Postural (Orthostatic) Tachycardia Syndrome (POTS)
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Clinical condition characterized by development of symptoms upon standing (e.g., lightheadedness, weakness, and palpitations), associated with an increase on the heart rate (HR) ≥30 bpm in the absence of orthostatic hypotension (1)
- Formal epidemiologic studies have not been performed; however, the estimated prevalence in the United States is about 500,000.
- Female to male ratio is 4:1.
- Usual onset is between ages 15 and 25 years.
Etiology and Pathophysiology
A variety of mechanisms have been proposed, and many of them 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 blood pressure (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).
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 (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
- Hypermobility syndrome
- Visceral pain and dysmotility
- Chronic headaches