Device algorithms to terminate/prevent PMTs
Summary of devices
Abbott
PVC option
PMT intervention
Biotronik
PMT protection
PVARP after PVC/PMT prevention
Boston
PMT Termination
PVARP after PAC/PVC
Medtronic
PVC response
PMT intervention
Microport
Anti PMT protection
Palliative protection
Abbott
PVC response
Accessed from parameters; refractions and blanking; additional settings, PVC and PMT
•OFF (or)
•+PVARP on PVC/ A Pace on PVC
The pacemaker automatically extends the PVARP to 480 ms
PVARP consists of an absolute refractory period (PVAB) and a relative refractory period
If an intrinsic atrial event is sensed during the relative refractory portion of the PVARP, the device considers it a “valid atrial event” if a sensed ventricular event occurs within 280 ms of that atrial event
This extended PVARP is followed by a 330 ms alert period which can cause slower-than-base-rate pacing
PMT intervention
Accessed from parameters; refractions and blanking; additional settings, PVC and PMT
•PMT options off auto-detect 10-beat detection
•PMT detection rate (just below max UTR)
10 beat detection
•The pacemaker confirms a PMT when it detects 10 consecutive AS-VP events above the PMT detection rate
•The pacemaker responds on the 10th event by automatically extending the PVARP to 480 ms and then applying a 330 ms alert period immediately after the extended PVARP
•The idea is that the next P-wave will fall into the refractory period and not be sensed, so the pacemaker can resume AP-VP pacing at the base rate
Auto-Detect
•When the intrinsic atrial rate exceeds the programmable PMT detection rate, the Auto-Detect algorithm goes into effect
•It measures the VP-AS intervals for 8 cycles
•It averages those 8 values (interval average) and compares the interval average to each of the individual 8 cycles
•The concept: retrograde conduction suggesting a PMT is very stable (not erratic)
•If all of the VP-AS intervals are within 16 ms of the interval average, the pacemaker confirms PMT
•On the 9th cycle, the AP-VP will be lengthened or shortened
•The AP-VP interval is shortened if it is > 100 ms (31ms in older devices/50ms in newer)
•The AP-VP interval is lengthened if it is < 100 ms
Biotronik
PMT protection
Accessed from parameters; refractory period/blanking
•PMT Protection: On, off
•VA criterion: 250, 260, .... 350, ....490, 500
A pacemaker-mediated tachycardia is recognized by the detection algorithm when the following conditions are met:
•If eight consecutive Vp-As intervals are shorter than the programmed VA interval and
•If the average standard deviation for the eight VpAs intervals is within the tolerance limit of the PMT stability criterion, then the device automatically extends or shortens the AV delay by a defined value.
•If the resulting Vp-As interval remains constant, the PMT is considered as confirmed. The algorithm for terminating the PMT is automatically started.
PMT terminating algorithm involves the following sequence of events
•The PMT is terminated by extending PVARP by one pacing cycle.
•After ending a PMT, AUTO PVARP automatically extends the PVARP and the PVARP after PVC by 50 ms.
The limit for the PVARP extension is: Value of the VA criterion + 50 ms.
•After 5 days without sensing a PMT, the AUTO PVARP function automatically reduces the PVARP extension and the PVARP after PVC by 50 ms.
•Note: A safety interval of 300 ms protects against competitive pacing and prevents the atrial pulse from reaching refractory and/or vulnerable tissue. This safety interval cannot be programmed and is only active when the PMT function is active.
PVARP after PVC
Accessed from parameters; refractory/blanking
•PVARP after PVC: 400 (PVARP +150ms)
In the case of ventricular detection without previous atrial event (PVC) PVARP is extended for that beat
Boston Scientific
PMT Termination
Accessed from brady parameters; A-Tachy Response
•PMT Termination: On, off
A pacemaker-mediated tachycardia is recognized by the detection algorithm when the following conditions are met:
•16 successive ventricular paces at the MTR following AS events
•All V-A intervals are within 32ms of each other.
PVARP is extended to 500ms for one cardiac cycle attempting to break the PMT
PVARP after PVC/PAC
Accessed from brady parameters; refractory
•PVARP after PVC/PAC: off, 150-500 (50ms increments) 400
PVARP is extended upon detection of
•PVC
•PAC or
•if Ap is inhibited due to Atrial flutter response (?)
Medtronic
PVC response
Accessed from parameters; Additional Features; refractory/blanking
•PVC Response: On, off
After a VS is detected in the presence of no preceding AP or AS, it is classified as a PVC, and the corresponding PVARP to that VS is lengthened (400ms) so if there is a retrograde p is falls in refractory, and thus cannot be tracked
PMT intervention
Accessed from parameters; Additional Features; refractory/blanking
•PMT Intervention On, off
Device sees 8 sequences of ventricular pacing (VP) followed by atrial sensing (AS), each with a VP-AS interval of less than 400 ms
Device will extend PVARP to 400 ms on the 9th sequence for 1 cycle to interrupt the PMT (if there is one).
After the PVARP extension, the device suspends PMT detection for 90 seconds. This prevents unnecessary intervention in the presence of fast intrinsic atrial rates.
Microport
Anti PMT protection
Accessed from parameters; special features
•Anti PMT protection: termin reprogam
Termin:
•The pacemaker can identify these PMTs based on the stability of the VP interval (from ventricular paced beat to retrograde P wave). Once a PMT has been confirmed, the pacemaker lengthens the atrial refractory period in order to reduce the PMT.
Reprog:
•In the event of recurrent PMTs, the pacemaker permanently shortens the rest and exercise AV delays
Palliative protection
Non programmable
The pacemaker does not trigger an AV delay on a P wave detected within 500 ms following an asynchronous ventricular event (PVC)