Inappropriate sinus tachycardia is sinus tachycardia inappropriate to the situation. It is defined as sinus rates above 100 beats per minute at rest or average sinus rate above 90 beats per minute over 24 hours without an underlying cause. Important secondary causes of sinus tachycardia like the use of caffeine, alcohol, nicotine, drugs of abuse like cocaine, increased function of thyroid gland, fever, anxiety, pain, and other illnesses which can increase the heart rate have to be excluded before considering IST.
