Tutorial 2b: Sinus Arrhythmia

Now we move on to our first arrhythmia - in fact the term Sinus arrhythmia is slightly misleading since variation of the heart rate with breathing is normal. Breathing in decreases the parasympathetic tone of the SA node causing it to pace more quickly and breathing out slows down the SA node through parasympathetic stimulation.

Sinus arrhythmia presents on the EKG as a variation in the PP distance with breathing. You should technically have a variation in rate of >10%.

Examine the tracing below and determine the maximum and minimum rate (Don't worry about any other abnormalities you may notice on this EKG, it will also appear in the case practice).