This Lead II rhythm strip is from a nine-year-old girl being monitored for an outpatient surgical procedure. She has no known heart disease. Her heart rate is 110 per minute. The PR interval is .12 seconds (120 ms), the QRS is upright and narrow at .06 seconds (60 ms), and the rhythm is regular.
This is an example of a junctional rhythm that is slower than what is considered "intrinsic rate" for the junction. The rate is around 30 bpm. We know this is a "supraventricular" rhythm because of the narrow QRS. Junctional beats travel to the ventricles via the bundle branches, which provides very fast conduction, resulting in a narrow QRS complex. The P waves can be seen at the end of each QRS. They are upside-down in this Lead II rhythm strip, indicating retrograde conduction from the junctional pacemaker to the atria.
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