What is the definition of sinus bradycardia?

Updated: Dec 27, 2017
  • Author: Mark W Livingston, MD; Chief Editor: Erik D Schraga, MD  more...
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Answer

Sinus bradycardia can be defined as a sinus rhythm with a resting heart rate of 60 beats per minute or less. However, few patients actually become symptomatic until their heart rate drops to less than 50 beats per minute. The action potential responsible for this rhythm arises from the sinus node and causes a P wave on the surface ECG that is normal in terms of both amplitude and vector. The presence of sinus bradycardia in itself does not cause a change in the QRS complex and T wave.

The frequency of sinus bradycardia is unknown, given that most cases represent normal variants. Although the frequency of sick sinus syndrome is unknown in the general population, in cardiac patients it has been estimated to be 3 in 5000.


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