As explained previously, when the pacemaker operates in DDD-ADI mode, the search for spontaneous conduction is based on an atrioventricular delay hysteresis with an AV delay of 450 ms during 8 cycles. Therefore, there can be no blocked P waves during this search, which allows preventing potentially symptomatic ventricular pauses that may, in a few patients, favor the occurrence of ventricular arrhythmias.

When there is a permanent or paroxysmal atrioventricular conduction disorder, as observed in this patient, this search results in failure and leads to a return to the DDD mode at the programmed AV delay. One of the limitations of this option is that in patients with altered anterograde conduction but preserved retrograde conduction, prolonging the AV delay favors the occurrence of retrograde conduction which can generate a pacemaker-mediated tachycardia without the need for other triggering factors (atrial or ventricular extrasystole, loss of atrial capture, etc.). The number of PMTs can thus be very substantial.  The simplest and most logical approach in the presence of a permanent complete atrioventricular block is not to program the Vp suppression algorithm. When the conduction disorder is paroxysmal and when it is deemed desirable to preserve the spontaneous conduction, it is therefore essential to verify that the PVARP is appropriately programmed longer than the retrograde conduction time.

Note that it is possible to program an automatic PVARP. Its operation differs completely from that of other manufacturers. Indeed, for Medtronic^TM devices, for example, the duration of an automatic PVARP decreases with the increase in heart rate. For Biotronik^TM devices, when the PVARP is programmed to Auto, the nominal PVARP is 250 ms without modification during exercise. The PVARP is prolonged by 50 ms when a PMT episode is diagnosed and treated by the device.