Postural orthostatic tachycardia syndrome (or POTS) is a condition of orthostatic intolerance in which a change from the supine position to an upright position causes an abnormally large increase in heart rate, often, but not always accompanied by a fall in blood pressure.

The syndrome was identified as such by Schondorf and Low in 1993. Similar symptoms were collectively described as "idiopathic hypovolemia" by Fouad in 1986. A comprehensive historical account is given by Grubb (2002).

Symptoms include an abnormally large increase in heart rate upon standing, lightheadedness, extreme fatigue, nausea, headache, exercise intolerance and impaired concentration. Patients may exhibit mild hypotension while standing, but most do not experience fainting. Patients with POTS may frequently be misdiagnosed as having panic attacks or chronic anxiety disorder (Grubb, 2002). POTS patients are usually significantly debilitated by their symptoms.

POTS is often difficult to diagnose. A routine physical examination and standard blood tests usually will not indicate POTS. A tilt table test is vital to diagnosing POTS although all symptoms must be considered before a final diagnosis is made. A test to rule out pheochromocytoma is usually performed. A blood test may be performed to verify abnormally high levels of norepinephrine usually present in POTS patients (Raj, 2006). Inappropriate sinus tachycardia must also be considered as there is an overlap in symptoms of IST and POTS. About 80 percent of patients diagnosed with POTS are female and of menstruating age.

The causes of POTS are not fully known, since the term describes a collection of symptoms rather than a disease. It is generally believed to be a case of dysautonomia. Its onset is sometimes associated with an inflammatory condition such as a viral infection. An overlap of symptoms with chronic fatigue syndrome may suggest a pathological overlap in some cases.

http://en.wikipedia.org/wiki/Postura...ardia_syndrome