From the Guidelines
Inappropriate Sinus Tachycardia (IST) is diagnosed by excluding secondary causes of tachycardia and is characterized by a resting heart rate >100 bpm and average rates >90 bpm in a 24-hour period, with associated debilitating symptoms.
Diagnosis
The diagnosis of IST is one of exclusion, and it is crucial to distinguish it from:
- Secondary causes of tachycardia, including hyperthyroidism, anemia, dehydration, pain, and use of exogenous substances 1
- Other forms of tachycardia, such as atrial tachycardia (AT) and sinus node reentrant tachycardia 1
- Postural Orthostatic Tachycardia Syndrome (POTS), which has predominant symptoms related to a change in posture 1
Treatment
The treatment of IST is predominantly symptom-driven, and the following options are recommended:
- Ivabradine is reasonable for ongoing management in patients with symptomatic IST, with a dosage of 2.5 to 7.5 mg twice daily 1
- Beta blockers may be considered for ongoing management in patients with symptomatic IST, with metoprolol succinate titrated to a target of 95 mg daily 1
- The combination of beta blockers and ivabradine may be considered for ongoing management in patients with IST, with close monitoring for excess bradycardia 1
- Sinus node modification by catheter ablation remains a potentially important therapeutic option in the most refractory cases of IST, with a reported acute success rate of 76% and long-term success rate of 66% 1
From the Research
Diagnosis of Inappropriate Sinus Tachycardia (IST)
- IST is characterized by 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 2
- Symptoms associated with IST include palpitations, chest pain, fatigue, shortness of breath, presyncope, and syncope 2
- Diagnosis of IST is often a diagnosis of exclusion, requiring the initial exclusion of potential causes of secondary sinus tachycardia 3, 4
- Evaluation of cardiac autonomic reflex function is essential to support the diagnosis of IST 4
Treatment Options for IST
- Various treatment options for patients with IST include ivabradine, beta-adrenergic blockers, calcium channel blockers, psychiatric evaluation, and exercise training 2
- Ivabradine, a novel sinus node If 'funny current' inhibitor, has shown promise in the treatment of IST 5
- Therapeutic approaches also include physical training, beta blockers or ivabradine 3
- Radiofrequency catheter ablation should be restricted to patients with refractory and longstanding symptoms 3
- Multidisciplinary management, including cardiac rehabilitation, pharmacotherapy, and occasionally radiofrequency modification of the sinus node, should be considered 4
- 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 2