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Introduction Postural Orthostatic Tachycardia Syndrome (POTS) is an extremely heterogeneous disorder defined by chronic symptoms of orthostatic intolerance alongside an abnormally large increase in heart rate upon standing [1]. While the diagnostic criteria primarily center around the exacerbated increase in heart rate when transitioning to a standing position, POTS typically manifests with symptoms that are more intricate than a simple heart rate elevation. POTS patients often present with gastrointestinal issues, cognitive dysfunction, temperature dysregulation, overactive bladder, and more which all relate to the dysfunction of the autonomic nervous system [2]. It is estimated that about 0.2% to 1% of the US population, which equates to 1-3 million people are affected by POTS [3]. However, this number is dramatically increasing due to the uptick in COVID-19 illness- related cases and additional research and awareness decreasing the number of undiagnosed cases. Due to the individualized nature of POTS from patient to patient, it takes on average 5 years for patients to receive a diagnosis and according to Bourne et al., “almost all (95%) participants reported POTS-related out-of-pocket medical expenses since diagnosis, with 51.1% of participants spending $10,000 USD or more” [4]. There are many underlying causes of POTS, often more than one coexisting within a single patient, including factors like:  Hypovolemia and deconditioning : reduced blood volume and physical deconditioning lead to rapid heart rates when upright, exacerbated by somatic hypervigilance [5]  Neuroendocrine dysfunction: increased adrenergic activity [6], abnormal hormone levels [7], and potential deficiencies in norepinephrine regulation [8]  Neuropathy: affecting up to half of POTS cases, plays a role in autonomic dysfunction, marked by abnormalities in sweat gland function and nerve activity [9,10]  Autoimmunity: can be triggered by viral illnesses and involves the presence of autoantibodies (anti-nuclear, G-protein coupled receptor, Angiotensin II type 1 receptor) targeting specific receptors in POTS patients [11,12,13,14] While POTS has been found to run in families in addition to scientists discovering mutations in the norepinephrine transporter and angiotensin system genes, no single mutation has been linked to the majority of POTS cases [15]. Certain environmental factors like predisposing viral infections (Barr-Epstein, Mononucleosis, Lyme Disease) and comorbidities such as “celiac disease, thyroiditis, and joint hypermobility” have been identified as possible triggers for POTS [16]. POTS is diagnosed by the evaluation of an elevated heart rate of more than 30 bpm going from supine/seated to standing with the presence of orthostatic intolerance symptoms (lightheadedness, heart palpitations, presyncope, fading vision, etc.) [17]. While some individuals with POTS experience relatively mild symptoms and can maintain their usual daily routines, others endure severe symptoms that profoundly restrict their ability to perform basic tasks. Physicians specializing in POTS have likened the functional impairment seen in POTS patients to that found in conditions like chronic obstructive pulmonary disease (COPD) or congestive heart failure, with approximately 25% of POTS patients unable to work due to their condition [18]. Since POTS alone does not increase mortality, treatment is focused on alleviating the vast collection of patient’s symptoms and enhancing their quality of life via a specialized combination of treatment strategies [19]. Such treatments include the amalgamation of both non- pharmacological (increased salt and water intake, compressive garments, etc.) and pharmacological (blood volume expanders, heart rate inhibitors, vasoconstrictors, sympatholytic drugs, etc.) treatments [19]. However, more research needs to be done on the underlying root causes of POTS to discover a curative treatment.

References: [1] Postural tachycardia syndrome (POTS) diagnosis and treatment: Basics and new developments . American College of Cardiology. (n.d.). https://www.acc.org/Latest-in-Cardiology/Articles/2016/01/25/14/01/Postural-Tachycardia- Syndrome-POTS-Diagnosis-and-Treatment-Basics-and-New-Developments [2] Dysautonomia International. (n.d.). Postural orthostatic tachycardia syndrome. http://dysautonomiainternational.org/page.php?ID=30 [3] Vernino, S., Bourne, K. M., Stiles, L. E., Grubb, B. P., Fedorowski, A., Stewart, J. M., Arnold, A. C., Pace, L. A., Axelsson, J., Boris, J. R., Moak, J. P., Goodman, B. P., Chémali, K. R., Chung, T. H., Goldstein, D. S., Diedrich, A., Miglis, M. G., Cortez, M. M., Miller, A. J., … Raj, S. R. (2021). Postural orthostatic tachycardia syndrome (POTS): State of the Science and Clinical Care from a 2019 National Institutes of Health Expert Consensus Meeting - Part 1. Autonomic Neuroscience , 235 , 102828. https://doi.org/10.1016/j.autneu.2021.102828 [4] Bourne KM, Chew DS, Stiles LE, Shaw BH, Shibao CA, Okamoto LE, Garland EM, Gamboa A, Peltier A, Diedrich A, Biaggioni I, Sheldon RS, Robertson D, Raj SR. Postural orthostatic tachycardia syndrome is associated with significant employment and economic loss. J Intern Med. 2021 Jul;290(1):203-212. doi: 10.1111/joim.13245. Epub 2021 Feb 15. PMID: 33586284; PMCID: PMC9156448. [5] Jacob, G., Biaggioni, I., Mosqueda-Garcia, R., Robertson, R. M., & Robertson, D. (1998). Relation of blood volume and blood pressure in orthostatic intolerance. The American journal of the medical sciences, 315(2), 95–100. https://doi.org/10.1097/00000441-199802000-00005 [6] Sandroni, P., Novak, V., Opfer-Gehrking, T. L., Huck, C. A., & Low, P. A. (2000). Mechanisms of blood pressure alterations in response to the Valsalva maneuver in postural tachycardia syndrome. Clinical autonomic research : official journal of the Clinical Autonomic Research Society, 10(1), 1–5. https://doi.org/10.1007/BF02291382 [ 7] Garland, E. M., Raj, S. R., Black, B. K., Harris, P. A., & Robertson, D. (2007). The hemodynamic and neurohumoral phenotype of postural tachycardia syndrome. Neurology, 69(8), 790–798. https://doi.org/10.1212/01.wnl.0000267663.05398.40 [8] Shannon, J. R., Flattem, N. L., Jordan, J., Jacob, G., Black, B. K., Biaggioni, I., Blakely, R. D., & Robertson, D. (2000). Orthostatic intolerance and tachycardia associated with norepinephrine-transporter deficiency. The New England journal of medicine, 342(8), 541– 549. https://doi.org/10.1056/NEJM200002243420803 [9] Jacob, G., Diedrich, L., Sato, K., Brychta, R. J., Raj, S. R., Robertson, D., Biaggioni, I., & Diedrich, A. (2019). Vagal and Sympathetic Function in Neuropathic Postural Tachycardia Syndrome. Hypertension (Dallas, Tex. : 1979), 73(5), 1087–1096. https://doi.org/10.1161/HYPERTENSIONAHA.118.11803 [10] Gibbons, C. H., Bonyhay, I., Benson, A., Wang, N., & Freeman, R. (2013). Structural and functional small fiber abnormalities in the neuropathic postural tachycardia syndrome. PloS one, 8(12), e84716. https://doi.org/10.1371/journal.pone.0084716

[11] Ruzieh, M., Batizy, L., Dasa, O., Oostra, C., & Grubb, B. (2017). The role of autoantibodies in the syndromes of orthostatic intolerance: a systematic review. Scandinavian cardiovascular journal : SCJ, 51(5), 243–247. https://doi.org/10.1080/14017431.2017.1355068 [12] Gunning, W. T., 3rd, Kvale, H., Kramer, P. M., Karabin, B. L., & Grubb, B. P. (2019). Postural Orthostatic Tachycardia Syndrome Is Associated With Elevated G-Protein Coupled Receptor Autoantibodies. Journal of the American Heart Association, 8(18), e013602. https://doi.org/10.1161/JAHA.119.013602 [13] Watari M, Nakane S, Mukaino A, Nakajima M, Mori Y, Maeda Y, Masuda T, Takamatsu K, Kouzaki Y, Higuchi O, Matsuo H, Ando Y. Autoimmune postural orthostatic tachycardia syndrome. Ann Clin Transl Neurol. 2018 Feb 28;5(4):486-492. doi: 10.1002/acn3.524. PMID: 29687025; PMCID: PMC5899914. [14] Yu X, Li H, Murphy TA, Nuss Z, Liles J, Liles C, Aston CE, Raj SR, Fedorowski A, Kem DC. Angiotensin II Type 1 Receptor Autoantibodies in Postural Tachycardia Syndrome. J Am Heart Assoc. 2018 Apr 4;7(8):e008351. doi: 10.1161/JAHA.117.008351. PMID: 29618472; PMCID: PMC6015435. [15] Postural orthostatic tachycardia syndrome (POTS). Johns Hopkins Medicine. (2022, December 21). https://www.hopkinsmedicine.org/health/conditions-and-diseases/postural-orthostatic- tachycardia-syndrome-pots#:~:text=POTS%20can%20run%20in%20families,tiny%20portion %20of%20POTS%20patients [16] Gunning, W. T., Kvale, H., Kramer, P. M., Karabin, B. L., & Grubb, B. P. (2019). Postural orthostatic tachycardia syndrome is associated with elevated g‐protein coupled receptor autoantibodies. Journal of the American Heart Association, 8(18). https://doi.org/10.1161/jaha.119.013602 [17] Raj SR, Fedorowski A, Sheldon RS. Diagnosis and management of postural orthostatic tachycardia syndrome. CMAJ. 2022 Mar 14;194(10):E378-E385. doi: 10.1503/cmaj.211373. PMID: 35288409; PMCID: PMC8920526. [18] Grubb, B. P. (2008). Postural tachycardia syndrome. Circulation, 117(21), 2814–2817. https://doi.org/10.1161/circulationaha.107.761643 [19] Miller, A. J., & Raj, S. R. (2018). Pharmacotherapy for postural tachycardia syndrome. Autonomic Neuroscience, 215, 28–36. https://doi.org/10.1016/j.autneu.2018.04.008

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