Inappropriate sinus tachycardia (IST) has been defined as a resting heart rate
of 100 beats per minute and an average 24-hour heart rate 90 bpm with
distressing symptoms resulting from the persistent tachycardia. IST is prevalent
in 1% of the middle-aged population, mostly females. Rarely can elderly patients
also present with IST. Possible mechanisms of IST include intrinsic sinus node
abnormality, beta-adrenergic receptor stimulating autoantibody, beta-adrenergic
receptor supersensitivity, muscarinic receptor autoantibody, or hyposensitivity,
impaired baroreflex control, depressed efferent parasympathetic/vagal function,
nociceptive stimulation, central autonomic overactivity, aberrant neurohumoral
modulation, etc. Symptoms associated with IST are palpitations, chest pain,
fatigue, shortness of breath, presyncope, and syncope. Despite these distressing
symptoms, IST has not been associated with tachycardia-associated cardiomyopathy
or increased major cardiovascular events. Various treatment options for patients
with IST are ivabradine, beta-adrenergic blockers, calcium channel blockers,
psychiatric evaluation, and exercise training. Although, endocardial
radiofrequency ablation targeting the sinus node has been used as a treatment
modality for otherwise treatment-refractory IST, the results have been dismal.
The other modalities used for refractory IST treatment are endocardial
modification of the sinus node using radiofrequency energy, combined endo and
epicardial ablation of the sinus node, thoracoscopic epicardial ablation of the
sinus node, sinus node sparing thoracoscopic and endocardial hybrid ablation. The
goal of this review is to provide the readership with the pathophysiological
basis of IST and its management options.