RESET-POTS: Multimodal Phenotyping and Stellate Ganglion Block in Postural Orthostatic Tachycardia Syndrome

Postural orthostatic tachycardia syndrome (POTS) is a condition in which standing causes an excessive increase in heart rate together with symptoms such as dizziness, palpitations, weakness, fatigue, exercise intolerance and difficulties with concentration. POTS is a heterogeneous condition, meaning that the underlying abnormalities may differ considerably between individuals. Changes in autonomic nervous system activity, regulation of blood volume and hormones, metabolism, and blood flow or oxygen delivery to the brain may all contribute to symptoms. However, the relationships between these abnormalities are not fully understood, and currently available treatments do not adequately control symptoms in all patients. RESET-POTS therefore focuses on adults with confirmed POTS who remain symptomatic despite standard non-pharmacological and pharmacological management.

The study consists of two phases. In Phase 1, patients with POTS and healthy volunteers will undergo detailed testing designed to provide a broad picture of how the body responds to standing. This includes a 10-minute standing test with continuous measurement of heart rate and blood pressure, assessment of heart-rate variability, and measurement of breathing and oxygenation in the brain and skeletal muscle. Blood samples obtained while lying down and standing will be used to examine hormones and other markers involved in sympathetic nervous system activity, blood-volume regulation and endocrine function. Additional assessments include glucose and insulin responses, continuous glucose monitoring, resting and standing energy expenditure, body composition, muscle strength, cortisol patterns and questionnaires assessing symptoms and quality of life. The aim of this phase is to identify physiological patterns that may help explain why POTS differs between individuals and to identify measurements that could be useful in future treatment studies.

In Phase 2, eligible patients with POTS will receive a stellate ganglion block (SGB). The stellate ganglion is a group of nerves in the neck that forms part of the sympathetic nervous system, which helps regulate heart rate, blood vessels and the body's response to stress. During SGB, a local anaesthetic is injected under ultrasound guidance near these nerves to temporarily reduce sympathetic nerve activity. In RESET-POTS, the right and left sides will be treated during separate procedures approximately 3-7 days apart. Participants will be monitored during and after each procedure. Changes in skin temperature and clinical signs will be used to confirm whether the nerve block has produced the expected physiological effect.

Participants who undergo SGB will repeat relevant assessments approximately 2 weeks and 3 months after completion of the bilateral intervention. The study is not designed to determine conclusively whether SGB is an effective treatment for POTS. Instead, its main goals are to determine whether this approach can be studied safely and practically, whether participants can complete the planned testing and follow-up, whether the SGB procedures can be performed successfully, and whether the collected physiological measurements are sufficiently reliable for a larger future trial. Changes in heart-rate responses to standing, autonomic nervous system activity, hormonal and metabolic measures, brain and muscle oxygenation, and POTS symptoms will also be explored.

The results will be used to design a future randomized, sham-controlled clinical trial. In particular, RESET-POTS aims to help determine which patients may be most suitable for sympathetic nervous system-targeted treatment, which objective measurements should be used to assess treatment effects, and how a larger trial should be designed to distinguish the physiological effects of SGB from placebo and expectancy effects.

Inclusion criteria

Participants with POTS:

• Age 18 to 65 years.
• Confirmed diagnosis of postural orthostatic tachycardia syndrome (POTS) by a cardiologist or neurologist within the previous 3 years.
• Persistent symptoms of orthostatic intolerance despite or regardless of current medication use.
• Ability to understand the study procedures and provide written informed consent.

Healthy control participants:

• Age 18 to 65 years.
• Where feasible, matched to the POTS group according to age, sex, and body mass index category and, in premenopausal women, menstrual-cycle phase.
• No known chronic disease.
• No regular use of medication that could substantially affect autonomic, endocrine, or metabolic measurements.
• Ability to understand the study procedures and provide written informed consent.

Exclusion criteria

For all participants:

• Pregnancy or breastfeeding.
• Active acute infection at the time of assessment.
• Significant comorbidity that could confound interpretation of study findings or increase procedural risk, including: type 1 or type 2 diabetes mellitus; heart failure; significant valvular heart disease; clinically relevant renal impairment; clinically relevant hepatic impairment; peripheral neuropathy; known central nervous system disease.
• Contraindication to any study procedure.
• An identified alternative explanation for orthostatic symptoms or tachycardia, including significant anemia, dehydration or hypovolemia, acute febrile illness or infection, hyperthyroidism, primary adrenal disease, a primary anxiety or panic disorder considered to be the principal cause of symptoms, or medication-induced tachycardia.

Additional exclusion criteria for the stellate ganglion block phase:

• Previous stellate ganglion block.
• Known allergy or hypersensitivity to amide local anesthetics.
• Current therapeutic anticoagulation or known bleeding disorder.
• History of glaucoma.
• Local infection or relevant anatomical abnormality at the planned injection site.
• Any clinical condition considered by the investigator or anesthesiologist to make stellate ganglion block unsafe.