 94% in normotensives. The positivity rate was significantly lower in hypertensives (55% vs 72%, P<0.03). There was no significant difference between young patients and patients >65 years. TT was well tolerated, and no serious side effects occurred. TT potentiated with TNT has a lower positivity rate and specificity in hypertensive than in normotensive patients with syncope.

Treatment of neurally mediated reflex syncope

Neurally mediated reflex syncope, more commonly known as vasovagal syncope (VVS), remains the most common cause of transient loss of consciousness and syncope in all age groups. Most evidence assessing treatment of VVS derived from randomized clinical trials is limited. Multiple modalities of both nonpharmacologic and pharmacologic strategies have been tested, with conflicting results. The treatment of VVS has been directed toward interventions that interrupt the reflex response at different levels, hypothetically preventing the onset of syncope. This article reviews the available evidence of the different nonpharmacologic and pharmacologic therapies available for the treatment of recurrent VVS.

Use of implantable loop recorders to unravel the cause of unexplained syncope

Syncope is a symptom of many underlying disease states, which range from the relatively benign to the life threatening. There are numerous investigations done for patients with recurrent unexplained syncope which may have very low yield when it comes to making a definitive diagnosis. Recently, the implantable loop recorder (ILR) for continuous monitoring of the cardiac rhythm has been launched in India. This review will briefly discuss these current available strategies and focus on the usefulness of an ILR in the definitive diagnosis and treatment of patients with a recurrent unexplained syncope.

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.

The Management of Vasovagal Syncope in a Patient with Brugada Syndrome

Vasovagal syncope is the most common cause of the neurally mediated reflex syncopes. A higher susceptibility to vasovagal syncope has been reported in patients with Brugada syndrome (BrS) and may be caused by associated autonomic dysfunction. It is unclear what risk vasovagal syncope confers to patients with BrS. This article reviews the pathophysiology of vasovagal syncope and autonomic dysfunction in patients with BrS and its association with BrS, treatment options for patients with BrS with vasovagal syncope, specific therapies and those that may be harmful in patients with BrS, and potential therapies and monitoring for patients with BrS with vasovagal syncope.

Are treatments for vasovagal syncope effective? A meta-analysis

BACKGROUND

Therapies used to treat vaso-vagal syncope (VVS) recurrence have not been proven effective in single studies.

METHODS

Comprehensive search of PubMed, EMBASE and Cochrane Central databases of published trials was done. Randomized or non-randomized studies, comparing the intervention of interest to control group(s), with the endpoint of spontaneous recurrence or syncope on head-up tilt test, were included. Data were extracted on an intention-to-treat basis. Study heterogeneity was analyzed by Cochran's Q statistics. A random-effect analysis was used.

RESULTS

α-adrenergic agonists were found effective (n=400, OR 0.19, CI 0.06-0.62, p<0.05) in preventing VVS recurrence. β-blockers were not found to be effective when only randomized studies comparing β-blockers to non-pharmacologic agents were assessed (9 studies, n=583, OR 0.48, CI 0.22-1.04, p=0.06). Tilt-training had no effect when only randomized studies were considered (4 studies, n=298, OR 0.47, CI 0.21-1.05, p=0.07). Selective serotonin reuptake inhibitors were found effective (n=131, OR 0.28, CI 0.10-0.74, p<0.05), though the analysis contained only 2 studies. Pacemakers were found effective in preventing syncope recurrence when all studies were analyzed (n=463, OR 0.13, CI 0.05-0.36, p<0.05). However, studies comparing active pacemaker to sensing mode only did not show benefit (3 studies, n=162, OR 0.45, CI 0.09-2.14, p=0.32).

CONCLUSIONS

This meta-analysis highlights the totality of evidence for commonly used medications used to treat VVS, and the requirement for larger, double-blind, placebo controlled trials with longer follow-up.

Neurocardiogenic syncope: mechanisms, evaluation and treatment

Syncope is the abrupt and transient loss of consciousness due to a temporary reduction in cerebral blood flow, associated with an absence of postural tone, followed by a rapid and usually complete recovery. It may result from several possible etiologies, ranging from the benign to the potentially fatal. Neurocardiogenic (vasovagal) syncope is the most common of a group of neurally mediated syncopes, characterized by a sudden failure of autonomic regulatory mechanisms to maintain adequate blood pressure and, occasionally, heart rate, to sustain cerebral perfusion and consciousness. The diagnosis may be suggested by a characteristic history and by exclusion of other causes of syncope; however, in some cases, upright tilt table testing may be required to provoke typical hemodynamic responses. Cardiologists and cardiac electrophysiologists are frequently expected to manage patients with suspected neurocardiogenic syncope. The following review aims to provide a basic framework for understanding its pathophysiology, clinical presentations, diagnosis and treatment.

Evaluation and Management of Syncope

Context

Syncope is a commonly encountered by primary care physicians and cardiologists. Etiology is frequently not apparent, and patients may undergo unnecessary tests. Treatment must be tailored to the likely etiology. Complexities of diagnosis and treatment often warrant referral to a specialist.

Objective

To highlight the evolving recommendations for managing syncope in a clinically and cost effective manner.

Evidence Acquisition

An electronic literature search was undertaken of the Medline database from January 1996 to April 2006, using the Medical Subject Heading syncope, defibrillators, pacemakers, echocardiogram, cardiomyopathy, long QT syndrome, Arrhythmogenic right ventricular dysplasia, and Brugada syndrome. Abstracts and titles were reviewed to identify English-language trials. Bibliographies from the references as well as scientific statements from the Heart Rhythm Society, American Heart Association, and American College of Cardiology were reviewed.

Evidence Synthesis

A methodical approach to syncope can improve diagnosis, limit testing, and identify patients at risk of fatal outcome. A thorough history, physical exam and electrocardiogram are critical to the initial diagnosis. Presence of heart disease determines the extent of work-up and treatment. A trans-thoracic echocardiogram should be performed in patients with an unclear diagnosis and a positive cardiac history or an abnormal ECG. Ventricular arrhythmias are the most common cause of syncope in patients with structural heart disease. Patients with an ejection fraction less than 30 percent should receive an implantable defibrillator with few exceptions. An electrophysiology study may assist risk stratification in syncopal patients with borderline ventricular function. In patients without structural heart disease, the presence of a well defined arrhythmia syndrome consistent with a genetically determined risk of sudden death must be sought. The 12-lead electrocardiogram, family history and clinical presentation will identify most high-risk patients. Patients without structural heart disease can often be managed conservatively with well defined strategies for preventing neurocardiogenic syncope.

Conclusions

Managing syncope requires a methodical approach. An understanding of the limitations of the diagnostic tools and treatments is important. Lethal causes of syncope make it imperative to recognize the appropriate timing of referring patients to specialists.

Current treatment of recurrent vasovagal syncope: between evidence-based therapy and common sense

Vasovagal syncope is very frequent and benign and the vast majority of subjects do not need any specific treatment, but only reassurance and education. An unknown but small percentage of patients require specific treatment when syncope is very frequent or is responsible for major trauma. For these patients, there are some evidence-based therapies available and some first-line treatments appear to be established. The therapeutic choice mainly depends on the presence and duration of prodromal symptoms. In subjects aged < 70 years with well recognizable prodromes, the first-line treatment is counterpressure manoeuvres. In patients with no or minimal prodromes, but with tilt testing and carotid sinus massage (CSM) both positive, cardiac pacing appear to be the first-line therapy. However, an area of uncertainty remains, represented by patients with no or minimal prodromes and negative CSM. For these patients, appropriate treatment (drugs, tilt training, cardiac pacing, relaxation-based treatment) can be chosen by considering the clinical context, the risk of trauma and possible comorbidities, in addition to utilizing the little or controversial knowledge available, as well as common sense.

Norepinephrine Transporter Inhibition Prevents Tilt-Induced Pre-Syncope

OBJECTIVES

We tested the hypothesis that pharmacological norepinephrine reuptake transporter (NET) inhibition delays the onset of head-up tilt-induced presyncope in healthy subjects.

BACKGROUND

Treatment of neurally mediated syncope is unsatisfactory. In a previous study in a small number of healthy subjects, pharmacologic NET inhibition delayed the onset of head-up tilt-induced pre-syncope.

METHODS

We combined data sets from 3 substudies comprising 51 healthy subjects without a history of syncope. In a double-blind, randomized, cross-over fashion, subjects underwent 2 head-up tilt tests, once with placebo and once with a NET inhibitor (sibutramine or reboxetine). Tilt testing was prematurely ended when pre-syncopal symptoms such as dizziness, nausea, or visual disturbances occurred together with a decrease in blood pressure and/or heart rate.

RESULTS

The mean tolerated tilt test duration was 29 +/- 2 min with placebo and 35 +/- 1 min with NET inhibition (p = 0.001). The odds ratio for premature abortion of head-up tilt testing was 0.22 (95% confidence interval 0.09 to 0.55, p < 0.001) in favor of NET inhibition. Norepinephrine reuptake transporter inhibition elicited a pressor response and increased upright heart rate.

CONCLUSIONS

In healthy subjects, NET inhibition prevents tilt-induced neurally mediated (pre)syncope. Therefore, NET inhibition may be a worthwhile target of drug intervention for larger trials in highly symptomatic patients with neurally mediated syncope.

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.

Seizure versus syncope

One of the most common but difficult management problems in medicine is that of patients who present with a paroxysmal loss of consciousness. All too often the underlying diagnosis remains elusive. This has a cost both in terms of mortality and ongoing morbidity and in terms of the financial burden associated with hospitalisation and repeated investigations. We describe a practical approach to this clinical dilemma, which is rooted in adherence to basic principles of history taking and examination, formulation of a reasonable differential diagnosis, followed by an intelligent use of specific investigations and selection of an appropriate treatment. We also discuss the effect of sudden unexpected death in epilepsy and sudden cardiac death. Despite a careful and thorough approach to the patient with a "seizure versus syncope" problem, many will require repeated assessment before a diagnosis is made.

[Syncope and epileptic seizures]

Syncope is one of the most common symptoms leading to hospital admission. Thereby syncope can be induced by several diseases. It is crucial to detect underlying structural heart disease or high grade arrhythmias, as these are associated with an increased mortality. The careful history and physical examination can often give sufficient evidence to evaluate the origin of syncope. Additional examinations should only be applied selectively. In patients with structural heart disease the specific treatment should be initiated, in patients with cardiac arrhythmias the implantation of a pacemaker or ICD might be indicated. The most common neurally-mediated and orthostatic syncopes can often be treated successfully by physical training. Beside syncope epilepsy might be responsible for a transient loss of consciousness. Again careful history taking helps to differentiate between these two entities.

Usefulness of pindolol for treatment of neurocardiogenic syncope

This study evaluated the efficacy of pindolol, a noncardioselective beta blocker with intrinsic sympathetic activity, on neurocardiogenic syncope using a head-up tilt-table test in 66 patients. Pindolol was equally effective in men and women and the 2 age groups (>60 and <60 years) of the study cohort. The earliest benefit was seen </=3 days after initiating treatment. Side effects were better tolerated in younger patients (age <60 years).

Pharmacological treatment of reflex syncope

Patient education, identification of possible triggers of syncope and reassurance are a central feature of the management of patients with reflex syncope. Patients should be advised as to the importance of adequate hydration and taught physical countermaneuvers to enhance cardiac venous return. These maneuvers are sufficient for most patients, however, for a small number of patients who continue to have recurrent syncopal events, pharmacological intervention may be considered. Volume expansion can be enhanced with salt and fludrocortisone. Agents from diverse pharmacological classes have been used to attenuate the reflex response, enhance vasoconstriction and attenuate vagal outflow. Alpha adrenoreceptor agonists, anticholinergic agents, theophylline, beta adrenoreceptor antagonists, serotonin reuptake inhibitors and disopyramide are the most widely studied. None of these agents has shown a consistent therapeutic benefit in clinical trials.

Current Management of Syncope: Treatment Alternatives

Syncope, defined as a transient loss of consciousness and postural tone with spontaneous recovery and no neurologic sequelae, is among one of the most common causes of consultation with a physician. The diagnostic workup is complex but can be simplified if focused on the underlying condition. Prognosis is highly dependent on the presence or absence of structural heart disease, primarily the presence of cardiomyopathy regardless of etiology, particularly if the left ventricular (LV) function is less than 35%. The diagnostic approach to the patient with recurrent syncope and no structural heart disease is targeted to rule out neurally mediated causes. This approach usually includes a tilt table test (ie, head-up tilt), carotid sinus massage in patients older than 55 years, and an adenosine challenge test in patients who remain with unexplained syncope. Unexplained syncope in patients with reduced LV function (< 35%) may be potentially life-threatening. Infrequent causes of syncope should be sought in younger patients with a family history of sudden cardiac death. Channelopathies such as the long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia are among this variety. Therapy should address the potential mechanism of syncope. In neurally mediated causes, restoration of orthostatic tolerance, primarily by increasing volume during orthostatic stress, is recommended. Physiologic countermaneuvers and increase in salt and water intake are usually the initial therapy. With syncope in patients with an LV dysfunction (< 35%), an ICD is frequently recommended after ruling out common causes of syncope. Syncope in the elderly is usually multifactorial and therapy should include reassessment of multiple medications, which can promote neurally mediated syncope as well as searching for bradycardic causes. Empiric pacing may be used in this complex group of patients.

New approaches to the treatment and prevention of neurally mediated reflex (neurocardiogenic) syncope

Neurally mediated reflex syncope (sometimes referred to as neurocardiogenic syncope), encompasses a group of disorders of which the best known and most frequently occurring forms are the vasovagal (or common) faint, and carotid sinus syndrome. Postmicturition syncope, defecation syncope, cough syncope, and other situational reflex faints are also included among these conditions. With the exception of carotid sinus syndrome in which cardiac pacing is effective, treatment of most neurally mediated reflex faints is shifting from reliance on various drugs to greater emphasis on education and nonpharmacologic therapy. Initial management should include counseling of patients regarding recognition of early warning symptoms, and avoidance of precipitating factors. Volume expansion with salt tablets or electrolyte-containing beverages and patient education on how to perform isometric arm contractions and/or leg crossing in order to abort impending syncope are also important. Thereafter, tilt-training has demonstrated benefit in several clinical studies. When symptoms remain despite the above-noted interventions, pharmacologic therapy with midodrine or a nonselective b-blocker can be considered. In the case of most neurally mediated reflex faints, permanent cardiac pacing should be reserved only for those older patients with significant bradycardia or asystole at time of syncope when all other interventions have failed.

Randomized clinical trials of neurally mediated syncope

Evidence for therapy of neurally mediated syncope is generally weak. Many drugs have been used for the treatment of vasovagal syncope (beta-blockers, disopyramide, scopolamine, clonidine, theophylline, fludrocortisone, ephedrine, dihydroergotamine, etilefrine, midodrine, clonidine, serotonin reuptake inhibitors, enalapril). In general, although the results have been satisfactory in uncontrolled trials or short-term controlled trials, the majority of long-term placebo-controlled prospective trials have not been able to show a benefit of the active drug over placebo. Only two well-designed double-blind placebo-controlled randomized trials have been performed-one for etilefrine and the other for atenolol-and both were unable to show a superiority of the active drug versus placebo. Four randomized clinical trials of pacing therapy-three positive and one negative-have been performed in patients affected by vasovagal syncope. The relationship between carotid sinus hypersensitivity and spontaneous, otherwise unexplained, syncope has been demonstrated. Cardiac pacing appears to be beneficial in carotid sinus syndrome; its efficacy has been demonstrated by two randomized controlled trials and confirmed by several pre-post comparative studies, one controlled trial, and one prospective observational study. There is evidence and general agreement that cardiac pacing is useful in patients with cardioinhibitory or mixed carotid sinus syndrome. Usefulness of the treatment is less well established and divergence of opinion exists with regard to cardiac pacing in patients with cardioinhibitory vasovagal syncope. The evidence fails to support the efficacy of beta-blocking drugs. As yet there are insufficient data to support the use of any other pharmacologic therapy for vasovagal syncope.

Dysfunctional baroreflex regulation of sympathetic nerve activity in patients with vasovagal syncope

BACKGROUND

The interplay of resting muscle sympathetic nerve activity (MSA) and the baroreceptor reflex in patients with vasovagal syncope remains elusive. Hence, the aim of the present study was to investigate MSA, baroreceptor sensitivity, heart rate, and blood pressure under resting conditions and during orthostatic stress in patients with a history of vasovagal syncope.

METHODS AND RESULTS

MSA was measured using microneurography at rest and during lower body negative pressure (LBNP) to mimic orthostatic stress in patients with a history of vasovagal syncope (n=10) and in age-matched healthy controls (n=8). Heart rate and blood pressure were simultaneously recorded. Cardiac baroreceptor sensitivity was calculated with the spectral technique (alpha coefficient). Resting MSA in the patients with syncope was significantly increased as compared with controls (42.4+/-2.3 versus 26.5+/-3.6 bursts/min, P=0.001), whereas activation of MSA during orthostatic stress in the patient group was significantly blunted (5.1+/-1.6 versus 15.2+/-2.1 bursts/min at LBNP -50 mm Hg, P=0.002). In the patients with syncope, cardiac baroreceptor sensitivity was significantly reduced under supine resting conditions (8.5+/-0.7 versus 13.0+/-1.1 ms/mm Hg, P=0.001), as well as under orthostatic stress (7.3+/-0.7 versus 13.4+/-1.5 ms/mm Hg, P=0.003).

CONCLUSIONS

This study shows that in patients with vasovagal syncope, resting MSA is increased and baroreflex regulation during orthostatic stress is blunted, thus leading to impaired MSA adaptation. These results provide new insights into mechanisms of vasovagal syncope and suggest that pharmacological modulation of baroreceptor sensitivity may represent a promising treatment of neuromediated syncope.

Role of pacemakers in treating neurocardiogenic syncope

Patients with frequent vasovagal syncope have a poor quality of life and often resist treatment with standard pharmacologic approaches. Clinical vasovagal syncope may be associated with some degree of bradycardia. Studies of temporary pacing during tilt table tests showed that pacing prevented syncope in a little more than half of patients who developed a vasovagal response. Six open-label studies of permanent pacing show that permanent pacemaker therapy is associated with substantial improvement over medical therapy. The roles of specific pacemaker modes have not been determined, although there is some evidence that rate-drop responsiveness helps. The second Vasovagal Pacemaker Study will quantify the true benefits of pacing for vasovagal syncope and assess the role of rate-drop response algorithms.

Clinical and physiological effects of an acute alpha-1 adrenergic agonist and a beta-1 adrenergic antagonist in chronic orthostatic intolerance

BACKGROUND

Adrenergic agents are commonly used in the treatment of chronic orthostatic intolerance with postural tachycardia syndrome (POTS). POTS may be associated with increased limb blood flow ("high flow") and defective orthostatic vasoconstriction or decreased limb blood flow ("low flow") and potentially with small blood volume.

METHODS AND RESULTS

We investigated the consequences of short-term intravenous administration of an alpha-1 adrenergic agonist, phenylephrine, and a beta-1 adrenergic antagonist, esmolol, in 14 patients with POTS aged 13 to 19 years. Indices of heart rate and blood pressure variability, peripheral blood flow, and arterial resistance were assessed, and the capacitance relation was computed for every subject using venous occlusion plethysmography. Patients were tilted to 35 degrees upright while medicated and while unmedicated, and measurements were repeated. Phenylephrine improved orthostatic tolerance and normalized hemodynamics and indices of heart rate/blood pressure variability while supine and while upright, producing significant peripheral vasoconstriction and venoconstriction (20% capacitance change). Esmolol did not improve orthostatic tolerance or hemodynamics. A subgroup of low-flow POTS patients had exaggerated venoconstriction to phenylephrine (50% capacitance change) but others had no response.

CONCLUSIONS

Phenylephrine, but not esmolol, improves orthostatic tolerance and hemodynamics in POTS. This lends support to the use of oral alpha-1 agonists in the treatment of patients with chronic orthostatic intolerance.

Syncope: investigation and treatment

Syncope is a common condition that can be both disabling and expensive to treat. Although investigative modalities are sometimes required, a diagnosis can often be made with a good history and physical exam. Recent reports have identified specific historic features that are more suggestive of cardiac syncope as compared with vasovagal syncope and seizures. Advances in ambulatory electrocardiography (in particular the implantable loop recorder) have proven invaluable in both difficult-to-diagnose syncope, and in advancing our knowledge of its mechanisms. When clear dysrhythmias are manifest, appropriate therapies are self-evident. However, recurrent vasovagal syncope continues to be a condition that can be difficult to treat. Fortunately, there are well-conducted trials of both pharmacologic therapies (b-blockers, alpha agonists, and selective serotonin reuptake inhibitors) and nonpharmacologic treatments (orthostatic physical training and dual-chamber pacemakers) that should provide more guidance in the near future.

Vasovagal syncope: a prospective, randomized, crossover evaluation of the effect of propranolol, nadolol and placebo on syncope recurrence and patients' well-being

OBJECTIVES

We sought to assess the relative therapeutic efficacy of propranolol, nadolol and placebo in recurrent vasovagal syncope (VVS).

BACKGROUND

Central and peripheral mechanisms have been implicated in the pathogenesis of VVS. Propranolol, nadolol and placebo have different sites of action on central and/or peripheral mechanisms. It has not yet been clarified whether one of the aforementioned treatments is more efficient than the others in reducing clinical episodes and exerting a beneficial effect on patients' well-being.

METHODS

We studied 30 consecutive patients with recurrent VVS and a positive head-up tilt test. All were serially and randomly assigned to propranolol, nadolol or placebo. Therapy with each drug lasted three months. On the day of drug crossover, patients reported the total number of syncopal and presyncopal attacks during the previous period. They also gave a general assessment of their quality of life, taking into account: 1) symptom recurrence; 2) drug side effects; and 3) their personal well-being during therapy (scale 0 to 4: 0 = very bad/discontinuation; 1 = bad; 2 = good; 3 = very good; 4 = excellent). At the end of the nine-month follow-up period, they reported whether they preferred a specific treatment over the others.

RESULTS

Spontaneous syncopal and presyncopal episode recurrence during each three-month follow-up period was reduced by all drugs tested (analysis of variance [ANOVA]: chi-square = 67.4, p < 0.0001 for syncopal attacks; chi-square = 60.1, p < 0.0001 for presyncopal attacks) No differences were observed in the recurrence of syncope and presyncope among the three drugs. All drugs improved the patients' well-being (ANOVA: chi-square = 61.9, p < 0.0001).

CONCLUSIONS

Propranolol, nadolol and placebo are equally effective treatments in VVS, as demonstrated by a reduction in the recurrence of syncope and presyncope, as well as an improvement in the patients' well-being.