Inappropriate Sinus Tachycardia (IST)

Also known as primary sinus tachycardia, inappropriate sinus tachycardia (IST) is a generally benign condition that has a prevalence of ~1% in the general population.

Diagnostic criteria

Causes

Exact aetiology is uncertain, but both intrinsic and extrinsic mechanisms have been proposed:

Intrinsic:

• Sinus node dysfunction causing increased automaticity

Extrinsic:

• IgG beta-receptor stimulating antibodies have been detected in some patient groups with IST
• Beta-receptor supersensitivity
• Impaired baroreflex control
• Vagal denervation

Differential diagnosis

• Postural Orthostatic Tachycardia Syndrome (POTS)
• Deconditioning

Clinical significance

• IST is generally a benign condition that rarely causes any life-threatening cardiovascular issues
• There is a higher prevalence of psychological disorders, in particular anxiety, in patients with IST. It is unclear as to whether this is a cause or effect of IST
• Isolated cases of IST-induced cardiomyopathy have been reported that respond to treatment with ivabradine

Treatment

• Once diagnosis has been established, first line treatment is avoidance of stimulants such as caffeine, tobacco, and illicit drugs
• Ivabradine is the only medical therapy that has demonstrated efficacy in literature. It is a blocker of cardiac I_f current, and has been shown to reduce HR and symptoms in patients with IST, even after cessation of therapy
• Beta-blockers are a second line medical option
• Ablation is not recommended

Related Topics

• Sinus tachycardia

References

• Still et al. Prevalence, characteristics and natural course of inappropriate sinus tachycardia. Europace. 2005;7:104–112
• Ptaszynski P., Kaczmarek K., Ruta J., Klingenheben T., Wranicz J.K. Metoprolol succinate vs. Ivabradine in the treatment of inappropriate sinus tachycardia in patients unresponsive to previous pharmacological therapy. Europace. 2013;15:116–121
• Sheldon et al. 2015 heart rhythm society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope. Heart Rhythm. 2015;12:e41–e63
• Kanjwal MY, Kosinski DJ, Grubb BP. Treatment of postural orthostatic tachycardia syndrome and inappropriate sinus tachycardia. Curr Cardiol Rep 2003;5:402–6
• Baruscotti et al. Current understanding of the pathophysiological mechanisms responsible for inappropriate sinus tachycardia: role of the If “funny” current. J Interv Card Electrophysiol 2016;46:19–28
• Chiale et al.  Inappropriate sinus tachycardia may be related to an immunologic disorder involving cardiac beta andrenergic receptors. Heart Rhythm 2006;3:1182–6
• Leon et al. Impaired baroreflex gain in patients with inappropriate sinus tachycardia. J Cardiovasc Electrophysiol 2005;16:64–8
• De Sisti et al. A case of inappropriate sinus tachycardia after atrio-ventricular nodal reentrant tachycardia cryoablation successfully treated by ivabradine. Europace 2010;12:1029–31
• Winum et al. A case of cardiomyopathy induced by inappropriate sinus tachycardia and cured by ivabradine. Pacing Clin Electrophysiol 2009;32:942–4
• Romeo E et al.  A pediatric case of cardiomyopathy induced by inappropriate sinus tachycardia: efficacy of ivabradine. Pediatr Cardiol 2011;32:842–5

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.
• Wiesbauer F. Little Black Book of ECG Secrets. Medmastery PDF

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest