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ECG Basics: Normal Sinus Rhythm

Dawn's picture
Mon, 05/19/2014 - 13:15 -- Dawn

We try to remember to include some good old "Normal Sinus Rhythm" strips from time to time.  Teachers often have large collections of strange and unusual strips that their colleagues have saved for them.  But, then they find themselves resorting to electronic rhythm generators for samples of "normal".  Here is a strip from a healthy, 23-year-old woman showing NSR.  The rate is 65 bpm, QRS duration 76 ms, PRI 136 ms, QTc 410.  There are no abnormal ST segments or T wave changes.  There are very slight rate changes from beat to beat, and the P waves appear to change morphology a bit.  This can be due to the patient's breathing movements, and we would not delve too deeply into this in light of the fact that this is an ECG from an asymptomatic young ECG student.  Absolute precision would come from an generator, but rarely from a human being. This is a good strip to teach rate and interval determination.

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Comments's picture

I completely agree with Dawn about the following:

  • It is good to have strips in one's collection on NSR (Normal Sinus Rhythm) - as sometimes we get overfocused on the abnormal so as to forget about the normal ...
  • There is slight variation in the R-R interval. It is good to be aware that the amount of variation needed to qualify as "sinus arrhythmia" = 0.08-0.12 = between 2-to-3 little boxes. Sinus arrhythmia per se is rarely an "abnormality" - but when interpreting tracings I refrain from using this term unless there is at least the above amount of variation.
  • ADVANCED POINT: I am not 100% certain this rhythm strip is "sinus rhythm" for its entirety. The change in P wave morphology for the 4th, 5th and 6th beats is a bit more-than-expected relative to the small amount of baseline undulation we see - AND - there IS variation in the R-R interval, such that this could reflect some wandering pacemaker. That said - there is not nearly enough monitoring to know for certain - and even if there was a "wandering atrial pacemaker" - that is a normal variant in an otherwise healthy adult - so this is an academic discussion.
  • IMPORTANT POINT for ALL: Regardless of how "picky" my last comment was - it IS important when interpreting any 12-lead or rhythm strip to closely scrutinize P wave morphology. So I WOULD want you (regardless of what level interpreter you are) to see that the P wave does change a bit on this tracing. Now that you have seen this - as per Dawn, this may simply reflect variation we sometimes see with sinus rhythm.

Ken Grauer, MD   [email protected] 

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