Sinus Bradycardia

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.

EKG monitor simulation of sinus bradycardia at a rate of 42bpm.
Sinus Bradycardia (sinus brady) EKG / ECG monitor capture (software gen.)

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.)

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EKG Vocabulary:
Sinus Bradycardia is shortened to "sinus brady" by many healthcare providers.
1:00 Sinus Bradycardia monitor capture.

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

Sinus Bradycardia tracing graph.
EKG tracing of a Sinus Bradycardia.

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.)

EKG tracing of Sinus Bradycardia at the maximum rate of 59bpm.
Sinus Bradycardia with the maximum HR of 59bpm and the R-R Interval marked in green.

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.

Cardiac Monitor capture of an Agonal Sinus Rhythm (Sinus Bradycardia @ 6bpm).
Monitor capture of Sinus Bradycardia with a HR of 6bpm, aka. an Agonal Rhythm.

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.

Sinus Bradycardia ECG example, split printout / monitor display.
Sinus Bradycardia practice ECG tracing.
Sinus Bradycardia EKG example, split printout / monitor display.
Practice Sinus Bradycardia EKG.
Sinus Bradycardia EKG example, split monitor / paper display.
Practice Sinus Bradycardia EKG.

After becoming confident in identifying EKG's 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 EKG's with our EKG Generator:

Basic EKG App

Our Basic EKG Generator is free with an email signup and covers Normal Sinus Rhythm along with common arrhythmia.

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Our Pro EKG Generator covers over 40 different rhythm categories, multiple display options, has Quiz and Simulation modes, and more! Try it out for just $5 for a month.