AF with failure to capture and intermittent undersening

A 75 yo with h/o DM, HTN, s/p PPM admitted for stroke. What is wrong in the ECG?

Figure 1 - ECG case

AF with slow ventricular response in a patient with VVI pacemaker with intermittent loss of capture and intermittent undersensing

Interpretation courtesy of Dr. Raed Abu Sham'a:

The underlying rhythm is AF [no clear P waves]. There are QRSs of 4 different morphologies. The ventricular rhythm is irregular which excludes underlying CAVB in AF patient. There is at irregular pacing  spikes. If you have completely irregular pacing spikes like this, then there is a combined problem!!! There is no capture after the spikes which indicates non-capture problem and the pacing spikes fall randomly that  indicate undersensing. Furthermore, they are irregular which indicates intermittent undersensing. Example of this is QRS 1 and 2 are undersensed and QRS 3 is sensed and the following spike is delayed to the lower pacing limit. There are two paced beats with capture [8, 12]. Here are all beats: QRS 1=US, 2=US, 3=S, 4=S, 5=S, 6=US, 7=S, 8=P, 9=S, 10=S, 11=S, 12=P, 13=S, 14=S, 15=S. Interestingly after the two paced beats there are two beats [9 and 13] of the same morphology and coupling intervals. These are called bundle branch reentrant beats. In conclusion: AF with slow ventricular response in a patient with VVI pacemaker [temporary or permanent] with intermittent loss of capture and intermittent undersensing.

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