[This corrects the article DOI: 10.3389/fphys.2014.00220.].

To explore the long-term outcomes of children and adolescents with postural tachycardia syndrome receiving conventional interventions. A total of 121 patients were recruited, but 6 (5.0%) of them were lost at follow-up. The detailed clinical data were collected, and the reoccurrence and frequency of orthostatic intolerance symptoms were evaluated with a mean followed-up period of 18.7 months (range, 14-74 months). The Kaplan-Meier curve was used to show the cumulative symptom-free rate of patients over time. Factors influencing the long-term outcomes were examined using the Cox's proportional hazards models. The cumulative symptom-free rate was gradually increased over time. It was 48.4% at the 1-year follow-up and increased to 85.6% at the 6-year follow-up. The duration of symptoms before treatment and the maximum upright heart rate in standing-up test were identified as independent indicators for the long-term outcomes. Each 1-month prolongation in the duration of symptoms before treatment was associated with a 1.2% decrease in the cumulative symptom-free rate. However, each 1-bpm increase in the maximum upright heart rate in standing-up test was associated with a 2.1% increase in the cumulative symptom-free rate. The long-term outcomes of postural tachycardia syndrome patients who received conventional interventions are benign and the cumulative symptom-free rate was gradually increased over time. The prolonged duration of symptoms before treatment and the reduced maximum upright heart rate in standing-up test are the independent risk indicators.

Postural tachycardia syndrome (POTS) is one of several disorders of orthostatic intolerance (OI). It is defined by the development of symptoms of cerebral hypoperfusion or sympathetic activation and a sustained heart rate increment of 30 beats/min or more (40 beats/min for teenagers) within 10min of standing or head-up tilt in the absence of orthostatic hypotension; the standing heart rate is often 120 beats/min or higher. POTS is approximately five times more common in women than men. This heterogeneous syndrome is caused by several pathophysiologic mechanisms (limited autonomic neuropathy, hyperadrenergic state, hypovolemia, venous pooling, deconditioning), which are not mutually exclusive. Anxiety and somatic hypervigilance play significant roles in POTS. Common comorbidities include visceral pain and dysmotility, chronic fatigue and fibromyalgia, migraine, joint hypermobility, mitral valve prolapse, and inappropriate sinus tachycardia. Patients with suspected POTS should undergo comprehensive cardiac and neurologic examinations and autonomic and laboratory tests to determine the most likely pathophysiologic basis of OI. The objectives of POTS management are to (1) increase the time that patients can stand, perform daily activities, and exercise and (2) avoid syncope. Management involves nonpharmacologic (fluid and salt loading, physical countermaneuvers, compression garments, exercise training) and pharmacologic (β-blockers, pyridostigmine, fludrocortisone, midodrine) approaches.

Postural tachycardia syndrome (POTS) is a form of autonomic dysregulation and is characterized by an excessive heart rate (HR) increment upon the upright body position while blood pressure is maintained. Patients experience typical symptoms of orthostatic intolerance such as dizziness, nausea and cognitive impairments. The present study assessed position-dependent attentional and cognitive functioning in POTS patients compared to healthy subjects and tested the response of cognitive performance to acute water intake. Data was obtained from eight patients with neuropathic POTS and eight healthy subjects of similar age and gender. All participants completed questionnaires that assessed health-related quality of life and depression and underwent four rounds of neuropsychological testing overall, each before and after the intake of 500 ml still mineral water and both in the supine and in the upright posture. Postural tachycardia syndrome patients showed deficits in working memory (WM) exclusively in the upright position compared to healthy subjects, but no position-dependent impairments in alertness or divided attention. Rapid water ingestion had a beneficial effect on WM in the upright posture, lead to a decrease in HR increment and to an improvement of subjective symptom experience. The results provide support for the occurrence of purely orthostatic cognitive deficits in POTS, especially when increased executive control and cognitive resources are required and document a favorable effect of water intake on cognitive performance. These findings have important implications for the management of cognitive symptoms in POTS as high water intake is an easy and accessible strategy.

This paper presents the diagnostic criteria for hemodynamic orthostatic dizziness/vertigo to be included in the International Classification of Vestibular Disorders (ICVD). The aim of defining diagnostic criteria of hemodynamic orthostatic dizziness/vertigo is to help clinicians to understand the terminology related to orthostatic dizziness/vertigo and to distinguish orthostatic dizziness/vertigo due to global brain hypoperfusion from that caused by other etiologies. Diagnosis of hemodynamic orthostatic dizziness/vertigo requires: A) five or more episodes of dizziness, unsteadiness or vertigo triggered by arising or present during upright position, which subsides by sitting or lying down; B) orthostatic hypotension, postural tachycardia syndrome or syncope documented on standing or during head-up tilt test; and C) not better accounted for by another disease or disorder. Probable hemodynamic orthostatic dizziness/vertigo is defined as follows: A) five or more episodes of dizziness, unsteadiness or vertigo triggered by arising or present during upright position, which subsides by sitting or lying down; B) at least one of the following accompanying symptoms: generalized weakness/tiredness, difficulty in thinking/concentrating, blurred vision, and tachycardia/palpitations; and C) not better accounted for by another disease or disorder. These diagnostic criteria have been derived by expert consensus from an extensive review of 90 years of research on hemodynamic orthostatic dizziness/vertigo, postural hypotension or tachycardia, and autonomic dizziness. Measurements of orthostatic blood pressure and heart rate are important for the screening and documentation of orthostatic hypotension or postural tachycardia syndrome to establish the diagnosis of hemodynamic orthostatic dizziness/vertigo.

Postural orthostatic tachycardia syndrome (POTS) is a condition in which a change from a supine to an upright position causes an abnormally large increase in heart rate which may be accompanied by a variety of physical complaints. We report two cases illustrating the heterogeneity of this syndrome. We give an update on the etiology of POTS, which is still poorly understood, and its overlap with other syndromes such as chronic fatigue syndrome. Clinicians should be aware of POTS, a fairly common clinical entity, that can result in significant impairments to a patient's quality of life. Lifestyle measures (under which adequate fluid and salt intake, exercise) are a first line of treatment; if insufficient, pharmacotherapy can be considered to improve quality of life.

To assess the efficacy of oral rehydration salts in children with neurally mediated syncope of different hemodynamic types. Children with unexplained syncope or pre-syncope who visited or were hospitalized between March 2012 and February 2015 were enrolled in the study. Checked by the head-up tilt test, 105 children (aged 4-18 years, with a mean age of 11.96 ± 2.86 years) were diagnosed with neurally mediated syncope. Of them, 73 had vasovagal syncope (vasodepressor type in 46, mixed/cardioinhibitory types in 27), and 32 had postural orthostatic tachycardia syndrome. They were randomized into the oral rehydration salts plus health education group (n = 55) and the health education alone group (n = 50). All treated children were followed up. The follow-up time ranged from 6 to 25 (14.82 ± 6.13) months. Short-term effects were assessed according to the recurrence of clinical symptoms and reviews of head-up tilt test results 6 months after drug withdrawal. Long-term effects were compared between both groups of children with neurally mediated syncope. Short-term effect: No significant differences were found in subjective response rate and head-up tilt test negative results rate among different hemodynamic types ( P > .05). Long-term effect: Compared with the health education alone group, the cumulative response rate increased after treatment with oral rehydration salts ( P < .05). Among oral rehydration salts-treated children, the cumulative response rate was higher in those with vasodepressor vasovagal syncope than with mixed/cardioinhibitory vasovagal syncope ( P < .05). Compared with children with mixed/cardioinhibitory vasovagal syncope, oral rehydration salt is more suitable for those with vasodepressor vasovagal syncope.

Intravenous immunoglobulin (IVIG) has recognized efficacy in autoimmune peripheral nerve disorders, but there has been limited study of the use of IVIG in autoimmune dysautonomias. To determine the efficacy and safety of IVIG in patients with disabling, refractory autoimmune dysautonomias, including patients with postural tachycardia syndrome and gastrointestinal dysmotility. Patients with one or more autonomic disorder(s) and persistent serological evidence for autoimmunity who were unable to work or attend school despite usual treatments for dysautonomia were treated with IVIG for at least 3 months at a dose of at least 1 gm/kg monthly. Outcome measures included the composite autonomic symptom scale 31 survey and a functional ability score. There were 38 patients, 84% female and mean age of 28.4 years. Of patients, 83.5% improved on IVIG as defined by at least 20% improvement in the composite autonomic symptom scale 31 and/or functional ability score. The mean pretreatment functional ability score was 21% (mostly bedridden), which improved to a mean of 74% (nearing able to return to work/school) for responsive patients after at least 1 year of IVIG. The mean time to the first sign of response was 5.3 weeks. There were no serious adverse events. The Mayo autoimmune dysautonomia panel antibodies and traditional Sjögren antibodies were present in only 13% and 8% of patients, respectively, but antiphospholipid antibodies and novel Sjögren antibodies were present in 76% and 42% of patients, respectively. There is increasing evidence that IVIG is safe and effective in a subset of patients with autonomic disorders and evidence for autoimmunity. A 4-month IVIG trial should be considered in severely affected patients who are refractory to lifestyle and pharmacological therapies. Antiphospholipid antibodies and novel Sjögren antibodies are often present in these patients and correlate with a high response rate to IVIG.

Pediatric patients with postural orthostatic tachycardia syndrome (POTS) often present with co-occurring struggles with chronic pain (POTS+pain) that may limit daily activities. POTS is a clinical syndrome characterized by orthostatic symptoms and excessive postural tachycardia without orthostatic hypotension. Active research from the medical and scientific community has led to controversy over POTS diagnosis and treatment, yet patients continue to present with symptoms associated with POTS+pain, making treatment recommendations critical. This topical review examines the literature on diagnosing and treating pediatric POTS+pain and the challenges clinicians face. Most importantly, clinicians must employ an interdisciplinary team approach to determine the ideal combination of pharmacologic (e.g., fludrocortisone), non-pharmacologic (e.g., physical therapy, integrative medicine), and psychological (e.g., cognitive behavioral therapy, psychoeducation) treatment approaches that acknowledge the complexity of the child's condition, while simultaneously tailoring these approaches to the child's personal needs. We provide recommendations for treatment for youth with POTS+pain based on the current literature.

Cerebral autoregulation is crucial for maintaining cerebral blood flow and perfusion. In recent years, the importance of cerebral oxygenation in syncope and orthostatic intolerance (OI) has received increased attention. Cerebral tissue oxygenation can be measured by using near-infrared spectroscopy (NIRS), which determines the ratio of oxygenated hemoglobin to total hemoglobin in cerebral tissue. NIRS is non-invasive technology using near-infrared light, which displays real-time cerebral tissue oxygenation. Normal values of cerebral tissue oxygenation in healthy subjects are 60 to 80%. Head-up tilt test (HUT) offers the opportunity to observe the haemodynamic changes precipitating syncope and is, today, the standard method for the evaluation of syncope and orthostatic intolerance syndromes. In previous studies where NIRS was applied during HUT, a significant decrease in cerebral tissue oxygenation both prior to and during loss-of-consciousness in vasovagal syncope (VVS) has been observed. Interestingly, cerebral tissue oxygenation appears to decrease even before haemodynamic changes can be observed. Apart from VVS, cerebral tissue oxygenation decreases during orthostatic provocation in patients with orthostatic hypotension (OH) and postural orthostatic tachycardia syndrome (POTS), in the latter even in the absence of hypotension. Importantly, decline of cerebral tissue oxygenation in VVS and POTS during HUT may not correlate with hemodynamic changes. In this mini review, we summarize the current knowledge of the application of cerebral oximetry in syncope and orthostatic intolerance syndromes, discuss its likely value as a clinical diagnostic tool and also emphasize its potential in the understanding of the relevant pathophysiology.

Puberty is initiated by hormonal changes in the adolescent body that trigger physical and behavioral changes to reach adult maturation. As these changes occur, some adolescents experience concerning pubertal symptoms that are associated with dysfunction of the autonomic nervous system (ANS). Vasovagal syncope (VVS) and Postural Orthostatic Tachycardia Syndrome (POTS) are common disorders of the ANS associated with puberty that are related to orthostatic intolerance and share similar symptoms. Compared to young males, young females have decreased orthostatic tolerance and a higher incidence of VVS and POTS. As puberty is linked to changes in specific sex and non-sex hormones, and hormonal therapy sometimes improves orthostatic symptoms in female VVS patients, it is possible that pubertal hormones play a role in the increased susceptibility of young females to autonomic dysfunction. The purpose of this paper is to review the key hormonal changes associated with female puberty, their effects on the ANS, and their potential role in predisposing some adolescent females to cardiovascular autonomic dysfunctions such as VVS and POTS. Increases in pubertal hormones such as estrogen, thyroid hormones, growth hormone, insulin, and insulin-like growth factor-1 promote vasodilatation and decrease blood volume. This may be exacerbated by higher levels of progesterone, which suppresses catecholamine secretion and sympathetic outflow. Abnormal heart rate increases in POTS patients may be exacerbated by pubertal increases in leptin, insulin, and thyroid hormones acting to increase sympathetic nervous system activity and/or catecholamine levels. Given the coincidental timing of female pubertal hormone surges and adolescent onset of VVS and POTS in young women, coupled with the known roles of these hormones in modulating cardiovascular homeostasis, it is likely that female pubertal hormones play a role in predisposing females to VVS and POTS during puberty. Further research is necessary to confirm the effects of female pubertal hormones on autonomic function, and their role in pubertal autonomic disorders such as VVS and POTS, in order to inform the treatment and management of these debilitating disorders.

Postural orthostatic tachycardia syndrome (POTS), an increasingly recognized dysautonomia, may affect as many as 3,000,000 Americans. Concurrently, prevalence estimates suggest 10% of individuals identify as lesbian, gay, bisexual, transgender, or questioning/queer. The preponderance of female POTS patients implies hormonal differences between natal sexes and their role in POTS. Transgender POTS patients using hormone therapies may offer further insight into the mechanism of POTS. There have been no previously published studies of transgender patients with POTS undergoing gender-affirming hormone therapy. We reviewed our electronic health record for clinical histories of transgender patients in our POTS Database. Three patients who transitioned from female to male demonstrated clinical improvement of their POTS symptoms with the addition of testosterone therapy. We present our clinical experience of three transgender POTS patients who transitioned from female to male with hormone therapy, all of whom demonstrated clinical improvement with testosterone. This may give further insight into the pathophysiology of POTS. However, the authors do not endorse the use of hormone therapy as primary therapy for the symptoms of POTS.

Patients with severe myalgic encephalomyelitis/Chronic fatigue syndrome (ME/CFS) experience debilitating physical and cognitive symptoms, which often result in the need to file disability claims. A significant number of ME/CFS patients are children or adolescents. ME/CFS patients often turn to physicians who are not trained to recognize and diagnose ME/CFS, and who might or might not understand that ME/CFS is a multi-system primarily physical illness. Such misperceptions can adversely affect the doctor-patient relationship, the clinical outcomes, as well as the results of disability claims. According to the National Academies of Science, Engineering and Medicine, "Between 836,000 and 2.5 million Americans suffer from myalgic encephalomyelitis/chronic fatigue syndrome… This disease is characterized by profound fatigue, cognitive dysfunction, sleep abnormalities, autonomic manifestations, pain, and other symptoms that are made worse by exertion of any sort. ME/CFS can severely impair patients' ability to conduct their normal lives." The prevalence of MECFS among children and adolescents has been estimated variously as between 0.11 and 4% (1). A large percentage of children and adolescents with ME/CFS suffer from orthostatic intolerance due to one or both of these syndromes: Neurally Mediated Hypotension (NMH) and Postural Orthostatic Tachycardia Syndrome (POTS). These elements of ME/CFS often respond well to proper treatment (2, 3).

Autonomic nervous system (ANS) symptoms are prevalent in multiple sclerosis (MS) as is neurodegeneration. Our aim was to explore the occurrence of ANS symptoms and retinal neurodegeneration in a newly diagnosed MS population with tools available in a clinical setting. Forty-three MS patients and 44 healthy controls took part in the study. We employed a bedside cardiovascular ANS test battery together with classical pupillometry, optical coherence tomography (OCT) evaluation of retinal neurodegeneration in eyes without previous optic neuritis (MSNON) and patients' self-report forms on fatigue, orthostatic and ANS symptoms. Half of the patients presented with ANS symptoms and a high level of fatigue. There was a significant difference in ganglion cell layer thickness (mean GCIPL) evaluated by OCT in MSNON compared to healthy control eyes. We found a negative linearity of mean GCIPL on group level with increasing disease duration. Three patients fulfilled the criteria of postural orthostatic tachycardia syndrome (POTS). Our results demonstrate retinal neurodegeneration in MSNON, a high frequency of fatigue and a high prevalence of ANS symptoms in newly diagnosed patients. Whether neurodegeneration precedes ANS dysfunction or vice versa is still open to debate, but as unveiled by the presence of POTS in this MS population, differences in stress-response regulation add to the understanding of variation in onset-time of ANS dysfunction in early MS.

Postural Orthostatic Tachycardia Syndrome (POTS) is a cardiovascular autonomic disorder characterized by orthostatic intolerance and high prevalence among young women. The etiology of POTS is uncertain, though autoimmunity and inflammation may play an important role. We aimed to identify novel inflammatory biomarkers associated with POTS. In the Syncope Study of Unselected Population in Malmö (SYSTEMA) cohort, we identified 396 patients (age range, 15-50 years) with either POTS ( = 113) or normal haemodynamic response during passive head-up-tilt test ( = 283). Blood samples were analyzed using antibody-based Proximity Extension Assay technique simultaneously measuring 57 inflammatory protein biomarkers. The discovery algorithm was a sequential two-step process of biomarker signature identification by supervised, multivariate, principal component analysis and verification by univariate ANOVA with Bonferroni correction. POTS patients were younger (26 vs. 31 years; < 0.001) and there was no significant difference in sex distribution (74% vs. 67% females, = 0.24). PCA and Bonferroni-adjusted ANOVA identified proconvertase furin as the most robust biomarker signature for POTS. Plasma level of proconvertase furin was lower (6.38 vs. 6.58 of normalized protein expression units (NPX); < 0.001 in POTS, compared with the reference group. Proconvertase furin met Bonferroni-adjusted significance criteria in both uni- and multivariable regression analyses. Patients with POTS have lower plasma level of proconvertase furin compared with individuals with normal postural hemodynamic response. This finding suggests the presence of a specific autoimmune trait with disruption of immune peripheral tolerance in this hitherto unexplained condition. Further studies are needed for external validation of our results.

The head-up tilt table test (HUT) is one of the primary clinical examinations for evaluating orthostatic intolerance (OI). HUT can be divided into three phases: dynamic tilt phase (supine to tilt up), static tilt phase (remain tilted at 70°), and post tilt phase (tilt down back to supine position). Commonly, blood pressure (BP) and heart rate (HR) are monitored to observe for OI symptoms, but are indirect measurements of cerebral perfusion and can lead to inaccurate HUT evaluation. In this study, we implemented a 108-channel near-infrared spectroscopy (NIRS) probe to characterize HUT performance by monitoring cerebral hemodynamic changes for healthy controls (HCs), OI patients with normal HUT results, and OI patients with positive HUT results: vasovagal syncope (VS), postural orthostatic tachycardia syndrome (POTS), orthostatic hypotension (OH), and orthostatic hypertension (OHT). By the end of the static tilt phase, OI patients typically did not show a complete recovery back to baseline cerebral oxygenation and total blood volume compared to HCs. We characterized the return to cerebral homeostasis by polynomial fitting total blood volume changes and determining the inflection point. The OI patients with normal HUT results, VS, OH, or OHT showed a delay in the return to cerebral homeostasis compared to the HC group during HUT.

In the 1970s, autoantibodies directed against G-protein-coupled receptors (GPCR, GPCR-AAB) were discovered. After receptor binding, GPCR-AAB trigger uncontrolled receptor mediated signal cascades, thus producing pathologies. Diseases associated with such functionally active autoantibody type (functional autoantibodies) can be called "functional autoantibody diseases". Here we focus exclusively on GPCR-AAB directed against the GPCR's extracellular loops. The GPCR's role in the pathogenesis and progression is accepted in idiopathic dilated cardiomyopathy and is increasingly considered in diseases such as Chagas' cardiomyopathy, peripartum cardiomyopathy, hypertension, diabetes mellitus and scleroderma and even dementia, complex regional pain syndrome and postural orthostatic tachycardia syndrome. We briefly summarize the mechanistic background of GPCR-AAB induced pathologies, mainly focused on autoantibodies targeting the β1-adrenergic and muscarinic 2 receptors, due to their importance for cardiomyopathies. Furthermore, treatment strategies for "functional autoantibody diseases", such as for GPCR-AAB removal (therapeutic plasma exchange, immunoadsorption) and GPCR-AAB attack (intravenous IgG treatment, B-cell depletion, GPCR-AAB binding and neutralization) are critically reflected with respect to their patient benefits focused on but not exclusive to patients with dilated cardiomyopathy.

A 24-year-old female presented to our clinic with symptomatic tachycardia. In the clinic, she was able to replicate her symptoms, which were due to tachycardia in a standing position that resolved upon sitting. The patient was then offered eight ounces (236.6 mL) of water and, after consumption of such, the standing tachycardia was no longer observed. A diagnosis of postural orthostatic tachycardia syndrome (POTS) was made. This case report discusses a novel approach to acute treatment for POTS.

To assess the utility of gastrointestinal (GI) diagnostic studies in the evaluation of patients with orthostatic intolerance. Medical records of 103 consecutive children/young adults with orthostatic intolerance and gastrointestinal symptoms were reviewed. All patients had undergone antroduodenal manometry in conjunction with the tilt table test, autonomic testing, and upper gastrointestinal endoscopy (EGD). A gastric emptying study (GES) was performed in 81 patients. The median age of the cohort was 17 years (IQR, 15-19) with a female predominance (females:males, 3:1). As expected, the tilt table test was abnormal in all patients. Antroduodenal manometry was abnormal in 83 of 103 patients (81%), showing neurogenic intestinal dysmotility in 50%, rumination in 20%, and visceral hyperalgesia in 10%. The GES results were abnormal in 23 of 81 patients (28.4%), mostly (21 of 23) with delayed GES. None of the tilt table test or autonomic results were predictive of abnormal antroduodenal manometry or GES. Analysis of EGD biopsy samples revealed nonspecific esophagitis and/or gastritis in 16 of 103 patients (15%). Antroduodenal manometry with the tilt table test were the most insightful investigations in adolescents and young adults with orthostatic intolerance and gastrointestinal symptoms. GES and EGD provided limited information. Gastrointestinal symptoms were related more to functional rather than mucosal or organic etiologies, suggesting a limited role of endoscopy alone in evaluating patients with orthostatic intolerance presenting with gastrointestinal symptoms.

Eosinophilic gastrointestinal disorders (EGIDs) have been linked with atopic conditions, connective tissue disorders, and autoimmunity, but the association between EGIDs and autonomic dysfunction has not been extensively described. We aimed to assess this association and determine the prevalence of autonomic dysfunction in our EGID population. In this retrospective cohort study, we analyzed adult patients in the University of North Carolina Eosinophilic Esophagitis (EoE)/EGID database who also had a diagnosis of comorbid autonomic dysfunction (postural orthostatic tachycardia syndrome [POTS] or gastroparesis). The electronic medical record was abstracted and disease characteristics summarized. We identified seven patients who had EGID and autonomic dysfunction. All had POTS and were Caucasian, and five (71%) were female; 2 also had gastroparesis. Onset of autonomic symptoms coincided with onset of EGID symptoms in 3 patients (43%) or with an acute EGID flare in 3. In no cases did successful control of EGID lead to improvement of autonomic symptoms. Two subjects (29%) had comorbid Ehlers-Danlos syndrome and mast cell activation syndrome. The prevalence of POTS in EGID patients was 7/560 (1.25%), compared to an estimated 0.17% prevalence of POTS in the general population. The prevalence of autonomic dysfunction was 5-10-fold higher in EGID than expected in the general population, suggesting an association between the two conditions, though the underlying mechanism is unclear. Providers should consider comorbid autonomic dysfunction in patients with EGID, particularly when symptoms persist despite treatment.

Dysautonomia is an increasingly recognized yet still poorly understood disease within the field of pediatrics. Symptoms, including dizziness, headaches, fatigue, joint pain, anxiety, and intolerance of heat or cold, are often significant and difficult to sort, especially in terms of their relation to each other. This often leads to referral to multiple subspecialists, who then proceed to treat seemingly familiar symptoms in kind. In the authors' experience, this leads to more frustration on the part of the patients and their physicians when symptom improvement does not follow (or can even worsen). On the other hand, by understanding the pathophysiology, treatment success is possible by directing therapies toward the root causes and just as importantly, enlisting the patient in a daily treatment plan. In the text that follows, we hope to convey these viewpoints by highlighting an involved case, discussing the pathophysiology, outlining the usual evaluation, and finally describing our approach to treatment.

Postural orthostatic tachycardia syndrome (POTS), the most common form of orthostatic intolerance in young people, affects approximately 500,000 people in the United States alone, typically young women at the peak of their education and the beginning of their working lives. This is a heterogeneous disorder, the pathophysiology and mechanisms of which are not well understood. There are multiple contributing factors and numerous potential mimics. This review details the most current views on the potential causes, comorbid conditions, proposed subtypes, differential diagnoses, evaluations, and treatment of POTS from cardiological and neurological perspectives.

Compression garments are used by patients with lower extremity edema to help regulate fluid distribution and to prevent orthostatic symptoms. Current compression stockings are often reported as uncomfortable and adherence is poor. The current study was conducted to assess the efficacy of a novel active compression garment on healthy individuals undergoing 60-degree head-up tilts for 10 min to induce venous pooling and subsequent physiological responses. During tilts while garments were on, participants' absolute change in heart rate relative to baseline was lower (16.7 ± 8.7 BPM) compared to control (20.9 ± 11.47 BPM, P = 0.002). There were no differences in changes in mean arterial blood pressure between conditions (P = 0.303). One participant had a pre-syncopal event which occurred during a tilt without garments. This participant did not experience pre-syncopal symptoms with the garments on. All together, these data suggest that a novel active compression garment is capable of blunting increases in heart rate during head-up tilt. While untested thus far in patient populations, these garments may prove efficacious in preventing orthostatic intolerance.

This perspective piece on head-up tilt table testing is part of a series on autonomic function testing. The tilt table can be a useful diagnostic test, but methodologies vary, and the results are sometimes misinterpreted. The intent here is not to review comprehensively the utility of various tilt table testing protocols but to convey a number of general points that may give perspective and have practical clinical value, based on an understanding of autonomic physiology and our long clinical and research experience in the evaluation of autonomic disorders. The goals of tilt table testing are to assess orthostatic hypotension (OH), chronic orthostatic intolerance (COI), and unexplained syncope. The testing is useful for distinguishing neurogenic from non-neurogenic OH, identifying failure of the sympathetic noradrenergic system in autonomic neuropathies and ganglionopathies, and assessing baroreflex-sympathoneural function in α-synucleinopathies. For COI, the testing can provide objective data related to the patient's symptoms, diagnose postural tachycardia syndrome (POTS), and distinguish POTS from other causes of tachycardia. Provocative tilt table testing can help understand bases for recurrent transient loss of consciousness in patients with syncope, distinguish neurally mediated syncope from psychogenic pseudosyncope, and separate syncope-related convulsion from epileptic seizures. For each of these purposes, the goals, formats, endpoints, and clinical utility are different. As for any autonomic test, tilt table findings must be interpreted in the context of the patient's clinical presentation.

To explore the value of frequency domain indices of heart rate variability (HRV) in the differential diagnosis between pediatric vasovagal syncope and postural tachycardia syndrome (POTS). Eighty-five patients aged 7-16 years with either vasovagal syncope or POTS were enrolled in the experimental group; 18 healthy children served as controls. Holter electrocardiography was used to detect HRV frequency-domain indices in patients with vasovagal syncope, patients with POTS, and control subjects. The differences in HRV indices were compared between the vasovagal syncope and POTS groups. The receiver operating characteristic (ROC) curve was calculated to analyze the predictive value of HRV for the differential diagnosis between vasovagal syncope and POTS in children. In addition, 37 children aged 7-17 years with either vasovagal syncope or POTS were recruited as an external validation group. The daytime ultra-low frequency (dULF), nighttime ULF (nULF), daytime very low frequency (dVLF), and nighttime VLF (nVLF) were higher in the vasovagal syncope group compared with the POTS group (P < .01 for dULF, dVLF, and nVLF; P < .05 for nULF). The dULF, nULF, dVLF, and nVLF yielded a sensitivity of 73.3%, 71.1%, 68.9%, and 62.2%, respectively, and a specificity of 72.5%, 62.5%, 60.0%, and 60.0%, respectively, to differentiate vasovagal syncope from POTS. The external validation with clinical diagnostic standard showed that a dULF cutoff value of 36.2 ms for differentiating POTS from vasovagal syncope yielded a sensitivity of 71.4%, a specificity of 75.0%, and an accuracy of 73.0%. dULF may be a useful measure for the differential diagnosis between vasovagal syncope and POTS in adolescents.