Medicine - Education Center
In sinus tachycardia, the heart rate is
above 100 beats/min and each QRS complex is preceded by a P wave.
It is a normal physiological response to stress (both physical and mental). It also occurs in
thyrotoxicosis, anxiety states, cardiac failure (due to an increased Bainbridge reflex)
and acute carditis. It usually accompanies fever and the sinus rate rises by 8 beats/min
for every one degree celsius rise in body temperature. A reduction in arterial oxygen saturation
due to high altitude or congenital heart disease will result in sinus tachycardia. Failure to
develop sinus tachycardia in response to stress may be a sign of the "sick sinus syndrome" or may be due to
iatrogenic causes such as the administration of adrenaline, atropine, caffeine or nitrates.
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