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In POTS, orthostatic symptoms (tremulousness, lightheadedness, palpitations, visual disturbances, weakness, fatigue, anxiety, hyperventilation, nausea) develop with a significant tachycardia (an increase of 30 beats/minute or more or a heart rate of 120 beats/minute or more) within 10 minutes of standing, in the absence of postural hypotension or an autonomic neuropathy. POTS is more common in women than men and in patients between 20 and 50 years of age. Other medical problems causing a tachycardia must be excluded.
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Its pathophysiology is uncertain but may involve cardiac deconditioning; impaired peripheral vasoconstriction due to peripheral sympathetic denervation, leading to venous pooling in the legs on standing and a compensatory tachycardia (“neuropathic POTS”); or an exaggerated sympathetic response to standing, with markedly elevated levels of plasma norepinephrine causing the tachycardia (“hyperadrenergic POTS”). Other possible mechanisms include hypovolemia, possibly from impaired function of the renin-angiotensin system (“volume dysregulation POTS”) and excessive mast cell activation leading to inappropriate release of histamine during physical activity. Psychological mechanisms have also been invoked. POTS may be associated with joint hypermobility syndrome and mitral valve prolapse, and it may follow pregnancy, surgery, trauma, chemotherapy, vaccinations, or viral infections.
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Management may involve volume repletion, a high salt diet and copious fluids, postural and psychophysiologic training, and a graduated exercise program. Medication treatment may include a beta-blocking agent (eg, propranolol 10–40 mg three times daily or metoprolol 12.5–50 mg twice daily), phenobarbital (15 mg in the morning, 60 mg at night), or clonidine (0.2 mg twice daily) for patients with hyperadrenergic POTS; and midodrine, droxidopa, pyridostigmine, or fludrocortisone at the doses described for postural hypotension if a neuropathic basis for symptoms is suspected. The long-term prognosis is unclear but approximately 50% of patients recover within 3 years.