Postural orthostatic tachycardia syndrome

**Definition:** Postural Orthostatic Tachycardia Syndrome is a type of chronic orthostatic intolerance lasting three months or longer associated with excessive upright tachycardia in the absence of orthostatic hypotension, plus a constellation of typically daily symptoms which may include lightheadedness, dizziness, nausea, dyspnoea, diaphoresis, headache, fatigue and other symptoms of autonomic dysfunction. Excessive tachycardia is defined by present consensus as a heart rate increase of at least 30 beats per minute in adults (40 beats per minute for adolescents), or a heart rate greater than 120 beats per minute, within 10 minutes of upright tilt table testing.