PMT Intervention Feature
A pacemaker mediated tachycardia (PMT) may result in ventricular pacing at the Upper Tracking Rate when retrograde P waves (due to the loss of AV synchrony) are sensed and tracked in an atrial tracking mode. PMT Intervention provides an automatic way to detect and interrupt a pacemaker defined PMT. If PMT Intervention is successful, physiologic tracking of the sinus node will resume.
PMT is nominally programmed Off and it operates in atrial tracking modes DDD, DDDR, VDD, and VDDR.
To program this feature in pacemakers, go to Params -> Additional Features.
To program this feature in ICDs, go to Pacing -> Params -> Additional Features.
Programming for pacemakers (excluding Azure™ DR MRI, Advisa DR™ MRI, Revo MRI™ and EnRhythm™)
Programming for other pacemakers, ICDs, and select CRT-P devices
A PMT may occur when retrograde P waves (caused by a loss of AV synchrony) are sensed and tracked. This can only occur in an atrial tracking mode (DDD, DDDR, VDD, VDDR in most devices). The PMT Intervention feature provides an automatic way for the device to detect and interrupt pacemaker-defined PMTs.
Detection Phase: When PMT Intervention is programmed On, the device monitors for a PMT when eight consecutive V-A intervals are detected that meet the following conditions:
- Duration less than 400 milliseconds (ms)
- Start with ventricular paced event
- End with atrial sensed event
If a pacemaker-defined PMT is detected, the PVARP will be forced to 400 ms for one cycle after the ninth paced ventricular event. The next atrial event should fall within the 400 ms PVARP becoming an atrial refractory (AR) event (refractory events are not tracked by the ventricle).
PMT Enhancement with the Azure DR Pacemakers, Percepta™, Serena™, Solera™ CRT-P devices
Confirmation Phase: In these devices a confirmation check before extending PVARP is added. The device temporarily extends the SAV interval by 50 ms for 1 beat and evaluates changes in the VP-AS interval. The check is performed three times if necessary. If the VP-AS interval remains consistent, the device will confirm PMT and intervene by extending PVARP to 400 ms for one pacing cycle.
Note that once a PMT Intervention occurs, this feature is automatically suspended for a period of time until PMT monitoring resumes. (The time period is 85 seconds for Azure DR, Percepta/Serena/Solara CRT-P, and 90 seconds for all other devices.)
The diagram below summarizes PMT Intervention. The pacemaker is tracking retrograde P-waves, which can be seen in the beginning of the strip. PMT Intervention extends the PVARP after the ninth beat to mask the retrograde P-wave, which breaks the PMT.
PMT Intervention Illustrating the Addition of a Confirmation Interval
In the example above, after initial detection, the confirmation check begins. The SAV interval is extended by 50 ms for 1 beat and the VP-AS interval is evaluated for change. This confirmation check occurs 3 times, looking for consistent VP-AS intervals before confirming PMT and the PVARP extension.
Sources: Medtronic Azure™/Astra™ Reference Manual; Medtronic Adapta™/Versa™/Sensia™ Reference Guide; Medtronic Consulta™ CRT-P Clinician Manual;Medtronic Protecta™ XT DR Clinician Manual; Medtronic Protecta™ XT CRT-D Clinician Manual.