VT on a PM owner

Trace category: 
EGM
Device/Field: 
PM
Company: 
Boston Scientific

70 years old man known for a ischaemic heart disease

First implantaiton of a PM Boston Ingenio in 2013 for sick sinus syndrome

He shows up after a syncope and a diagnosis of sustained VT requirring the delivery of an electric shock.

The memories of the device showed an episode of sustained: VT (V> A) 190 min¯¹

Interrogation of the device showed stable impedances, atrial sensing at 5mV /  ventricular at 10mV, atrial threshold at 0.8V / ventricular threshold at 0.5V.

What do you think about the mecanism of this arythmia???

What would you do???

Amazing tracing!

In short: this VT was probably induced by the PMT which was caused by the RYTHMIQ.algorithm. 

In the beginning of the EGM, RYTHMIQ (specifically AV SEARCH+) is attempting to switch back from DDD-mode to AAI-mode (with VVI-back-up). This is evident from the VS-Hys events; after the AP-Sr, a long AV-interval enables the search for intrinsic conduction. Unfortunately there is a PVC which occurs during the post-atrial pacing ventricular refractory period,  marked [VS]. Then, RYTHMIQ is waiting for an intrinsic event, which obviously won't occur because of the PVC, and the ventricle is paced after a long AV-interval. There is not only capture of the ventricule but there is also retrograde VA-conduction. Since the pacemaker is in DDD-mode, a PMT is initiated at maximal tracking rate. After 16X VP-MT (with stable VP-AS intervals) the device declares PMT (marked by PMT-B). The PVARP is extended for one beat to terminate the PMT but by coincidence, the PMT is terminated spontaneously. Because of the PMT (short), DDD-mode (long) and a new PVC (short), a short-long-short cycle exists which may be responsible for the VT.

PVC falling in the post-atrial pacing ventricular refractory period is in fact quite common. In our series of over 1000 RYTHMIQ episodes, we saw that 21% wer associated with this AP-[VS]-VP phenomenon  (PMID 26899544). Similarly, we showed that most cases of PMTs in patients with the RYTHMIQ algorithm activated, was associated with the RYTHMIQ algorithm. (PMID: 27199031). 

My advise is to disable the RYTHMIQ algorithm. In addition, do NOT forget to also switch off the AV Search+ algorithm otherwise the risk remains the same as every 32 beats, there is a prolongation of AV-interval.