Challenges in Treatment of Inappropriate Sinus Tachycardia

Inappropriate Sinus Tachycardia (IST) is a clinical syndrome characterized by a sinus heart rate inexplicably higher than one hundred beats per minute at rest that is associated with symptoms like palpitations, dyspnea or dizziness in the absence of primary causes of tachycardia. The diagnosis requires exclusion of other causes of tachycardia including medications/substances (such as anti-cholinergic, beta-blocker withdrawal, caffeine, and alcohol) or medical conditions (such as panic attacks, pulmonary embolism, fever, hyperthyroidism, hypovolemia, anemia, and pain).

Work up should include an EKG to differentiate other causes of tachycardia, 24 hour- Holter monitor if indicated, serum thyroid levels, hemoglobin levels and toxicology screen. Electrophysiological studies are not routinely recommended, but should be considered in certain patients in whom concurrent supraventricular tachycardia is suspected.

The underlying pathology in IST is yet to be completely understood. However, it is thought that the causes of IST can be broadly classified into two groups; either as an intrinsic increase in sinus node automaticity or an extrinsic cause. Among extrinsic causes, there is evolving evidence that IgG anti-β receptor antibodies are found in IST causing tachycardia. Managing patients with IST includes lifestyle modification, non-pharmacological and pharmacological interventions. Ivabradine has recently emerged as an effective treatment of IST and was shown to be superior to beta-blockers.