This is a good example of an AV Sequential pacemaker in a patient with an intact AV conduction system. The pacemaker is pacing the right atrium, and the impulse is being transmitted normally down through the AV node and the interventricular conduction system. The pacer spike is seen before the P waves, and the QRS complex is narrow, reflecting normal conduction through the ventricles.
If you are teaching about ST elevation MI, this patient has no ST elevation M.I., but this type of pacing does not affect the ST segments, and an M.I. will still show as ST elevation.
This strip for your basic students is a nice example of atrial pacing in a patient with an intact interventricular conduction system. Generally, the pacemaker will behave this way when the sinus node is not functioning well enough to provide adequate rate for the patient, and the conduction system from the AV node down is functioning properly.
Pacemakers in the modern age are very complicated to understand for the beginner, and pacemaker programming and malfunctions often cannot be determined from a simple rhythm strip. It can be a challenge to teach beginning students about the programming options available today. This strip is nice because it is clear, and the pacer spikes are readily seen. The patient is being paced 100% of the time in this strip.