Patients with atrioventricular (AV) block and sinus rhythm now have a leadless alternative to traditional pacemakers. In the recently completed MARVEL 2 (Micro Atrial tRacking using a Ventricular accELerometer 2) trial, the new Micra AV VDD pacemaker has demonstrated significant efficacy for this population.
This new device joins the original Micra AV leadless pacemaker introduced in 2016 for those who need a single-chamber ventricular pacemaker due to permanent atrial fibrillation (AF) or occasional dropped beats that create a syncope risk.
Christopher Ellis, M.D., cardiac electrophysiologist at Vanderbilt University Medical Center, has implanted several of the new devices in patients who previously would have required a two-lead pacemaker. Ellis has been a member of the Medtronic advisory group since its inception in 2012.
“The Micra AV will catch on fairly quickly, as the first Micra did,” Ellis said. “Not only do patients avoid the leads, but they can also avoid a hospital stay. We put it in through catheterization and can send the patient home potentially within four hours.”
“Not only do patients avoid the leads, but they can also avoid a hospital stay. We put it in through catheterization and can send the patient home potentially within four hours.”
The Reprogrammed Micra AV
The new model essentially constitutes a reprogramming of the older VVIR device to make it function as a VDD device (AV synchronizer). “It’s a bullet with tines and little hooks that is implanted in the right ventricle, just like the original Micra device. It just has a different chip inside with a different algorithm and improved sensor,” Ellis said.
The device’s sensor is a piezoelectric crystal that vibrates with the contraction of the right atrium, interpreting how fast and how hard the heart is beating and detects the small surge of blood that comes when the atrium contracts. “It picks up just a little wiggle, a little auditory signal from the atrium contracting, and it ignores a bunch of other signals as ventricular contractions or ‘noise’,” Ellis said.
This MARVEL 2 algorithm also enables mode switching to VVI-40 and VVIR pacing to accommodate changes in patient rhythm and activity level. It automatically checks for intrinsic AV conduction, avoiding unnecessary pacing that can lead to cardiomyopathy and shorten battery life.
The MARVEL 2 Study
In the MARVEL 2 trial, 40 patients with normal sinus rhythm and complete AV block were evaluated after Micra AV VDD device implantation. In 38 patients, the AV synchrony rate was at or above 70 percent during algorithm-mediated VDD pacing, whereas none of the 40 patients had greater than 70 percent AV synchrony during VVI-50 pacing. Among all 40 patients, the algorithm demonstrated AV synchrony ranging from 69.8 percent (while standing) to 89.2 percent (at rest).
The study also reported that the average sinus rate fell from 73 beats per minute with VVI-50 pacing to 66.2 beats per minute with VDD pacing and that ventricular performance (as assessed by left ventricular outflow tract velocity time interval (LVOT VTI)) improved by about nine percent. All patients met the primary safety endpoint of no ventricular pauses lasting more than two cardiac cycles and no instances of oversensing-induced tachycardia for more than three minutes.
Expanding the Field of Candidates
One in eight patients implanted with a traditional pacemaker experiences a complication, but the Micra AV demonstrates a 60 percent reduction in these complications. New advances in Micra AV are pushing leadless implantables further along the continuum of pacemaker candidates.
“The Micra AV covers patients in permanent afib or at intermittent syncope risk and now, additionally, patients with AV block who are in sinus rhythm,” Ellis said. “Shortly, Medtronic will also have an atrial Micra device for patients who only need to pace the top chamber of the heart, typically needed by older patients who have age-related sinus node dysfunction.”
That still leaves a subpopulation who needs pacing due to heart failure without a wireless option. These patients require a three-lead biventricular device for cardiac resynchronization.
“Switching to a leadless pacemaker is so much cleaner and eliminates the long-term risk of abandoned wires in the heart.”
Ellis expects that certain patients will increasingly opt to have their old pacemakers replaced with a Micra AV, often when their battery is scheduled for replacement. “If you are in a center with an experienced lead extraction program, switching to a leadless pacemaker is so much cleaner and eliminates the long-term risk of abandoned wires in the heart,” Ellis said.
