VIP and risk of PMT

Tracing
N° 13
Manufacturer Abbott Device PM Field Pacing Modes
Patient

72-year-old man implanted with an Assurity MRITM pacemaker for paroxysmal atrioventricular block; programming of the VIP algorithm; recording of PMT episodes in the device memory.

Graph and trace

Initially, the patient is paced in both the atrium and ventricle at the set rate response (sensor, SIR ratio); the device extends the AV delay for one cycle (from 195 to 297 ms, VIP programming: 1 cycle, extension of 100 ms); the prolongation promotes retrograde atrial conduction which is sensed outside the refractory periods (classified as AS) and triggers an AV delay; onset of a PMT; after 8 VP-AS cycles with VP-AS intervals and rate higher than the programmed PMT rate limit (110 beats/minute), suspicion of PMT by the device; extension of the AV delay of 50 ms (from 191 to 242 ms) one one cycle; on the next cycle, prolongation of the AS-AS cycle by approximately 40 ms, which demonstrates that the timing of atrial activity is contingent on the timing of ventricular pacing (in favor of a PMT relative to sinus tachycardia); the next atrial activity does not trigger an AV delay; atrial pacing 330 ms after the last AS cycle followed by ventricular pacing; termination of the tachycardia confirming the diagnosis of PMT.

Comments

As explained previously, when the VIP is programmed, the search for intrinsic conduction is based on an AV delay hysteresis with an extended AV delay, during 1 to 3 cycles, with a maximum value of 450 ms. There can therefore be no P waves blocked during this search thus avoiding ventricular pauses that may be symptomatic or, in a few rare patients, favor the occurrence of ventricular arrhythmias. When there is a permanent or paroxysmal atrioventricular conduction disorder, as in this patient, this search is ultimately unsuccessful with a subsequent return to the DDD mode at the programmed AV delay. One of the limitations of this option is that, in patients with impaired anterograde conduction but preserved retrograde conduction, prolongation of the AV delay can favor the occurrence of retrograde conduction able to trigger a pacemaker-mediated tachycardia without the need of other triggering factors (premature atrial or ventricular contraction, loss of atrial capture, etc). The number of PMTs can therefore be very significant when increasing the AV delay induces retrograde conduction. The simplest and most logical approach in the presence of a complete permanent atrioventricular block is not to program the VP-suppression algorithm. When the conduction disorder is paroxysmal and when preserving intrinsic conduction appears desirable, it is then essential to verify that the PVARP is appropriately programmed longer than the retrograde conduction time.

Message to remember

In patients with impaired anterograde atrioventricular conduction but preserved retrograde atrial conduction, it is advisable not to program the VIP so as not to increase the risk of PMT.

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