The incidence of malignant vasovagal syndrome in patients with recurrent syncope

A predictive index of biomarkers for ictogenesis from tier I safety pharmacology testing that may warrant tier II EEG studies

Three significant contributions to the field of safety pharmacology were recently published detailing the use of electroencephalography (EEG) by telemetry in a critical role in the successful evaluation of a compound during drug development (1] Authier, Delatte, Kallman, Stevens & Markgraf; JPTM 2016; 81:274-285; 2] Accardi, Pugsley, Forster, Troncy, Huang & Authier; JPTM; 81: 47-59; 3] Bassett, Troncy, Pouliot, Paquette, Ascaha, & Authier; JPTM 2016; 70: 230-240). These authors present a convincing case for monitoring neocortical biopotential waveforms (EEG, ECoG, etc) during preclinical toxicology studies as an opportunity for early identification of a central nervous system (CNS) risk during Investigational New Drug (IND) Enabling Studies. This review is about "ictogenesis" not "epileptogenesis". It is intended to characterize overt behavioral and physiological changes suggestive of drug-induced neurotoxicity/ictogenesis in experimental animals during Tier 1 safety pharmacology testing, prior to first dose administration in man. It is the presence of these predictive or comorbid biomarkers expressed during the requisite conduct of daily clinical or cage side observations, and in early ICH S7A Tier I CNS, pulmonary and cardiovascular safety study designs that should initiate an early conversation regarding Tier II inclusion of EEG monitoring. We conclude that there is no single definitive clinical marker for seizure liability but plasma exposures might add to set proper safety margins when clinical convulsions are observed. Even the observation of a study-related full tonic-clonic convulsion does not establish solid ground to require the financial and temporal investment of a full EEG study under the current regulatory standards.

PREFATORY NOTE

For purposes of this review, we have adopted the FDA term "sponsor" as it refers to any person who takes the responsibility for and initiates a nonclinical investigations of new molecular entities; FDA uses the term "sponsor" primarily in relation to investigational new drug application submissions.

Dominant Transmission Observed in Adolescents and Families With Orthostatic Intolerance

BACKGROUND

Orthostatic intolerance is typically thought to be sporadic and attributed to cerebral autonomic dysfunction. We sought to identify families with inherited autonomic dysfunction manifest as symptomatic orthostatic intolerance to characterize mode of inheritance and clinical features.

METHODS

Sixteen families with two or more first- or second-degree relatives with autonomic dysfunction and orthostatic intolerance were enrolled. A clinical diagnosis of autonomic dysfunction defined by symptomatic orthostatic intolerance diagnosed by head-up tilt table testing was confirmed for each proband. Clinical features and evaluation were obtained from each proband using a standardized intake questionnaire, and family history information was obtained from probands and available relatives.

RESULTS

Comprehensive pedigree analysis of 16 families (39 individuals with orthostatic intolerance and 40 individuals suspected of having orthostatic intolerance) demonstrated dominant transmission of autonomic dysfunction with incomplete penetrance. Affected individuals were predominantly female (71.8%, 28/39; F:M, 2.5:1). Male-to-male transmission, although less common, was observed and demonstrated to transmit through unaffected males with an affected parent. Similar to sporadic orthostatic intolerance, probands report a range of symptoms across multiple organ systems, with headaches and neuromuscular features being most common.

CONCLUSIONS

Familial occurrence and vertical transmission of autonomic dysfunction in 16 families suggest a novel genetic syndrome with dominant transmission, incomplete penetrance, and skewing of the sex ratio. Elucidation of potential genetic contributions to orthostatic intolerance may inform therapeutic management and identification of individuals at risk. Adolescent evaluation should include identification and treatment of potential at-risk relatives.

A long-term follow-up of patients with prolonged asystole of greater than 15s on head-up tilt testing

BACKGROUND

Head-up tilt (HUT) is used for diagnosis of vasovagal syncope (VVS), and can provoke cardioinhibition. VVS is usually considered benign, however pacemaker insertion may be indicated in some patients. We sought to characterize the long-term outcomes of patients with prolonged asystole (>15s) on HUT.

METHODS

We conducted a retrospective study on patients with asystole >15s on HUT identified from 5133 patients who were investigated between 1998 and 2012 at our institution. Patients were mailed questionnaires or telephoned to ascertain outcomes. Where contact was not possible, the patients' general practitioners were contacted to request up-to-date information.

RESULTS

A total of 26 patients with a mean age of 45 ± 18 years and a mean duration of asystole on HUT of 26 ± 7s were successfully followed up from a total of 77 patients identified. The follow-up duration was 99 ± 39 months. Six patients had undergone pacemaker (PPM) implantation. Of the patients without PPM, 16 reported spontaneously improved symptoms. Ten patients sustained injury prior to HUT compared with one after HUT, when a clear diagnosis was made and management advice was given. There were no major injuries or deaths after HUT. The 6 patients with PPMs had a mean age of 60 ± 16 (67% male) at HUT. Four patients had no further syncope after PPM and two demonstrated improvement but still experienced recurrent syncope.

CONCLUSIONS

Prolonged asystole (>15s) on tilt does not necessarily predict adverse outcomes with most patients improving spontaneously over the long-term. Pacemaker insertion in selected patients may reduce syncope recurrence but does not always abolish it.

Cerebral blood flow of children with vasovagal syncope

INTRODUCTION

We aimed to evaluate changes in the cerebral blood supply in children during vasovagal syncope and to clarify the diagnostic value of transcranial Doppler for vasovagal syncope.

MATERIALS AND METHODS

Patients were divided into three groups. Group 1 consisted of 31 patients who were symptomatic and whose head-up tilt test was positive. Group 2 comprised 21 patients who were symptomatic but whose tilt test was negative. Group 3 included 22 healthy children. For the diagnosis of vasovagal syncope, the tilt test was applied. For the subjects of the patient and control groups, the tilt test was repeated. The flow rates of bilateral middle cerebral arteries were continuously and simultaneously recorded with temporal window transcranial Doppler.

RESULTS

There were no statistically significant differences between the three groups with respect to age and gender distribution (p>0.05). When the bed was at an upright position, the maximum blood flow rate of the right middle cerebral artery was lower in Group 1 than in Group 2, although the decrease was more significant in comparison to the healthy control group (p<0.05). The minimum blood flow rate of the right middle cerebral artery was lower in Group 1 than the Group 2, although the decrease was more significant in comparison with the healthy control group (p<0.05). The maximum blood flow rate of the left middle cerebral artery was significantly lower in Group 1 than in the control group (p<0.05).

CONCLUSION

Minimum and maximum blood flow rates are significantly decreased in patients tilt test (+) patients with vasovagal syncope during orthostatic stress.

Cardiac asystole during head up tilt (HUTT) in children and adolescents: is this benign physiology?

Cardiac asystole during HUTT has been described by some investigators as a benign finding with no major sequelae. Our aim in this study is to correlate the severity of clinical symptoms and physiologic findings prior and during the asystole occurrence. This is a retrospective study review of 536 patients who underwent HUTT for dysautonomia symptoms for the last 3 years. HUTT in our institution consists of 10 min in supine, 30 min of head up at 70°, and recline to supine for 10 min. Physiologic parameters recorded include continuous heart rate, BP, cardiac stroke volume, brain blood flow by near-infra red spectroscopy, sympathetic and parasympathetic tones. Patients' complaints and signs during HUTT were recorded. Follow-up was conducted up to 34 months. Cardiac asystole was defined as the absence of ventricular activity for ≥3 s with cessation of BP signal for the same period on the monitor. Of the 536 patients studied, 25 patients developed cardiac asystole (4.7%). The asystolic group age was 15.1 + 3.8 years and weighed 56.7 + 21 kg. All the patients fainted and were not able to complete the test with average head up time of 13.8 + 7.1 min. The cardiac asystole duration was 9.2 + 5.8 s. Sixteen patients developed convulsions during the asystole. There was sudden intense vagal tone prior to and during the asystole. Brain perfusion was significantly decreased in all the patients after head up and sharply dropped by 20-35% in patients who developed convulsions. All patients completely recovered their consciousness after reposition to supine. During recovery, there was overshoot of the brain perfusion above the baseline for several minutes and the HR returned to baseline. Follow-up of these patients: only one patient had a single lead pacemaker, otherwise the 24 patients had no cardiac pacing and were treated by medical therapy. During mean follow-up of 19 + 10 months, five patients developed syncope which resolved after optimizing medical therapy. Cardiac asystole due to neurocardiogenic syncope and dysautonomia has high association with brain anoxia that can lead to convulsions. Such patients require intense medical therapy and close observation with possible intervention by cardiac pacing if prolonged asystole occurs. There is a concern of consequence future brain function.

Neurocardiogenic syncope during a routine colonoscopy: an uncommon malignant presentation

Neurocardiogenic syncope (NCS) is a common clinical entity. Most of these patients are managed medically by internists and general practitioners. Though NCS is frequently a benign disease, a malignant form of this disorder with episodes of prolonged cardioinhibition culminating in asystole is described. Here, we describe a 52-year-old woman who had such a life threatening malignant form of arrhythmia during a routine colonoscopy and review the literature of similar cases.

Late Recognition of Malignant Vasovagal Syncope

A 21-year-old female with a history of seizures since the age of 5 presented for long-term electroencephalographic (EEG) monitoring, but was found instead to have neurocardiogenic syncope. Is it appropriate for this patient to get a pacemaker?

Orthostatic syndromes differ in syncope frequency

BACKGROUND

There are conflicting opinions on whether postural tachycardia syndrome predisposes to syncope. We investigated this relationship by comparing the frequency of syncope in postural tachycardia syndrome and orthostatic hypotension.

METHODS

We queried our autonomic laboratory database of 3700 patients. Orthostatic hypotension and postural tachycardia syndrome were defined in standard fashion, except that postural tachycardia syndrome required the presence of orthostatic symptoms and a further increase in heart rate beyond 10 minutes. Syncope was defined as an abrupt decrease in blood pressure and often, heart rate, requiring termination of the tilt study. Statistical analysis utilized Fisher's exact test and Student's t test, as appropriate.

RESULTS

Of 810 patients referred for postural tachycardia syndrome, 185 met criteria while another 328 patients had orthostatic hypotension. Of the postural tachycardia syndrome patients, 38% had syncope on head-up tilt, compared with only 22% of those with orthostatic hypotension (P<.0001). In the postural tachycardia group, syncope on head-up tilt was associated with a clinical history of syncope in 90%, whereas absence of syncope on head-up tilt was associated with a clinical history of syncope in 30% (P<.0001). In contrast, syncope on head-up tilt did not bear any relationship to clinical history of syncope in the orthostatic hypotension group (41% vs 36%; P=.49).

CONCLUSION

Our results demonstrate that syncope (both tilt table and clinical) occurs far more commonly in patients who have postural tachycardia syndrome than in patients with orthostatic hypotension. These findings suggest that one should be clinically aware of the high risk of syncope in patients with postural tachycardia syndrome, and the low-pressure baroreceptor system that is implicated in postural tachycardia syndrome might confer more sensitivity to syncope than the high pressure system implicated in orthostatic hypotension.

Brain perfusion assessed by 99mTc-ECD SPECT imaging in pediatric patients with neurally mediated reflex syncope

BACKGROUND

The involvement of cardiogenic and neurogenic mechanisms in neurally mediated reflex syncope is well documented. In our previous studies in patients with neurally mediated reflex syncope, we have found evidence for differential regulation of the noradrenergic receptors in tilt-positive and tilt-negative patients. The present work concentrates on the observations of differences in regional brain perfusion using brain SPECT via injecting the patient at the completion of the tilt test.

METHODS AND RESULTS

The following study was designed to assess the reduction and regional differences in cerebral blood flow by means of SPECT using technetium-99m labeled V-oxo-1,2-N1ethylenedylbisl-cysteine diethylester (ECD) in patients with an injection during tilt testing. Twenty patients with NMS were included in the study with a mean age of 12.2 years (age range; 8-16 years). HUT was positive in 10 patients and negative in 10 patients. When tilt (+) and tilt (-) were evaluated together, regional cortical/cerebellum ratios were ranging from 0.85 to 1.25 in different cortical areas with highest variability of perfusion index in left frontoparietal cortex. The lowest perfusion index values were observed in the left anterior frontal region followed by the left prefrontal-frontoparietal-anterior, parietal-orbito frontal, and anterior temporal regions where perfusion is predominantly supplied via the anterior and middle cerebral arteries, while these differences did not reach statistical significance in a single dominant region compared to the other regions examined using ANOVA (P > 0.05) with this sample size. Decreases in [99mTc]ECD uptake were more widespread regionally on the left hemisphere than were decreases in right side of the brain. However when tilt- and tilt+ groups were compared, perfusion was significantly lower in the right periinsular posterior parietal and temporal regions (P < 0.05) in tilt + group.

CONCLUSION

These tilt induced regional differences in brain perfusion suggest the distinct roles of middle cerebral artery dominant territory-related vasodepressor compensation mechanisms in neurally mediated reflex syncope phenomena where cerebral lateralization of cardiac control and insular ischemia may play an important role.

Predictors of positive head-up tilt test in patients with suspected neurocardiogenic syncope or presyncope

Neurocardiogenic syncope is the most common cause of syncope in patients who present in outpatient clinics. Head-up tilt test (HUT) has been widely used to diagnose neurocardiogenic syncope. However, the HUT does not always produce a positive response in patients with suspected neurocardiogenic syncope. The aim of the present study was to assess the clinical history and characteristics of patients with suspected neurocardiogenic syncope or presyncope who undertook HUT, and to identify prognostic factors of a positive HUT response. During the first phase of HUT, patients were tilted to a 70-degree angle for 30 minutes. If the first phase produced a negative response, the second phase was subsequently performed involving intravenous isoproterenol administration. Of 711 patients, 423 (59.5%) patients showed a positive HUT response. In contrast to previous studies, this study showed that the vasodepressive type (76.6%) was the most common pattern of positive response, and that the rate of positive response during the first phase was low (7.1%). By multivariate analysis, the occurrence of junctional rhythm was found to be a predictor of an impending positive response in HUT (P < 0.001). The shorter time interval between the last episode and HUT was also a predictor of positive response (P = 0.0015). Younger age (P = 0.0003) and a history of physical injury during a syncopal episode (P = 0.019) were found to be associated with a positive response in the first phase of HUT.

[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.

[Diagnostic accuracy of a protocol in the evaluation of unexplained syncope]

INTRODUCTION AND OBJECTIVES

To assess the diagnostic capacity of a protocol to study syncope of unknown cause in which electrophysiological studies and tilting table tests are selectively used.

PATIENTS AND METHODS

The study was performed in 137 consecutive patients (94 men and 43 women, with a mean age of 57.6+/-18.3 years) with syncope of unknown cause after the initial clinical evaluation, who were divided into two groups. Group A consisted of 77 patients meeting any of the following criteria: a) presence of structural heart disease; b) abnormal ECG; c) presence of significant non-symptomatic arrhythmia in the Holter recording, and d) presence of paroxysmal palpitations. These patients initially underwent an electrophysiological study. Group B consisted of 60 patients not meeting any of the above criteria, who were initially submitted to tilting table tests.Results. In group A, the electrophysiological study was positive in 43 patients (55%). In group B, the tilting test was positive in 41 patients (68%). Among patients in group A with a negative study, 20 (59%) were submitted to the tilting table test, with positive results in 7 cases (35%). Five patients from group B with a negative tilting test underwent the electrophysiological study, which was negative in all of them. Overall, a positive diagnosis was achieved in 91 of 137 patients (66%).

CONCLUSIONS

In patients with syncope of a non-apparent cause in the initial assessment, selective use of electrophysiological studies or tilting table tests, guided by clinical criteria, allows for a positive diagnosis in over 60% of the cases. Our results suggest that the tilting table test should be performed in cases of group A with a negative electrophysiological study.

Formal analysis of the optimal duration of tilt testing for the diagnosis of neurally mediated syncope

BACKGROUND

Although tilt testing has emerged as the test of choice for assessing patients with suspected neurally mediated syncope, the optimum duration of tilt testing is poorly defined. This in part relates to the absence of a gold standard to assess test performance.

OBJECTIVE

Our purpose was to formally estimate the effects of varying duration of drug-free tilt testing on test performance in diagnosing neurally mediated syncope.

DESIGN

If a test's specificity is known, then in the absence of a gold standard an imputed (estimated) sensitivity may be calculated on the basis of the observed diagnostic yield in a given population as a function of assumed population prevalence. We determined the relationship of specificity to drug-free tilt test duration by use of data from 11 previous studies reporting the results of drug-free tilt testing in a total of 435 control subjects (60 to 80 degrees of tilt, footboard support, 15- to 60-minute duration). Data (weighted for study size) were fit to an exponential function relating specificity to tilt duration. Test yield was evaluated as a function of tilt duration in 213 consecutive patients referred to our laboratory for the evaluation of suspected neurally mediated syncope who underwent passive tilt testing for up to 30 to 60 minutes.

RESULTS

The estimated specificity of tilt testing was 94% at 30 minutes, 92% at 40 minutes, and 88% after 60 minutes of passive tilt. The cumulative yield of tilt testing was only 17% at 30 minutes, 22% at 40 minutes, and 28% after 60 minutes. On the basis of an estimated population prevalence of 25% to 50% in this referral population, imputed sensitivity is 27% to 48% at 30 minutes, 36% to 64% at 40 minutes, and 43% to 74% after 60 minutes of passive tilt. The overall diagnostic accuracy was not strongly influenced by tilt duration beyond 30 minutes and ranged from 60% to 84%.

CONCLUSIONS

Passive tilt testing (ie, tilt testing without pharmacologic provocation) for durations of up to 60 minutes has limited sensitivity for diagnosing neurally mediated syncope. For populations with a pretest likelihood of 25% to 50%, test results are inaccurate in one to two fifths of patients.

Provocation of neurocardiogenic syncope by clomipramine administration during the head-up tilt test in vasovagal syndrome

OBJECTIVES

We sought to test the hypothesis that activation of the serotonergic system in patients with vasovagal syndrome during the head-up tilt test provokes syncope.

BACKGROUND

Central serotonergic activation participates in the pathogenesis of neurocardiogenic syncope. Drugs increasing serotonin (5-HT) in the central nervous system have not been tested as drug challenges during the head-up tilt test with clomipramine (Clom-HUT).

METHODS

The serotonergic re-uptake inhibitor clomipramine was infused (5 mg in 5 min) at the start of Clom-HUT in 55 patients (mean age 40 +/- 17 years) with a positive history of recurrent neurocardiogenic syncope and in 22 healthy control subjects (mean age 46 +/- 15 years). Blood samples were taken at 0, 5, 10 and 20 min for estimation of plasma prolactin and cortisol as neuroendocrine indicators of central serotonergic responsivity. All subjects had been previously tested with a basic 60 degrees head-up tilt test (B-HUT) for 30 min, and if negative, isoproterenol infusion was given at the end of the test.

RESULTS

Twenty-nine (53%) of the 55 patients and none of the 22 control subjects had a positive result in the B-HUT. With Clom-HUT, the proportion of patients who experienced a positive response increased to 80% (n = 44), although this happened to only one control subject. Prolactin and cortisol plasma levels increased significantly in the positive Clom-HUT patient group only.

CONCLUSIONS

The results indicate an increased responsivity of the central serotonergic neural system in subjects with vasovagal syndrome, the activation of which leads to sympathetic withdrawal. The use of clomipramine infusion with the tilt test seems to considerably improve its diagnostic value.

Misdiagnosis of epilepsy: many seizure-like attacks have a cardiovascular cause

OBJECTIVES

We sought to investigate the value of cardiovascular tests to diagnose convulsive syncope in patients with apparent treatment-resistant epilepsy.

BACKGROUND

As many as 20% to 30% of epileptics may have been misdiagnosed. Many of these patients may have cardiovascular syncope, with abnormal movements due to cerebral hypoxia, which may be difficult to differentiate from epilepsy on clinical grounds.

METHODS

Seventy-four patients (33 men, mean age 38.9 +/- 18 years [range 16 to 77]) who were previously diagnosed with epilepsy were studied. Inclusion criteria included continued attacks despite adequate anticonvulsant drug treatment (n = 36) or uncertainty about the diagnosis of epilepsy, on the basis of the clinical description of the seizures (n = 38). Each patient underwent a head-up tilt test and carotid sinus massage during continuous electrocardiography, electroencephalography and blood pressure monitoring. Ten patients subsequently underwent long-term electrocardiographic (ECG) monitoring with an implantable loop recorder.

RESULTS

In total, an alternative diagnosis was found in 31 patients (41.9%), including 13 (36.1%) of 36 patients taking an anticonvulsant medication. Nineteen patients (25.7%) developed profound hypotension or bradycardia during the head-up tilt test, confirming the diagnosis of vasovagal syncope. One other patient had a typical vasovagal reaction during intravenous cannulation. Two patients developed psychogenic symptoms during the head-up tilt test. Seven patients (9.5%) had significant ECG pauses during carotid sinus massage. In two patients, episodes of prolonged bradycardia correlated precisely with seizures according to the insertable ECG recorder.

CONCLUSIONS

A simple, noninvasive cardiovascular evaluation may identify an alternative diagnosis in many patients with apparent epilepsy and should be considered early in the management of patients with convulsive blackouts.

Safety and tolerability of an aggressive tilt table test protocol in the evaluation of patients with suspected neurocardiogenic syncope

Safety and tolerability of a one-step tilt table test with high dose (5 micrograms/min) isoproterenol (ISO) without intermediate stages were evaluated in a symptomatic population of 300 patients referred for clinical syncope, near syncope, or dizziness. ISO has been used as a provocative test but remains controversial. A population of 118 male and 182 female patients with a mean age of 45 (range 5-90) years underwent 300 tests. Heart rate and blood pressure were monitored continuously. A positive test was one in which clinical symptoms were reproduced or hemodynamic criteria met. Patients were initially supine for 5 minutes followed by head upright tilt (HUT) to an angle of 80 degrees for 10 minutes. Negative tests were repeated with an infusion of ISO at a rate of 5 micrograms/min. HUT was positive in 133 (44.3%) of 300 tests. With a 10-minute HUT alone, only 17 (5.7%) of 300 of tests were positive. Of the initial negative tests, 273 of 283 were tested with ISO. With ISO, 116 (42.5%) of 273 were positive. ISO in high dose (5 micrograms/min) was used in 264 of 273 patients, while low dose (1.0-2.5 micrograms/min) was used in 9 of 273 under special circumstances. High dose ISO was tolerated in 164 (62.1%) of 264 patients, reduced in 87 (33%) of 264, and discontinued in 11 (4.2%) of 264. Reasons for reduction included tachycardia (40 patients), nausea (31 patients), chest pain (2 patients), arrhythmia (5 patients), or other (9 patients). Adverse effects resolved within 1 minute of dose reduction. This one-step high dose ISO protocol reproduced neurocardiogenic syncope in symptomatic patients who tested negative without ISO and was safe, tolerated, and expeditious.

False positive head-up tilt: hemodynamic and neurohumoral profile

OBJECTIVES

This study examined differences in mechanisms of head-up tilt (HUT)-induced syncope between normal controls and patients with neurocardiogenic syncope.

BACKGROUND

A variable proportion of normal individuals experience syncope during HUT. Differences in the mechanisms of HUT-mediated syncope between this group and patients with neurocardiogenic syncope have not been elucidated.

METHODS

A 30-min 80 degrees HUT was performed in eight HUT-negative volunteers (Group I), eight HUT-positive volunteers (Group II) and 15 patients with neurocardiogenic syncope. Heart rate and blood pressure (BP) were monitored continuously. Epinephrine and norepinephrine plasma levels, as well as left ventricular dimensions and contractility determined by echocardiography, were measured at baseline and at regular intervals during the test.

RESULTS

The main findings of this study were the following: 1) All parameters were similar at baseline in the three groups; and 2) During tilt: a) the time to syncope was shorter in Group III than in group II (9.5 +/- 3 vs. 17 +/- 3 min p < 0.05); b) there was an immediate, persisting drop in mean BP in Group III; c) the decrease rate of left ventricular end-diastolic dimensions was greater in Group III than in Group II or Group I (-1.76 +/- 0.42 vs. -0.87 +/- 0.35 and -0.67 +/- 0.29 mm/min, respectively, p < 0.05); d) the leftventricular shortening fraction was greater in Group III than in the other two groups (39 +/- 1 vs. 34 +/- 1 and 32 +/- 1%, respectively, p < 0.05); and e) although the norepinephrine level remained comparable among the groups, there was a significantly higher peak epinephrine level in Group III than in Group II and Group I (112.3 +/- 34 vs. 77.6 +/- 10 and 65 +/- 12 pg/ml, p < 0.05).

CONCLUSIONS

Mechanisms of syncope during HUT appeared to be different in normal volunteers and patients with neurocardiogenic syncope. In the latter, there was evidence of an impaired vascular resistance response from the beginning of the orthostatic challenge. Furthermore, in the patients there was more rapid peripheral blood pooling, as indicated by the echocardiographic measurements of left ventricular end-diastolic changes, leading to more precocious symptoms. In syncopal patients, the higher level of plasma epinephrine probably mediated the increased cardiac contractility and possibly contributed to the impaired vasoconstrictive response.

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.

Using a tilt table to evaluate syncope

Upright tilt testing is commonly used in the evaluation of patients with syncope to provoke hypotension and/or bradycardia in the laboratory. The most common type of response is provocation of neurally mediated syndrome (vasovagal syncope). The American College of Cardiology Expert Consensus has proposed indications for tilt testing. The most common indication is recurrent syncope of unexplained cause. Upright tilt testing methods have not been standardized. The most common protocols in this country use a tilt angle of 60-80 degrees and use isoproterenol infusion after a period of drug-free tilt testing. The sensitivity of upright tilt testing is estimated to be 67-83%, and the specificity is between 75 and 100%. The reproducibility of the test has been variable. In patients with unexplained syncope, positive responses are found to be 50% without the use of isoproterenol and 64% with the use of isoproterenol. Many different treatments have been used. At this time, there is no consensus regarding the most effective treatment. Beta-blockers and fludrocortisone plus salt are the most commonly used drugs. Pacemakers have been used, but their role is ill-defined at this time.

Neurally mediated syncope: pathophysiology and implications for treatment

Neurally mediated syncope may occur in patients whose hemodynamic picture does not fit the characteristics of orthostatic intolerance as described elsewhere in this issue. Nonetheless, patients who suffer from neurocardiogenic or vasovagal syncope may be seriously incapacitated by their episodes of syncope or presyncope. Although it has been assumed that vagal activation as a result of stimulation of ventricular mechanoreceptors is essential to the production of these episodes, several critical observations are presented that suggest that other mechanisms may also be operative in some patient subsets. In addition, evidence is presented that the sympathetic responses of many of these patients may be reduced rather than increased and that abnormal baroreflex responsiveness may also play an causative role. These findings suggest new avenues for therapy in this field in which carefully controlled, randomized, double-blind trials are scarce.

Central serotonergic responsiveness in neurocardiogenic syncope: a clomipramine test challenge

BACKGROUND

Central serotonergic mechanisms appear to participate in the pathogenesis of recurrent neurally mediated syncope. The aim of the study was to investigate the responsiveness of the central serotonergic system by measuring the prolactin and cortisol responses to intravenous administration of the serotonin reuptake inhibitor clomipramine.

METHODS AND RESULTS

Twenty subjects free of any medical treatment were tested. Twelve had a history of recurrent syncopal attacks and positive tilt test (patient group, mean age 47+/-18 years, 8 men); 8 subjects without syncope and a negative tilt test result served as control subjects (mean age 49+/-10 years, 5 men). Twenty-five milligrams of clomipramine was administered intravenously within 15 minutes, and blood samples were taken at 0, 15, 30, 45, and 60 minutes. Two days later, a tilt test was performed at 60 degrees for 30 minutes and blood samples were taken at 0, 10, 20, and 30 minutes. During the clomipramine challenge, plasma prolactin levels increased in both groups. The levels at 30 minutes were higher in the patient group compared with the control group (17.3+/-7.2 vs 9.3+/-7.6 ng/mL, P=0.05). Similar results were observed for cortisol at 30 minutes (172+/-15 vs 118+/-21 ng/mL P=0. 04) and at 45 minutes (189+/-20 vs 116+/-23 ng/mL, P=0.03). The tilt test was positive in 8 (67%) out of 12 of the patient group and negative in all control subjects. In the samples taken during the tilt test, significant increases in prolactin and cortisol were observed only in the subjects with positive tilt test results.

CONCLUSIONS

Patients with a history of neurocardiogenic syncope show a higher responsiveness of the central serotonergic system to clomipramine challenge. The results support the view that central serotonergic mechanisms are involved in the pathophysiology of the syndrome.

Yohimbine in neurally mediated syncope. Pathophysiological implications

In this study, we evaluated if increased sympathetic stimulation is an essential requirement for the development of neurally mediated syncope (NMS) by manipulating overall sympathetic outflow in subjects susceptible to tilt-induced syncope. Eight previously characterized patients with recurrent NMS (five females and three males; 34+/-2 yr) were recruited from the Vanderbilt Syncope Unit and eight age-matched controls underwent initial administration of clonidine (CLO) or yohimbine (YHO). This was done, prospectively, to determine doses of these agents that would increase or decrease plasma norepinephrine levels by >/= 30%. On a different day, in all subjects we determined intraarterial blood pressure, EKG and muscle sympathetic nerve activity (MSNA) both supine and during upright tilt. After this, subjects randomly received either CLO or YHO, and 3 h later another tilt was performed. After 1 wk, a similar procedure with the other drug was performed. During the two basal tilts, all the control subjects completed the study, whereas all the NMS patients developed syncope. Reduction in sympathetic tone by CLO resulted in a decreased tolerance to tilt in three out of eight controls and in all the NMS patients. In contrast, YHO not only increased basal plasma NorEpi levels and MSNA, but also prevented syncope in seven out of eight patients. In a selected population of patients, increased sympathetic activity is not a prerequisite for the development of syncope. Yohimbine-induced enhancement of sympathetic tone in patients with NMS improves orthostatic tolerance and raises the possibility that this drug may be a useful agent in the treatment of NMS.

Variable cerebral dysfunction during tilt induced vasovagal syncope

Electroencephalographic (EEG) monitoring was performed during head-up tilt testing (HUT) in a group of 63 consecutive patients (27 males, 36 females, mean age 41.5 years) with a history of recurrent syncope of unknown origin despite extensive clinical and laboratory evaluation. Syncope occurred in 27/63 patients (42.8%) during HUT and was cardioinhibitory in 11/27 (40.7%) and vasodepressor in 16/27 (59.3%). All patients with a negative response to HUT had no significant EEG modifications. In patients with vasodepressor syncope a generalized high amplitude 4-5 Hz (theta range) slowing of EEG activity appeared at the onset of syncope, followed by an increase in brain wave amplitude with a reduction of frequency at 1.5-3 Hz (delta range). The return to the supine position was associated with brain wave amplitude reduction and frequency increase to 4-5 Hz, followed by restoration of a normal EEG pattern and arousal (mean total duration of syncope 23.2 s). In patients with cardioinhibitory syncope, a generalized high amplitude EEG slowing in the theta range was noted at the onset of syncope, followed by a brain wave amplitude increase and slowing in the delta range. A sudden reduction of brain wave amplitude ensued leading to the disappearance of electroencephalographic activity ("flat" EEG). The return to the supine position was not followed by immediate resolution of EEG abnormalities or consciousness recovery, both occurring after a longer time interval (mean total duration of syncope 41.4 s). EEG monitoring during HUT allowed the recording and systematic description of electroencephalographic abnormalities developing in the course of tilt induced vasovagal syncope.

Randomized, double-blind, placebo-controlled trial of oral enalapril in patients with neurally mediated syncope

BACKGROUND

The purpose of this study was to study the effect of enalapril on neurally mediated syncope (NMS). Several agents (except for angiotensin-converting enzyme [ACE] inhibitors) have been used to treat patients with NMS. It is unknown whether ACE inhibitors have beneficial effects on NMS.

METHODS AND RESULTS

Thirty subjects who had reproducible NMS induced with head-up tilt table test (HUT) were randomly assigned and divided in double-blind fashion into placebo and enalapril (an ACE inhibitor) groups. Hemodynamics and plasma catecholamine concentrations were studied. Before administration of enalapril, syncope induced by HUT was associated with vigorous hypotension and bradycardia. Plasma catecholamine concentrations were significantly elevated during NMS compared with the supine position before tilt. Oral enalapril rather than placebo produced a marked reduction in diastolic blood pressure during supine positioning before tilt. Administration of enalapril prevented HUT-induced NMS and increase of plasma catecholamine concentrations in all patients examined. Conversely, placebo had no effect in the majority of patients with NMS (12 of 15 subjects). Follow-up data showed that NMS disappeared in 14 (93%) of 15 patients treated with enalapril.

CONCLUSIONS

This study demonstrates that ACE inhibitors may efficiently prevent NMS, presumably through inhibition of sympathetic system activation and peripheral hypotensive effect.

Electroencephalographic correlates of vasovagal syncope induced by head-up tilt testing

BACKGROUND AND PURPOSE

We sought to determine whether the introduction of EEG monitoring during head-up tilt testing could significantly improve the understanding of the cerebral events occurring during tilt-induced vasovagal syncope and the potential danger to the patient of this diagnostic procedure.

METHODS

EEG monitoring was performed during head-up tilt testing in a group of 63 consecutive patients (27 males and 36 females; mean age, 41.5 years) with a history of recurrent syncope of unknown origin despite extensive clinical and laboratory assessment.

RESULTS

Syncope occurred in 27 of 63 patients (42.8%) during head-up tilt testing and was found to be cardioinhibitory in 11 of 27 (40.7%) and vasodepressor in 16 of 27 (59.3%). All patients with a negative response to head-up tilt testing showed no significant EEG modifications. In patients with vasodepressor syncope, a generalized high-amplitude, 4- to 5-Hz (theta range) slowing of EEG activity appeared at the onset of syncope, followed by an increase of brain-wave amplitude with the reduction of frequency at 1.5 to 3 Hz (delta range). The return to the supine position was associated with brain-wave amplitude reduction and frequency increase to 4 to 5 Hz, followed by restoration of a normal EEG pattern and arousal (mean total duration of syncope, 23.2 seconds.). In patients with cardioinhibitory syncope, a generalized high-amplitude EEG slowing in the theta range was noted at the onset of syncope, followed by a brain-wave amplitude increase and slowing in the delta range. A sudden reduction of brain-wave amplitude then ensued, leading to the disappearance of electrocerebral activity ("flat" EEG). The return to the supine position did not allow either the immediate resolution of EEG abnormalities or consciousness recovery, both of which occurred after a further time interval (mean total duration of syncope, 41.4 seconds.).

CONCLUSIONS

EEG monitoring during head-up tilt testing allowed recording and systematic description of electrocerebral abnormalities developing in the course of tilt-induced vasovagal syncope.

Autonomic control of vasovagal syncope

In the pathophysiological study of vasovagal syncope, the nature of the interaction between baroreceptor sensitivity (BS), sympathetic withdrawal, and parasympathetic activity has yet to be ascertained. Altered BS may predispose toward abnormal sympathetic and parasympathetic responses to orthostasis, causing hypotension that may progress to syncope if there is sympathetic withdrawal. To examine this hypothesis, we monitored blood pressure (BP), heart rate (HR), BS, forearm blood flow, and muscle nerve sympathetic activity (MNSA) continuously in 18 vasovagal patients during 60 degrees head-up tilt, syncope, and recovery. Results were compared with those of 17 patients who were able to tolerate tilt for 45 min. During early tilt, BP was maintained in both groups by an increase in HR and MNSA from baseline (P < 0.01), but BS decreased more in the syncopal group (P < 0.05). At the start of presyncope (mean 2.7 +/- 0.2 min before syncope and 15.2 +/- 12 min after tilt), when BP fell, HR and sympathetic activity remained increased from baseline (P < 0.01). Thereafter, BP and HR correlated directly with sympathetic activity and regressed in linear fashion until syncope (P < 0.001), whereas BS increased to baseline. At syncope, BP, HR, and sympathetic activity fell below baseline (P < 0.01, P < 0.05, and P < 0.01, respectively), but BS did not increase. During recovery, sympathetic activity increased to baseline and BS increased (P < 0.05), whereas HR and BP remained low (P < 0.01 and P < 0.05, respectively). The mechanism for the initiation of hypotension during presyncope remains unknown, but BS may contribute. Vasodilatation and bradycardia during presyncope appear to be more closely related to withdrawal of sympathetic activity than to increased parasympathetic cardiac activity.

Reproducibility of tilt table testing in patients with vasovagal syncope and its relation to variations in autonomic nervous system activity

To assess the variability of head-up tilt table testing, 35 patients with vasovagal syncope, shown by a positive tilt table test, underwent a second test 1 week later. Also, on the day before each test, spectral and time-domain indexes of heart rate variability were derived from Holter recordings to examine the stability of autonomous nervous system activity in these patients. Fifteen healthy volunteers served as a control group and also underwent two tilt table tests with prior Holter monitoring. Twenty-one (60%) of the 35 patients had a second positive test. None of the patients in the control group experienced syncope during either of the tests. The heart rate variability measures in the control group varied slightly from 1 day to the other, in contrast to the syncopal patients, where only low frequency spectral power and the mean of all 5-minute standard deviations of RR intervals showed comparable behavior. The indexes which reflect parasympathetic activity exhibited significant fluctuations in the syncopal patients. These fluctuations were due entirely to the patients who did not reproduce the outcome of the tilt table test, where high parasympathetic tone was associated with the positive test and normal parasympathetic tone with the negative test. In contrast, the patients with two positive tests had high parasympathetic tone during both test periods, with low individual variability. In conclusion, patients with vasovagal syncope show variations in vagal autonomic tone and appear to be more prone to syncope when their parasympathetic tone is elevated.

Spectral analysis of heart rate variability during tilt-table testing in patients with vasovagal syncope

Spectral analysis of heart rate variability was used to assess changes in autonomic function in 44 patients with vasovagal syndrome and 20 normal controls before and during postural tilt and to attempt to relate such changes to specific types of haemodynamic response to tilt. Frequency domain measurements of the high (HF) and low (LF) frequency bands and the ratio LF/HF were derived from Holter recordings, computed by Fast Fourier Analysis for 4 min intervals immediately before tilt testing, immediately after tilting and just before the end of the test. In the syncopal patients the mean values of LF and HF decreased significantly in response to tilting, while the LF/HF ratio remained constant. All parameters showed a statistically significant increase just before the onset of syncope. In the control group there was an increase in the LF and LF/HF ratio and a decrease in the HF immediately after tilting. The three subgroups of patients had similar patterns of changes in autonomic activity. The results of this study show that syncopal patients have a different pattern of response to the tilting test. The pathological mechanism leading to vasovagal syncope appears to be independent of the specific type of haemodynamic response to tilt testing.

Hormonal responses during tilt-table test in neurally mediated syncope

The hormonal profile during tilt testing was examined in syncopal patients. An increase in the growth hormones cortisol and prolactin was found during syncope, suggesting an implication of central serotonergic activation.

Sympathetic and baroreceptor reflex function in neurally mediated syncope evoked by tilt

The pathophysiology of neurally mediated syncope is poorly understood. It has been widely assumed that excessive sympathetic activation in a setting of left ventricular hypovolemia stimulates ventricular afferents that trigger hypotension and bradycardia. We tested this hypothesis by determining if excessive sympathetic activation precedes development of neurally mediated syncope, and if this correlates with alterations in baroreflex function. We studied the changes in intraarterial blood pressure (BP), heart rate (HR), central venous pressure (CVP), muscle sympathetic nerve activity (MSNA), and plasma catecholamines evoked by upright tilt in recurrent neurally mediated syncope patients (SYN, 5+/-1 episodes/mo, n = 14), age- and sex-matched controls (CON, n = 23), and in healthy subjects who consistently experienced syncope during tilt (FS+, n = 20). Baroreflex responses were evaluated from changes in HR, BP, and MSNA that were obtained after infusions of phenylephrine and sodium nitroprusside. Compared to CON, patients with SYN had blunted increases in MSNA at low tilt levels, followed by a progressive decrease and ultimately complete disappearance of MSNA with syncope. SYN patients also had attenuation of norepinephrine increases and lower baroreflex slope sensitivity, both during tilt and after pharmacologic testing. FS+ subjects had the largest decrease in CVP with tilt and had significant increases in MSNA and heart rate baroreflex slopes. These data challenge the view that excessive generalized sympathetic activation is the precursor of the hemodynamic abnormality underlying recurrent neurally mediated syncope.

[Long-term prognosis of patients with syncope of unknown origin in prolonged asystole induced by the head-up tilt test]

INTRODUCTION AND OBJECTIVES

Prognosis and therapeutic assessment of patients with syncope and prolonged asystole during head-up tilt test remain unclear. The aim of the present study was to analyze the clinical evolution of patients with syncope of unknown origin, no heart disease and severe cardioinhibitory response induced by head-up tilt.

METHODS

A prospective follow-up study was performed in 12 patients (6 male and 6 female, mean age 31 +/- 20 years) with recurrent syncope, no heart disease and affected by severe cardioinhibitory syncope induced by head-up tilt test. This was defined as syncope or near-syncope induced by baseline or isoproterenol tilt with asystole of > or = 3 seconds. All patients were re-tilted twice: with salt and fluid and with metoprolol (25 mg/b.i.d). According to the results of these tests, 5 patients were discharged with dietetic measures (salt & fluid) and 5 with metoprolol. In 2 patients who showed recurrent prolonged asystole a DDD pacemaker was implanted.

RESULTS

After follow-up of 34 +/- 20 months all patients ae alive. The number of recurrences was small (2 syncopes and 2 near-syncopes). No relationship was observed between the number of syncopal recurrences and the applied treatment.

CONCLUSIONS

We conclude that prolonged asystole induced by head-up tilt test does not confer an adverse prognosis in patients with syncope of unknown origin and no heart disease, thus, the clinical evolution of these patients is benign.

Driving issues related to arrhythmic syncope

The safety of driving in patients with cardiac arrhythmias is a common concern. Although the risk of driving in these patients cannot be reduced to zero, available data and expert consensus suggest that most patients with arrhythmias can return to driving with a relatively low risk of harm to themselves and others, that is, a risk within the limits deemed acceptable by society. Specific recommendations for allowing patients with various cardiac rhythm abnormalities to drive are reviewed in detail.

Clinical approach to diagnosis of syncope. An Overview

Effective management of the syncope patient is critically dependent on excluding conditions in which altered consciousness is not due to syncope (e.g., seizure and sleep disorders) then establishing the basis for syncopal symptoms. The initial diagnostic step in syncope patients is differentiation of those individuals with normal cardiovascular status from those with structural heart disease. In the former, tilt-table testing and related studies of autonomic nervous system function are usually the most productive direction in which to proceed. In patients with structural heart disease, a functional assessment of the suspected structural disturbance (i.e., hemodynamic, angiographic, imaging as appropriate) and evaluation for susceptibility to symptomatic arrhythmias by monitoring or conventional electrophysiologic testing is appropriate. Autonomic function testing should follow if the diagnosis remains unclear. In only a few instances should specialized neurologic studies be undertaken as an initial step. The ultimate objective is always to obtain a sufficiently strong correlation between syncopal symptoms and detected abnormalities to feel confident in the diagnosis, permit an accurate assessment of prognosis, and develop an appropriate treatment plan.

Cardiac pacing for vasovagal syncope: a reasonable therapeutic option?

A number of studies have evaluated the effect of cardiac pacing for prevention of tilt induced vasovagal syncope. The findings are relatively consistent. Pacing does not prevent the onset of vasovagal syncope. This is predictable since hypotension (vasodepressor effect) typically occurs prior to bradycardia. However, dual chamber may prolong the presyncopal period in patients with a prominent cardioinhibitory component. Further, the relation of laboratory observations to spontaneous events is uncertain. In the largest retrospective assessment of pacing efficacy, 89% of patients reported improved symptoms and 62% remained free of symptom recurrence over 50 months.

Tilt testing: a useful screen for rate-drop response

Tilt testing is accepted as the main tool for the diagnosis of neurocardiogenic syncope, particularly in the "malignant" vasovagal form. As a result of experience with tilt testing, the cardiovascular responses to head-up tilting in patients with malignant vasovagal syncope (MVVS) have been defined in respect of the vasodepressor (hypotensive) and cardioinhibitory (bradycardic) components. Pacing therapy has been of limited value in the past, with controversy about its role, even in the cardioinhibitory form of MVVS. With the advent of more sophisticated algorithms for pacing (i.e., rate-drop response [RDR], Thera DR) in response to the onset of bradycardia in MVVS, however, this therapy is being reexamined. This article examines the blood pressure and heart rate responses to head-up tilt in patients with MVVS and examines the role of this test in screening such patients for the benefits of pacing with RDR. Careful analysis of the pattern of blood pressure and heart rate response during the tilt test may allow selection of those patients likely to respond to RDR and may provide useful information for initial programming of the algorithm.

Neurally mediated syncopal syndromes: pathophysiological concepts and clinical evaluation

The neurally mediated syncopal syndromes encompass a number of apparently related disturbances of reflex cardiovascular control characterized by transient inappropriate bradycardia and/or vasodilation of various arterial and venous beds. Certain of these syndromes (e.g., carotid sinus syndrome, postmicturition syncope) are encountered occasionally in clinical practice, whereas others are quite rare (e.g., swallow syncope). On the other hand, vasovagal syncope occurs so frequently, that as a group, the neurally mediated syncopal syndromes are among the most important causes of syncope. The pathophysiology of the neurally mediated syncopal syndromes is incompletely understood, but can be considered in terms of four basic elements: (1) the afferent limb; (2) central nervous system (CNS) processing; (3) the efferent limb; (4) feedback loops. The afferent limb consists of several peripheral and CNS trigger sites and the associated connections to medullary cardiovascular centers. CNS processing and efferent signals result in both bradycardia, which may be marked or relative, and vasodilatation. Failure of baroreceptor feedback controls to prevent hypotension is important in facilitating development of symptomatic hypotension. Head-up tilt table testing has become the diagnostic technique of choice for clinically assessing susceptibility to neurally mediated syncope, particularly of the vasovagal type. Most studies suggest that such testing discriminates relatively well between symptomatic patients and asymptomatic control subjects, of whom 10%-15% have a false-positive test results. Sensitivity of tilt table testing is more difficult to evaluate because there is no accepted diagnostic gold standard. However, sensitivity (measured against a classic presentation) has been estimated to range from 32%-85%, with most reports favoring the higher end of this range. Treatment strategies for neurally mediated syncope remain controversial. Many single episodes do not warrant treatment unless physical injury has occurred, or a high risk occupation or avocation is involved. Tilt test exposure alone may prove beneficial in educating patients with recurrent syncope to recognize warning signs of an imminent faint. Large controlled clinical studies have not been performed to test the efficacy of pharmacological therapy (e.g., beta-adrenergic blockers, disopyramide, serotonin reuptake blockers, vasoconstrictors) or pacing therapy. Such studies may be difficult to undertake due to the variable frequency of spontaneous symptoms and apparent long periods of remission. Nonetheless, many investigators and clinicians have come to rely on these agents, and on tilt testing to guide treatment decisions. Studies employing careful correlation of long-term clinical follow-up with results of early and perhaps later repeat tilt studies are still needed.

Baroreflex sensitivity in patients with vasovagal syncope

BACKGROUND

In the present study, we tested the hypothesis that baroreflex sensitivity is reduced in patients with vasovagal syncope compared with normal control subjects.

METHODS AND RESULTS

We investigated 30 patients with vasovagal syncope (mean age, 43.6 +/- 16.7 years; 14 men and 16 women) and 32 normal control subjects (mean age, 41.8 +/- 17.0 years; 24 men and 8 women). Cardiopulmonary baroreceptor sensitivity was assessed by measuring the change in forearm vascular resistance during subhypotensive lower body negative pressure (LBNP). Carotid baroreflex sensitivity was assessed by measuring the change in RR interval during the manipulation of carotid transmural pressure. Phenylephrine baroreceptor sensitivity was assessed on the basis of the linear regression slope of the RR interval versus systolic blood pressure during the increment in blood pressure after intravenous administration of phenylephrine. In patients with vasovagal syncope, during the application of -10 mm Hg LBNP, forearm vascular resistance decreased by 0.7 +/- 11.6 U versus an increase of 8.3 +/- 6.2 U in control subjects (P = .002). Phenylephrine baroreceptor sensitivity was 11 +/- 7 ms/mm Hg in patients versus 14 +/- 6 ms/mm Hg in control subjects (P = NS). Carotid baroreflex sensitivity was 4 +/- 6 versus 4 +/- 2 ms/mm Hg in patients and control subjects, respectively (P = NS).

CONCLUSIONS

In patients with vasovagal syncope, during the application of subhypotensive LBNP, there is impaired forearm vasoconstriction or paradoxical forearm vasodilation. This suggests impaired cardiopulmonary baroreceptor inactivation or paradoxical activation of these receptors and is consistent with reduced cardiopulmonary baroreceptor sensitivity.

Reproducibility of time-domain indexes of heart rate variability in patients with vasovagal syncope

The aim of this study was to examine whether the indexes of heart rate variability (HRV) are stable from day-to-day in patients with vasovagal syncope and whether the stability of the HRV indexes is linked with that of the clinical results of the tilt test. Nineteen patients with a history of syncopal episodes and a positive tilt test underwent a second test 1 week later. Of these, 11 (group P-P) also had a positive second test, whereas 8 (group P-N) had a negative second test. Fifteen healthy volunteers served as a control group. Five time domain indexes were derived: the mean of all coupling intervals between normal beats (mean NN), the SD about the mean of all coupling intervals between normal beats (SDNN), the mean of all 5-minute standard deviations of NNs (SD), the proportion of adjacent normal RR intervals differing by >50 ms (pNN50), the root-mean-square of the difference between successive RRs (rMSSD) and the standard deviations of 5-minute mean NN intervals (SDANN). The control group showed good reproducibility of all HRV indexes (slope 0.86 to 0.97). The syncopal patients taken as a whole had significantly less reproducibility than the controls in the pNN50 parameter. This difference was due entirely to the patients in the P-N group, who had a remarkable lack of reproducibility in both the pNN50 and rMSSD measures (slope pNN50, 0.52; rMSSD, 0.78), whereas the P-P group had a reproducibility of all HRV indexes, which was no different from that in controls (slope 0.83 to 1.04). In patients with vasovagal syncope, certain HRV measures that express parasympathetic tone did not show the high reproducibility found in normal subjects. Syncopal patients who lack reproducibility in these HRV parameters also show a lack of reproducibility in the clinical result of tilt testing.