Sinus Tachycardia

Sinus tachycardia is a normal sinus rhythm occurring at a faster-than-normal rate (typically >100 beats per minute in adults). It is usually a physiological response to an underlying stimulus rather than a primary arrhythmia.

Educational Videos

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1. Autonomic Control of Heart Rate

Heart rate is regulated by the autonomic nervous system:

• Sympathetic nervous system increases heart rate via adrenaline and noradrenaline.
• Parasympathetic nervous system (vagus nerve) slows heart rate.

Sinus tachycardia may result from:

• Increased sympathetic tone (exercise, anxiety, stimulants).
• Reduced parasympathetic (vagal) activity.

Blocking vagal activity with drugs such as atropine increases heart rate. Conversely, excessive vagal stimulation may cause bradycardia, as seen in a vasovagal episode (common faint), where heart rate and blood pressure temporarily fall.

2. Common Physiological Causes

• Exercise
• Stress or anxiety
• Fever / hyperthermia
• Dehydration / hypovolaemia
• Blood loss
• Pain

3. Medical Causes

• Hyperthyroidism (most common endocrine cause)
• Anaemia
• Infection / sepsis
• Pheochromocytoma (rare adrenal tumour)

4. Drug-Related Causes

• Adrenaline / epinephrine
• Cocaine
• Amphetamines
• Salbutamol (beta-agonist asthma medication)
• Tricyclic antidepressants (e.g., amitriptyline)
• Anticholinergics (atropine, hyoscine, scopolamine)
• Caffeine

5. Investigations

• Thyroid function tests
• Full blood count (anaemia)
• Electrolytes
• Infection markers if febrile

6. Treatment

• Treat the underlying cause
• Rehydrate if dehydrated
• Rest and anxiety management
• Modify causative medications
• Gradually improve cardiovascular fitness

Sinus tachycardia itself is usually not dangerous unless the underlying cause is serious. Persistent inappropriate sinus tachycardia may require specialist review.

Compare with: SVT | Atrial Fibrillation | Atrial Flutter