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.