The ventricular rate of the patient is about 72 beats/minute and it would appear that there is a p wave in front of each QRS complex. The "pr" interval is a little short at about 120 ms. The pacer should have started to pace he atrium when set at 100/min. The failure to do so suggests that the pacing system is non-functional (depleted pacemaker battery, broken lead etc.) or that the pacer is sensing an atrial rhythm faster than 100/min. In this case the pacer is sensing an SVT with an atrial rate of about 150/min. which explains the lack of pacing when the pacer is set to 100/min. The treating physician decided to leave the patient in this rhythm. It is interesting to note that some SVTs and atrial fibrillation can "cure" a sick sinus patient of their bradycardia and the need for a pacemaker. In those cases though that convert to atrial fibrillation anticoagulants are usually considered.