20 - Inappropriate sinus tachycardia

Abstract

Sinus tachycardia is a physiological response to sympathetic activation and/or parasympathetic withdrawal. Inappropriate sinus tachycardia (IST) is a nonparoxysmal tachyarrhythmia characterized by a persistent increase in resting sinus rate unrelated to, or out of proportion of, the level of physical, emotional, pathological, or pharmacological stress, or an exaggerated heart rate response to minimal exertion or a change in body posture. IST is neither a response to a pathological process (e.g., heart failure, hyperthyroidism, or drug effects) nor a result of physical deconditioning. Crucial to this definition is the presence of associated symptoms. The underlying mechanism(s) of IST is poorly understood and remains controversial. The vast majority of patients afflicted with IST are young women. IST is an ill-defined clinical syndrome with diverse clinical manifestations. There is no gold standard to make a definitive diagnosis of IST, and the diagnosis remains a clinical one, after exclusion of other causes of symptomatic tachycardia. Conservative medical management with a multidisciplinary approach is the mainstay of therapy for patients with IST and generally is directed at controlling symptoms. Heart rate reduction is a goal for most treatment strategies. Lifestyle changes are beneficial, including avoiding stimulants (drugs, alcohol, and caffeine) and preserving consistent sleep patterns. Beta-blockers are the first-line pharmacological therapy for most patients. Verapamil, diltiazem, and ivabradine can be considered when beta-blocker therapy is ineffective or not tolerated. Sinus node modification by catheter ablation remains a potentially important therapeutic option in the most refractory cases of IST.