AV synchrony in lead-less Micra AV pacemaker: How does it sense Atria ?

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The Medtronic leadless Micra TPS pacemaker

In 2016, EP world saw a major breakthrough when Medtronic introduced leadless Micra TPS pacemaker. This device that looked like a small bullet, was implanted in the RV apex without the need for lead insertion and surgical pocket. It was real innovation but was not able to take off even after 4 years of marketing. The reason was simple. Though it was a smart device, it was a journey backward in time, as Micra TPS provided only non-physiological VVI pacing. (In the current era of multi-site and His bundle pacing)

Physiological pacing requires two are more leads.(Except single lead VDD, now obsolete AAI ) . Atria must be sensed for AV synchrony to happen. Atrial sensing is accomplished by

  1. A dedicated atrial lead as in AAI or DDD
  2. A floating atrial lead as in VDD mode

How does the leadless pacemaker attached to RV apex bring in AV synchrony without any add on leads ?

Medtronic, has come out with new add on to TPS ie “Micra AV” .The same gadget has been upgraded with a software to do atrial sensing. The accelerometer in the pacemaker senses the motion of the blood in early diastole followed by atrial contraction mediated S4 . This is sensed, and ventricular lead is set to fire after a programmed Interval.

Medtronic micr AV pacing 2

The initial experience appears promising. The results of the MARVEL study is published (Ref 1) However, there are important limitations. The atrial sensing function is not fully tested in real-life exertion. Further, It’s actually a form of mechanical sensing. The atrial electromechanical association has been taken for granted. The absence of electrical atrial sensing can mislead the ventricle. Currently, I guess it is a software patch that converts Micra TPS to AV . One more issue is, the soft ware consumes more energy and cut shorts the life of the pacemaker.

Reference

Clemens Steinwender, Surinder Kaur Khelae, Christophe Garweg Atrioventricular Synchronous Pacing Using a Leadless Ventricular Pacemaker Results From the MARVEL 2 Study JACC: Clinical Electrophysiology