Sinus Bradycardia is a Sinus Rhythm with a rate less than 60bpm and is otherwise identical to NSR. This slow rate results in a long R-R Interval on the EKG tracing and fewer complexes per length.
Being in the category of Sinus Rhythms, we know to expect the P-QRS-T pattern defined in Normal Sinus Rhythm, as all Sinus Rhythms originate from the SA Node and follow the natural electrical path. The brady in Sinus Bradycardia means slow. A Sinus Rhythm is slow when its HR is less than 60 (the lowest rate of NSR.)
Sinus Bradycardia is shortened to "sinus brady" by many healthcare providers.
Once a tracing is identified as a Sinus Rhythm with a Heart Rate (HR) less than 60bpm it can be called sinus bradycardia. Sinus Bradycardia means:
An EKG rhythm starting at the SA Node with a rate below 60 which follows the expected electrical path through the heart.
Defining Characteristic of Sinus Bradycardia in Lead II
The only differentiating factor of Sinus Bradycardia from other Sinus Rhythms is the rate:
- Rate: < 60 | R-R Intervals greater than 1sec (25mm) [5 large boxes].
In the below example you can see the minimum R-R Interval (marked in dark green) that a Sinus Bradycardia can have, 24.5mm (0.98sec) [4.5 large boxes]. A shorter R-R Interval would result in a HR of 60bpm or more (making it NSR or Sinus Tachycardia.)
Extremely Slow Rates of Sinus Bradycardia
When a bradycardia becomes too slow to reasonably expect it to be producing cardiac output it is defined as an Agonal Rhythm. Different educational organizations and textbooks have different definitions for the specific rate at which a rhythm becomes agonal.
The ECG tracing above shows a Sinus Bradycardia with a HR of 6bpm, which would be considered an Agonal Rhythm by most clinicians.
There is no official number for how slow a Sinus Bradycardia must be to become agonal. Some textbooks define Agonal Rhythm as rates less than 30, 20, and as low as 6. Reference your textbook, teacher, or local protocols for the specific cutoff in your area.
Below are several more examples of Sinus Bradycardia presented as monitor captures as well as on EGK graphs.
After becoming confident in identifying EKGs as Sinus Bradycardia you can continue by learning about the faster rate of Sinus Rhythm: Sinus Tachycardia, or review Normal Sinus Rhythm. Head back to our EKG Rhythm Index to find information on another ECG. Otherwise practice interpreting novel EKGs with our EKG Generator:
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