Implications of Antimuscarinic Autoantibodies in Postural Tachycardia Syndrome

G protein-coupled receptors related to autoimmunity in postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is characterized by exaggerated orthostatic tachycardia in the absence of orthostatic hypotension. The pathophysiology of POTS may involve hypovolemia, autonomic neuropathy, a hyperadrenergic state, and cardiovascular deconditioning, any of which can co-occur in the same patient. Furthermore, there is growing evidence of the role of autoimmunity in a subset of POTS cases. In recent years, investigators have described an increased rate of autoimmune comorbidities as evidenced by the finding of several types of neural receptor autoantibody and non-specific autoimmune marker in patients with POTS. In particular, the association of the disease with several types of anti-G protein-coupled receptor (GPCR) antibodies and POTS has frequently been noted. A previous study reported that autoantibodies to muscarinic AChRs may play an important role in POTS with persistent, gastrointestinal symptoms. To date, POTS is recognized as one of the sequelae of coronavirus disease 2019 (COVID-19) and its frequency and pathogenesis are still largely unknown. Multiple autoantibody types occur in COVID-related, autonomic disorders, suggesting the presence of autoimmune pathology in these disorders. Herein, we review the association of anti-GPCR autoantibodies with disorders of the autonomic nervous system, in particular POTS, and provide a new perspective for understanding POTS-related autoimmunity.

Autoimmunity in Syndromes of Orthostatic Intolerance: An Updated Review

Orthostatic intolerance is a broad term that represents a spectrum of dysautonomic disorders, including postural orthostatic tachycardia syndrome (POTS) and orthostatic hypotension (OH), as manifestations of severe autonomic failure. While the etiology of orthostatic intolerance has not yet fully been uncovered, it has been associated with multiple underlying pathological processes, including peripheral neuropathy, altered renin-aldosterone levels, hypovolemia, and autoimmune processes. Studies have implicated adrenergic, cholinergic, and angiotensin II type I autoantibodies in the pathogenesis of orthostatic intolerance. Several case series have demonstrated that immunomodulation therapy resulted in favorable outcomes, improving autonomic symptoms in POTS and OH. In this review, we highlight the contemporary literature detailing the association of autoimmunity with POTS and OH.

Non-invasive Vagus Nerve Simulation in Postural Orthostatic Tachycardia Syndrome

Postural orthostatic tachycardia syndrome (POTS) is a chronic debilitating condition of orthostatic intolerance, predominantly affecting young females. Other than postural tachycardia, symptoms of POTS include a spectrum of non-cardiac, systemic and neuropsychiatric features. Despite the availability of widespread pharmacological and non-pharmacological therapeutic options, the management of POTS remains challenging. Exaggerated parasympathetic withdrawal and sympathetic overdrive during postural stress are principal mechanisms of postural tachycardia in POTS. Non-invasive, transcutaneous, vagus nerve stimulation (tVNS) is known to restore sympathovagal balance and is emerging as a novel therapeutic strategy in cardiovascular conditions including arrhythmias and heart failure. Furthermore, tVNS also exerts immunomodulatory and anti-inflammatory effects. This review explores the effects of tVNS on the pathophysiology of POTS and its potential as an alternative non-pharmacological option in this condition.

Chronic Fatigue and Dysautonomia following COVID-19 Vaccination Is Distinguished from Normal Vaccination Response by Altered Blood Markers

SARS-CoV-2 mRNA vaccination can entail chronic fatigue/dysautonomia tentatively termed post-acute COVID-19 vaccination syndrome (PACVS). We explored receptor autoantibodies and interleukin-6 (IL-6) as somatic correlates of PACVS. Blood markers determined before and six months after first-time SARS-CoV-2 vaccination of healthy controls (N = 89; 71 females; mean/median age: 39/49 years) were compared with corresponding values of PACVS-affected persons (N = 191; 159 females; mean/median age: 40/39 years) exhibiting chronic fatigue/dysautonomia (≥three symptoms for ≥five months after the last SARS-CoV-2 mRNA vaccination) not due to SARS-CoV-2 infection and/or confounding diseases/medications. Normal vaccination response encompassed decreases in 11 receptor antibodies (by 25-50%, p < 0.0001), increases in two receptor antibodies (by 15-25%, p < 0.0001) and normal IL-6. In PACVS, serological vaccination-response appeared significantly (p < 0.0001) altered, allowing discrimination from normal post-vaccination state (sensitivity = 90%, p < 0.0001) by increased Angiotensin II type 1 receptor antibodies (cut-off ≤ 10.7 U/mL, ROC-AUC = 0.824 ± 0.027), decreased alpha-2B adrenergic receptor antibodies (cut-off ≥ 25.2 U/mL, ROC-AUC = 0.828 ± 0.025) and increased IL-6 (cut-off ≤ 2.3 pg/mL, ROC-AUC = 0.850 ± 0.022). PACVS is thus indicated as a somatic syndrome delineated/detectable by diagnostic blood markers.

Predicting Therapeutic Efficacy of Pharmacological Treatments in Children with Postural Orthostatic Tachycardia Syndrome: A Mini-Review

Postural orthostatic tachycardia syndrome (POTS) is common in children, with an excessive increment in heart rate when moving from the supine to upright position. It has significant negative impacts on the daily life of pediatric patients. The pathogenesis of POTS includes peripheral vascular dysfunction, central hypovolemia, abnormal autonomic function, a high-adrenergic state, impaired skeletal-muscle pump function, the abnormal release of vasoactive factors, and autoimmune abnormalities. Therefore, the empirical use of pharmacological treatments has limited therapeutic efficacy due to the diversity of its mechanisms. A crucial aspect of managing POTS is the selection of appropriate treatment targeting the specific pathogenesis. This review summarizes the commonly used pharmacological interventions, with a focus on their predictive indicators for treatment response. Factors such as heart rate variability, plasma biomarkers, and cardiac-function parameters are discussed as potential predictors of therapeutic efficacy, enabling the implementation of individualized treatment to improve therapeutic effectiveness. This review consolidates the current knowledge on POTS, encompassing its clinical characteristics, epidemiological patterns, underlying pathogenic mechanisms, and predictive indicators for treatment response. Further research is warranted to enhance the understanding of POTS and facilitate the development of more effective therapeutic approaches for this challenging syndrome.

Transcutaneous vagus nerve stimulation attenuates autoantibody-mediated cardiovagal dysfunction and inflammation in a rabbit model of postural tachycardia syndrome

PURPOSE

Previous studies demonstrated M2 muscarinic acetylcholine receptor-activating autoantibodies (M2R-AAb) were present in some patients with postural tachycardia syndrome (POTS). This study examines how these autoantibodies might contribute to the pathophysiology of POTS, and whether low-level tragus stimulation (LLTS) can ameliorate autoantibody-mediated autonomic dysregulation in the rabbit.

METHODS

Five New Zealand white rabbits were immunized with a M2R second extracellular loop peptide to produce cholinomimetic M2R-AAb. Tilt test and infusion studies were performed on conscious rabbits before immunization, 6 weeks after immunization, and 8 weeks after immunization with 2-week daily LLTS treatment. Each rabbit served as its own control.

RESULTS

Compared to preimmune state, an enhanced heart rate increase and decreased parasympathetic activity upon tilting were observed in immunized rabbits. Furthermore, these rabbits demonstrated an attenuated heart rate-slowing response to infusion of the M2R orthosteric agonist arecaidine propargyl ester (APE), suggesting an inhibitory allosteric effect of M2R-AAb. There was also a significant increase in serum inflammatory cytokines in immunized rabbits. LLTS treatment suppressed the postural tachycardia, improved the sympathovagal balance with increased acetylcholine secretion, reduced the levels of inflammatory cytokines, and reversed the attenuated heart rate response to APE in immunized rabbits. No suppression of M2R-AAb expression by LLTS was found during this short-term study period. Receptor-modulating activity of M2R-AAb produced in immunized rabbits was confirmed with in vitro bioassay.

CONCLUSIONS

Autoantibody inhibition of cholinergic ligand activity may be involved in the development of cardiovagal dysfunction and inflammation associated with POTS, both of which can be improved by vagal stimulation.

Self-reported symptom burden in postural orthostatic tachycardia syndrome (POTS): A narrative review of observational and interventional studies

BACKGROUND AND OBJECTIVE

Postural Orthostatic Tachycardia Syndrome (POTS) is a chronic health condition affecting mostly women of childbearing age, and significantly impacting their health and quality of life. It is currently poorly understood with no approved licensed treatments. The aim of this systematic review was to contextualize the symptom burden of POTS, and review factors associated with this burden that may guide future treatments. The specific questions were (1) How does symptom burden in POTS compare to the burden in other long term conditions (LTCs), (2) Which factors are associated with POTS symptom burden, and (3) Which interventions show promise in reducing symptom burden in POTS.

DATABASES AND DATA TREATMENT

Electronic databases (CENTRAL, MEDLINE, EMBASE, CINAHL, PsycINFO, Web of Science, APA PsycArticles, OpenGrey) were searched from inception to January 2022 for observational studies reporting on the association between any biological, psychological or social factors and symptom burden, and randomized controlled trials reporting on interventions for symptom burden in adults with POTS. Two reviewers independently conducted eligibility screening, data extraction and quality assessment. A narrative synthesis was undertaken.

RESULTS/CONCLUSION

5159 entries were screened for eligibility. Twenty-nine studies were included (1372 participants with POTS of a total sample size of 2314, 17 High-, 12 Medium-quality), seventeen were observational and twelve were randomized controlled experimental and intervention trials. Overall methodological quality of the evidence was medium-high but heterogeneity was high and sample sizes modest, allowing moderately robust conclusions. Orthostatic symptom burden was higher in POTS than other LTCs. Serum activity against adrenergic α1 receptors, physical functioning, depression, catastrophizing, prolonged cognitive stress testing and anxiety were significantly associated with symptom burden in medium-high quality studies. Preliminary medium-high quality evidence from predominantly proof-of-concept (n = 11) studies and one 3-month 2 × 2 factorial design trial suggest that compression garments, propranolol, pyridostigmine, desmopressin, and bisoprolol may hold promise in reducing symptom burden. Directions for future research include investigating associated factors over time, the development of complex interventions which address both biological and psychosocial factors associated with symptom burden, and effectiveness trials of these interventions.

SIGNIFICANCE

POTS symptom burden is high, particularly in relation to orthostatic intolerance when compared to other long-term conditions (LTCs). Despite this burden, there are no effectiveness randomized controlled trials of treatment to reduce symptoms in POTS. This review provides a starting point to understanding researched biological and psychosocial factors associated with this burden. There was however inconsistency in the measurement of symptom burden, lowering the confidence of cross-study inferences. A coherent definition of POTS symptom range, severity and impact along with a validated and reliable POTS-specific instrument is currently lacking. A standardized questionnaire to assess POTS symptom burden as a core outcome measure will help clarify future research and clinical practice.

Post-Acute Sequelae of COVID-19 and Cardiovascular Autonomic Dysfunction: What Do We Know?

Post-acute sequelae of SARS-CoV-2 (PASC), or long COVID syndrome, is emerging as a major health issue in patients with previous SARS-CoV-2 infection. Symptoms commonly experienced by patients include fatigue, palpitations, chest pain, dyspnea, reduced exercise tolerance, and “brain fog”. Additionally, symptoms of orthostatic intolerance and syncope suggest the involvement of the autonomic nervous system. Signs of cardiovascular autonomic dysfunction appear to be common in PASC and are similar to those observed in postural orthostatic tachycardia syndrome and inappropriate sinus tachycardia. In this review, we report on the epidemiology of PASC, discuss current evidence and possible mechanisms underpinning the dysregulation of the autonomic nervous system, and suggest nonpharmacological and pharmacological interventions to treat and relieve symptoms of PASC-associated dysautonomia.