PMT and ADI-DDD mode
Tracing
Manufacturer Biotronik
Device PM
Field Refractory periods
N° 15
Patient
83-year-old man implanted with an Evia DR-T pacemaker for complete paroxysmal atrioventricular block; programming of the DDD-ADI mode; feeling of palpitations; interrogation of the pulse generator.
Graph and trace
Programming in DDD mode;
- atrial pacing and ventricular pacing (AP-VP);
- programming of the DDD-ADI mode (vertical line);
- search for spontaneous conduction with prolongation of the AV delay to 450 ms;
- crosstalk with sensing in the far-field protection (FFP) period;
- ventricular pacing with long AV delay;
- probable retrograde conduction sensed outside the refractory periods (AS);
- ventricular pacing with long AV delay;
- new retrograde conduction;
- eighth cycle with AV delay at 450 ms; the search for atrioventricular conduction failed;
- AV delay shorter than previous delay but longer than that programmed so as not to exceed the synchronous maximum tracking rate;
- due to this long AV delay, retrograde conduction;
- PMT with adjustment of the AV delay so as not to exceed the maximum rate, which favors the occurrence of retrograde conduction;
- after 8 VP-AS cycles > 100 beats per minute, with stable VP-AS intervals and a VP-AS interval duration less than the programmed value, suspicion of PMT; prolongation of the AV delay over one cycle;
- the prolongation of the AV delay leads to a prolongation of the AS-AS interval (the time of occurrence of the atrial activity is contingent on when the ventricle is paced): suggestive of a PMT;
- prolongation of the PVARP for one cycle; the ensuing atrial activity falls within the PVARP and does not trigger an AV delay;
- termination of the tachycardia.
Other articles that may be of interest to you
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 MedtronicTM devices, for example, the duration of an automatic PVARP decreases with the increase in heart rate. For BiotronikTM 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.