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Inappropriate Sinus Tachycardia (IST)
Inappropriate sinus tachycardia (IST) is a condition in which the resting heart rate is abnormally high (greater than 100 beats per minute), and increases rapidly with minimal exertion, accompanied by symptoms of palpitations, fatigue, and exercise intolerance.
While IST can occur in anybody, it is most often a disorder of young women. The average IST sufferer is a woman in her late 20s or early 30s who has been having symptoms for months to years. In addition to the most prominent symptoms of palpitations, fatigue and exercise intolerance, IST can also be associated with a host of other symptoms including a drop in blood pressure upon standing, blurred vision, dizziness, tingling, shortness of breath, and sweating.
Treatment for IST is reasonably effective in many patients, but achieving optimal results often requires trial-and-error attempts with several drugs, singly or in combination.
- Beta blockers block the effect of adrenaline on the sinus node, and since patients with IST have an exaggerated response to adrenaline, using beta blockers is logical. They are reasonably effective in many patients with IST.
- Calcium blockers can slow the action of the sinus node, but have been only marginally effective in for IST.
- Recently, the new drug Ivabradine has been used successfully patients with IST.