Sinus tachycardia denotes sinus rhythm with a rate > 100 beats/min.
It is not usually considered as an actual arrhythmia but a physiological mechanism which increases cardiac output to correspond with the demands of the body.
Keep in mind that sinus tachycardia may be a sign of another emerging or worsening disease (cardiac failure, anaemia, disorder of thyroid function etc.).
Aetiology
Physical exertion (poor physical condition)
Mental stress, anxiety, nervous tension
Obesity
Pain
Fever
Hyperthyroidism (sometimes also hypothyroidism)
Anaemia
Hypovolaemia
Medication (sympathomimetics, alpha-blockers, some psychopharmacological drugs)
Respiratory distress or failure (regardless of cause)
In inappropriate sinus tachycardia, no underlying disease is identifiable.
Differential diagnosis
Sinus tachycardia usually starts and stops gradually, which differentiates it from most supraventricular tachycardias.
The morphology of the P wave is normal in sinus tachycardia, which differentiates it from ectopic atrial tachycardia and a nodal rhythm.
Atrial tachycardia with a 2:1 atrioventricular block may simulate sinus tachycardia (picture 1), particularly if one of the P waves is obscured by the preceding T wave or QRS.
May occur after atrial fibrillation ablation therapy, for example.
If necessary, vagal stimulation or adenosine may be used as a diagnostic aid.
To differentiate sinus tachycardia from other supraventricular tachycardias it should be noted that sympathicotonia or fever rarely causes sinus tachycardia faster than 120 beats/min in adults.
Treatment
The cause of sinus tachycardia should be identified and treated.
Symptomatic treatment, with the aim to slow the heart rate, must not be initiated until the secondary causes (see above) have been excluded.
Of non-pharmacological therapies, physical exercise and weight reduction have proved to be beneficial, because with the improving physical condition and weight loss usually the pulse rate will decrease.
In inappropriate sinus tachycardia not responding to medication, catheter ablation may be considered if the symptoms are particularly severe. Nowadays, ablation therapy is very rarely used.