Sublingual nitrates during head-up tilt testing for the diagnosis of vasovagal syncope

Nitrate reduction capacity of the oral microbiota is impaired in periodontitis: potential implications for systemic nitric oxide availability

The reduction of nitrate to nitrite by the oral microbiota has been proposed to be important for oral health and results in nitric oxide formation that can improve cardiometabolic conditions. Studies of bacterial composition in subgingival plaque suggest that nitrate-reducing bacteria are associated with periodontal health, but the impact of periodontitis on nitrate-reducing capacity (NRC) and, therefore, nitric oxide availability has not been evaluated. The current study aimed to evaluate how periodontitis affects the NRC of the oral microbiota. First, 16S rRNA sequencing data from five different countries were analyzed, revealing that nitrate-reducing bacteria were significantly lower in subgingival plaque of periodontitis patients compared with healthy individuals (P < 0.05 in all five datasets with n = 20-82 samples per dataset). Secondly, subgingival plaque, saliva, and plasma samples were obtained from 42 periodontitis patients before and after periodontal treatment. The oral NRC was determined in vitro by incubating saliva with 8 mmol/L nitrate (a concentration found in saliva after nitrate-rich vegetable intake) and compared with the NRC of 15 healthy individuals. Salivary NRC was found to be diminished in periodontal patients before treatment (P < 0.05) but recovered to healthy levels 90 days post-treatment. Additionally, the subgingival levels of nitrate-reducing bacteria increased after treatment and correlated negatively with periodontitis-associated bacteria (P < 0.01). No significant effect of periodontal treatment on the baseline saliva and plasma nitrate and nitrite levels was found, indicating that differences in the NRC may only be revealed after nitrate intake. Our results suggest that an impaired NRC in periodontitis could limit dietary nitrate-derived nitric oxide levels, and the effect on systemic health should be explored in future studies.

Does glyceryl trinitrate cause central sympatholytic effects? Insights from a case of baroreflex failure

Whether part of the blood pressure lowering effects of glyceryl trinitrate (GTN) is the result of centrally mediated reduction in sympathetic activity is debated. In humans, baroreflex activity potentially obscures the central sympatholytic effects of GTN. We examined this in a routine clinical tilt test in a patient with baroreflex failure secondary to previous neck radiotherapy. With reduced baroreflex function we observed an exaggerated fall in blood pressure and reduced sympathetic activity with GTN, supporting a peripheral vasodilation and central sympatholytic effect.

Venepuncture during head-up tilt testing in patients with suspected vasovagal syncope – implications for the test protocol

BACKGROUND AND PURPOSE

Head-up tilt (HUT) testing is a widely used diagnostic tool in patients with suspected vasovagal syncope (VVS). However, no gold standard exists for this examination and the various protocols used have a limited sensitivity and specificity. Our aim was to determine the sensitivity of a sequential HUT testing protocol including venepuncture (VP) and sublingual nitroglycerin application.

METHODS

This was a retrospective analysis of the diagnostic gain of a sequential HUT testing protocol including VP applied 10 min after the start of HUT testing and sublingual application of nitroglycerin 20 min after the start of the test protocol in 106 patients with a final diagnosis of VVS. The sensitivity of the test protocol was compared between patients with positive and negative history for VP induced VVS.

RESULTS

Overall, pre-syncope or syncope occurred in 68 patients (64.2%). Only 17% of all patients fainted spontaneously within 10 min of passive HUT. Another 39.6% fainted within 20 min. Application of nitroglycerin after 20 min of HUT evoked syncope in another 7.5% until the end of 45 min of HUT. The sensitivity of the test protocol for evoking (pre-)syncope was 94.4% in patients with a positive history for VP associated VVS and 58% in patients with a negative history (P < 0.01**); 85.7% of patients with a positive history and 42.9% of patients with a negative history fainted within 20 min of HUT testing (P < 0.01**).

CONCLUSIONS

Implementation of VP in sequential HUT testing protocols allows the sensitivity of HUT testing to be increased, especially in patients with a positive history for VP associated VVS.

Head-up tilt testing for diagnosing vasovagal syncope: a meta-analysis

BACKGROUND

A systematic evaluation focused on sensitivity and specificity of head-up tilt testing (HUT) for diagnosing vasovagal syncope has not been previously performed. We conducted a meta-analysis of studies comparing HUT outcome between patients with syncope of unknown origin and control subjects without previous syncope.

METHODS

We searched Pubmed and Embase databases for all English-only articles concerning case-control studies estimating the diagnostic yield of HUT, and selected 55 articles, published before March 2012, including 4361 patients and 1791 controls. The influence of age, test duration, tilt angle, and nitroglycerine or isoproterenol stimulation on tilt testing outcome was analyzed.

RESULTS

Head-up tilt testing demonstrated to have a good overall ability to discriminate between symptomatic patients and asymptomatic controls with an area under the summary receiver-operating characteristics curve of 0.84 and an adjusted diagnostic odds ratio of 12.15 (p<0.001). A significant inverse relationship between sensitivity and specificity of tilt testing for each study was observed (p<0.001). At multivariate analysis, advancing age and a 60° tilt angle showed a significant effect in reducing sensitivity and increasing specificity of the test. Nitroglycerine significantly raised tilt testing sensitivity by maintaining a similar specificity in comparison to isoproterenol.

CONCLUSIONS

The results from this meta-analysis show the high overall performance of HUT for diagnosing vasovagal syncope. Our findings provide useful information for evaluating clinical and instrumental parameters together with pharmacological stressors influencing HUT accuracy. This could allow the drawing of tilt testing protocols tailored on the diagnostic needs of each patient with unexplained syncope.

Head Up Tilt Testing: An Appraisal of Its Current Role in the Management of Patients with Syncope

Head up tilt testing (HTT) is now commonly used to investigate otherwise unexplained syncope and presyncope. This test has been used for over 20 years primarily to diagnose neurally mediated syncope, but HTT's exact role in the diagnostic process remains uncertain. Recognized limitations include poor reproducibility, lack of prognostic role, and insufficient randomized studies to guide therapeutic choice. In this review, we describe the indications and methods recommended by present guidelines on utilizing HTT. In addition, present criticisms and limitations of this test, along with future perspectives, are outlined.

Reduced systemic vascular resistance in healthy volunteers with presyncopal symptoms during a nitrate-stimulated tilt-table test

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Nitrates may facilitate syncope through various pathways, but the precise mechanism of nitrate-induced syncope is still under debate. The purpose of the present study was to compare the underlying haemodynamic mechanisms in subjects without and with presyncopal symptoms during a nitroglycerin-stimulated tilt-table test.

WHAT THIS STUDY ADDS

A major decrease in systemic vascular resistance was documented in subjects with presyncope during 0.25 mg nitroglycerin-stimulated tilt-table test, in the absence of changes in cardiac output. These findings indicated that even a small dose of nitroglycerin significantly decreased arterial resistance and cardiac afterload. AIMS The mechanism of nitrate-induced syncope remains controversial. We examined the haemodynamic changes in healthy volunteers during nitroglycerin-stimulated tilt-table test.

METHODS

Continuous radial pulse wave analysis, whole-body impedance cardiography and plethysmographic finger blood pressure were recorded in a supine position and during head-up tilt in 21 subjects with presyncopal symptoms (6 male/15 female, age 43 ± 3 years) after 0.25 mg sublingual nitroglycerin and 21 control subjects (6 male/15 female, age 43 ± 2 years). The drug was administered in the supine position and a passive head-up tilt followed 5 min later. Additionally, nitroglycerin was only administered during head-up tilt in 19 subjects and the haemodynamics were recorded.

RESULTS

Supine and upright haemodynamics were similar before nitroglycerin administration in the two groups. During the nitroglycerin-stimulated tilt test, aortic and radial mean blood pressure decreased significantly more in the presyncope group when compared with the controls (P= 0.0006 and P= 0.0004, respectively). The decreases in systemic vascular resistance (P= 0.0008) and heart rate (P= 0.002), and increase in aortic reflection time (P= 0.0002) were greater in the presyncope group, while the change in cardiac index was not different between the groups (P= 0.14). If nitroglycerin was administered during the upright tilt and not in supine position, the haemodynamic changes were quite corresponding.

CONCLUSIONS

Presyncopal symptoms during nitrate-stimulated tilt test were explained by decreased systemic vascular resistance and increased aortic reflection time, while cardiac output remained unchanged. These findings indicated reduced arterial resistance in nitroglycerin-induced presyncope.

Endothelial function and peripheral vasomotion in the brachial artery in neurally mediated syncope

BACKGROUND

Paradoxical peripheral vasodilation is one of the suspected mechanisms of neurally mediated syncope. Parasympathetic stimulation following sympathetic activation during orthostatic stress mainly contributes to this vasodilation.

HYPOTHESIS

Since endothelial function modulates peripheral vascular tone, this study aimed to determine whether endothelial function and inappropriate peripheral vasomotion has a significant role in the pathogenesis of neurally mediated syncope.

METHODS

To investigate whether endothelial function is augmented or whether abnormal peripheral vasomotion exits, flow-mediated dilation (FMD, endothelium-dependent vasodilation) and sublingual glyceryl trinitrate-induced dilation (0.3 mg, GTN-D, endothelium-independent vasodilation) were measured in the brachial artery in 16 patients with neurally mediated syncope, aged 33 +/- 10 years, by using high-resolution ultrasound. All patients underwent positive head-up tilt testing. These measures were compared with those in 16 control subjects matched with the patients by age, gender, and coronary risk factors. For FMD, percent diameter changes were obtained from baseline to hyperemic conditions (1 min after 5 min occlusion of the forearm artery). There were five smokers in both the patient and the control groups, but there was no structural heart disease in either group.

RESULTS

Baseline brachial artery diameters were comparable (3.8 +/- 0.6 vs. 3.8 +/- 0.7 mm, NS). Flow-mediated dilation in patients with neurally mediated syncope had a normal value of 9.8 +/- 5.0% despite the inclusion of five smokers. Flow-mediated dilation and GTN-D in patients with neurally mediated syncope were significantly greater than those in controls (9.0 +/- 5.0 vs. 3.0 +/- 3.5%, p<0.05; 18.4 +/- 5.5 vs. 14.1 +/- 4.4%, p<0.05).

CONCLUSIONS

Augmented endothelial function and/or abnormal peripheral vasomotion in peripheral arteries are important in patients with neurally mediated syncope in selected populations.

Head-up tilt table testing in syncope: safety and efficiency of isosorbide versus isoproterenol in pediatric population

BACKGROUND

The aim of this study was to compare the diagnostic value and safety of sublingual isosorbid dinitrate (ISDN) with intravenous isoproterenol (ISOP) during head-up tilt table testing (HUTT) in pediatric patients with suspected neurocardiogenic syncope.

METHODS

One hundred thirty-six consecutive pediatric patients complaining of presyncope or syncope were submitted to HUTT for the first time. Those who did not develop syncope or presyncope during passive HUTT for 20 minutes underwent repeated HUTT with either 1.25 to 2.5 mg sublingual ISDN or intravenous ISOP (1-3 mug/min) for 20 minutes. There were 54 boys and 82 girls, aged 10 to 18 years with an average of 15.5 +/- 2.4 years and a median of 16 years. Among the patients with cardioinhibition or mixed responses, the severity of the bradyarrhythmia was scored 1 to 3 (restoration of effective rhythm within 10 seconds, 10-20 seconds, and >20 seconds while back to supine position, respectively).

RESULTS

During the passive period, 24 (17.6%) of 136 patients had a positive response to HUTT. Syncope was observed in another 44 patients during either ISDN or ISOP period (14/58 [24.1%] and 30/54 [55.5%] with ISDN vs ISOP, respectively, P < .05). The time to symptoms was shorter with both ISDN and ISOP compared with passive period (6.5 +/- 2.9, 6.3 +/- 5.9, and 10.3 +/- 4.4, minutes, respectively, P < .05). The severity score for cardioinhibition response was significantly higher with ISDN compared with the passive period and ISOP (2 +/- 0.8, 1.25 +/- 0.45, and 1.26 +/- 0.45, respectively, P < .01).

CONCLUSIONS

Sublingual ISDN is less sensitive and less safe compared to intravenous ISOP in assessing pediatric age patients with suspected neurocardiogenic syncope and with a negative result in tilt test without provocation. The simplicity of ISDN use should be weighed against the risk of longer symptoms with ISDN.

Value of Symptoms to Predict Tilt Testing Outcome in Patients with Clinical Suspicion of Vasovagal Syncope

Studies to assess the value of clinical symptoms to predict the head-up tilt test (HUT) outcome in patients with suspicion of vasovagal syncope have shown controversial results. We undertook this study to compare the frequency of symptoms between subjects with and without history of syncope, its association with syncopal spells in those with a history of syncope and positive or negative HUT, and to identify clinical predictors of HUT outcome. Sixty seven subjects with a history of unexplained syncope and 26 subjects without a history of syncope were interviewed using a structured questionnaire before undergoing HUT, which was performed first in a passive phase and, if negative, was repeated with pharmacological challenge using 5 mg of sublingual isosorbide. Questionnaire included the 16 symptoms most frequently reported in previous studies. Only five symptoms were reported more frequently by subjects with history of syncope in comparison with subjects without it: visual blurring, dysesthesia, sighing dyspnea, tremor in fingers, and diaphoresis. Comparison of symptom frequency between patients with history of syncope and positive or negative HUT revealed that only two were significantly different: nausea and hot flashes. However, a detailed analysis of the data indicates that only hot flashes occurring just before the syncope were more common in those with a positive HUT. Although some symptoms were found more frequently in patients with a history of syncope than in those without it, the use of a structured questionnaire in the group of patients failed to predict the outcome of the HUT.

Investigating syncope: a review

PURPOSE OF REVIEW

This review focuses on recent literature on the cardiovascular investigation of syncope.

RECENT FINDINGS

Syncope is a common and complex clinical entity with many varied etiologies, the diagnosis of which can often be elusive. Recent advances in the area of investigation in syncope include improvements in technologies for arrhythmia event monitoring and an increase in applicability and efficacy of traditional investigations. These advances have increased our ability to manage syncope.

SUMMARY

A better understanding of the etiology of syncope in certain cohorts has allowed tailoring of investigations and management of syncope. This is evident when syncope occurs in the presence of structural heart disease, which is associated with a higher incidence of arrhythmias and an increased 1-year mortality. Patients with left-ventricular dysfunction should be considered candidates for an implantable cardioverter defibrillator based on heart function and syncopal presentation. In the absence of significant heart disease, investigations need to be tailored to diagnose neurally mediated causes for syncope and detection of intermittent bradycardia. The improved understanding of syncope has arisen from studies using improved investigational tools for syncope, in particular loop recorders, which are able to monitor cardiac rhythm over long periods. In those without structural heart disease and undifferentiated syncope, neurally mediated causes should be pursed initially. Tilt testing and loop recorders are employed most often in this cohort. Electrophysiological studies have largely been supplanted by implantable cardioverter defibrillator use in structural heart disease, with a low yield in patients with preserved heart function.

Short Head-Up Tilt Test Potentiated with Oral Nitroglycerine:. Comparison with a Conventional Test Using Isoproterenol

Conventional tilt test protocols are time consuming and there is no consensus regarding the optimal duration of the test and the provocative drug to be used. This study evaluated the diagnostic power of a short nitroglycerine test against a conventional isoproterenol protocol. A cohort of 128 patients with unexplained syncope was studied. A group of 64 consecutive patients were tilted with a short nitroglycerine test consisting of a passive phase of 15 minutes and if this proved negative, 400 microg of sublingual nitroglycerin spray for a further 15 minutes. The control group consisted of 64 patients tilted with a conventional isoproterenol protocol with a passive phase of 30 minutes and a drug-challenge phase of 20 minutes. In the nitroglycerine protocol 39 (60.9%) patients showed a positive response versus 27(42.2%) in the isoproterenol group (P = 0.034). The duration of the protocol was 23.2 +/- 7.2 minutes in the nitroglycerine group versus 41.1 +/- 15.5 minutes with isoproterenol (P = 0.001). The time until syncope was 18.87 +/- 6.1 versus 29 +/- 18, respectively (P = 0.002). For evaluating unexplained syncope the short tilt test protocol with nitroglycerine is less time consuming, easier to perform, and has a higher rate of positive response than a conventional isoproterenol protocol.

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.

Simplified tilt table test protocol with continuous upright position during medication administration and no hydration

Recommendations for head-up tilt testing (HUT) often include the prolonged abstaining from food and water consumption (nothing by mouth [NPO]) and intravenous fluids administration before HUT. After the baseline test, supine equilibration periods are recommended before and between each dose of medication. The aim of this study was to determine if similar results are obtainable with a simpler protocol. After 2-3 hours NPO, 1,540 HUTs were performed at 70 degrees for 30 minutes unless predetermined endpoints were reached. Then, with the patient remaining in the tilted position, isoproterenol (ISO) (1 microgram/min), titrated every 3 minutes to a maximum of 5 micrograms/min (n = 803 patients), sublingual nitroglycerin (NTG) (300-400 micrograms) (n = 143 patients), or edrophonium (EDP) (5 mg) repeated once after 3 minutes (n = 46 patients) were administered. No aspiration or other adverse effects attributable to the abbreviated fasting period were observed. ISO was well tolerated as doses were increased. Vasovagal manifestations developed in 31% of ISO tests, in 11% with EDP, and in 50% with NTG (P < 0.001). Time consumed with rehydration before and postural changes during HUTs may be avoided when ISO is administered. With NTG the response may be excessive.

[Head-up tilt test potentiated with nitroglycerin. What is the optimal duration of the test after administration of the drug?]

INTRODUCTION AND OBJECTIVES

Numerous variations of the head-up tilt-table test potentiated with nitrates have been reported. After the administration of nitroglycerin, between 10 and 25 min of continued tilting have been recommended. The aim of this study was to assess the optimal duration of the pharmacological phase of the head-up tilt-table test potentiated with sublingual administration of nitroglycerin spray (NTG-TT).

METHOD

The records of 498 consecutive NTG-TT were reviewed. Our protocol consisted of a 20-min drug-free phase at a 60o angle. If syncope does not develop, 400 microgram of sublingual nitroglycerin spray is administered and the patient continues to be tilted for a further 25 min. The test results and time to a positive response were analyzed.

RESULTS

The result of NTG-TT was positive in 288 procedures, most of them after nitroglycerin administration (255, 88.5%). The mean time to a positive response was 10.7 6.7 and 5.0 2.4 min during the control and pharmacological phases respectively. Most positive responses were concentrated in the 3 to 5 min after drug administration. The time to syncope after nitroglycerin administration was over 10 min in 9 patients and 15 min in only 2 patients.

CONCLUSIONS

The duration of the pharmacological phase of NTG-TT using the described protocol can be reduced to 15 min without loss of sensitivity. A further reduction to 10 min would decrease the rate of positive responses by a small amount and might be considered clinically acceptable.

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

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

[Diagnostic 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.

Comparison of diagnostic accuracy of sublingual nitroglycerin test and low-dose isoproterenol test in patients with unexplained syncope

Despite the widespread use of head-up tilt testing as a means for diagnosing vasovagal syncope, standardization of test methodology remains a controversial issue. The aim of this study was to compare the diagnostic value of head-up tilt testing potentiated with sublingual nitroglycerin with that of head-up tilt testing potentiated with low-dose isoproterenol. For this purpose, 71 patients with unexplained syncope (mean age 43 years) and 30 asymptomatic controls were studied. All underwent the sublingual nitroglycerin and low-dose isoproterenol tests on separate days in a randomized fashion. The protocol of the 2 tests was similar and consisted of 2 phases. Initially, subjects were tilted at 60 degrees for 20 minutes without medication; then, if syncope did not occur, patients and controls received sublingual nitroglycerin (300 microg) or low-dose intravenous isoproterenol (mean infusion rate 1.3 +/- 0.5 microg/min) and continued to be tilted at 60 degrees for a further 20 minutes. During the sublingual nitroglycerin test, a positive response (syncope associated with sudden hypotension and bradycardia) occurred in 35 patients (49%), a negative response in 36 (51%), and drug intolerance in none (0%). During the low-dose isoproterenol test, these percentages were 41%, 59%, and 6%, respectively. A concordant response was observed in 53 cases (75%). Among controls, 3 subjects (10%) had a positive response to the sublingual nitroglycerin test and 4 (13%) to the low-dose isoproterenol test. It is concluded that sublingual nitroglycerin and low-dose isoproterenol are equivalent tests for evaluating patients with unexplained syncope. The sublingual nitroglycerin test, however, is simpler, better tolerated, and safer than the low-dose isoproterenol test and, thus, more suitable for routine clinical use.

Susceptibility to neuromediated syncope after acute myocardial infarction

BACKGROUND

Syncope after acute myocardial infarction (AMI) is a common clinical problem. It may be hypothesised that remodelling and neurohormonal changes following AMI may predispose to neuromediated syncope.

DESIGN

To address this issue we prospectively evaluated the incidence of positive results of head-up tilt-table testing in 40 patients following AMI and 40 age and sex matched controls without a history of syncope. The mechanisms of tilt-induced changes in autonomic tone were assessed using spectral analysis of heart rate variability. The patients were followed-up for one year.

RESULTS

Positive results of tilt-test occurred in 4 (10%) controls and 13 (33%) AMI patients (P = 0.01). No significant differences in sympathovagal interaction (assessed by a low frequency/high frequency ratio) were detected between the groups before tilting (2. 9 +/- 1.9 vs. 3.1 +/- 2.2; NS). However, dynamic changes of this parameter differed significantly during the first 5 symptomless minutes of the active phase of tilt-test. The ratio increased in the majority of controls (87%) and decreased in the majority of patients (62%) (P < 0.0001). During one year follow-up, syncope or presyncope occurred in 10 (25%) AMI patients but did not occur in any control subject (P < 0.001). The sensitivity, specificity and predictive accuracy of an early tilt-test after AMI for the prediction of syncope or presyncope was 70%, 80% and 78%, respectively.

CONCLUSION

Patients after AMI are prone to neuromediated reactions. Sympathetic withdrawal seems to be the most likely mechanism of syncope. The role of tilt testing for identification of patients susceptible to syncope or presyncope after AMI needs further investigation.

A review of pathophysiology and therapy of patients with vasovagal syncope

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

Early heart rate variations during head-up tilt table testing as a predictor of outcome of the test

Head-up tilt table testing (HUTT) is a useful tool for the diagnosis of unknown origin of syncope. A setback is its duration. This study tries to establish a specific parameter that, according to the heart rate elevation in the test's initial phase, allows a reliable prediction of its outcome. In a prospective study, every patient being under unknown syncope workup was included. A two-phase 20-minute tilt table test was performed. The initial phase was passive, and the second required pharmacological stimulation with isoproterenol. The basal and 5- and 10-minute heart rate values of the passive phase were measured and compared within the group and against negative tests. During a 1-year period, 115 HUTT were performed: 88 were positive and 27 negative. The negative HUTT patients had an increase in HR of 5.05 (+/- 13.5) beats/min at 5 minutes, and 5.79 (+/- 12.9) beats/min at 10 minutes (P = 0.2). Those with a positive HUTT had an increase of 9.05 (+/- 14.5) beats/min at 5 minutes, and of 10 (+/- 13.4) beats/min at 10 minutes (P < 0.001). There were no significant changes in HR when comparing positive to negative HUTT. There is no specific number that allows predication of outcome early in HUTT. Within the group, variations are important. Only a group tendency can be established, which strongly correlates with the results obtained during the test.

Intravenous nitrates for pharmacological stimulation during head-up tilt testing in patients with suspected vasovagal syncope and healthy controls

Nitrates may be used for pharmacological stimulation during tilt testing for the diagnosis of vasovagal syncope. In this study we assessed the diagnostic value of intravenous nitrates during tilt testing in patients with a typical history of vasovagal syncope. Twenty patients and 23 controls were tilted at 700 for a maximum duration of 30 minutes. After a 10-minute baseline supine phase, the test started with a continuous nitrate infusion at 1 microg/kg/min and increased every 5 minutes by 1 microg/kg/min, to a maximum of 6 microg/kg/min at the end of the test. The test was ended if the subjects developed a positive response (syncope or presyncope). Nineteen patients (95%) and 17 (74%) of the controls had a positive response. At test end sensitivity was 95%, but specificity was 26% and accuracy was 58%. Receiver operator characteristics (ROC) analysis revealed a maximum accuracy of 79% at 18 minutes, with a sensitivity of 80% and a specificity of 78%. Intravenous nitrates during tilt testing in patients with typical clinical criteria of vasovagal syncope is highly effective in provoking vasovagal syncope. Based on the ROC analysis, a maximum accuracy of 79% was attained at 18 minutes (at a dose of 4 microg/kg/min), suggesting a good diagnostic performance when tilt duration is limited to this point. A positive result requiring more than 18 minutes of stimulated tilting should be interpreted with caution, due to the accompanying considerable decrease of specificity.