Pharmacologic approaches to therapy for vasovagal syncope

Predicting Vasovagal Responses: A Model-Based and Machine Learning Approach

Vasovagal syncope (VVS) or neurogenically induced fainting has resulted in falls, fractures, and death. Methods to deal with VVS are to use implanted pacemakers or beta blockers. These are often ineffective because the underlying changes in the cardiovascular system that lead to the syncope are incompletely understood and diagnosis of frequent occurrences of VVS is still based on history and a tilt test, in which subjects are passively tilted from a supine position to 20° from the spatial vertical (to a 70° position) on the tilt table and maintained in that orientation for 10–15 min. Recently, is has been shown that vasovagal responses (VVRs), which are characterized by transient drops in blood pressure (BP), heart rate (HR), and increased amplitude of low frequency oscillations in BP can be induced by sinusoidal galvanic vestibular stimulation (sGVS) and were similar to the low frequency oscillations that presaged VVS in humans. This transient drop in BP and HR of 25 mmHg and 25 beats per minute (bpm), respectively, were considered to be a VVR. Similar thresholds have been used to identify VVR's in human studies as well. However, this arbitrary threshold of identifying a VVR does not give a clear understanding of the identifying features of a VVR nor what triggers a VVR. In this study, we utilized our model of VVR generation together with a machine learning approach to learn a separating hyperplane between normal and VVR patterns. This methodology is proposed as a technique for more broadly identifying the features that trigger a VVR. If a similar feature identification could be associated with VVRs in humans, it potentially could be utilized to identify onset of a VVS, i.e, fainting, in real time.

Fludrocortisone in Pediatric Vasovagal Syncope: A Retrospective, Single-Center Observational Study

Background and Purpose

The purpose of this study was to determine the effect of fludrocortisone in patients with pediatric vasovagal syncope (VVS).

Methods

This retrospective observational single-tertiary-center study based on chart reviews included 74 patients who were newly diagnosed with VVS in the head-up tilt-table test (HUTT). Some of the patients had been treated with fludrocortisone. All patients were assessed using a brain and cardiac workup before treatment to rule out the syncope being due to other causes, which resulted in seven of them being excluded: two for epilepsy and five for brain pathologies. The remaining 67 patients were analyzed. The effect of fludrocortisone was evaluated based on the results of a follow-up HUTT, with a response to the treatment considered to be present if there was a negative change at the follow-up HUTT. Univariate logistic regression were used for statistical analyses, with the criterion for significance being p<0.05.

Results

There were no significant differences in the characteristic of the patients between the no-medication (n=39) and fludrocortisone (n=28) groups, including age, sex, and duration of treatment. The recurrence rate of syncopal or presyncopal events was significantly lower in the fludrocortisone group (39.3%, 11 of 28) than in the no-medication group (64.1%, 25 of 39) (p=0.044), as was the rate of negative change at the follow-up HUTT: 57.1% (16 of 28) and 28.2% (11 of 39), respectively (p=0.017).

Conclusions

Our findings suggest that fludrocortisone is more effective than no medication in pediatric patients with VVS.

Vestibular Activation Habituates the Vasovagal Response in the Rat

Vasovagal syncope is a significant medical problem without effective therapy, postulated to be related to a collapse of baroreflex function. While some studies have shown that repeated static tilts can block vasovagal syncope, this was not found in other studies. Using anesthetized, male Long–Evans rats that were highly susceptible to generation of vasovagal responses, we found that repeated activation of the vestibulosympathetic reflex (VSR) with ±2 and ±3 mA, 0.025 Hz sinusoidal galvanic vestibular stimulation (sGVS) caused incremental changes in blood pressure (BP) and heart rate (HR) that blocked further generation of vasovagal responses. Initially, BP and HR fell ≈20–50 mmHg and ≈20–50 beats/min (bpm) into a vasovagal response when stimulated with Sgv\S in susceptible rats. As the rats were continually stimulated, HR initially rose to counteract the fall in BP; then the increase in HR became more substantial and long lasting, effectively opposing the fall in BP. Finally, the vestibular stimuli simply caused an increase in BP, the normal sequence following activation of the VSR. Concurrently, habituation caused disappearance of the low-frequency (0.025 and 0.05 Hz) oscillations in BP and HR that must be present when vasovagal responses are induced. Habituation also produced significant increases in baroreflex sensitivity (p < 0.001). Thus, repeated low-frequency activation of the VSR resulted in a reduction and loss of susceptibility to development of vasovagal responses in rats that were previously highly susceptible. We posit that reactivation of the baroreflex, which is depressed by anesthesia and the disappearance of low-frequency oscillations in BP and HR are likely to be critically involved in producing resistance to the development of vasovagal responses. SGVS has been widely used to activate muscle sympathetic nerve activity in humans and is safe and well tolerated. Potentially, it could be used to produce similar habituation of vasovagal syncope in humans.

A Model of Blood Pressure, Heart Rate, and Vaso-Vagal Responses Produced by Vestibulo-Sympathetic Activation

Blood Pressure (BP), comprised of recurrent systoles and diastoles, is controlled by central mechanisms to maintain blood flow. Periodic behavior of BP was modeled to study how peak amplitudes and frequencies of the systoles are modulated by vestibular activation. The model was implemented as a relaxation oscillator, driven by a central signal related to Desired BP. Relaxation oscillations were maintained by a second order system comprising two integrators and a threshold element in the feedback loop. The output signal related to BP was generated as a nonlinear function of the derivative of the first state variable, which is a summation of an input related to Desired BP, feedback from the states, and an input from the vestibular system into one of the feedback loops. This nonlinear function was structured to best simulate the shapes of systoles and diastoles, the relationship between BP and Heart Rate (HR) as well as the amplitude modulations of BP and Pulse Pressure. Increases in threshold in one of the feedback loops produced lower frequencies of HR, but generated large pulse pressures to maintain orthostasis, without generating a VasoVagal Response (VVR). Pulse pressures were considerably smaller in the anesthetized rats than during the simulations, but simulated pulse pressures were lowered by including saturation in the feedback loop. Stochastic changes in threshold maintained the compensatory Baroreflex Sensitivity. Sudden decreases in Desired BP elicited non-compensatory VVRs with smaller pulse pressures, consistent with experimental data. The model suggests that the Vestibular Sympathetic Reflex (VSR) modulates BP and HR of an oscillating system by manipulating parameters of the baroreflex feedback and the signals that maintain the oscillations. It also shows that a VVR is generated when the vestibular input triggers a marked reduction in Desired BP.

The effect of paediatric syncope on health-related quality of life

BACKGROUND

Syncope is common in children and adolescents and most commonly represents neurocardiogenic syncope. No information has been reported regarding the effect of syncope on health-related quality of life in children.

METHODS

This was a retrospective cohort study of patients seen in the Heart Institute Syncope Clinic at Cincinnati Children's Hospital Medical Center between July, 2009 and June, 2010. Health-related quality of life was assessed using the PedsQL™ tool. PedsQL™ scores were compared with both healthy historical controls and historical controls with chronic illnesses.

RESULTS

A total of 106 patients were included for analysis. In all, 90% were Caucasian and 63% were girls. The median age was 15.1 years (8.2-21.6). Compared with healthy controls, patients had lower PedsQL™ scores: Total score (75.2 versus 83.8, p < 0.0001); Physical Health Summary (78.8 versus 87.5, p < 0.0001); Psychosocial Health Summary (73.9 versus 81.9, p < 0.001), Emotional Functioning (68.9 versus 79.3, p < 0.001); and School Functioning (66.4 versus 81.1, p < 0.001). No difference was seen in Social Functioning (86.2 versus 85.2, p = 0.81). Patients also had lower PedsQL™ Total scores than patients with diabetes mellitus (p < 0.0001) and similar scores to patients with asthma, end-stage renal disease, obesity, and structural heart disease.

CONCLUSION

Children with syncope, although typically benign in aetiology, can have low health-related quality of life.

Drugs and pacemakers for vasovagal, carotid sinus and situational syncope

BACKGROUND

Neurally mediated reflex syncope is the most common cause of transient loss of consciousness. In patients not responding to non-pharmacological treatment, pharmacological or pacemaker treatment might be considered.

OBJECTIVES

To examine the effects of pharmacological therapy and pacemaker implantation in patients with vasovagal syncope, carotid sinus syncope and situational syncope.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 1, 2008), PubMed (1950 until February 2008), EMBASE on OVID (1980 until February 2008) and CINAHL on EBSCOhost (1937 until February 2008). No language restrictions were applied.

SELECTION CRITERIA

We included parallel randomized controlled trials and randomized cross-over trials of pharmacological treatment (beta-blockers, fludrocortisone, alpha-adrenergic agonists, selective serotonine reuptake inhibitors, ACE inhibitors, disopyramide, anticholinergic agents or salt tablets) or dual chamber pacemaker treatment. Studies were included if pharmacological or pacemaker treatment was compared with any form of standardised control treatment (standard treatment), placebo treatment, or (other) pharmacological or pacemaker treatment. We did not include non-randomized studies.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the risk of bias. Using a standardised data extraction form, they extracted characteristics and results of the various studies. In a consensus meeting they discussed any disagreements that had occurred during data extraction. If no agreement could be reached, a third reviewer was asked to make a decision. Summary estimates with 95% confidence intervals of treatment effect were calculated using relative risks, rate ratios or weighted means differences depending on the type of outcome reported.

MAIN RESULTS

We included 46 randomized studies, 40 on vasovagal syncope and six on carotid sinus syncope. No studies on situational syncope matched the criteria for inclusion in our review. Studies in general were small with a median sample size of 42. A wide range of control treatments were used with 22 studies using a placebo arm. Blinding of patients and treating physicians was applied in eight studies. Results varied considerably between studies and between types of outcomes.For vasovagal syncope, the occurrence of syncope upon provocational head-up tilt testing was lower upon treatment with beta-blockers, ACE-inhibitors and anticholinergic agents compared to standard treatment. For carotid sinus syncope, the occurrence of syncope upon carotid sinus massage was lower on midodrine treatment compared to placebo treatment in one study.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support the use of any of the pharmacological or pacemaker treatments for vasovagal syncope and carotid sinus syncope. Larger studies using patient relevant outcomes are needed.

Management and therapy of vasovagal syncope: A review

Vasovagal syncope is a common cause of recurrent syncope. Clinically, these episodes may present as an isolated event with an identifiable trigger, or manifest as a cluster of recurrent episodes warranting intensive evaluation. The mechanism of vasovagal syncope is incompletely understood. Diagnostic tools such as implantable loop recorders may facilitate the identification of patients with arrhythmia mimicking benign vasovagal syncope. This review focuses on the management of vasovagal syncope and discusses the non-pharmacological and pharmacological treatment options, especially the use of midodrine and selective serotonin reuptake inhibitors. The role of cardiac pacing may be meaningful for a subgroup of patients who manifest severe bradycardia or asystole but this still remains controversial.

Prospective evaluation of psychological distress and psychiatric morbidity in recurrent vasovagal and unexplained syncope

Syncope is experienced by a third of the population, and in the absence of cardiac pathology is most commonly of vasovagal (VVS) or unexplained origin (US). Psychiatric morbidity has been observed in up to 81% of patients with US but findings with VVS are contradictory. Little is known regarding the chronicity of their psychiatric morbidity.

OBJECTIVE

To determine the psychological profile of patients with recurrent syncope prior to and following diagnostic head-up tilt testing (HUT), and whether it predicts syncope recurrence.

METHOD

Seventy-three women and 43 men (mean age=48+/-16.6) were recruited from all consenting patients referred for HUT. Psychological status (Psychiatric Symptom Index, Anxiety Sensitivity Index (ASI), Fear of Blood Injury Subscale) and presence of mood/anxiety disorders (Primary Care Evaluation of Mental Disorders) were evaluated 1 month prior to and 6 months following HUT. Follow-up data were collected for 83 patients (mean age=48+/-17.34).

RESULTS

At baseline, clinically significant levels of distress were observed in 60% of patients. Those with US (negative HUT) had a fivefold greater risk of suffering from a depressive or anxiety disorder compared to VVS (positive HUT) after controlling for significant covariates. There was no significant change in distress level over follow-up, although psychiatric morbidity dropped from 33% to 22% (P=.049). Syncope recurrence was predicted by elevations in baseline psychological distress (OR=1.544, P=.013) independently of lifetime number of syncopes.

CONCLUSIONS

Patients exhibited high levels of psychological distress and psychiatric morbidity despite reassurance and education received after HUT. Improved screening for and treatment of psychological distress in these patients is critical.

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.

In vivo pharmacodynamic interactions between two drugs used in orthostatic hypotension ? midodrine and dihydroergotamine

A combination of midodrine and dihydroergotamine (DHE) is frequently used clinically in patients suffering from severe orthostatic hypotension (OH). Whereas midodrine acts as a selective, peripheral alpha1-receptor agonist, DHE displays complex pharmacology and can behave as an alpha-adrenergic receptor agonist or antagonist. Surprisingly, the consequences of such a combination on blood pressure have never been investigated. The present study was performed in order to evaluate the pressor effects induced by the administration of both midodrine and DHE in old conscious dogs (n = 6) in experimental condition reproducing autonomic failure-related baroreflex dysfunction (atropine 0.1 mg/kg). For this purpose, we first studied the relative potency and intrinsic activity of each agonist and noradrenaline (NA) for the alpha1-adrenergic receptor. The orders of potency obtained in our study were 0.35, 11 and 400 microg/kg for NA, DHE and midodrine, and intrinsic activity: NA > midodrine > DHE. These results strongly suggest that DHE really acts in vivo as an alpha1-adrenoceptor partial agonist. Afterwards, the pressor effects of coadministration of midodrine (0.4 mg/kg) and DHE (15 microg/kg) were investigated: in one setting, midodrine was first administered, followed by DHE; in another, DHE was first administered, followed by midodrine. Our results show that in conscious dogs, the combination of midodrine and DHE leads to near-complete abolition of the pressor effect induced by the first administered drug. This in vivo proof of such antagonistic effects on blood pressure could explain clinical observations of worsening of OH in humans administered midodrine plus DHE. Although in vivo results obtained in conscious healthy dogs need to be experimentally and clinically confirmed in humans suffering from OH, these results strongly suggest that a midodrine-DHE combined treatment should be avoided in clinical practice.

Long-term outcome of patients with vasovagal syncope

BACKGROUND

After abnormal head-up tilt test (HUT), several trials have evaluated treatment strategies for vasovagal syncope (VVS). However, few unequivocal results have been obtained. The aim of the study was to prospectively analyze the natural history of patients with VVS who did not undergo specific treatment but received education for avoiding syncope after an abnormal HUT.

METHODS

From 1996, 334 consecutive patients with VVS and an abnormal HUT result were followed. All of them received education for avoiding syncope as first-line therapy.

RESULTS

During 30.4 +/- 21 months, there were no cardiac deaths. However, 101 patients (30.2%) had recurrences (1 recurrence, n = 64; > or =2, n = 37), which were not influenced by the type of response during HUT or by age. Time to first recurrence was correlated with the number of recurrences (r: -0.34, P =.0001). Mean recurrence-free time was 50.1 months (95% CI 46-54) and the cumulative probability of no recurrence was 69.8%. Receiver operator character curve analysis, demonstrated significant differences in the recurrence rate between patients with <5 or > or =5 previous episodes of syncope (25.1% vs 44%; P =.001). In addition, the mean recurrence-free time of patients with <5 episodes was significantly longer (54.1 months) than in patients with > or =5 episodes (39.6 months; P =.0005). Multivariate logistic regression identified the previous number of episodes as an independent risk marker of recurrences (odds ratio 2.34, 95% CI 1.4-3.8, P =.001). Age (at HUT performance) as a continuous variable was not a predictor of outcome.

CONCLUSIONS

Survival of patients with VVS presenting after an abnormal HUT is excellent. Although the broad majority of those patients do not suffer recurrences after education, the number of previous syncopal episodes critically influences the recurrence rate.

Autonomic syncope in pediatrics: a practice-oriented approach to classification, pathophysiology, diagnosis, and management

This paper presents a practice-oriented approach to the problem of syncope in pediatrics. Autonomic syncope is the major etiologic category in pediatrics and consists of 2 types: reflex and dysautonomic. The latter type is rare in pediatrics. Reflex syncope has 4 subtypes: neurocardiogenic, central, situational, and cerebral. Neurocardiogenic syncope, the most common subtype, is easily diagnosed by taking a careful, detailed history; identifying diagnostic red flags; performing a complete physical examination; and ordering a minimum of laboratory tests. Patient and parent education is essential, and usually, without medication, outcomes are good.

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.

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.

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.

Specificity and total positive rate of head-up tilt testing potentiated with sublingual nitroglycerin in older patients with unexplained syncope

The aim of this study was to assess the specificity and total positive rate of head-up tilt testing (HUTT) potentiated with sublingual nitroglycerin in detecting the vasovagal origin of unexplained syncope in the elderly, since the diagnostic value of this non-invasive test has not yet been proven in this age group. In a period of 3 years, 128 elderly patients (mean age 71.6+/-5.1 years, 50% males) with syncope of unknown origin, and 101 control subjects matched for age and gender were tilted upright to 60 degrees for 45 minutes. If syncope did not occur, sublingual nitroglycerin (0.4 mg) was administered, and observation was continued for 20 minutes. The positive response was defined as the reproduction of syncope or pre-syncope according to VASIS definition. During the unmedicated phase, syncope occurred in 26 patients (20.3%) and in no members of the control group. After nitroglycerin, 53 patients (41.4%) and 2 control subjects (2%) displayed syncope. The total positive rate of the test was 61.8% with a specificity of 98.0%. In conclusion, HUTT potentiated with sublingual nitroglycerin provides an adequate specificity and total positive rate in old patients with unexplained syncope; therefore it can be proposed as a useful diagnostic tool to detect the vasovagal origin of syncope not only in middle but also in advanced age.

Diagnostic evaluation and management of patients with syncope

This article focuses on the evaluation of patients with syncope, a symptom not a disease. Syncope is a transient loss of consciousness associated with loss of postural tone with spontaneous recovery. The authors discuss the utility of an indications for different diagnostic tests, the indications for hospital admission, and the management of patients with certain known causes of syncope, including vasovagal and arrhythmic.

Syncope

Syncope is a common clinical presentation. Although most commonly benign, it may herald a pathology with a poor prognosis. The work-up of syncope includes a careful history, physical examination, electrocardiogram, risk stratification, and appropriately directed testing. The key factor in the investigation of syncope is the presence (or absence) of structural heart disease or an abnormal electrocardiogram. The most useful investigation in unexplained syncope with a normal heart is the tilt table test for evaluating predisposition to neurocardiogenic (vasovagal) syncope. In the setting of structural heart disease or an abnormal electrocardiogram, electrophysiologic studies play a more important role. The utility of noninvasive cardiac monitoring for symptom-rhythm correlation may be limited by infrequent symptoms. The availability of external and implantable loop recorders allows prolonged periods of monitoring to increase diagnostic yield. The management of patients with syncope may be complex. Early referral to a cardiac electrophysiologist is warranted in patients who are at high risk.

Putting it together: a new treatment algorithm for vasovagal syncope and related disorders

The consensus process that culminated in this symposium established an algorithm to guide the diagnosis and treatment of patients with vasovagal syncope and related disorders. In some patients, the hemodynamic response to standing may identify an abnormality-postural orthostatic tachycardia syndrome or orthostatic hypotension-that can often be treated without further testing. When the response to standing is normal, tilt-table testing may be useful in making the diagnosis of vasovagal syncope and guiding treatment. In some patients, however, the diagnosis is clear from the history, and tilt-table testing may not be necessary. Not all patients with vasovagal syncope need to be treated, and many can be treated effectively with education, reassurance, and a simple increase in dietary salt. In evaluating the results of tilt-table testing, an important consideration is the distinction between vasovagal syncope and the dysautonomic response to tilt characterized by a gradual and progressive decrease in blood pressure that leads to syncope. Current practice patterns suggest that beta blockers, fludrocortisone, and midodrine, are commonly used to treat patients with vasovagal syncope, and patients with the dysautonomic response are generally treated with fludrocortisone and midodrine. Permanent pacing with specialized pacing algorithms should be considered for patients with frequent vasovagal syncope that is refractory to medical therapy. The guidelines proposed here are an amalgam of clinical experience, expert opinion, and research evidence; however, they do not suggest a standard of care for all patients.