Log in to MyACC
AV Synchronous Pacing Using a Leadless Ventricular Pacemaker
Study Questions:
How well does an automated, accelerometer-based algorithm facilitate atrioventricular (AV) synchronous pacing in a leadless ventricular pacemaker?
Methods:
MARVEL 2 (Micra Atrial tRacking using a Ventricular accELerometer 2) was an international multicenter study of 75 patients with a Micra (Medtronic) leadless pacemaker in the right ventricle. Patients had to have recently or newly implanted Micras and history of AV block. The automated algorithm was temporarily (for approximately 5 hours) downloaded into the Micra. A specialized Holter monitor recorded pertinent data. Once programmed to VDD (pacing in the ventricle [V], sensing by the atrium [A] and V, response to sensing by A and V), the patient was assessed in a series of positions: supine/sitting, lying on bilateral sides, standing, and then assessed while walking. The primary efficacy endpoint was a paced or sensed V event within 300 msec of an A event ≥70% of the time. The primary safety endpoint was freedom from both pauses and oversensing-induced heart rates over 100 bpm. As a secondary endpoint, the left ventricular outflow tract velocity-time interval (LVOT-VTI) was obtained at baseline and during VDD pacing.
Results:
The primary efficacy analysis focused on the 40 patients with sinus rhythm and complete AV block. No patients had AV synchrony with VVI pacing; with VDD pacing (via algorithm), 38 (95%) patients had ≥70% AV synchrony. The mean observed AV synchrony (due to intermittent intrinsic AV conduction) increased from 26.8% (VVI) to 89.2% (VDD). AV synchrony was best at rest and decreased the most when patients were standing (69.8%) and walking (72.7%). LVOT-VTI increased 9% with VDD pacing. All 75 patients met the primary safety endpoint.
Conclusions:
A leadless ventricular pacemaker programmed with an algorithm featuring accelerometer–based atrial sensing significantly improved AV synchrony and stroke volume in patients with sinus rhythm and complete AV block.
Perspective:
This study follows the MARVEL study and another feasibility study demonstrating that the 3-axis accelerometer within the Micra can detect passive ventricular filling and atrial contraction and thereby promote AV synchrony. Enhancements in signal filtering, automatic threshold adjustments, and mode switching were incorporated into the algorithm in MARVEL 2.
Limitations: Because the algorithm was transiently programmed, we do not have long-term data on endpoints and symptoms. For example, AV synchrony could further decrease with time in the most active patients due to motion artifact and/or fusion of signals; indeed, battery drain was given as one reason why programming was limited. We also do not have data comparing the leadless pacemaker programmed VDD with transvenous pacemakers. And the current Micras, even with the new algorithm, do not address chronotropic incompetence from sinus node dysfunction.
The ability to avoid pocket and lead-related complications is a major draw for implanting a Micra. However, at present, Micras are typically chosen for patients in whom AV synchrony is not paramount, such as those with permanent atrial fibrillation or infrequent need for pacing. The ability to reliably pace with AV synchrony as demonstrated in MARVEL 2 is a welcomed advancement that will expand the utilization of this novel technology.
Clinical Topics: Arrhythmias and Clinical EP, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias
Keywords: Arrhythmias, Cardiac, Accelerometry, Atrial Fibrillation, Atrioventricular Block, Electrocardiography, Ambulatory, Pacemaker, Artificial, Sick Sinus Syndrome, Stroke Volume
< Back to Listings
