STARS Patient Information

Inappropriate Sinus Tachycardia

What is IST?

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Inappropriate Sinus Tachycardia (IST) is a condition in which an individual’s resting heart rate is abnormally high – greater than 100 beats per minute or rapidly accelerating to over 100 beats per minute without an identifiable cause for the tachycardia, although small amounts of exercise, emotional or physical stress are triggering factors.

An ECG will not show any abnormalities as IST arises within the Sinus Node where normal sinus rhythm is generated. It is a relatively new disorder (first recognized in the late 1970s) that is under appreciated by many in the medical profession and with many doctors regarding it as a psychological condition. Individuals with this condition can find themselves increasingly disabled and experiencing high levels of anxiety.


What causes IST?

Unfortunately, to date nobody knows. There is a belief that IST is a result of the sinus node having an abnormal structure. There is another view that individuals with IST might be super-sensitive to adrenaline as the smallest amount of exertion can cause a pronounced rise in the heart rate. However, a number of informed medical professionals believe there are a number of factors and disorders which point to disturbance within the autonomic nervous system. It is for this reason that it is a condition that is frequently mistaken for POTS (Postural OrthostaticTachycardia Syndrome).

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