Repetitive nonreentrant ventriculoatrial synchrony
75-year-old man implanted with an Evia DR-T pacemaker for sinus dysfunction; hospitalization for palpitations and dyspnea; recording of this EGM tracing on arrival.
- effective ventricular pacing;
- retrograde conduction and detection of atrial activity in the PVARP;
- ineffective atrial pacing since falling in the refractory period following the previous atrial depolarization;
- the cycle repeats itself with retrograde conduction in the PVARP and ineffective atrial pacing favoring retrograde conduction.
This tracing illustrates a particular form of "PMT" in conjunction with the detection of retrograde conduction in the PVARP (functional undersensing) and an inefficient atrial pacing (loss of functional capture) since delivered in the physiological refractory period. This patient presented a normal atrial threshold (<1V for 0.5 ms) with an adjusted programming margin (2.5V for 0.4 ms). This type of repetitive sequences can
- be generated by all of the causes associated with loss of atrioventricular synchrony (same as those for a PMT). This loss of synchrony results in a PMT or NRVAS (non-reentrant ventriculoatrial synchrony) as a function of the retrograde conduction time and the various pacemaker settings (PVARP, minimum rate, programming of different specific algorithms, etc);
- be associated with a symptomatology similar to that of a conventional PMT in conjunction with the loss of the active atrial component and with retrograde conduction (dyspnea, palpitations, pacemaker syndrome, etc.);
- occur for the DDD mode but also for the DDI mode (possible atrial pacing) but not for the VDD mode (atrial pacing needed).
Atrial pacing occurs at the end of the escape interval. If atrial pacing is effective, the cycle is interrupted. The higher the rate (minimum rate or rate response), the greater the risk that atrial pacing falls within the atrial myocardial refractory period and that the pacing is ineffective. To avoid this type of problem, one must therefore
- avoid all causes associated with a dissociation (PVC, PAC, myopotential oversensing, loss of atrial capture, etc.);
- decrease the pacing rate (minimum rate and rate response) and reduce the AV delay in order to allow the atrial myocardium more time to exit its refractory period;
- deprogram the prolongation of post-PVC PVARP if it is not accompanied by an automatic prolongation of the atrial escape interval.