The correct answer is option 1. On observing the device (figure 1: upper trace, pacing channel; middle trace, atrial electrogram; lower trace, ventricular electrogram), T-wave oversensing can be seen (ovals). This affects detection of the following intrinsic atrial activity in the blanking period (Ab), which is not followed by ventricular pacing.1

Figure 1

(0.07MB).

Atrial activity corresponds to sinus rhythm at 90 bpm, with occasional far-field ventricular sensing (Ab intercalated between As and Ab from the third complex onwards), not to atrial tachycardia (response 2 incorrect).2

There is no progressive lengthening of the atrioventricular signal prior to the onset of slow frequencies, and Wenckebach behavior at this frequency would not be expected (response 3 incorrect).2

There is no sinus tachycardia that could lead to capture of every other P wave within the postventricular atrial refractory period (response 4 incorrect).2

Reductions were implemented in ventricular sensitivity (avoiding T-wave oversensing) and atrial sensitivity (avoiding far-field sensing), thereby resolving both problems.