Timing Cycles of Implantable Devices

Complex pacemaker troubleshooting: A syntactic plus semantic approach

“…However, the algorithm will decipher this instead as PVC if the As–Vs interval is less than 80 ms (Medtronic algorithm). Based on the PVC response algorithm, the modified atrial‐based timing of this Medtronic pacemaker is expected to switch from atrial‐based timing (LRI: As–Ap or Ap–Ap) to a ventricular‐based timing predicated on ventriculo atrial escape interval (VAEI) 2 . The calculated VAEI here is 600 ms (LRI of 850 ms—sensed AV delay of 250 ms).…”

“…Based on the PVC response algorithm, the modified atrial-based timing of this Medtronic pacemaker is expected to switch from atrial-based timing (LRI: As-Ap or Ap-Ap) to a ventricular-based timing predicated on ventriculo atrial escape interval (VAEI). 2 The calculated VAEI here is 600 ms (LRI of 850 ms-sensed AV delay of 250 ms). Assuming that the PVC response is triggered within the first 80 ms following an As, this elegantly explains the premature forced atrial pacing (As-Ap of around 670 ms) faster than the LRI (850 ms).…”

Pacemaker-induced tachycardia in a DDI-programmed ICD: What is the mechanism?

“…Whereas managed ventricular pacing and DDD pacing modes rely on modified atrial-based algorithms, DDI pacing mode uses ventricular-based timing cycles. 1 Hence, the cycle length between 2 atrial paced events is dictated not on the A-A interval but on the V-A interval. This feature is illustrated in Figure 1 .…”

“…DDI is a ventricular-based pacing mode and the cycle length between 2 atrially paced events is dictated by the V-A interval. 1 With greater emphasis on minimizing right ventricular pacing, the programmed paced AV delay is often lengthened, thus resulting in a shorter V-A interval. When intrinsic conduction times through the AV node are faster than the programmed paced AV delay, the lower rate of pacing (ie, cycle length between 2 AP events) is necessarily faster than what is programmed.…”

Atypical Initiation of Endless‐Loop, Pacemaker‐Mediated Tachycardia

“…PMT was initiated following the 6 th QRS complex of Figure 1. Variability in the AV delay of the first six complexes resulted from the programmable Dynamic AV Delay feature that assigned a paced AV delay for each beat based on the interval between sensed atrial events (AA interval) that immediately preceded the current beat 1,2 . A programmable maximum‐paced AV delay was assigned to AA intervals equal to the lower rate limit (LRL) interval, and a programmable minimum value was assigned to AA intervals equal to the upper rate limit (URL) interval (Fig.…”