An 82 year-old man presents to the pacemaker clinic.  He is asymptomatic, and is 98% atrially paced upon interrogation.  His interrogation shows several episodes of tachycardia as noted below:

• Pacemaker Mediated Tachycardia (PMT)

Comment: At the outset, this tachycardia is close to the upper tracking rate of the pacemaker and thus is likely to be either PMT or atrial tachycardia; sinus tachycardia would be unlikely given the patient is dependent on atrial pacing. On the second line, one can see that the AV interval of the beat with the asterisk is actually 50ms longer than the others.  This is a feature built into this type of pacemaker to diagnose PMT.  If the AA interval on either side of that late paced ventricular beat (noted to be 547ms) is also 50ms longer than the baseline AA interval (approximately 500ms in this case), then the atrial activation is “linked” to ventricular pacing and must be PMT, NOT atrial tachycardia.