Efficacy of different treatment strategies for neurocardiogenic syncope

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.

Theophylline in patients with syncope without prodrome, normal heart, and normal electrocardiogram: a propensity-score matched study verified by implantable cardiac monitor

AIMS

Syncope without prodromes in subjects with normal heart and normal electrocardiogram (ECG) is classified as non-classical neurally mediated syncope and is characterized by low adenosine plasma levels (APLs) and frequent asystolic syncope. We assessed the efficacy of theophylline, a non-selective adenosine receptor antagonist, in preventing syncopal events.

METHODS AND RESULTS

Participants received an implantable cardiac monitor, underwent APL measurement, and received oral theophylline at maximum tolerated dose (starting dose 300 mg b.i.d.). They were compared with a historical cohort of untreated patients with implantable cardiac monitor who had the same inclusion criteria and were balanced with the propensity score (PS) method as regard age, sex, lifetime syncopal episodes, APL, and antihypertensive drugs. Primary endpoint was time to first syncopal recurrence at 24 months. There were 76 patients in the theophylline group and 58 in the control group. Syncope recurred in 25 (33%) patients in the theophylline group and in 27 (47%) patients in the control group, with an estimated 2-year recurrence rate of 33% and 60%, respectively, and a hazard ratio of 0.53 [95% confidence interval (CI), 0.30-0.95; P = 0.034]. Most of the benefit of theophylline is derived from reduction of syncope due to asystolic atrioventricular (AV) block (hazard ratio of 0.13; 95% CI, 0.03-0.58; P = 0.008). Thirty (39%) patients discontinued theophylline after a median of 6.4 (interquartile range 1.7-13.8) months due to side effects.

CONCLUSION

Theophylline was effective in preventing recurrences in patients with syncope without prodromes, normal heart, and normal ECG. The benefit was greater in patients with syncope due to asystolic AV block.

CLINICALTRIALS.GOV IDENTIFIER

NCT03803215.

Efficacy of theophylline in patients with syncope without prodromes with normal heart and normal ECG

BACKGROUND

Patients affected by syncope without or with very short (≤5 s) prodrome with normal heart and normal ECG have been seen to present low plasma adenosine levels. We investigated whether chronic treatment of these patients with theophylline, a non-selective adenosine receptor antagonist, results in clinical benefit.

METHODS

In a consecutive case-series of 16 patients (mean age 47 ± 25 years, 9 females) who had ECG documentation of asystolic syncope, we compared the incidence of syncopal recurrence during a period without and a period with tailored theophylline therapy.

RESULTS

During a median of 60 months before ECG documentation of the index episode, the patients had a median of 2 syncopes per year. During the 6 months of the study phase without therapy, the patients had a median of 2.6 syncopes per year, p = 0.63. During the 23 months of the study phase with theophylline, the patients had a median of 0.4 syncopes per year, p = 0.005 vs history and p = 0.005 vs no therapy. In the 13 patients who had an implantable loop recorder during both study phases, the incidence of asystolic episodes > 3 s decreased from 9.6 per year to 1.1 per year, p = 0.0007. During theophylline treatment, syncope recurred in 1/5 (20%) patients who had an idiopathic atrioventricular block as the index event versus 9/11 (81%) patients who had a sinus arrest, p = 0.005.

CONCLUSION

Theophylline is effective in reducing syncopal burden in patients with syncope without prodromes with normal heart and normal ECG. Its efficacy is greater in those with idiopathic atrioventricular block.

Comparison of recurrence rate based on the frequency of preceding symptoms in patients with neurocardiogenic syncope or presyncope

BACKGROUND AND OBJECTIVES

In patients with neurocardiogenic syncope or presyncope, symptoms developed unpredictably and intermittently. The purpose of this study was to determine whether there was any significant difference in the recurrence rate of symptoms during the follow-up period between patients with many episodes of symptoms and those with fewer episodes of symptoms before diagnosis, as well as to assess the clinical significance of previous episodes of symptoms during treatment.

SUBJECTS AND METHODS

A total of 100 patients with neurocardiogenic syncope or presyncope were divided in two groups (high episode group, n=54; low episode group, n=46) according to the frequency of symptoms before the head-up tilt test. We retrospectively analyzed the recurrence of symptoms using telephone interviews and medical record reviews.

RESULTS

The clinical characteristics were not significantly different between the two groups. However, the recurrence rate was significantly lower in the high episode group than in the low episode group (5.6% vs. 19.6%, p=0.001). In the high episode group, patients treated with medication showed higher recurrence of symptoms than those without medication. In the lower episode group, a similar result was observed.

CONCLUSION

The frequency of previous symptoms at the diagnosis of neurocardiogenic syncope or presyncope did not predict the occurrence of symptoms during the follow-up period. Therefore, to continue drug treatment based on the frequency of symptoms in patients with neurocardiogenic syncope or presyncope may not be the best option.

Neurological aspects of syncope and orthostatic intolerance

Sudden falling with loss of consciousness from syncope and symptoms of orthostatic intolerance are common, dramatic clinical problems of diverse cause, but cerebral hypoperfusion is the ultimate mechanism in most. Cardiac, reflex, and orthostatic hypotension are important forms to consider. Syncope must be differentiated from seizures, psychiatric events, drop attacks, and other mimics. However, factors such as syncopal induced movements, ictal bradycardia, and insufficient clinical information can confound accurate diagnosis and hamper appropriate treatment. Progress in the diagnosis, treatment, and understanding of underlying mechanisms is continually advancing.

Basic autonomic nervous function in patients with neurocardiogenic syncope

Basic autonomic nervous function was evaluated in patients with neurocardiogenic syncope (NCS). Atropine, isoproterenol, propranolol, phenylephrine, and phentolamine were administered successively, and parasympathetic nerve activity and beta- (and alpha-) activity, sensitivity, and secretion of the sympathetic nerve were determined in patients with NCS and control subjects. In patients with NCS, beta- and alpha- sensitivity were higher and beta-activity and beta- and alpha-secretion lower than in control subjects. In patients with NCS, the increased basic beta-sensitivity may contribute to induce strong cardiac contractions and augment ventricular mechanoreceptor response, and a compensatory state against diminished neuronal sympathetic activity is suggested by the increased alpha-sensitivity.

A patient responding to combined therapy with pirmenol and midodrine for refractory neurally mediated syncope complicated by prostatic hypertrophy

A 67-year-old man with neurally mediated syncope (NMS) complicated by prostatic hypertrophy responded well to combined therapy with pirmenol and midodrine. In 2003, syncope occurred while the patient was driving a car. Results of head-up tilt-table testing (HUT) suggested a mixed type of NMS. Oral administration of disopyramide provided severe urinary obstruction. Pirmenol treatment was not associated with syncope during ordinary HUT, but nausea, sweating, and syncope occurred during HUT with provocative administration of isosorbide dinitrate. Combined therapy with pirmenol and midodrine avoided syncope during HUT, and has prevented attacks since discharge from the hospital.

Diagnosis and Management of Vasovagal Syncope and Dysautonomia

Vasovagal syncope is a condition better known as neurocardiogenic or neurally mediated syncope. Dysautonomic syncope is the irregular neuroautonomic response during the body's attempt to maintain homeostasis. Both types of syncope are associated with orthostatic hypotension and are nonlethal. The underlying pathophysiology manifests the vast symptoms suffered by the individual. Research continues to develop new markers to improve diagnostic testing and therapies for treatment. Advanced practice nurses now have a new tool with Head-Up Tilt Training Programs to offer the patients who suffer from frequent and refractory neurocardiogenic and dysautonomic syncope.

Long-term outcome of patients with recurrent syncope of unknown cause in the absence of organic heart disease and relation to results of baseline tilt table testing

Among 123 patients with unexplained syncope in the absence of heart disease who were followed up for 24 +/- 7 months, syncope recurred in a similar minority of them regardless of baseline tilt table testing results. An initially unsuspected cardiac or neuropsychiatric disorder was uncovered in 17 patients later on follow-up examination.

Syncope and orthostatic intolerance

Syncope and orthostatic intolerance remain common and significant clinical problems with many undocumented, misdiagnosed, or cryptogenic cases. Careful clinical assessment and application of advancing laboratory support can further improve diagnosis and treatment. Despite the depth of existing research into these common problems, many underlying mechanisms remain unproven.

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.

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.

[Vasovagal syncope in pediatric patients: a medium-term follow-up analysis]

INTRODUCTION AND OBJECTIVES

Little information is available on the evolution of pediatric patients with vasovagal syncope. We therefore aimed to assess the medium-term clinical outcome of children evaluated by tilt testing for syncope of unknown origin.

PATIENTS AND METHOD

Fifty-one children under 17 years of age who had undergone tilt testing were identified from a data base and studied prospectively. Kaplan-Meier and Cox regression analyses were performed to estimate syncope-free survival, its predictors, and the relative risks of several patient subgroups.

RESULTS

Forty-seven (92%) of the children were followed for a mean 21 9 months. The rate of recurrence of syncope was considerably lower than that estimated during history taking before the tilt test (19% vs 47%; p < 0.01). Although the low rate made it difficult to identify predictors, several potential predictors emerged from the multivariate analysis. Only the history of more than one syncope before the tilt test (vs. isolated syncope) was found to have independent predictive value (p = 0.04). The cumulative probability of recurrence projected for a period of 38 months was 66.2% (SEM = 16.5%) for children with more than one syncope before testing vs. 0% for those who had experienced only one. No other events occurred.

CONCLUSIONS

The medium-term prognosis seems to be good for children with vasovagal syncope of unknown origin, given the low rate of recurrence, regardless of the results of tilt testing. The only predictor of recurrent syncope was pretest history, such that children with only one syncope before testing experience no recurrence and those with one or more episodes are estimated to have an increasingly higher likelihood of recurrence. These data may be useful for the recommending tilt testing and for planning therapy for children with vasovagal syncope.

Neurocardiogenic syncope: aetiology and management

Neurocardiogenic syncope is the most common cause of syncope presenting in the outpatient setting. It is usually encountered among individuals without an underlying heart disease, but not uncommonly participates in the syncope mechanism of patients with an obstructive or an arrhythmic cardiac cause for syncope as well. The vasovagal event is caused by a transient profound hypotensive reaction most commonly associated with inappropriate bradycardia resulting from activation of a complex autonomic reflex. The pathophysiology of neurocardiogenic syncope has been elucidated by tilt table testing, a noninvasive and well-tolerated method for reproducing the event in susceptible individuals. Although the majority of people with vasovagal fainting need no specific treatment, treatment is required for those presenting with problematic features such as frequent events accompanied by trauma or accidents, and occasionally by a severe cardioinhibitory pattern response. A number of different drugs have been proposed to favourably act on different aspects of the neurocardiogenic reflex but only a few randomised, placebo-controlled, drug-specific trials are currently available. Alternatively, cardiac pacing has also been introduced for patients who have symptoms that are drug-refractory or for those with a severe cardioinhibitory hypotensive response. The selection of the appropriate treatment plan should be individualised after consideration of patient history, clinical characteristics and preference, results of the baseline tilting study, and the existing evidence from the few randomised, controlled studies performed so far.

Syncope

Successful treatment of patients with syncope depends on the accuracy of the diagnosis, because syncope is a symptom, not a disease; diagnosis of the cause for syncope therefore creates a blueprint for treatment. Most experienced practitioners can diagnose the cause of syncope for less than half of their patients. Excessive and repeat testing is expensive and may not improve the chance of a correct diagnosis. Patient history is the key to the diagnosis. Treatment may vary from a lifestyle change to open heart surgery. The great challenge of treating patients with syncope is to provide cost-effective, safe therapy to those with a benign course and still provide needed treatment for those whose syncope is life threatening.

Medical therapy of neurocardiogenic syncope

Neurocardiogenic syncope, alternatively called vasovagal, vasodepressor, or neurally mediated syncope, is a clinical syndrome faced by many clinicians. Its pathophysiology is complicated and not fully understood. Multiple pharmacologic therapies have been evaluated, with no clear ideal agent. Decisions regarding tilt-table testing, selection of pharmacotherapy, and assessment of drug efficacy are not straightforward. This article attempts to assess these issues.

Lack of efficacy of atenolol for the prevention of neurally mediated syncope in a highly symptomatic population: a prospective, double-blind, randomized and placebo-controlled study

OBJECTIVES

This study was designed to evaluate the efficacy of atenolol for the long-term management of patients with vasovagal syncope. The primary hypothesis was that atenolol is not superior to placebo for the treatment of vasovagal syncope.

BACKGROUND

There is no definitive well-controlled analysis of the efficacy of beta-adrenergic blocking agents in patients with recurrent vasovagal syncope.

METHODS

This is a prospective, randomized, double-blind, placebo-controlled study. Fifty patients with recurrent vasovagal syncope were included (at least two episodes in the last year). A baseline tilt test was performed. Twenty patients (40%) had a positive tilt test. Intravenous atenolol prevented a second positive tilt in five patients. The patients were randomized to receive either atenolol or a placebo (26 patients atenolol 50 mg/day, 24 patients placebo). The follow-up procedure lasted one year. The primary end point of the study was the time to first recurrence of syncope.

RESULTS

In the intention-to-treat analysis, the group treated with atenolol had a similar number of patients with recurrent syncopal episodes as the placebo group. The Kaplan-Meier actuarial estimates of time to first syncopal recurrence showed that the probability of remaining free of syncope drops similarly in both groups and that there was no statistical difference between both curves (patients treated with atenolol vs. the placebo) with a log-rank test p value of 0.4517.

CONCLUSIONS

The recurrence of neurocardiogenic syncope in highly symptomatic patients treated with atenolol is similar to that of patients treated with placebo.

A review of pathophysiology and therapy of patients with vasovagal syncope

Vasovagal syncope is a common disorder that can compromise quality of life and lead to significant morbidity. It is characterized by an initial exaggerated sympathetic output followed by parasympathetic activation and sympathetic withdrawal, as shown by diagnostic head-up tilt (HUT) table testing. Numerous drugs have been evaluated for treating this disorder. beta-Blockers are well studied and commonly administered but are specifically more efficacious in patients with isoproterenol HUT than in those with regular HUT. The role of the serotonergic system has captured new interest. Selective serotonin reuptake inhibitors show promising results in preventing vasovagal syncope in treatment-refractory patients. Also, new investigations suggest that serotonin receptor antagonism may be beneficial. Despite these findings, definitive treatment does not exist.

Midodrine hydrochloride in the treatment of vasovagal syncope

Therapy of vasovagal syncope is still a subject of debate. Various pharmacotherapies were proposed. However, they are often not tolerated or ineffective. The purpose of this prospective, nonrandomized study was to evaluate the usefulness of alpha-agonist midodrine hydrochloride in the treatment of vasovagal syncope. Forty-one patients (mean age 34 years, 18 men) with history of recurrent syncope and positivity of head-up tilt testing were included (28 patients with type 1, 10 patients with type 2, 3 patients with type 3 according to VASIS classification). In all patients oral therapy with midodrine was started. Initial dose was 2.5 mg two times daily. When necessary, the dose was increased to 5 mg two times daily. Efficacy of treatment was assessed by repeated head-up tilt testing after 1-2 weeks of therapy and by long-term follow-up. After midodrine hydrochloride treatment, 39 of 41 patients (95%) had no inducible presyncope or syncope on repeated tilt table testing. Effective dose was 2.5 mg two times daily in 25 patients and 5 mg two times daily in 16 patients. During a mean follow-up period 19+/-9 months, 38 of 39 patients (97%) with negative repeated tilt table test remained free of syncope recurrence.

Driving safety among patients with neurocardiogenic (vasovagal) syncope

Neurocardiogenic syncope is one of the most common causes of syncope. However, the important issue of driving related injury due to syncope in this population is not well defined. Risk of injury due to syncope while driving and driving behavior was evaluated in 155 consecutive patients (92 women and 63 men; mean age 49 +/- 19 years) with history of syncope in whom hypotension and syncope or presyncope could be provoked during head-up tilt testing. Patients with syncope and positive head-up tilt table test were treated with pharmacological therapy. All participants were asked to fill out a detailed questionnaire regarding any driving related injuries and their driving behavior before tilt table testing and during follow-up. Prior to head-up tilt testing two patients had syncope while driving, and one of these patients had syncope related injury during driving. The mean duration of syncopal episodes was 50 +/- 14 months (range 12-72 months). Of the 155 patients, 52 (34%) had no warning prior to syncope, while 103 (6%) had warning symptoms such as dizziness prior to their clinical syncope. Following a diagnosis of neurocardiogenic syncope established by head-up tilt testing, six patients stopped driving on their own. During a median follow-up of 22 months recurrent syncope occurred in five (3.2%) patients. No patient had syncope or injury during driving. In conclusion, syncope and injury while driving in patients with neurocardiogenic syncope is rare. The precise mechanism of this is unclear but may be related to posture during driving. Consensus among the medical community will be needed to provide specific guidelines in these patients.

Usefulness of a tilt training program for the prevention of refractory neurocardiogenic syncope in adolescents: A controlled study

BACKGROUND

Recurrent syncope represents a debilitating disorder and quality of life deteriorates as a function of recurrence of symptoms. Although the administration of beta-blockers, vasoconstrictors, fludrocortisone, and serotonin reuptake inhibitors may be helpful in preventing episodes, many patients are intolerant of or respond poorly to these agents. Orthostatic training has been reported to be effective in preventing refractory syncope. Thus, to determine whether a tilt training program could prevent symptoms in adolescents, the following controlled study was undertaken.

METHODS AND RESULTS

Forty-seven consecutive adolescents (18 male and 29 female, mean age 16.0+/-2.2 years) with recurrent syncope and positive head-up tilt test refractory to previous traditional therapies were distributed between 2 groups, depending on their consent (24 patients) or refusal (controls, 23 patients) to enter the program. Orthostatic training was started, in the presence of a family member, with a series of 5 in-hospital sessions. The 24 patients and their relatives were then instructed to perform the tilt training at home by standing against a wall twice a day for a planned duration of up to 40 minutes, depending on the in-hospital orthostatic tolerance. Head-up tilt response was reevaluated after 1 month, and the clinical effect was noted over a mean follow-up of 18. 2+/-5.3 months (range 15 to 23); 26.1% of patients in the control group and 95.8% of patients in the training group became tilt-negative (P<0.0001). Spontaneous syncope was observed in 56.5% versus 0% in the control and training group, respectively (P<0.0001).

CONCLUSIONS

Orthostatic training was found to significantly improve symptoms of adolescents with neurocardiogenic syncope unresponsive to or intolerant of traditional medications. Twice-a-day training sessions of 40 minutes were well accepted by patients.

Pharmacologic approaches to therapy for vasovagal syncope

Vasovagal syncope is a common disorder of autonomic cardiovascular regulation. Many pharmacologic agents have been proposed as effective in the management of this condition based on nonrandomized clinical trials. Notably, only 3 agents--atenolol, midodrine, and paroxetine--have demonstrated efficacy in the treatment of vasovagal syncope in at least 1 prospective, randomized, placebo-controlled clinical trial. Other therapies commonly used in treating syncope include increased salt and fluid intake and fludrocortisone. In this review, we provide a summary of currently available data that support or question the use of various pharmacologic agents for treatment of vasovagal syncope.

Pharmacotherapy of neurally mediated syncope

A wide variety of pharmacological agents are currently used for prevention of recurrent neurally mediated syncope, especially the vasovagal faint. None, however, have unequivocally proven long-term effectiveness based on adequate randomized clinical trials. At the present time, beta-adrenergic receptor blockade, along with agents that increase central volume (eg, fludrocortisone, electrolyte-containing beverages), appear to be favored treatment options. The antiarrhythmic agent disopyramide and various serotonin reuptake blockers have also been reported to be beneficial. Finally, vasoconstrictor agents such as midodrine offer promise and remain the subject of clinical study. Ultimately, though, detailed study of the pathophysiology of these syncopal disorders and more aggressive pursuit of carefully designed placebo-controlled treatment studies are essential if pharmacological prevention of recurrent neurally mediated syncope is to be placed on a firm foundation.

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.

Management of vasovagal syncope

Vasovagal syncope is a common disorder of autonomic cardiovascular regulation that can be very disabling and result in a significant level of psychosocial and physical limitations. The optimal approach to treatment of patients with vasovagal syncope remains uncertain. Although many different types of treatment have been proposed and appear effective based largely on small nonrandomized studies and clinical series, there is a remarkable absence of data from large prospective clinical trials. However, based on currently available data, the pharmacologic agents most likely to be effective in the treatment of patients with vasovagal syncope include beta blockers, fludrocortisone, and alpha-adrenergic agonists. In this article, we provide a summary of the various therapeutic options that have been proposed for vasovagal syncope and review the clinical studies that form the basis of present therapy for this relatively common entity.

Contribution of head-up tilt testing and ATP testing in assessing the mechanisms of vasovagal syndrome: preliminary results and potential therapeutic implications

BACKGROUND

In patients with vasovagal syndrome, head-up tilt testing may reproduce symptoms generally associated with vasodepression. Recent research suggests ATP testing identifies patients with abnormal vagal cardiac inhibition. This preliminary study examined the joint contribution of both tests in identifying underlying mechanisms in the general population with vasovagal syndrome.

METHODS AND RESULTS

Both tests were performed in random order during 1 session and outside of predominant sympathetic periods in 72 patients hospitalized for syncope (n=56) or presyncope (n=16) for whom no cardiac or extracardiac cause was found. For passive and isoproterenol-provocative tilt testing by standard protocol, reproduction of symptoms defined a positive test. The ATP test consisted of injecting ATP 20 mg IV at bedside, continuously monitoring ECG and blood pressure; a vagal cardiac pause >10 seconds defined a positive test. For most patients (64%), >/=1 test was positive. Of the 41 patients (57%) with a positive tilt test (either passive or provoked by isoproterenol), 32% had cardiac disease; none had significant bradycardia (<50 bpm). Of the 8 patients (11%) with a positive ATP test, 62% had cardiac disease; the probability of a positive result increased with age (P=0.015). Both tests were positive in 3 patients and negative in 26 patients; the tilt and ATP test results were uncorrelated (P=0.28).

CONCLUSIONS

Results suggest tilt and ATP tests individually and jointly determine the mechanism of vasovagal symptoms in most patients and that vagal cardiac inhibition increases with age.

Effects of age on outcome of tilt-table testing

Although neurally mediated syncope is thought to be common in the young and rare in the elderly, there are few data evaluating the effects of age on the outcome of tilt-table testing (TTT), especially in patients aged > or =80 years. We examined the results of TTT in 352 subjects with unexplained syncope including 133 patients >65 years of age and 43 patients >80 years of age. The average age was 54 +/- 20.8 years (range 11 to 99) and 51% were men. The TTT protocol included at least 45 minutes of upright tilt in the drug-free state with or without repeat TTT with isoproterenol or 15 minutes of upright tilt in the drug-free state followed by repeat TTT with isoproterenol. One hundred sixty-four subjects (47%) had a positive TTT. As expected, there was an age-related decline in positive TTT. A high proportion of elderly patients with unexplained syncope had a positive TTT (37% of patients aged > or =65, and 23% patients aged > or =80). Thus, TTT is a useful diagnostic test in patients aged > or =65 years with unexplained syncope.

Effect of etilefrine in preventing syncopal recurrence in patients with vasovagal syncope: a double-blind, randomized, placebo-controlled trial. The Vasovagal Syncope International Study

BACKGROUND

Etilefrine is an alpha-agonist agent with a potent vasoconstrictor effect, which is potentially useful in preventing vasovagal syncope by reducing venous pooling and/or by counteracting reflex arteriolar vasodilatation. The present multicenter, randomized, placebo-controlled study was designed to evaluate the efficacy of this drug for the long-term management of patients with recurrent vasovagal syncope.

METHODS AND RESULTS

In the 20 participating centers, 126 patients with recurrent vasovagal syncope (at least 3 episodes in the last 2 years) and a positive baseline head-up tilt response were randomly assigned to placebo (63 patients) or etilefrine at a dosage of 75 mg/d (63 patients) and were followed up for 1 year or until syncope recurred. The primary end-point of the study was the first recurrence of syncope. There were no differences between the 2 study groups in the patients' baseline characteristics. During follow-up, the group treated with etilefrine had a similar incidence of first syncopal recurrence to that of placebo group both in the intention-to-treat analysis (24% versus 24%) and in on- treatment analysis (26% versus 24%). Moreover, the median time to the first syncopal recurrence did not significantly differ between the 2 study groups (106 days in the etilefrine arm and 112 days in the placebo arm).

CONCLUSIONS

Oral etilefrine is not superior to placebo in preventing spontaneous episodes of vasovagal syncope. Randomized controlled studies are essential to assess the real usefulness of any proposed therapy for patients with vasovagal syncope.

Resumption of motor vehicle operation in vasovagal fainters

This study surveyed current practice patterns with respect to the manner by which cardiac arrhythmia specialists advise patients with vasovagal syncope regarding resumption of motor vehicle operation. Among 66 physician-respondents from 9 countries, 98% indicated that they rely on tilt-table testing to establish a diagnosis, and, if an effective treatment is found based on serial tilt-table testing, they recommend a 6- to 7-week symptom-free waiting period before advising return to driving.

Efficacy and safety of clonazepam in refractory neurally mediated syncope

Neurally mediated syncope is a complex syndrome that is often difficult to manage using currently available treatment strategies. The efficacy and safety of clonazepam was evaluated in 35 patients with refractory neurally mediated syncope. All patients had syncope (n = 33) or disabling presyncope (n = 2) and a positive head-up tilt table test (HUTT) despite treatment with one or more of the following therapies: beta-blocker, high-salt diet, fludrocortisone, elastic compression stockings, and disopyramide. Clonazepam was initiated at 0.5 mg/day and titrated in 0.25-0.5 mg/day increments for symptom control. Early (first 8 weeks) symptomatic response was achieved in 31 of 35 (89%) patients. Early HUTT reverted to negative in 29 of 35 (83%) patients. Two patients discontinued clonazepam during early follow-up due to side effects. Thirty-three patients received long-term clonazepam therapy. Twenty-five patients had late HUTT with 21 remaining negative. Of the eight patients who did not have late HUTT, one patient discontinued clonazepam prior to HUTT due to side effects. Seven patients refused late HUTT. All seven patients achieved symptomatic control on clonazepam with two requiring dose titration. Of the 21 patients with a negative late HUTT, 18 achieved symptomatic control with two of these patients requiring dose titration. Two patients who had only partial symptom control despite dose titration achieved total symptomatic control with the addition of disopyramide and beta-blockers. Two patients with a negative late HUTT discontinued clonazepam due to side effects. One patient had been symptomatically controlled while the other had recurrent symptoms with dose limiting side effects occurring after clonazepam dose titration. In the 4 patients with a positive late HUTT, 2 patients were symptomatically controlled, 1 patients required combination therapy with a beta-blocker to achieve symptomatic control, and 1 patient discontinued therapy due to side effects. Overall, 29 of 35 (83%) patients continue to receive clonazepam with symptom control. Based on intention-to-treat HUTT results, 21 of 35 (60%) patients were responders. Four patients required clonazepam dose titration and three required combination therapy with clonazepam plus disopyramide and/or a beta-blocker to achieve control. Clonazepam was discontinued in 6 patients, 5 for side effects and 1 following a transient ischemic attack. Clonazepam appears to be an effective therapeutic alternative in patients with refractory neurally mediated syncope. Based on our preliminary findings, a placebo controlled evaluation of clonazepam in neurally mediated syncope is warranted.

Poor reproducibility of false-positive tilt testing results in healthy volunteers

Positive responses to head-up tilt testing occur in healthy subjects. However, the reproducibility of "false-positive" tilt testing results has not been clarified. To study the reproducibility of "false-positive" responses, we prospectively performed 2 tilt tests separated by 1 to 10 (mean 3.2) weeks in 20 healthy males aged 23 to 40 years (mean 30 years). The baseline tilt test (80 degrees for 30 minutes) ended positive in 4 (20%) subjects on the initial test and 2 (10%) on the second test with only 1 (5%) who had consecutive positive responses. No additional positive responses were noted during the isoproterenol (0.01 microgram/kg/min)-tilt test for 10 minutes. We demonstrated that a false-positive response occurred in 5 (25%) of 20 young males who underwent 2 tilt tests, however, only 1 (5%) subject had consecutive positive responses. Poor reproducibility may be characteristic of false-positive responses in head-up tilt testing.

Use of sublingual nitroglycerin during head-up tilt-table testing in patients >60 years of age

Previous work had demonstrated a reduced specificity associated with head-up tilt protocols using high-dose isoproterenol in patients between 20 and 50 years of age. We evaluated the specificity of head-up tilt testing using different isoproterenol infusion doses and administration of nitroglycerin in patients aged >60 years. In addition, whether the same protocols have impact on the sensitivity of the test was also assessed. One hundred sixty subjects were included in this study. Seventy-six were volunteers randomized to either head-up tilt test with low-dose, 3- and 5-microg/min of isoproterenol (group I) or to a protocol including 0.4 mg of sublingual nitroglycerin (group II). In addition, after an upright tilt drug-free state, 58 patients with a history of syncope underwent repeat head-up tilt with increasing doses of isoproterenol infusion, followed by sublingual nitroglycerin if the test result remained negative. The remaining 33 patients were subjected to the nitroglycerin protocol after the drug-free state phase. In the control groups, the incidence of false-positive responses was 88% and 95%, respectively. In patients with syncope after a negative test result during 5 microg of isoproterenol infusion, nitroglycerin administration increased the number of positive responses from 45% to 79%. The percentage of positive tilt in patients undergoing nitroglycerin administration after the drug-free state part of the protocol was 78%. Administration of nitroglycerin was the most significant predictor of a positive upright tilt in patients with syncope. In subjects aged >60 years, head-up tilt protocols with high-dose isoproterenol infusion and nitroglycerin maintained an adequate specificity. In this subset of patients, nitroglycerin seemed to provide a better sensitivity than isoproterenol.

Usefulness of pindolol in neurocardiogenic syncope

We prospectively studied the efficacy of pindolol, a beta-adrenergic blocker with intrinsic sympathomimetic activity (ISA), for the prevention of syncope recurrences in 31 patients with recurrent neurocardiogenic syncope. Pindolol proved to be an effective treatment, even in patients who had previously failed treatment with conventional beta blockers, suggesting a clinical benefit from addition of ISA to beta blockade in this setting.

Long-term effects of pharmacological therapy for vasovagal syncope on the basis of reproducibility during head-up tilt testing

The purpose of this study was to determine the efficacy of long-term pharmacological therapy selected on the basis of a head-up tilt test (HUT) in patients in whom reproducibility of the HUT response was demonstrable in the initial study. The HUT (80 degrees upright) was performed for 15 min with or without an infusion of isoproterenol (0.01-0.03 microgram/kg per min) in 54 patients with recurrent unexplained syncope. When vasovagal syncope was induced (positive response), the HUT was repeated to examine the test reproducibility. Vasovagal syncope was induced in 24 patients during HUT alone, and in 30 patients during the HUT with isoproterenol. Acute reproducibility was observed in 49/54 (91%) patients. In the tilt-positive patients, HUT was repeated after an intravenous administration of propranolol (0.1 mg/kg) or disopyramide (1 mg/kg) (acute test). Propranolol proved effective in 21 (80%) of 26 patients, and disopyramide in 13 (56%) of 23 patients. Thereafter, evaluation was done on the long-term clinical follow-up of the pharmacological intervention selected on the basis of the acute test in the 34 patients in whom the HUT could not induce vasovagal syncope after the oral administration of the pharmacological agent (propranolol 60 mg/day, disopyramide 300 mg/day). Thirty-two of 34 patients (94%) did not develop syncopal attacks during a 44 +/- 12-month period. Thus, in patients with unexplained syncope, HUT appears to have a high degree of acute reproducibility, and the acute drug response guided by HUT may be used to develop an effective long-term pharmacological therapy.

Usefulness of intravenous metoprolol to prevent syncope induced by head-up tilt

Intravenous metoprolol was found to be significantly more effective than placebo in preventing head-up tilt-table induced neurally mediated syncope. The reproducibility of acute tilt-table testing is only 63% and suggests caution in the interpretation of acute drug testing during tilt-table studies.

Midodrine: a role in the management of neurocardiogenic syncope

OBJECTIVE

To determine the benefit of midodrine, an alpha agonist, on symptom frequency and haemodynamic responses during head up tilt in patients with neurocardiogenic syncope.

SETTING

Cardiovascular investigation unit (a secondary and tertiary referral centre for the investigation and management of syncope).

PATIENTS

16 outpatients (mean (SD) age 56 (18) years; five men) with frequent hypotensive symptoms (more than two syncopal episodes and fewer than 20 symptom free days per month), and reproducible syncope with glyceryl trinitrate (GTN) during head up tilt.

DESIGN AND INTERVENTION

Randomised double blind placebo controlled study. Patients were randomised to receive either placebo or midodrine for one month. Symptom events were recorded during each study month. At the end of each study month patients completed a quality of life scoring scale (Short Form 36) and a global assessment of therapeutic response. They received GTN with head up tilt for measurement of heart rate (electrocardiography), phasic blood pressure (digital photoplethysmography), and thoracic fluid index (transthoracic impedance plethysmography) during symptom provocation.

RESULTS

Patients administered midodrine had an average of 7.3 more symptom free days than those who received placebo (95% confidence interval (CI) 4.6 to 9; p < 0.0001). Eleven patients reported a positive therapeutic response with midodrine (p = 0.002). All domains of quality of life showed improvement with midodrine, in particular physical function (8.1; 95% CI 3.7 to 12.2), energy and vitality (14.6; 95% CI 7.3 to 22.1), and change in health status (22.2; 95% CI 11 to 33.4). Fourteen patients who were given placebo had tilt induced syncope compared with six given midodrine (p = 0.01). Baseline supine systolic blood pressure was higher and heart rate lower in patients who received midodrine than in those who were given placebo (p < 0.05). A lower thoracic fluid index in patients administered midodrine indicates increased venous return when supine and during head up tilt. There were no serious adverse effects.

CONCLUSIONS

Midodrine had a conspicuous beneficial effect on symptom frequency, symptoms during head up tilt, and quality of life. Midodrine is recommended for the treatment of neurocardiogenic syncope in patients with frequent symptoms.

Can adenosine 5'-triphosphate be used to select treatment in severe vasovagal syndrome?

BACKGROUND

Selection of treatment in vasovagal syndrome should be guided by the mechanism of symptoms. This study determined whether a simple drug test may assess one mechanism.

METHODS AND RESULTS

To identify patients at risk of severe cardioinhibitory response of vagal origin, we infused 20 mg ATP into 316 patients hospitalized for recurrent syncope (n=195) or presyncope (n=121) of unknown origin and into normal subjects (n=51). We then assessed the ECG and clinical responses to the drug, recommended therapy, and followed up the subjects chronically. A cardiac pause > 10 seconds was seen in only 3 normal subjects (6%). Therefore, a pause < or = 10 seconds yielded the approximately 95th percentile of the normal range. ATP provoked a pause > 10 seconds in 130 symptomatic patients (41%) and a pause < or = 10 seconds in 186 symptomatic patients (59%). Thus, symptomatic patients with pauses > 10 seconds were proposed for pacemaker implantation; all other patients and normal subjects were simply monitored. Among long-pause patients with follow-up, the observed recurrence rate for the 104 with pacemakers was one-third that for the 21 who were only monitored (P<.0001). Among followed-up short-pause patients, the rate in the 153 monitored-only patients did not differ from the 20 implanted patients (P=.432).

CONCLUSIONS

The vagal effect of ATP may identify the subgroup of patients at high risk of severe cardioinhibitory response of vagal origin who likely will benefit from pacemaker therapy. This fast, uncomplicated test should be considered for further use in screening patients with vasovagal syndrome.

Systolic blood pressure at rest, not the degree of beta blockade, predicts the result of follow-up tilt-table testing for vasovagal syncope

Tilt-table testing after therapy with beta blockade is frequently used to predict clinical success. This study found that heart rate and blood pressure reductions after beta-blocker therapy did not predict the results of the follow-up tilt-table test, but low blood pressure at rest before the initial test predicts failure of this therapy.

Induction of paradoxic bradycardia in rats by inferior vena cava occlusion during the administration of isoproterenol: the essential role of augmented sympathetic tone

INTRODUCTION

Testing human susceptibility for vasodepressor reactions involves combining venous return restriction by passive upright tilting and administering isoproterenol. While sympathetic tone is usually increased by the stimuli that incite a vasodepressor reaction, it is not known if the increased sympathetic tone is an essential or passive component of the mechanism that triggers the reaction. Given that paradoxic bradycardia is a major manifestation of vasodepressor reactions and allowing for the possible extrapolation between paradoxic bradycardia in rats and vasodepressor reactions, we examined the role of sympathetic tone in the paradoxic bradycardia reaction. Paradoxic bradycardia was induced in rats by inferior vena cava occlusion during an isoproterenol infusion. To examine the role of increased sympathetic tone on this reaction, we studied whether carotid artery perfusion (80 to 100 mmHg) during inferior vena cava occlusion, a maneuver that blunts the rise in sympathetic tone, inhibits paradoxic bradycardia.

METHODS AND RESULTS

The maximum changes in R-R were measured during 60 seconds of inferior vena cava occlusion as follows: (a) in control the heart rate accelerated (delta R-R - 10.2 +/- 2.3 msec, P < 0.001); (b) during an infusion of isoproterenol, paradoxic bradycardia occurred (delta R-R + 140.6 +/- 18.2 msec, P < 0.001), and this was inhibited by common carotid artery perfusion (delta R-R - 6.6 +/- 1.5 msec, P < 0.001); and (c) following carotid sinus denervation and during an infusion of isoproterenol, paradoxic bradycardia was induced without and with carotid artery perfusion (delta R-R + 122.6 +/- 12.0 msec, P < 0.001; delta R-R + 151.8 +/- 12.7 msec, P < 0.001, respectively).

CONCLUSIONS

Since carotid artery perfusion during inferior vena cava occlusion inhibits paradoxic bradycardia only when the carotid sinus is innervated, we conclude that carotid artery perfusion blocks the reaction by increasing carotid sinus afferents, thereby limiting the increased sympathetic tone during inferior vena cava occlusion, and not as a result of cerebral perfusion. Thus, the paradoxic bradycardia resulting from inferior vena cava occlusion requires activation of sympathetic tone as a result of carotid sinus hypotension.