In an implantable double or triple-chamber defibrillator, any pacing in one of the chambers (atrial channel or ventricular channel) generates a blanking in the other chamber (ventricular channel or atrial channel) to avoid the risk of crosstalk. The programming of long windows without sensing in the atrium following sensing or ventricular pacing increases the risk of undersensing of an atrial arrhythmia and limits the capabilities of the device to discriminate the origin of the atrial arrhythmias which is based on the comparison between atrial and ventricular rates. The optimization of post ventricular atrial blanking represents an essential step of the programming with the aim of finding a balance between proper sensing of atrial signals and minimal risk of crosstalk. In the new pacemaker and defibrillator platforms, 3 options are programmable:

1. absolute blanking corresponding to a traditional blanking with total absence of sensing and absence of markers,
2. partial blanking: if programmed at 150 ms for example, it partitions into 30 ms of absolute blanking without sensing and then 120 ms with possible sensing without modification of the programmed atrial sensitivity level, with any sensed atrial signal being marked Ab on the marker chain,
3. partial blanking +: if programmed at 150 ms for example , it partitions into 30 ms of absolute blanking without sensing and then 120 ms with possible sensing but with a temporary decrease in the level of programmed atrial sensitivity in order to reduce the risk of crosstalk, any sensed atrial signal being marked Ab on the marker chain. The sensing of an atrial signal in partial blanking or partial blanking + does not induce an AV delay but is taken into account for the analysis of atrial rhythm in the discrimination process and in the fallback algorithm.

The device memory and the electrograms of the recorded episodes must be systematically verified to confirm the diagnosis made by the device. In this patient, the defibrillator memory was saturated with short-duration episodes erroneously diagnosed as atrial arrhythmias in conjunction with crosstalk. These repeated episodes were responsible for a significant decrease in the percentage of biventricular pacing. A change in programming from partial to partial + did not correct the problem. On the other hand, a reprogramming of the constant atrial sensitivity to 0.6 mV was conversely effective.