The first channel is lead I of the surface ECG with the markers superimposed, the second shows the atrial EGM, the third and fourth show the ventricular EGM, and the last channel is lead III;

1. accurate atrial sensing initiating an AV delay and ventricular pacing (AS-VP); the ventricular EGM and both surface leads show the absence of ventricular capture (no ventricular signal after the pacing stimulus);
2. the spontaneous ventricular event after the preceding P wave is properly sensed (VS);
3. a new atrial sensing-ventricular pacing sequence (AS-VP) is ineffective; the P wave is blocked; the rhythm is consistent with type I (Wenckebach) second degree AV block (progressive prolongation of the PR interval followed by blocked P wave);
4. ineffective ventricular pacing; the following QRS was not sensed, not due, however, to faulty sensing; instead, the QRS fell in the post-ventricular pacing ventricular blanking period, a period of absolute ventricular refractoriness and, therefore, was not sensed;
5. continuation of missing ventricular capture;