Tilt table testing for evaluation of neurally-mediated (cardioneurogenic) syncope: rationale and proposed protocols

Vasovagal syncope is associated with poor prognosis in patients with left ventricular dysfunction

Vasovagal syncope (VVS) is known to have a benign prognosis and be associated with enhanced contraction and activation of the left ventricular (LV) mechanoreceptors. However, a little is known about VVS in patients with LV dysfunction. The present study aimed to investigate the prevalence and prognosis of VVS in patients with LV dysfunction. We enrolled 368 patients with unexplained syncope. In 7 of these patients, LV ejection fraction was lower than 40%. The results of a head-up tilt test (HUT) and the recurrence of syncope were compared between these 7 patients with LV dysfunction and the remaining patients. Positive HUT was obtained in the 6 patients (86%) with LV dysfunction; this rate tended to be higher as compared with normal cardiac function (192/361, 53%, P = 0.069). In patients with LV dysfunction, response in HUT was mostly vasodepressor type (62%); however, most of HUT responses were mixed type in patients with normal LV function (67%). Among patients with positive HUT, the recurrent rate of syncope after HUT was higher in those with LV dysfunction than in those with normal LV function (67 vs. 21%, P = 0.008). VVS in patients with LV dysfunction may be refractory to treatment and could be associated with poor prognosis.

Modified Calgary score in differential diagnosis between cardiac syncope and postural orthostatic tachycardia syndrome-associated syncope in children

The present study was designed to analyse the usefulness of a modified Calgary score system during differential diagnosis between cardiac syncope and postural orthostatic tachycardia syndrome-associated syncope through a large sample sized clinical investigation. The study included 213 children, including 101 boys and 112 girls, with cardiac syncope or postural orthostatic tachycardia syndrome-associated syncope in the age group of 2-19 years (mean 11.8 ± 2.9 years). A modified Calgary score was created, which was analysed to predict differential diagnoses between cardiac syncope and postural orthostatic tachycardia syndrome-associated syncope using a receiver operating characteristic curve. The median of modified Calgary scores for cardiac syncope was -5.0, which significantly differed from that of postural orthostatic tachycardia syndrome (0.0; p < 0.01). The sensitivity and specificity of a differentiation score of less than -2.5 was 96.3% and 72.7%, respectively. Owing to the fact that the modified Calgary score was an integer, when less than -3.0 the diagnosis could be considered as cardiac syncope. The modified Calgary score could be used to make an initial differential diagnosis between cardiac syncope and postural orthostatic tachycardia syndrome-associated syncope in the clinic.

[Heart rate variability and vasovagal syncope]

OBJECTIVE

Tilt Table testing is widely used for the diagnosis and evaluation of vasovagal syncope. By evaluating the fluctuations of the autonomic nervous system that play an important role in syncope genesis, heart rate variability (HRV) can be considered as a tool of added value.

METHODS

We evaluated prospectively 123 patients admitted for recurrent syncope with a positive tilt Table testing. A time domain analysis of a 24 hours ambulatory electrocardiography was used in all patients to asses the particularities of their autonomic function. We compared their results with those obtained from a group of 82 healthy volunteers.

RESULTS

Statistical analysis of the results showed a significant increase of all HRV parameters in the group of vasovagal syncope compared to the healthy volunteers. SDNNidx (58 vs 42; p < 0.001), rMSSD (40 vs 27; p < 0.001), SDNN (102 vs 83; p < 0.001), SDANN (79 vs 67; p< 0.001), pNN50 (11 vs 4.9; p <0.001).

CONCLUSION

Time domain analysis of heart rate variability reveals increased values in patients with vasovagal syncope. It seems to be an interesting, easy and complementary test in the evaluation of syncope of unknown etiology.

A model of orthostatic hypotension in the conscious monkey using lower body negative pressure

INTRODUCTION

Methods most commonly used for detecting susceptibility to orthostatic hypotension in humans include head-up tilt and the application of lower body negative pressure (LBNP). The objective of this study was to evaluate the use of LBNP for detecting drug-induced changes in susceptibility to orthostatic hypotension in conscious monkeys (Macaca fascicularis).

METHODS

Orthostatic responses were produced using an airtight chamber, which sealed around the stomach (umbilical area) and enclosed the lower body, to which were applied successive decrements of 10 mmHg chamber pressure every 5 min until the orthostatic response was observed. Cardiovascular measurements, involving arterial pressures, heart rate, and left ventricular pressures were recorded. The hypotensive agents prazosin and minoxidil were administered to evaluate the ability of the procedure to detect drug-induced changes in the susceptibility to orthostatic hypotension.

RESULTS

A rapid decrease in systolic arterial pressure of >20 mmHg occurring within a 30 s time period was determined to be the best indicator of an orthostatic response. The application of LBNP produced an orthostatic response in all monkeys and on all occasions (100% response). The onset, rate and magnitude of the decrease in systolic blood pressure were also consistent for each monkey. Prazosin (>or=0.16 mg/kg, iv) produced an increase in the susceptibility to the orthostatic response, whereas minoxidil (10 mg/kg, po) had no effect. These results are consistent with previous findings in humans, where similar decreases in arterial pressures occur following the administration of prazosin and minoxidil, whereas increased susceptibility to orthostatic hypotension only occurs with prazosin.

DISCUSSION

The results of this study demonstrate that the application of the LBNP is a reliable method for producing an orthostatic hypotensive response in conscious monkeys. In addition, the use of positive (prazosin) and negative (minoxidil) controls demonstrated that the use of LBNP is a valid method for evaluating the effect of drug treatment on susceptibility to orthostatic hypotension.

Cardiovascular autonomic nervous response to postural change in 610 healthy Japanese subjects in relation to age

To determine the effect of aging on the cardiovascular response to postural change, we examined the cardiovascular sympathetic and parasympathetic response to active standing in 610 healthy Japanese subject (6-83 years) measuring the initial heart rate (HR) response for 3 min in the supine and standing position, we also measured the coefficient of variation of R-R interval (CV(R-R)). As a result, the cardiovascular response to active standing demonstrated a different change with aging between sympathetic and parasympathetic. Sympathetic function was in a sthenia state in young subjects, and that this function declined with age increasing. Whereas, parasympathetic function was immature enough to inhibit the sympathetic tone in young subjects and matured at 20 years of age, and had an ability to inhibit sympathetic tone. CV(R-R) show a linear change that decline with age increasing. These results indicated that the cardiovascular parasympathetic response to active standing shows a characteristic change with aging that differs from cardiovascular parasympathetic at rest represented by CV(R-R). The present study is the first report to demonstrate the cardiovascular response to standing in relation to aging in large population. These results suggested that the cardiovascular response to postural change is dependent on subject's age.

A randomised prospective comparison of three protocols for head-up tilt testing and carotid sinus massage

INTRODUCTION

Head-up tilt testing is an important tool in the diagnosis of syncope. Several different protocols are in use. This study aimed to compare three different protocols in an unselected population of patients with recurrent unexplained syncope and to assess long-term outcome using conventional tilt-directed management or implantable loop recorder (Reveal Plus)-directed management, allowing evaluation of the sensitivity and specificity of the technique.

METHODS

Patients with recurrent unexplained syncope were randomized to one of three tilt protocols: Drug-free--70 degree tilt, 45 min, CSM at 5 and 45 min. GTN--70 degree tilt, 35 min, CSM at 5 min, 400 microg of glyceryl trinitrate spray administered sublingually at 20 min. Adenosine--70 degree tilt, 5 min, CSM when blood pressure is stable in upright position, adenosine bonus at 150 microg/kg after CSM. Tilts were terminated at the onset of syncope, when systolic BP reached 60 mm Hg, or in the presence of prolonged hypotension (> 3 min systolic BP < 80 mm Hg). Appropriate therapies were commenced according to the result of the tilt test. All patients without a definite indication for immediate cardiac pacing (asystolic tilt) were randomized to conventional management or ILR implantation. Recurrent syncopal events were compared to tilt outcome, allowing estimation of sensitivity and specificity.

RESULTS

Of 214 patients, aged 68+/-18 years, 55% were female, with a median of three previous syncopes. 13 patients received pacemakers due to asystolic syncope during tilt testing. The proportion of VASIS classification diagnoses was similar with each protocol; however more positive diagnoses resulted from the GTN protocol (p=0.0013). 47% of patients achieved a diagnosis with tilt testing. We were able to correlate a subsequent spontaneous syncope to tilt result in 36 patients (18%). Heart rate during a spontaneous event was similar to that obtained during tilt testing (+/- 10%) in 55% of cases. Sensitivities for combined protocols, adenosine, GTN, and drug-free protocols were 50%, 50%, 100%, and 21%, respectively. Specificities were 85%, 100%, 75%, and 71%, respectively.

CONCLUSIONS

A high diagnosis rate for unexplained syncope can be achieved with tilt testing. The GTN protocol resulted in significantly more diagnoses than the other compared protocols with good sensitivity and adequate specificity. Sensitivity of the drug-free tilt test was lower than drug-augmented tilt testing.

Autonomic nervous system activity during autologous blood donation for orthognathic surgery

PURPOSE

The aim of this study was to assess by means of power spectral analysis the immediate response of autonomic regulation that occurs with postural change from supine to sitting position (modified head-up tilt test [m-HUT]) during autologous blood donation (ABD) and postphlebotomy infusion.

PATIENTS AND METHODS

We investigated 37 healthy adults who required preoperative ABD before elective orthognathic surgery. Measurements were conducted with m-HUT during ABD and postphlebotomy infusion. The data were analyzed using the maximum entropy method and the difference between supine and tilt was determined by analysis of variance.

RESULTS

When m-HUT was conducted at the resting state, cardiac parasympathetic nervous activity was significantly decreased, whereas cardiac and vascular sympathetic nervous activities were significantly increased. When m-HUT was conducted following blood collection, cardiac parasympathetic nervous activity showed a tendency to increase, whereas vascular sympathetic nervous activity was significantly increased. These changes were not observed during postphlebotomy infusion.

CONCLUSIONS

The m-HUT, which involves postural change from supine to sitting position, may be useful for observing autonomic nervous activity in the clinical setting. ABD carries the risk of imbalance of autonomic regulation. However, postphlebotomy infusion may reduce this imbalance.

Dynamic changes in the QT-R-R relationship during head-up tilt test in patients with vasovagal syncope

BACKGROUND

QT interval is influenced by preceding R-R intervals and autonomic nervous tone. Changes in QT intervals during vasovagal reflex might reflect autonomic modulation of ventricular repolarization; however, this issue has not been fully elucidated. This study aimed to evaluate dynamic response of QT interval to transient changes in R-R interval during vasovagal syncope (VVS) induced by head-up tilt test.

METHODS

Eighteen patients with VVS and 18 age-and sex-matched controls were studied. All patients with VVS had a positive mixed-type response to head-up tilt and all controls had a negative response. CM5-lead digital electrocardiogram (ECG) was recorded and QT intervals were analyzed using Holter ECG analyzer. Using scatter plots of consecutive QT and the preceding R-R intervals, QT-R-R relations during tilt-up and tilt-back or during vasovagal reflex were independently fitted to an exponential curve: QT (second) = A + B x exp[k x R-R (second)].

RESULTS

During the tilt-up, A, B, and k did not differ between patients with VVS and controls. During the tilt back, k showed equivalent positive value compared to the tilt-up (4.1 +/- 1.3 vs -4.6 +/- 0.9) in controls. However, k remained negative (-1.3 +/- 1.5) during vasovagal reflex in patients with VVS. In six patients, in whom metoprolol was effective in eliminating VVS, QT-R-R relationship during the tilt-back became similar to that in controls.

CONCLUSIONS

In patients with VVS, hysteresis of the QT-R-R relation is similarly shown during tilt-up as in controls, whereas this hysteresis is no longer evident and failure of QT prolongation is observed during VVS.

Single-stage adenosine tilt testing in patients with unexplained syncope

INTRODUCTION

We previously have shown that a 3-minute single-stage adenosine tilt test has a diagnostic yield comparable to a two-stage protocol consisting of a 30-minute drug-free tilt followed by a 15-minute isoproterenol tilt. In this study, we sought to further define the clinical utility of adenosine tilt testing in patients with unexplained syncope by prospectively evaluating test specificity and determining predictors of a positive test response.

METHODS AND RESULTS

The specificity of single-stage adenosine tilt testing was determined using 30 control subjects. To determine the diagnostic yield of this protocol, adenosine tilts were performed in 129 patients with unexplained syncope. The adenosine tilt test protocol had high specificity (100%) but a low overall diagnostic yield (18%). However, the yield was affected significantly by age. In patients </=40 years of age, the tilt test was positive in 15 (41%) of 37 patients, which was significantly greater than the yield in patients between the ages of 41 and 64 years (6/41 patients [15%], P = 0.012) and those >/=65 years of age (2/41 patients [5%], P < 0.0001).

CONCLUSION

These data support single-stage adenosine tilt testing in patients </=40 years of age because the diagnostic yield of the test is maximal in this group and the test can be completed in </=3 minutes. Conversely, the diagnostic yield of adenosine tilt testing in patients >40 years of age is low, suggesting that the clinical utility of this protocol is limited in these patients.

Altered fractal behavior and heart rate variability in daily life in neurally mediated syncope

Autonomic imbalance is thought to play an important role in the pathogenesis of neurally mediated syncope (NMS). Heart rate variability (HRV) indices and fractal dimension derived from 24 h ambulatory electrocardiogram (AECG) reflects the cardiac autonomic activity and provides useful information for understanding the pathogenesis of NMS. In this study, we sought the cardiac autonomic activity and the status of fractal dimension in daily life in patients with NMS. The 24 h ambulatory ECG recordings were performed in 36 NMS patients (NMS group) and in 11 healthy volunteers (CTRL group). Six time domain and frequency domain HRV indices were calculated. The regression of log (power) on log (frequency) was also calculated and the slope of the regression line (beta) was analyzed in three different periods such as total 24 h, awake and sleep phases. The values of mean RR, SDNN and SDANN were not significantly different, but the values of S.D. index, rMSSD, pNN50 and all the frequency domain HRV indices were significantly higher in NMS group than in CTRL group. For 24-h period, there was no significant difference in the values of beta. For awake phase, the value of beta was significantly higher in NMS group than in CTRL group. For sleep phase, the value of beta was significantly lower in NMS group than in CTRL group. Augmented autonomic activity and the deterioration of fractal dimension in daily life might contribute to the pathogenesis of NMS.

Sublingual Nitroglycerin Used in Routine Tilt Testing Provokes a Cardiac Output-Mediated Vasovagal Response

OBJECTIVES

We set out to determine the effect of sublingual nitroglycerin (NTG), as used during routine tilt testing in patients with unexplained syncope, on hemodynamic characteristics and baroreflex control of heart rate (HR) and systemic vascular resistance (SVR).

BACKGROUND

Nitroglycerin is used in tilt testing to elicit a vasovagal response. It is known to induce venous dilation and enhance pooling. Also, NTG is lipophilic and readily passes cell membranes, and animal studies suggest a sympatho-inhibitory effect of NTG on circulatory control.

METHODS

Routine tilt testing was conducted in 39 patients with suspected vasovagal syncope (age 36 +/- 16 years, 18 females). Patients were otherwise healthy and free of medication. Before a loss of consciousness set in, oncoming syncope was cut short by tilt-back or counter-maneuvers. Finger arterial pressure was monitored continuously (Finapres). Left ventricular stroke volume (SV) was computed from the pressure pulsations (Modelflow). Spontaneous baroreflex control of HR was estimated in the time and frequency domains.

RESULTS

During tilt testing, 22 patients developed presyncope. After NTG administration but before presyncope, SV and cardiac output (CO) decreased (p < 0.001), whereas SVR and HR increased (p < 0.001) in all patients. Arterial pressure was initially maintained. Baroreflex sensitivity decreased after NTG. On Cox regression analysis, the occurrence of a vasovagal response was related to a drop in SV after NTG (hazard ratio 0.86, p = 0.005).

CONCLUSIONS

The cardiovascular response to NTG is similar in vasovagal and non-vasovagal patients, but more pronounced in those with tilt-positive results. The NTG-facilitated presyncope appears to be CO-mediated, and there is no evidence of NTG-induced sympathetic inhibition.

Near-infrared spectroscopy in evaluation of cerebral oxygenation during vasovagal syncope

Near-infrared spectroscopy (NIRS) offers a non-invasive, real-time monitoring of cerebral oxygenation. This method is based on the oxygenation and the light wavelength dependent absorption of near-infrared light by tissue chromophores, e.g. oxyhaemoglobin and deoxyhaemoglobin. The objective of the present study was the application of NIRS for evaluation of the brain function during vasovagal syncope (VVS). The VVS is a clinical syndrome affecting ca 3.5% of the population and for which the widely used diagnostic examination in this disease entity is the head-up tilt table test (HUT). In this study 69 patients with a history of VVS were examined using HUT. In 42 patients VVS was provoked. Results of the examination have shown that the changes in cerebral oxygenation measured by the NIRS technique are distinctly visible before the syncope. A gradual decrease of oxyhaemoglobin followed by its sudden drop was observed in all the VVS patients. Changes in the oxyhaemoglobin concentration measured by NIRS were observed on average 3.3 min before the syncope. They preceded the presyncope symptoms about 1.3 min (p < 0.005), the blood pressure and heart rate drop 2.2 min (p < 0.0001) and the arterial blood saturation 2.6 min (p < 0.00001).

Holter monitoring vs tilt testing in the investigation of suspected vasovagal syncope

The aim of this study was to compare the diagnostic yield of 48-hour Holter monitoring with head-up tilt (HUT) test in patients presenting with blackouts suggestive of vasovagal syncope. One hundred and eighteen consecutive patients, 68 women, aged (mean [SD])50 +/- 20 years(range 16-88 years), underwent 48-hour Holter monitoring and 60 degrees HUT test within 3 months. Endpoints were symptom-ECG correlation during Holter monitoring and positive HUT test. Syncope occurred in 3 (3%) patients during Holter monitoring, the rhythm being sinus tachycardia in all. Presyncope was reported in 22 (19%), the rhythm being sinus tachycardia in 6, persistent atrial fibrillation in 2, and normal sinus rhythm in the remainder. Asymptomatic arrhythmias were recorded in 103 (87%) patients. Positive HUT tests occurred in 39 (33%), the pattern being mixed (VASIS type 1) in 14 (36%), cardioinhibitory (VASIS type 2) in 3 (8%), and vasodepressor (VASIS type 3) in 22 (56%). Change in patient management occurred in 3 (3%) patients following Holter monitoring and 39 (33%) patients following HUT test. Holter monitoring produces a low yield of clinically useful information in the investigation of suspected vasovagal syncope. An HUT test should be considered the primary investigation of choice in such patients.

Impairment of coronary microvascular function in patients with neurally mediated syncope

Recent evidence suggests that myocardial ischemia may occur in patients with neurally mediated syncope and normal coronary angiograms. This study was conducted to evaluate if coronary microvascular function is impaired in such patients. Coronary hemodynamic studies and head-up tilt table tests (HUTs) were performed on 30 consecutive patients with normal coronary angiograms and recurrent syncope. Another ten subjects with atypical chest pain and no evidence of myocardial ischemia or syncope served as a control. Great cardiac vein flow (GCVF) and coronary sinus flow (CSF) were measured by the thermodilution method at baseline and after dipyridamole infusion (0.56 mg/kg i.v. for 4 minutes). Coronary flow reserve (CFR), derived from CSF and GCVF, was significantly lower in the 15 patients with positive HUT than in the other 15 patients with negative HUT (1.75 +/- 0.48 vs 2.64 +/- 0.8, P < 0.01 and 2.29 +/- 0.45 vs 3.07 +/- 0.63, P < 0.01, respectively). Ischemic-like ECG was noted during treadmill exercise test in 40% of the former and in 7% of the latter group (P = 0.01). There was no significant difference in CFR between patients with negative HUT and control subjects. Coronary microvascular function was impaired in syncopal patients with positive HUT and relatively preserved in those with negative HUT, suggesting the possible linkage between coronary microvascular dysfunction and the development of neurally mediated syncope.

Strategy for the management of vasovagal syncope

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

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

INTRODUCTION AND OBJECTIVES

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

PATIENTS AND METHOD

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

RESULTS

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

CONCLUSIONS

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

Neurally mediated syncope

The prevalence and incidence of syncope increases with advancing years due to age related physiological changes in the neurocardiovascular, endocrine and renal systems. Cardiovascular syncope can present as falls because of amnesia for loss of consciousness or postural instability due to hypotension. Drop attacks or non accidental falls should thus be investigated for causes of syncope. The most common causes of neurally mediated syncope in older adults are carotid sinus syndrome, orthostatic hypotension and vasovagal syncope.

The repeatability of left ventricular volume assessment by a new ambulatory radionuclide monitoring system during head-up tilt

The precise measurement of changes in left ventricular volume is important to elucidate the mechanisms of neurally mediated syncope. This study was conducted to determine whether or not a brand-new ambulatory radionuclide monitoring system (C-VEST system) can be clinically used to easily and precisely measure left ventricular volume and function in tilt testing. To assess the repeatability of the C-VEST system, 12 healthy volunteers (mean age 24+/-4 years old) underwent 20 minute head-up tilt testing and we measured the temporal changes in left ventricular volume and ejection fraction twice a day (first and second studies). To investigate the changes in the C-VEST measurements and the detector position in the first and second studies, tilt testing was performed with an 80-degree passive tilt, which is the same as the standard procedure used in diagnosing neurally mediated syncope. The coefficient of repeatability for both the C-VEST and detector position was well within the clinical range (coefficient of repeatability in left ventricular volume ranged from 1.7 to 2.8; coefficient of repeatability in the detector position ranged from 2.3 to 3.1). Precise evaluation of the left ventricular volume can be achieved by an ambulatory radionuclide monitoring system in tilt testing.

Neurally mediated syncope and cardiac beta-adrenergic receptor function

To evaluate the mechanism of neurally mediated syncope (NMS), we investigated basal autonomic nerve function using a conventional pharmacological method and [123I]-metaiodobenzyl-guanidine (MIBG) single photon emission computed tomography (SPECT). Nine patients with NMS, whose syncope was induced by head-up tilt test with or without isoproterenol, underwent [123I]-MIBG SPECT. Eight of nine NMS patients showed reduced myocardial uptake (two patients, diffuse; four patients, anteroseptal and inferior; one patient, anteroseptal; one patient, inferior). In the study of pharmacological autonomic nervous function test, atropine sulfate (atr.) (0.04 mg/kg), isoproterenol (isp.) (5 x 10(-3) microg/kg/min), propranolol (prop.) (0.2 mg/kg), phenylephrine (phenyl.) (0.4 microg/kg/min), and phentolamine (phent.) (0.2 mg/kg) were successively administered to patients with NMS (n = 5) and control subjects (n = 5). The heart rate (HR) after atr. and prop., and systolic blood pressure (SBP) after phent. were defined as intrinsic HR (IHR) and intrinsic SBP (ISBP). Parasympathetic activity (increase in HR by atr.), beta-sympathetic tone (HR after atr. minus IHR), beta-sensitivity (change in HR by 1 microg isp./kg/min), beta-secretion (beta-tone/beta-sensitivity), alpha-sympathetic tone (SBP before phenyl. minus ISBP), alpha-sensitivity (change in SBP by 1 microg phenyl./kg/min) and alpha-secretion (alpha-tone/alpha-sensitivity) were also calculated. The beta-secretion was decreased (0.0027+/-0.0008 versus 0.0060+/-0.0004 microg/kg/min/isp.; p < 0.05), while the beta-sensitivity was increased (5850+/-947 versus 3150+/-292 beats/microg/kg/min isp.; p < 0.05) in NMS compared with control subjects. In the other indexes, there were no significant differences between two groups. The results of the present study suggest that increased beta-sensitivity may contribute hypercontraction of left ventricles, which might partially explain the mechanism of NMS.

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.

Cardioinhibition during tilt testing identifies patients who may benefit from pacing

This study examined whether the various hemodynamic collapse patterns observed during tilt testing in patients with suspected neurocardiogenic syncope are relevant when planning therapy, particularly whether a predominantly cardioinhibitory response predicts a beneficial response from pacing.

METHODS

The effects of temporary atrioventricular (A-V) sequential pacing were studied during tilt testing in 34 patients 48.2 +/- 18.5 years of age. The patient population was divided into a cardioinhibitory group (VASIS classes 2A and 2B) or mixed group (VASIS classes 1 and 3) according to their response to baseline tilt testing. The test was then repeated during A-V pacing with rate hysteresis. A positive response to A-V pacing was defined as a > or = 30-second increase between onset of symptoms and syncope, or mitigation of symptoms compared with the baseline tilt test.

RESULTS

The study protocol was not successfully completed in three patients. Among the remaining 31 patients, a baseline cardioinhibitory response was observed in 17, and a mixed response in 14 patients. A-V sequential pacing was successful in 13 of 17 patients with a cardioinhibitory response versus 5 of 14 patients with a mixed response (P = 0.024).

CONCLUSION

The presence of a predominantly cardioinhibitory collapse pattern (VASIS 2A and 2B) during baseline tilt testing doubled the likelihood of successful temporary A-V sequential pacing, and may identify patients with neurocardiogenic syncope most likely to benefit from permanent dual chamber pacing.

The normal response to prolonged passive head up tilt testing

OBJECTIVE

To define the responses to head up tilt in a large group of normal adult subjects using the most widely employed protocol for tilt testing.

METHODS

127 normal subjects aged 19-88 years (mean (SD), 49 (20) years) without a previous history of syncope underwent tilt testing at 60 degrees for 45 minutes or until syncope intervened. Blood pressure monitoring was performed with digital photoplethysmography, providing continuous, non-invasive, beat to beat heart rate and pressure measurements.

RESULTS

13% of subjects developed vasovagal syncope after a mean (SD) tilt time of 31.7 (12. 4) minutes (range 8.5-44.9 minutes). Severe cardioinhibition during syncope was observed less often than is reported in patients investigated for syncope. There were no differences in the age or sex distributions of subjects with positive or negative outcomes, or in the proportions with cardioinhibitory and vasodepressor vasovagal syncope compared with previously reported patient populations. Subjects with negative outcomes showed age related differences in heart rate and blood pressure behaviour throughout tilt.

CONCLUSIONS

False positive results with tilting appear to be common. This has important implications for the use of diagnostic tilt testing. The magnitude of the heart rate and blood pressure changes observed during negative tilts largely invalidates previously suggested criteria for abnormal non-syncopal outcomes.

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.

Indications, methodology, and classification of results of tilt-table testing

Tilt-table testing has become an important part of the evaluation of patients with unexplained syncope, although not every patient with vasovagal syncope requires it. Studies have attested to the effectiveness of the technique for providing direct diagnostic evidence of a patient's susceptibility to vasovagal syncope. This article reviews the need for tilt-table testing and the recommended methods for performing a test. In addition, a detailed classification of the hemodynamic patterns of collapse displayed over the course of a tilt-table study is provided. These distinctive collapse patterns document the evolution of a syncopal event and are particularly important to identify because they can influence the selection of therapy.

Usefulness of tilt test-induced patterns of heart rate and blood pressure using a two-stage protocol with glyceryl trinitrate provocation in patients with syncope of unknown origin

This study assesses the vasovagal collapse pattern changes, i.e, heart rate (HR) and arterial blood pressure (BP) with a 2-stage tilt-test protocol using glyceryl trinitrate (GTN) provocation. With use of the 45-minute 60 degrees head-up Westminster protocol, 102 consecutive patients were studied. Sublingual GTN 300 microg was given to those with a negative passive tilt. Heart rate and BP patterns were classified according to the Vasovagal International Study classification (VASIS) and then compared between those with a positive passive tilt and those with a positive tilt after having been given GTN. Twelve patients did not tolerate tilt testing, and 16 had a negative response despite taking GTN. Thirty-five patients (20 women and 15 men, mean age 45 +/- 21 years [mean +/- SD]) did not take GTN and 38 (26 women and 12 men, mean age 53 +/- 22 years) had positive passive test results. When comparing the VASIS classification between the 2 groups, results showed: type 1, mixed BP and HR decreased without severe bradycardia (31% [passive] vs 54% [with GTN], p = NS); type 2A, BP decreased before HR decreased (20% vs 22%, p = NS); type 2B, HR decreased before or coincident with BP (34% vs 8%, p = 0.003); type 3, BP decreased without HR decrease (9% vs 0%, p = NS); exception 1, chronotropic incompetence (0% vs 13%, p = 0.026); and exception 2, excessive HR increase (6% vs 3%, p = NS). Thus, GTN use increases frequency of positive results from 34% to 73%. Older people with chronotropic incompetence, who may benefit from pacing, were identified. In younger people there was an increase in those with cardioinhibition.

Neurally mediated syncope and arrhythmias: a study of syncopal patients using the head-up tilt test

Understanding the causes of syncope in patients with arrhythmia is important in determining the therapeutic interventions. Neurally mediated syncope (NMS) was evaluated in 55 patients with various arrhythmias. The head-up tilt test with or without isoproterenol infusion induced NMS in 41 (74%) patients. When these patients was categorized into 3 types, depending on the development of syncope, vasodilatation was significant in a majority of patients. In 46% of patients with tachyarrythmias, NMS was accompanied by an increase in extrasystole. It was concluded that the evaluation of vasodilatation is important for the preventive strategy of NMS in patients with arrhythmias and that NMS may induce arrhythmias.

Value of sublingual isosorbide dinitrate before isoproterenol tilt test for diagnosis of neurally mediated syncope

Head-up tilt-table test is valuable in diagnosing type of syncope. Sensitivity varies in reports and is mostly poor. Isoproterenol or nitroglycerin is regularly used to increase head-up tilt-table test sensitivity. The aim of this study was to assess the value of sublingual isosorbide dinitrate administration before isoproterenol tilt test as a simple, practical test for diagnosis of neurally mediated syncope. Ninety-six patients (45 men and 51 women, mean age 42.5 years) with recurrent (median 4 times) loss of consciousness that remained unexplained after clinical and noninvasive assessment and 72 healthy volunteers (36 men and 36 women, mean age 40.1 years) were randomly divided into groups: isosorbide-isoproterenol test and isoproterenol test. During isosorbide-isoproterenol test, a positive response (syncope in association with sudden hypotension or bradycardia) occurred in 35 patients (72.9%) with unexplained syncope, an exaggerated response (minor symptoms in association with slowly increasing hypotension alone) occurred in 7 (14.6%), a negative response in 2 (4.2%), and drug intolerance in 4 (8.3%). During isoproterenol testing, these percentages were 52.1%, 16.7%, 25.0%, and 6.2%, respectively. Only 3 control volunteers (8.3%) had a positive response to isosorbide-isoproterenol test and 2 (5.6%) to isoproterenol test. The duration of the test and the time for syncope induction in the isosorbide-isoproterenol test were shorter than those in the isoproterenol test (24.84 +/- 5.15 vs 35.70 +/- 6.28 minutes [p <0.01]; 4.53 +/- 2.86 vs 6.27 +/- 4.11 minutes [p <0.05]). This study concluded that isosorbide-isoproterenol test could be valuable in diagnosing unexplained syncope for its high sensitivity, powerful specificity, and short duration.

Induction of neurally mediated syncope with adenosine

BACKGROUND

Tilt testing is used to establish the diagnosis of neurally mediated syncope. However, applicability of the tilt test is limited by test sensitivity and length of time required to perform the test. We hypothesized that adenosine could facilitate the induction of neurally mediated syncope through its sympathomimetic effects and therefore could be used as an alternative to routine tilt testing.

METHODS AND RESULTS

In protocol 1, the yield of adenosine tilt testing (12 mg while upright, followed by 60 degrees tilt for 5 minutes) and a 15-minute isoproterenol tilt test were compared in 84 patients with a negative 30-minute drug-free tilt test. In protocol 2, 100 patients underwent an initial adenosine tilt test followed by our routine tilt test (30-minute drug-free tilt followed by a 15-minute isoproterenol tilt). Six additional control patients underwent microneurography of the peroneal nerve to compare the sympathomimetic effects during bolus administration of adenosine and continuous infusion of isoproterenol. In protocol 1, the yields of adenosine (8 of 84, 10%) and isoproterenol (7 of 84, 8%) tilt testing were comparable (P=NS). In protocol 2, the yields of adenosine (19 of 100, 19%) and routine (22 of 100, 22%) tilt testing were also comparable (P=NS). Although the yield of adenosine tilt testing was comparable in both protocols, patients with a negative adenosine tilt test but a positive routine tilt test usually required isoproterenol to elicit the positive response. Microneurography confirmed discordant sympathetic activation after adenosine and isoproterenol administration.

CONCLUSIONS

Adenosine is effective for the induction of neurally mediated syncope, with a diagnostic yield comparable to routine tilt testing. However, the discordant results obtained with adenosine and the isoproterenol phase of routine tilt testing suggest that adenosine and isoproterenol tilt testing may have complementary roles in eliciting a positive response. Therefore, a tilt protocol that uses an initial adenosine tilt followed, if necessary, by an isoproterenol tilt would be expected to increase the overall yield and reduce the duration of tilt testing.

[The tilt-table test in assessing syncope of unknown origin: do differences exist between children and adults?]

BACKGROUND AND OBJECTIVES

Little is known about the differences between children and adults in the results of head-up tilt test. This study sought to investigate the potential differences concerning: a) the clinical profile and circumstances of spontaneous syncope; b) the overall diagnostic performance of the test, and c) the type of positive response obtained.

MATERIAL AND METHODS

We studied 31 children and 123 adults with unexplained syncope. If baseline test (tilting at 70 degrees for 30 min) resulted negative, it was repeated under isoprenaline low-dose infusion.

RESULTS

There were no differences in either clinical profile, except for severe traumatism more frequent in adults (25% vs. 3% in children; p < 0.05), or overall diagnostic performance (39% in children vs. 33% in adults; p = NS). However, the way the test rendered positive (via basal tilting in 92% of children vs. 50% in adults; p < 0.05) and the rate of cardioinhibitory response (42% in children vs 8% in adults; p < 0.01) were significantly different.

CONCLUSIONS

In this study children, in contrast to adults, rarely have a positive response in tilting under isoprenaline infusion. They also present a much higher rate of cardio-inhibitory response than adults.

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.

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.

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

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

[Diagnosis and treatment of vasovagal syncope in the child and adolescent]

Recurrent unexplained syncope is a common and often frustrating clinical problem in paediatrics. Over the last decade, head upright tilt table testing has emerged as an important diagnostic method for the identification of patients whose syncope is likely to be neurocardiogenic in origin. At the same time, tilt table testing, by providing syncopal episodes in a controlled setting, has allowed for a greater understanding of their physiopathology. Treatment strategies remain controversial but beta-blocker therapy appears to be very efficient.

Autonomic function in manganese alloy workers

The observation of orthostatic hypotension in an index case of manganese toxicity lead to this prospective attempt to evaluate cardiovascular autonomic function and cognitive and emotional neurotoxicity in eight manganese alloy welders and machinists. The subjects consisted of a convenience sample consisting of an index case of manganese dementia, his four co-workers in a "frog shop" for gouging, welding, and grinding repair of high manganese railway track and a convenience sample of three mild steel welders with lesser manganese exposure also referred because of cognitive or autonomic symptoms. Frog shop air manganese samples 9.6-10 years before and 1.2-3.4 years after the diagnosis of the index case exceeded 1.0 mg/m3 in 29% and 0.2 mg/m3 in 62%. Twenty-four-hour electrocardiographic (Holter) monitoring was used to determine the temporal variability of the heartrate (RR' interval) and the rates of change at low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz). MMPI and MCMI personality assessment and short-term memory, figure copy, controlled oral word association, and symbol digit tests were used. The five frog shop workers had abnormal sympathovagal balance with decreased high frequency variability (increased ln LF/ln HF). Seven of the eight workers had symptoms of autonomic dysfunction and significantly decreased heart rate variability (rMSSD) but these did not distinguish the relative exposure. Mood or affect was disturbed in all with associated changes in short-term memory and attention in four of the subjects. There were no significant correlations with serum or urine manganese. Power spectrum analysis of 24-h ambulatory ECG indicating a decrease in parasympathetic high frequency activation of heart rate variability may provide a sensitive index of central autonomic dysfunction reflecting increased exposure to manganese, although the contribution of exposures to solvents and other metals cannot be excluded. Neurotoxicity due to the gouging, welding, and grinding of mild steel and high manganese alloys (11-25%) merits air manganese and neuropsychologic surveillance including autonomic function by Holter monitoring of cardiovagal activation.

Head-up tilt testing potentiated with low-dose sublingual isosorbide dinitrate: a simplified time-saving approach for the evaluation of unexplained syncope

BACKGROUND

Head-up tilt testing is widely used in the clinical assessment of patients with unexplained syncope. However, the lack of a standard methodology and the conflicting results concerning sensitivity and specificity of the procedure have prompted further studies to define a more cost-effective approach for tilt testing.

OBJECTIVES

Our clinical investigation was undertaken to assess the diagnostic value in unexplained syncope of a simple and time-saving protocol for head-up tilt testing, including low-dose sublingual isosorbide dinitrate administration.

PATIENTS AND METHODS

A group of 73 consecutive patients (43 women and 30 men, mean age 39.6+/-21.8 years) with unexplained syncope despite conventional clinical cardiovascular and neurologic assessment and 10 asymptomatic control subjects underwent head-up tilt testing with isosorbide dinitrate challenge. Participants were tilted at 60 degrees for 30 minutes without medication; if no symptoms occurred, 1.25 mg of isosorbide dinitrate was administered sublingually and tilting was continued for an additional 15 minutes.

RESULTS

During the drug-free phase of the test 14 (19.2%) patients had syncope. After isosorbide dinitrate administration syncope occurred in another 28 patients (38.3%); minor symptoms in association with hypotension developed in 10 (13.7%) patients. The test result was negative in all control subjects. The positive rate and specificity of head-up tilt testing with isosorbide dinitrate provocation were 57.5% and 100%, respectively.

CONCLUSIONS

This new practical diagnostic procedure was found to be fairly sensitive and clearly specific in inducing a vasovagal reflex in patients with syncope of uncertain origin. Consequently, such approach could give a significant contribution in the diagnostic workup of these patients.

[Role of adenosine triphosphate (ATP) in head-up tilt-induced syncope]

INTRODUCTION AND OBJECTIVES

Recent studies have demonstrated that adenosine is an endogenous modulator of the cardiac excitatory afferent nerves, and could provoke a vasovagal response during head-up tilt test. Isoproterenol has been the drug of choice to increase the sensitivity of this testing. The aim of the present study was to analyze the role of adenosine in head-up tilt-induced syncope in susceptible patients, and to compare the relative sensitivities of adenosine and isoproterenol.

METHODS

Thirty patients with unexplained syncope (16 female and 14 male, mean age 37.1 +/- 18 years), no heart disease and negative baseline head-up tilt test were studied. After the baseline test, patients were randomized to receive adenosine triphosphate (bolus injections of 3, 6 and 9 mg/ 5 min) or isoproterenol (bolus injections of 2, 4 and 6 micrograms/5 min) and underwent a second tilt test. After 15 min at rest, patients received the alternative drug and a third test was performed. Eleven normal control subjects were tested with adenosine in the upright position to determine its effects.

RESULTS

A vasovagal response was induced in 7 patients (23.3%) after ATP administration. Nine patients (30%) showed a positive response with isoproterenol. Only 2 patients (6.6%) showed a positive response with both drugs. Of the control subjects, one (9%) had a vasovagal response after ATP administration.

CONCLUSIONS

We conclude that adenosine triphosphate seems to be a useful tool to provoke vasovagal reaction in susceptible patients during head-up tilt test.

Midodrine: a role in the management of neurocardiogenic syncope

OBJECTIVE

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

SETTING

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

PATIENTS

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

DESIGN AND INTERVENTION

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

RESULTS

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

CONCLUSIONS

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

Comparison of heart rate variability in patients with chronic fatigue syndrome and controls

Recent studies have reported a close association between chronic fatigue syndrome and neurally mediated hypotension. We hypothesized that this association may result from an abnormality in autonomic function among patients with chronic fatigue syndrome, which may be detectable using an analysis of heart rate variability. We prospectively studied 19 patients who fulfilled the Centers for Disease Control criteria for chronic fatigue syndrome and 11 controls. Each subject underwent a two-stage tilt-table test while wearing a Holter monitor. Heart rate variability was assessed in the supine baseline position and during upright tilt using frequency domain parameters. In the baseline supine position, high frequency (HF) power, low frequency (LF) power, and the ratio of low frequency power to high frequency power (LF/HF ratio) were similar. In both patient groups, upright tilt resulted in a similar decrease in HF power, increase in LF power, and increase in the LH/HF ratio. In conclusion, autonomic function, as assessed using an analysis of heart rate variability, does not differ in the baseline supine state, nor in response to upright tilt among patients with chronic fatigue syndrome and healthy controls.

Immediate reproducibility of tilt-table test results in elderly patients referred for evaluation of syncope or presyncope

We studied the immediate reproducibility of the results of the head-up tilt-table test in elderly patients (age > or =60 years). Twenty-seven consecutive men underwent 51 tests. The overall reproducibility was 98%, including 92% of a positive test and 100% of a negative test. The finding of this study validates the use of intravenous pharmacologic intervention in the elderly population.

Comparison of sensitivity and specificity of tilt protocols with and without isoproterenol in children with unexplained syncope

Head-up tilt testing with or without isoproterenol is extensively used in the evaluation of patients with unexplained syncope. However, sensitivity and specificity of tilt protocols with and without isoproterenol have not been clarified in children, due to lack of age matched control subjects. This study was designed to assess and to compare the sensitivity and specificity of tilting alone and tilting in conjunction with isoproterenol. Thirty children with unexplained syncope (group I) and 15 age-matched control subjects (control group I) underwent successive 60 degrees head-up tilts for 10 minutes during infusions of 0.02, 0.04, and 0.06 microgram/kg/min of isoproterenol, after a baseline tilt to 60 degrees for 25 minutes. Also, 35 children (group II) with unexplained syncope and 15 healthy control subjects (control group II) were evaluated by head-up tilt to 60 degrees for 45 minutes without an infusion of isoproterenol. In response to tilt protocol with graded isoproterenol, 23 (76.6%) of the patients in group I and 2 of the 15 (13.3%) control subjects developed syncope. Accordingly, the sensitivity of tilt testing with isoproterenol was 76.6%, and its specificity was 86.7%. Tilt testing without isoproterenol was positive in 17 (48.5%) of the patients in group II but in only 1 of the 15 (6.6%) control subjects. Thus, sensitivity and specificity of tilt testing without isoproterenol were 48.5% and 93.4%, respectively. The mean heart rate and systolic blood pressure decreased significantly (P < 0.001) in all tilt positive patients during syncope. In conclusion, the head-up tilt test is a valuable diagnostic test in the evaluation of children with unexplained syncope, and isoproterenol is likely to increase the sensitivity of the test without decreasing its specificity.