VIP algorithm and risk of PMT

Tracing
N° 3
Manufacturer Abbott Device PM Field Pacing Modes
Patient
  • 72-year-old man
  • Assurity MRITM pacemaker (Abbott) for paroxysmal atrioventricular block
  • VIP algorithm
  • Recording of PMT episodes in the device memory
Graph and trace
  • Atrial sensing and ventricular pacing
  • VIP: the device extends the AV delay for one cycle (from 175 to 275 ms, VIP programming: 1 cycle, extension 100 ms)
  • The prolongation promotes retrograde atrial conduction which is sensed outside the refractory periods (classified as AS) and triggers an AV delay
  • PMT
  • After 8 VP-AS cycles with stable VP-AS intervals and rate higher than the programmed PMT rate limit (110 beats/minute), suspicion of PMT
  • Extension of the AV delay (from 195 to 245 ms) on 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)
  • 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
  • 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 be no dropped P waves during this search thus avoiding ventricular pauses that may be symptomatic or, in a few rare patients, favor the occurrence of ventricular arrhythmias
  • The search for intrinsic conduction is carried out only for rates below 110 bpm so as to reduce the risk of 2:1 block during exercise in a patient with complete atrioventricular block
  • The 2:1 block is dependent on the total atrial refractory period (AV delay + PVARP) which is substantially prolonged when searching for intrinsic conduction (very long AV delay)
  • Prolongation of the AV delay can favor the occurrence of retrograde conduction able to trigger a pacemaker-mediated tachycardia
  • 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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