Postural Orthostatic Tachycardia Syndrome
|Postural orthostatic tachycardia syndrome (POTS) is a form of dysautonomia that is estimated to impact between 1,000,000 and 3,000,000 Americans, and millions more around the world. POTS is a form of orthostatic intolerance that is associated with the presence of excessive tachycardia and many other symptoms upon standing.1
The current diagnostic criteria for POTS is a heart rate increase of 30 beats per minute (bpm) or more, or over 120 bpm, within the first 10 minutes of standing, in the absence of orthostatic hypotension.1,2,3,4 In children and adolescents, a revised standard of a 40 bpm or more increase has recently been adopted.4,5 POTS is often diagnosed by a Tilt Table Test, but if such testing is not available, POTS can be diagnosed with bedside measurements of heart rate and blood pressure taken in the supine (laying down) and standing up position at 2, 5 and 10 minute intervals. Doctors may perform more detailed tests to evaluate the autonomic nervous system in POTS patients, such as Quantitative Sudomotor Axon Reflex Test (QSART, sometimes called Q-Sweat), Thermoregulatory Sweat Test (TST), skin biopsies looking at the small fiber nerves, gastric motility studies and more.
Signs and Symptoms
While the diagnostic criteria focus on the abnormal heart rate increase upon standing, POTS usually presents with symptoms much more complex than a simple increase in heart rate. It is fairly common for POTS patients to have a drop in blood pressure upon standing, but some POTS patients have no change or even an increase in blood pressure upon standing.1 POTS patients often have hypovolemia (low blood volume) and high levels of plasma norepinephrine while standing, reflecting increased sympathetic nervous system activation.3 Approxiamtely 50% of POTS patients have a small fiber neuropathy that impacts their sudomotor nerves. Many POTS patients also experience fatigue, headaches, lightheadedness, heart palpitations, exercise intolerance, nausea, diminished concentration, tremulousness (shaking), syncope (fainting), coldness or pain in the extremities, chest pain and shortness of breath.1,3,4 Patients can develop a reddish purple color in the legs upon standing, believed to be caused by blood pooling or poor circulation. The color change subsides upon returning to a reclined position.
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