Postural (Orthostatic) Tachycardia Syndrome (POTS)
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Clinical condition characterized by development of symptoms upon standing (e.g., postural light-headedness, weakness, and palpitations), associated with an increase in the heart rate (HR) of ≥30 beats/min in adults (>40 beats/min in children aged 12 to 19 years) in the absence of orthostatic hypotension (decrease in systolic blood pressure [BP] of 20 mm Hg and diastolic BP of 10 mm Hg) and symptoms associated with orthostatic intolerance (e.g., tachycardia, presyncope) persisting for 6 months (1)
Etiology and Pathophysiology
Likely a disorder with multiple potential causes. A variety of mechanisms have been proposed, and more than one may coexist in these patients (1):
- Hypovolemia: 70% of patients have a decreased plasma volume without a compensatory increase in plasma renin and aldosterone activity.
- Peripheral autonomic denervation: Present in up to 50% of patients, this is characterized by decreased vasoconstriction in the extremities and splanchnic vessels, resulting in venous blood pooling.
- Increased sympathetic tone (hyperadrenergic): This is seen in up to 50% of patients. Patients with this mechanism usually experience an increase of ≥10 mm Hg in the systolic BP upon standing and sympathetic symptoms, such as palpitations, anxiety, and tremors, due to increase in circulating catecholamines and adrenergic hypersensitivity.
- Cardiovascular deconditioning: Some of these patients have reduced left ventricular mass, stroke volume, blood volume, and oxygen uptake. It is uncertain whether deconditioning is a contributing cause or consequence of postural (orthostatic) tachycardia syndrome (POTS).
- Autoimmune hypothesis: Some studies have isolated autoantibodies that target receptors of the autonomic nervous system in POTS patients. Specifically, IgG from POTS patients have been shown to activate β1 and β2 receptors and simultaneously partially block the vasoconstrictive α1 adrenoceptor. These findings support the notion that POTS may be an autoimmune condition elicited in genetically susceptible individuals by an immunogenic trigger (2).
Most cases of POTS are sporadic; however, some patients have family history of orthostatic intolerance, which suggests a certain degree of heritability. Some of the genetic markers associated with this condition are:
- Mutations of SLC6A2 (norepinephrine [NE] transporter gene), involved in NE uptake at the synaptic cleft
- Polymorphisms of NOS3 (nitric oxide synthase gene)
- Polymorphisms of ADRB2 (β2 receptor gene)
No specific risk factors have been described.
No strategies for prevention have been described. However, patients with a history of POTS should avoid dehydration. Furthermore, such individuals may benefit from regular physical activity.
Commonly Associated Conditions
- Chronic fatigue syndrome
- Mitral valve prolapse
- Mast cell activation abnormalities
- Ehlers-Danlos syndrome
- Multiple sclerosis
- Hypermobility syndrome
- Visceral pain and dysmotility
- Chronic headaches
- Anxiety disorders
- Other autoimmune diseases (Sjögren syndrome, celiac disease, Hashimoto thyroiditis, systemic lupus, etc.)