Syncope and the autonomic nervous system

The autonomic nervous system and the origins of neurocardiology

Following new concepts by Bichat in the early 19th century, of organic and animal life centered around the ganglionic nervous system, over 100 years of anatomic studies and physiologic experimentation eventually resulted in Gaskell's 1916 book entitled "The Involuntary Nervous System" and Langley's 1921 book entitled "The Autonomic Nervous System." Neurology and cardiology emerged as specialties of medicine in the early 20th century. Although neurology made several prominent discoveries in neurophysiology during the first half of the 20th century, cardiology developed coronary care units and cardiac catheterization in the 1960s. Programmed electrical stimulation of the heart and noninvasive ambulatory monitoring provided new methodologies to study clinical cardiac arrhythmias. Experimentally, direct cardiac nerve stimulation of sympathetic nerve endings, as well as parasympathetic control of the atrioventricular node, provided the background to new detailed autonomic studies of the heart. Neurocardiology, perhaps initially more directed towards our understanding of sudden cardiac death, ultimately embraced an even significantly more complex scheme of local circuit neurons and near-endless loops of interconnecting neurons in the heart. Intrathoracic extracardiac and intracardiac ganglia have been recharacterized, both anatomically and physiologically, laying the groundwork for potential new therapies of cardiac neuromodulation.

Computational modeling for the quantitative assessment of cardiac autonomic response to orthostatic stress

Objective.The autonomic nervous system (ANS) plays a critical role in regulating not only cardiac functions but also various other physiological processes, such as respiratory rate, digestion, and metabolic activities. The ANS is divided into the sympathetic and parasympathetic nervous systems, each of which has distinct but complementary roles in maintaining homeostasis across multiple organ systems in response to internal and external stimuli. Early detection of ANS dysfunctions, such as imbalances between the sympathetic and parasympathetic branches or impairments in the autonomic regulation of bodily functions, is crucial for preventing or slowing the progression of cardiovascular diseases. These dysfunctions can manifest as irregularities in heart rate, blood pressure regulation, and other autonomic responses essential for maintaining cardiovascular health. Traditional methods for analyzing ANS activity, such as heart rate variability (HRV) analysis and muscle sympathetic nerve activity recording, have been in use for several decades. Despite their long history, these techniques face challenges such as poor temporal resolution, invasiveness, and insufficient sensitivity to individual physiological variations, which limit their effectiveness in personalized health assessments.Approach.This study aims to introduce the open-loop Mathematical Model of Autonomic Regulation of the Cardiac System under Supine-to-stand Maneuver (MMARCS) to overcome the limitations of existing ANS analysis methods. The MMARCS model is designed to offer a balance between physiological fidelity and simplicity, focusing on the ANS cardiac control subsystems' input-output curve. The MMARCS model simplifies the complex internal dynamics of ANS cardiac control by emphasizing input-output relationships and utilizing sensitivity analysis and parameter subset selection to increase model specificity and eliminate redundant parameters. This approach aims to enhance the model's capacity for personalized health assessments.Main results.The application of the MMARCS model revealed significant differences in ANS regulation between healthy (14 females and 19 males, age: 42 ± 18) and diabetic subjects (8 females and 6 males, age: 47 ± 14). Parameters indicated heightened sympathetic activity and diminished parasympathetic response in diabetic subjects compared to healthy subjects (p < 0.05). Additionally, the data suggested a more sensitive and potentially more reactive sympathetic response among diabetic subjects (p < 0.05), characterized by increased responsiveness and intensity of the sympathetic nervous system to stimuli, i.e. fluctuations in blood pressure, leading to more pronounced changes in heart rate, these phenomena can be directly reflected by gain parameters and time response parameters of the model.Significance.The MMARCS model represents an innovative computational approach for quantifying ANS functionality. This model guarantees the accuracy of physiological modeling while reducing mathematical complexity, offering an easy-to-implement and widely applicable tool for clinical measurements of cardiovascular health, disease progression monitoring, and home health monitoring through wearable technology.

The Haemodialysis Session Effect on the Choroidal Thickness and Retinal and Choroidal Microcirculation-A Literature Review

Haemodialysis (HD) is currently the most commonly used method of renal replacement therapy. The process of dialysis involves numerous changes that affect many systems, including the eye. The changes occurring in the course of HD may affect the ocular parameters, such as intraocular pressure, central corneal thickness, retinal thickness, retinal nerve fibre layer thickness, and choroidal thickness (CT). The choroid, being one of the most vascularized tissues, is characterized by the highest ratio of blood flow to tissue volume in the entire body, may be particularly susceptible to changes occurring during HD, and at the same time reflect the microcirculatory status and its response to HD. Patients with end-stage renal disease subjected to dialysis are highly susceptible to systemic microvascular dysfunction. Moreover, it is considered that the process of HD itself contributes to vascular dysfunction. Nowadays, thanks to the development of imaging techniques, the widely available optical coherence tomography (OCT) tests allow for the assessment of CT, while OCT-angiography allows for a quick, non-invasive, and repeatable assessment of the condition of retinal and choroidal microcirculation, which significantly expands our knowledge regarding the reaction of ocular microcirculation due to HD. The assessment of both retinal and choroidal circulation is even more attractive because retinal circulation is autoregulated, while choroidal circulation is mainly controlled by extrinsic autonomic innervation. Thus, assessment of the choroidal response to an HD session may provide the possibility to indirectly evaluate the functions of the autonomic system in patients subjected to HD. At a time when the importance of microcirculation in systemic and renal diseases is becoming increasingly evident, the assessment of ocular microcirculation appears to be a potential biomarker for assessing the condition of systemic microcirculation. In this work, we present a review of the literature on the effect of the HD session on CT and the retinal and choroidal microcirculation.

Cardiac syncope recurrence in type 2 diabetes mellitus patients vs. normoglycemics patients: The CARVAS study

STUDY HYPOTHESIS

Cardiac autonomic dysfunction might lead to higher vaso vagal syncope (VVS) recurrence rate in type 2 diabetes mellitus (T2DM) patients vs. non diabetics patients.

BACKGROUND

VVS recurrence might be due to alterations of autonomic system function, as assessed by heart rate variability (HRV). To date, in this study we investigated the correlation between HRV alterations and VVS recurrence at 12 months of follow up in T2DM vs. non T2DM patients.

MATERIALS AND METHODS

In a prospective multicenter study we studied a propensity score matching (PSM) analysis of 121 T2DM vs. 121 non T2DM patients affected by VVS.

RESULTS

T2DM vs. non T2DM patients had at baseline a higher rate of HRV dysfunction, and this was linked to higher rate of VVS recurrence at 12 months of follow up (p < 0.05). Blood pressure alterations and lower LF/HF ratio were linked to higher rate of all cause syncope recurrence, and of vasodepressor, cardio inhibitory, and mixed syncope recurrence (p < 0.05). Anti hypertensive drug therapies increased the number of vasodepressor and mixed syncope events (p < 0.05); alterations of heart rate increased syncope recurrence and mixed syncope recurrence events (p < 0.05). Finally, T2DM was linked to higher rate of VVS recurrence, and specifically of vasodepressor and mixed VVS recurrence (p < 0.05).

CONCLUSIONS

T2DM patients have alterations of the autonomic nervous system, as result of cardiac autonomic neuropathy. However, T2DM diagnosis and autonomic dysfunction assessed by HRV alterations predicted VVS recurrence.

Small-cell lung cancer with recurrent syncope as the initial symptom: A case report and literature review

Small-cell lung cancer (SCLC) presenting with syncope as the initial symptom is rare in adults. This onset of tumour-induced syncope cannot be screened or differentiated by coronary angiography, magnetic resonance angiography of the neck or 24-hour dynamic electrocardiogram. We herein describe the case of a 61-year-old man who presented with recurrent syncope that resolved after the first course of chemotherapy (carboplatin plus etoposide) for SCLC. A mass measuring 57×53 mm was identified in the left hilum, and a diagnosis of limited-disease SCLC (T4N2M0, IIIB) was made. Considering the rapid and complete remission after the treatment of the primary lesion, we hypothesised that the syncope was neurogenic and associated with cancer. Thus, 8 similar cases retrieved from PubMed were reviewed and, for the first time, the mechanism underlying the syncope was identified, which may involve tumour location, neurobiology and other inducing factors. Thus, for the treatment of such SCLC patients, standard chemotherapy is crucial for preventing syncopal attacks.

The Management of Vasovagal Syncope in a Patient with Brugada Syndrome

Vasovagal syncope is the most common cause of the neurally mediated reflex syncopes. A higher susceptibility to vasovagal syncope has been reported in patients with Brugada syndrome (BrS) and may be caused by associated autonomic dysfunction. It is unclear what risk vasovagal syncope confers to patients with BrS. This article reviews the pathophysiology of vasovagal syncope and autonomic dysfunction in patients with BrS and its association with BrS, treatment options for patients with BrS with vasovagal syncope, specific therapies and those that may be harmful in patients with BrS, and potential therapies and monitoring for patients with BrS with vasovagal syncope.

Neurocardiogenic syncope: mechanisms, evaluation and treatment

Syncope is the abrupt and transient loss of consciousness due to a temporary reduction in cerebral blood flow, associated with an absence of postural tone, followed by a rapid and usually complete recovery. It may result from several possible etiologies, ranging from the benign to the potentially fatal. Neurocardiogenic (vasovagal) syncope is the most common of a group of neurally mediated syncopes, characterized by a sudden failure of autonomic regulatory mechanisms to maintain adequate blood pressure and, occasionally, heart rate, to sustain cerebral perfusion and consciousness. The diagnosis may be suggested by a characteristic history and by exclusion of other causes of syncope; however, in some cases, upright tilt table testing may be required to provoke typical hemodynamic responses. Cardiologists and cardiac electrophysiologists are frequently expected to manage patients with suspected neurocardiogenic syncope. The following review aims to provide a basic framework for understanding its pathophysiology, clinical presentations, diagnosis and treatment.

Heart rate and stroke volume response patterns to augmented orthostatic stress

AIMS

Combined head up tilt (HUT) and lower body negative pressure (LBNP) can be used to exploit the full spectrum of cardiovascular control mechanisms and to reveal characteristics of individual blood pressure control. We studied whether the response to combined HUT and LBNP was reproducible within subjects and whether characteristic response patterns could be distinguished between different subjects.

MATERIALS AND METHODS

Ten healthy young males were subjected to combined HUT and graded LBNP to achieve a presyncopal end point in four tests, each separated by more than 2 weeks. Heart rate, blood pressure and thoracic impedance were monitored, cardiac output and peripheral vascular resistance were computed.

RESULTS

From supine control to presyncope, heart rate, mean arterial blood pressure, pulse pressure and stroke index changed as expected. The time courses of heart rate and stroke volume as well as orthostatic tolerance times (15 +/- 6 to 18 +/- 7 minutes, n.s) appeared reproducible between trials within subjects but different between different subjects.

CONCLUSION

LBNP-tilt approach was repeatable in time and pattern. Furthermore, differences observed between subjects indicated preferred activation of selected pathways of blood pressure control in different individuals while at the same time, reproducibility measured within the same subject showed that preferential mechanisms were highly conserved within the same individual. These characteristics are a prerequisite to use the combined graded orthostatic paradigm for hemodynamic testing and identification.

A new blood pressure and heart rate signal analysis technique to assess Orthostatic Hypotension and its subtypes

Orthostatic Hypotension is a sudden drop in blood pressure upon assumption of upright posture. This drop in blood pressure is often results in symptoms such as dizziness, light-headedness, blurred vision, and syncope. Since 1986, tilt table testing has become widely used in the diagnosis of Orthostatic Hypotension. In this study, new algorithms for artifact removal and data extraction in Finometer data were developed. Algorithms were also developed to assess the rates of change of haemodynamic variables in response to head up tilt testing. These algorithms were applied to the Finometer measurements of 20 patients, who underwent tilt table testing in the Mid-Western Regional Hospital, Limerick. The techniques developed were shown to effectively reduce artifact noise without loss of clinically relevant data. The data extraction algorithms were shown to accurately record changes in haemodynamic variables. It was also demonstrated that rate of change of blood pressure during head-up tilt table testing could have prognostic significance for Orthostatic Hypotension.

Neurocardiogenic syncope: frequency and consequences of its misdiagnosis as epilepsy

BACKGROUND

Neurocardiogenic syncope (NCS) can be mistaken as a seizure. We reviewed the frequency and diagnostic consequences of this misdiagnosis.

METHODS

A retrospective review of outpatient adult epilepsy clinic charts (QEII Health Sciences Centre, Halifax, NS) was conducted to identify NCS patients referred with a provisional diagnosis of seizures. Charts were reviewed in detail with an emphasis on the consequences of misdiagnosis.

RESULTS

Of 1506 consecutive referrals to the epilepsy clinic, 194 (12.9%) ultimately had a clinical diagnosis of NCS. Mean age was 38 +/- 16 years (mean age of syncopal onset was 28 +/- 16 years). Two-thirds of referrals were from primary care physicians (including emergency departments) and 18% from neurologists. Thirty-five percent were prescribed antiepileptic drugs (AEDs) prior to referral with eight patients (4.1%) experiencing hypersensitivity reactions. Three of five women had adverse pregnancy outcomes while taking AEDs. One-third of patients had restrictions placed on their driving privileges while 11 patients (5.7%) had their employment interrupted. Diagnostic modalities used in the work-up included EEG (90%), CT head (51%), and MRI head (15%).

CONCLUSIONS

NCS is commonly misdiagnosed as epilepsy. Some patients had an incorrect diagnosis for > 10 years. Patients with this misdiagnosis are often excessively investigated, inappropriately treated, and have unnecessary restrictions placed on driving and employment.

Influence of sympathetic tone on heart rate during vagal stimulation and nitroprusside induced hypotension in ovine fetus

OBJECTIVE

To characterize effects of sympathetic tone on fetal heart rate (FHR) reflex responses and FHR variability in late gestation.

DESIGN/METHODS

Changes in FHR and autonomic tones were studied (i) after electrical vagal stimulation and (ii) during nitroprusside-induced hypotension, in seven late gestation ovine fetus in control condition (ctrl), after dobutamine (beta1-activation) and atenolol (beta1-blockade). Results are expressed as mean +/- SEM.

RESULTS

(i) Minimal FHR after vagal stimulation was not influenced by atenolol or dobutamine but dobutamine accelerated FHR normalization. (ii) During nitroprusside induced hypotension atenolol inhibited the initial increases in FHR and FHR variability (measured by SD and LFnu) but not the bradycardia occurring below a mean arterial pressure of 38 +/- 2 mmHg. Dobutamine did not abolish the depressor reflex. During hypotension the positive chronotropic effect of sympathetic tone increased from 15 +/- 2 to 42 +/- 7 bpm then decreased at a rate of -7.6 +/- 1.5 bpm mmHg(-1), vagal negative chronotropic influence steadily increased at a rate of 1.9 +/- 0.4 bpm mmHg(-1). Changes in FHR variability were not correlated with vagal or sympathetic chronotropic effects.

CONCLUSIONS

beta1-stimulation does not affect sinus-node response to vagal stimulation but improves the speed of FHR normalization. FHR response to hypotension depends on an initial increase in both sympathetic and parasympathetic chronotropic effects that is associated with a sympathetic dependent increase in FHR variability and is followed by a withdrawal of sympathetic tone.

[Standardized oculocardiac reflex in ex-premature near full term (93 cases)]

The aim of the study was to present data investigating vagal reactivity in a population of premature infants reaching term, using the oculo-cardiac reflex.

PATIENTS AND METHODS

Ninety three premature infants, free of any disease, near full term at the moment of testing, were prospectively investigated at a time close to discharge from neonatal unit. After an all-night polygraphic recording, a standardized oculo-cardiac reflex test was performed during quiet sleep. Data were classified in relation to both chronological and postconceptional ages. Simple liner regression analyses were performed on the selected variables.

RESULTS

The results showed heterogeneity of the vagal response in this population: longest asystole (1049 ms +/- 540; 95th percentile = 1894 ms); maximal percentage of deviation between two successive RR intervals (88% +/- 90; 95th percentile = 200%); and duration between the beginning of decrease in heart rate and return to mean heart rate (14 s +/- 10; 95th percentile = 30 s).

CONCLUSION

Our healthy premature infants at time of discharge exhibited a wider range of vagal reactivity than previously reported for the full term newborns. Considering our findings, we recommend caution before proceeding with treatment of vagal bradycardia in a similar premature infant population.

Does an early increase in heart rate during tilting predict the results of passive tilt testing?

Head-up tilt testing is a useful but time-consuming procedure. If we could accurately predict the tilt testing results; we would be able to substantially shorten the duration of tilt protocol. To clarify the hypothesis that an early increase in heart rate (HR) during tilting can predict the passive tilt results in our protocol (80-degree angle for 30 minutes), we studied 115 consecutive patients (72 men, 43 women, mean age 46 +/- 19 years) who were clinically diagnosed with neurally mediated syncope. Twenty-nine (25%) patients had a positive tilt test (P group), whereas 86 (75%) patients had a negative test (N group). The early HR increase was defined as the maximum HR during the first 5 minutes of tilting minus the resting HR before tilting. The early HR increase was significantly higher in the P group (23.8 +/- 9.5 beats/min) than in the N group (17.5 +/- 8.2 beats/min, P = 0.0008), but it was negatively correlated with the tilt duration to positive response (r = -0.52, P = 0.0032) and the patient age in the entire study population (r = 0.62, P < 0.0001). Results of multiple regression analysis indicated that age, tilt result, and tilt duration were independently associated with the early HR increase. As a result, an early HR increase > or = 18 beats/min, the best apparent cut-off point obtained in our study, was a sensitive (100%) marker for prediction of a positive response at < or = 15 minutes of tilting, but it showed a low specificity (61%). In conclusion, an early HR increase during 80-degree tilting may be only predictive for a positive result < or = 15 minutes because it depends on the tilt duration to a positive response and patient age.

24-hour heart rate variability in patients with vasovagal syncope

Since alterations in the autonomic nervous system are thought to play a major role in the pathogenesis of vasovagal syncope, we characterized the chronic autonomic profile of 44 patients with syncope and 20 healthy subjects by means of heart rate variability using 24-hour Holter recordings (time- and frequency-domain indexes), and evaluated whether the different types of responses to tilting (vasodepressive versus cardioinhibitory) could be associated with different cardiac autonomic patterns. Twenty-three patients exhibited a positive response to tilting, which was vasodepressive in 11 patients and cardioinhibitory in 12 patients. All vasodepressive patients had a standard deviation of the averages of NN (SDANN) intervals in all 5-minute segments lower than 100 ms. Patients with vasodepressive syncope also had significantly lower values of RMSSD (the 24-hour square root of the mean of the sum of the squares of differences between adjacent normal RR intervals) than those with cardioinhibitory response, and lacked the day-night rhythm of the low frequency/high frequency ratio. However, only SDANN values correctly identified patients with vasodepressive response to tilting. We conclude that (1) the population of patients with vasovagal syncope is heterogeneous, (2) patients with vasodepressive syncope have a peculiar chronic autonomic profile as assessed by 24-hour heart rate variability analysis, and (3) the evaluation of the autonomic profile in 24-hour Holter recordings could be of value in the diagnosis of patients with syncope.

Triggering mechanism for neurally mediated syncope induced by head-up tilt test: role of catecholamines and response to propranolol

OBJECTIVES

We studied the triggering mechanism for neurally mediated syncope.

BACKGROUND

Although increased transient sympathetic tone is thought to be necessary for the development of neurally mediated syncope, little is known about the triggering mechanism for neurally mediated syncope.

METHODS

Plasma epinephrine (EP) and norepinephrine (NE) levels were assessed in 20 syncope patients during tilt test (80 degrees, 15 min) with and without isoproterenol (ISP, 0.01, 0.02 microg/kg/min). If syncope occurred, propranolol (0.1 mg/kg) was injected.

RESULTS

Eight patients experienced syncope during tilting alone, and 9 patients required ISP for syncope. In the negative response without ISP, NE showed a small statistical 1.7-fold increase at end of tilting and EP did not change during tilting. When syncope occurred during tilting alone, a significant 11.7-fold increase in EP at syncope was registered concomitant with a small 2.5-fold increase in NE. When patients experienced syncope during tilting with ISP, a significant 5.0-fold increase in EP at syncope was registered concomitant with a small 1.7-fold increase in NE. In patients without ISP, propranolol did not interrupt syncope. In patients with ISP, six of eight receiving propranolol responded to tilting negatively.

CONCLUSIONS

An increase of NE levels may result in inhibition of syncope and an EP surge may be a triggering mechanism for neurally mediated syncope. Comparatively low levels of EP may be enough to induce syncope during tilting with ISP compared with tilting alone. Propranolol is not effective in patients without ISP, but it frequently inhibits syncope in patients with ISP. Propranolol (0.1 mg/kg) may be insufficient to block the actions of high levels of circulating EP.

Heart rate variability during head-up tilt testing in patients with suspected neurally mediated syncope

The relation between heart rate variability (HRV) and outcome of head-up tilt testing (HUT) in patients with neurally mediated syncope (NMS) was studied in 30 patients with presumed NMS (33 +/- 13 years) and in 11 age-matched controls. After 15 minutes of baseline supine observation, patients were tilted to 60 degrees for 45 minutes or until syncope occurred. HRV parameters included RR intervals, standard deviation of normal-to-normal RR intervals (SDNN), and root mean square successive differences (RMSSD). HRV analysis was performed during 5-minute intervals in the supine position immediately after onset of HUT and before syncope or after 30-35 minutes of tilt in patients without syncope. Syncope occurred after a mean tilt duration of 32 minutes in 14 (47%) of 30 patients with presumed NMS, whereas all controls had an uneventful HUT. In the supine position, RR intervals and RMSSD were comparable among HUT-positive patients, HUT-negative patients, and controls (RR intervals: 799 +/- 92, 854 +/- 137, and 818 +/- 128 ms, P = NS; RMSSD: 43 +/- 40, 36 +/- 34, and 53 +/- 42 ms, P = NS). Baseline SDNN was also comparable in HUT-positive patients versus HUT-negative patients with presumed NMS (50 +/- 26 vs 52 +/- 20 ms, P = NS). Within 5 minutes preceding syncope or after 30-35 minutes of tilt, RR intervals and RMSSD were shorter in HUT-positive patients compared to HUT-negative patients, or to controls (RR intervals: 606 +/- 86 vs 710 +/- 117 and 739 +/- 123 ms, P < 0.05; RMSSD: 12 +/- 5 vs 23 +/- 19 and 40 +/- 32 ms, P < 0.05). Thus, HRV analysis in the baseline supine position was not a predictor of HUT outcome in patients with suspected NMS. Syncope during HUT seemed to be preceded by increased sympathetic activity manifested by an increase in heart rate and by a decreased parasympathetic tone manifested by a decrease in RMSSD measured for 5 minutes before the event, in comparison with HUT-negative patients and with controls.

Usefulness of plasma catecholamines during head-up tilt as a measure of sympathetic activation in vasovagal patients

Vasovagal syncope is a common clinical disorder which has been traditionally related to a vasovagal reflex precipitated by an initial excess sympathetic stimulation. We hypothesized that the increase in plasma catecholamines during head-up tilt is more accentuated in patients with tilt induced vasovagal syncope. To test this hypothesis, plasma catecholamines were measured in supine posture and during head-up tilt in patients with a history suggestive of vasovagal syncope. Of these, 13 had a normal response to tilt (nonvasovagal group; age 41 +/- 19 [SD]years) and 11 had a vasovagal response to tilt (vasovagal group; 39 +/- 20 years). In the supine posture at rest, plasma epinephrine and norepinephrine were not significantly different between the nonvasovagal and the vasovagal groups (39 +/- 28 ng/L vs 46 +/- 38 ng/L, P = 0.5792, 335 +/- 158 ng/L vs 304 +/- 124 ng/L, P = 0.6007, respectively). Furthermore, the tilt induced changes in plasma epinephrine and norepinephrine were not different between the two groups (20 +/- 20 ng/L vs 35 +/- 55 ng/L, P = 0.3562, 264 +/- 158 ng/L vs 242 +/- 205 ng/L, P = 0.7724, respectively) suggesting that differences in the hemodynamic response to tilt are not predictable by the supine levels of circulating plasma catecholamines, and that the extent of plasma catecholamines increase during tilt does not determine the hemodynamic outcome of the tilt test. Since orthostatic changes of plasma catecholamines could be influenced by volume factors, we assessed plasma renin activity and aldosterone as surrogates of blood volume. Baseline plasma renin activity and aldosterone were not significantly different between the two groups. We conclude that inasmuch as plasma catecholamines reflect the status of sympathetic activity, our data do not support the hypothesis that accentuation of sympathetic activity precedes necessarily the tilt induced vasovagal syncope. However, one should take in consideration that multiple factors may influence catecholamine levels and catecholamines kinetics. A hyperresponsiveness of beta-receptors to catecholamines in patients with vasovagal syncope may be suggested but needs to be tested.

Head-upright tilt table testing. A safe and easy way to assess neurocardiogenic syncope

Head-upright tilt table testing has emerged as an exciting technique for evaluating episodes of autonomically mediated syncope. It may be performed using gravity alone as the provocative stimulus or with the addition of isoproterenol. The classic neurocardiogenic response to the test is a sudden drop in blood pressure followed by a decrease in heart rate, but other abnormal response patterns have also been reported. Continuing investigations will improve understanding of autonomic disturbances that cause orthostatic intolerance and will help elaborate the role of tilt table testing in their evaluation and management.

Acute pericarditis presenting with sinus bradycardia: a case report

Acute pericarditis is almost invariably associated with sinus tachycardia. Recent-onset chest pain in the presence of (sinus) bradycardia is considered to be associated with an acute ischemic syndrome rather than acute pericarditis. This report describes a patient with acute pericarditis initially presenting with sinus bradycardia, probably due to a vasovagal response to (chest) pain.

Vasodepressor syncope. Diagnosis and management

Vasodepressor syncope is a common medical problem that can be diagnosed through an accurate history and upright tilt testing. In most cases, patients experience a striking decrease in syncopal episodes following a tilt test, and long-term therapy is not necessary. In the rare patient who experiences no prodrome and continues to experience injury-causing syncope, empiric therapy with drugs or dual-chamber pacing has to be considered despite the lack of controlled trials establishing the efficacy of such therapies.

Rate-drop response programming

Effective programming of the rate-drop response algorithm requires careful attention to the heart rate and blood pressure responses seen during diagnostic tilt testing. In order to undertake effective programming, additional tilt testing procedures may be necessary, and it is vital that the protocol should be identical on each occasion and very careful note taken of exact times of onset of symptoms and relative timing of onset of changes in heart rate and blood pressure. The algorithm settings in the Thera DR generator as delivered (factory or "shelf" parameter settings) must be considered nontherapeutic (an unusual situation for a pacemaker algorithm) and will require adjustment for each individual patient. Effective therapeutic settings are likely to result in an excess of pacing interventions; these, however, tend to be less symptomatic than the syncope or presyncope suffered by the patient and are generally well tolerated or not noticed.

Tilt table testing: concepts and limitations

Recurrent unexplained syncope is a common and often frustrating clinical problem. Over the last decade, head upright tilt table testing has emerged as an important diagnostic method for the identification of individuals 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 much greater understanding of these disorders. This article reviews the concepts behind tilt table testing, as well as the uses and limitations of the evolving diagnostic modality.

Tilt testing: a useful screen for rate-drop response

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