Answer:

The EKG demonstrates an underlying rhythm consistent with an accelerated junctional rhythm. Sequential pacemaker stimuli are seen occurring in every other beat. The first pacemaker spike occurs before the QRS complex and does not capture and the second stimulus occurs at an interval of 200msec and occurs on the t-wave and does not capture. This is consistent with committed DVI pacing mode where the ventricular lead senses the slower preceding junctional beat and results in A-V sequential pacing but the pacing stimuli do not capture.

The R-R is slightly longer every other cycle which could represent 3:2 exit block from the junction.

Although the putative ventricular pacing stimulus falls in the ventricular refractory period (ST segment) it is possible that the atrial pacing stimulus, which occurs immediately before the QRS complex, results in a P wave which is masked by the QRS.