Introduction

• Sinus rhythm with a heart rate >100 beats per minute
• Impulse comes from sinoatrial node

Causes

• Increase in sympathetic activity increases the rate of SA node
• Sinus tachycardia is a physiologic response to the body’s needs rather than a pathologic cardiac condition
• Treatment of the tachyarrhythmia should be directed at correcting the underlying condition and not at suppression of the SA node itself
• Maximal sympathetic stimulation can increase the heart rate produced by the SA node to 200 beats/min or, rarely, 220 beats/min in younger individuals
• Formula for maximal sinus rate = 220 beats/min - age

Classification

Physiological sinus tachycardia

• caused by physiological increase in sympathetic activity brought by - emotions, physical exercise, pain, pregnancy
• or in some pathological cases – anxiety, panic attack, anaemia, fever, pulmonary embolism, hypoglycaemia and many more

Inappropriate sinus tachycardia

• sinus tachycardia >100 bpm at rest or during minimal activity that is out of proportion with the level of stress
• occurs in individuals without apparent heart disease or other cause for sinus tachycardia and is generally considered a diagnosis of exclusion
• tachycardia tends to be persistent and symptomatic - palpitations, presyncope, rarely syncope.
• Characteristically the mean heart rate drops during sleep.
• ECG: P wave axis and morphology similar or identical to sinus rhythm.

ECG findings

• one P wave for every QRS complex
• The PR interval is shorter than during normal sinus - increased sympathetic tone also speeds AV nodal conduction
• P wave morphology:
  - Upright in leads I, II and usually aVF
  - Inverted in aVR
  - Upright, biphasic or inverted in III and aVL
  - The right to left activation results in P waves that are upright or biphasic in V1 and V2, and upright in V3 through V6
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• The QRS complex is usually normal (if there is no fixed or transient intraventricular conduction disturbance).
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• This distinction of sinus tachycardia from atrial tachycardias is generally based on the clinical presentation and the onset and termination of the tachycardia. Unlike sinus tachycardia, atrial tachycardias typically have abrupt onset and termination.

ECG 1  Sinus tachycardia

• regular narrow complex tachycardia at rate 115 bpm
• every QRS complex has a preceding P wave
• P wave morphology and axis typical for sinus rhythm
  - positive in leads I, II, aVF
  - inverted in aVR

Management

Treat the underlying cause

• sinus tachycardia will improve or resolve following treatment directed at the underlying etiology
• The heart rate usually declines over time to a level that reflects the degree of activation of the sympathetic nervous system.

Management of inappropriate sinus tachycardia

• prognosis of IST is benign
• lifestyle interventions such as exercise training, volume expansion, and avoidance of cardiac stimulants should be tried before drug treatment
• in highly symptomatic patients - Ivabradine alone or in combination with a beta-blocker should be considered 
• radiofrequency ablation

References

1. Strauss, David G., et al. Marriott's Practical Electrocardiography. Wolters Kluwer, 2021
2. Brugada J, Katritsis DG, Arbelo E, Arribas F, Bax JJ, Blomström-Lundqvist C, Calkins H, Corrado D, Deftereos SG, Diller GP, Gomez-Doblas JJ, Gorenek B, Grace A, Ho SY, Kaski JC, Kuck KH, Lambiase PD, Sacher F, Sarquella-Brugada G, Suwalski P, Zaza A; ESC Scientific Document Group. 2019 ESC Guidelines for the management of patients with supraventricular tachycardiaThe Task Force for the management of patients with supraventricular tachycardia of the European Society of Cardiology (ESC). Eur Heart J. 2020 Feb 1;41(5):655-720. doi: 10.1093/eurheartj/ehz467. PMID: 31504425.
3. Munther K Homoud, MD.(2020). Sinus tachycardia: Evaluation and management (2020). In I. Susan B Yeon, MD, JD, FACC (Ed.), UpToDate. Retrieved February 5, 2021 from https://www-uptodate-com.ezproxy.is.cuni.cz/contents/sinus-tachycardia-evaluation-and-management?search=inappropriate%20sinus%20tachycardia&source=search_result&selectedTitle=1~20&usage_type=default&display_rank=1