Tracé

At the beginning of the tracing, the atrial EGM reveals the presence of atrial tachycardia with regular, monomorphic atrial cycles; one out of two signals is sensed by the atrial channel, the second signal falling in the post-ventricular atrial blanking; switching according to an AVB I criterion (vertical line), with the PR interval exceeding the limit value over 6 consecutive cycles; fast ventricular pacing, one in two atrial activities falling in the post-ventricular atrial blanking;

Commentaires

This tracing shows an example of atrial tachycardia misdiagnosed by the device, one in two atrial activities falling in the post-ventricular atrial blanking thus preventing mode switch to DDI mode; however, the pacemaker inappropriately switches to DDD mode when faced with a pseudo-pattern of first degree AV block. The problem subsequently persists with rapid ventricular pacing, with one in two atrial activities still in the post-ventricular atrial blanking.

The post-ventricular atrial blanking (PVAB) is an absolute refractory period applied in the atrium after ventricular sensing and pacing.

Its purpose is to prevent the sensing, by the atrial lead, of the ventricular pacing artifact and the depolarization of intrinsic or paced ventricular activity. This blanking is used when the pacemaker is operating in DDD, DDI, VDD and VDI modes.

For a Microport™ pacemaker, after ventricular pacing, an absolute refractory period of 150 ms (nominal value, programmable) is triggered at the atrial stage. The first 100 ms represent an absolute refractory period while the next 50 ms are automatically retriggerable. Following ventricular sensing, an absolute refractory period of 100 ms (nominal value) is triggered on the atrial channel. The first 50 ms represent an absolute refractory period while the next 50 ms are automatically retriggerable. When the user modifies the PVAB value (post-pacing), the post-sensed PVAB is also modified. The post-ventricular paced PVAB is the value that is programmed.

This tracing shows the limitations of programming an unnecessarily long post-ventricular atrial blanking. Failure to sense one out of two atrial signals during an episode of atrial flutter/tachycardia may lead to the occurrence of poorly-supported paced tachycardia. The combined deleterious effect of the tachycardia and right ventricular pacing can favor symptom onset. A reduction of the blanking value allows the detection of the second atrial signal (in the WARAD), the diagnosis of atrial arrhythmia and thus rapid switching to an asynchronous mode. To maintain the proper ability to detect atrial arrhythmias and avoid crosstalk, programming must balance blanking periods with atrial sensitivity.

Setting a post-ventricular atrial blanking that is too long exposes the patient to the risk of non-detection of atrial flutter-tachycardia. In contrast, when the blanking is too short, the risk of crosstalk is increased.