New generation of LCPM and left atrial strain: a promising predictor of atrio-ventricular synchrony in leadless pacemaker pacing
Authors: Troisi F , Caccavo V P , Guida P , Vitulano N , Quadrini F , Di Monaco A , Sgarra L , Grimaldi M 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Introduction
Leadless cardiac pacemakers (LCPMs) are a new alternative to traditional transvenous pacemaker. They recently have evolved from a single chamber VVI-R pacemaker to devices that can provide atrio-ventricular synchrony (AVS) in patient with sinus rhythm through an 3-axis accelerometer, detecting atrial contractions. To date, Micra AV Transcatheter Pacing System (Medtronic) is the only LCPM on the market that provides AVS.

Purpose
Many efforts have been made to identify clinical predictors of a good A4 signal amplitude, that determines the ability of the Micra-AV to pace while maintaining AVS (1). Our exploratory study investigates the utility of Left Atrial strain (LAs) for this purpose.

Methods
Data was extracted from the Cardiac Interventional Registry implemented at our hospital and approved by local ethic committee. Six patients, implanted with Micra-AV (72±13 years), underwent to a complete echocardiography focused on left atrium (LA). Morphological (LA diameters, 2d LA volume and 2d LA area) and functional (EA ratio and LAs study) parameters were assessed. An echocardiography core laboratory studied LAs (Figure A), using a dedicated software (Philips, Epiq 7-Auto Strain Tomtec Application): LA Reservoir Strain (LAsr), LA Conduit Strain (LAscd) and LA Contraction Strain (LAsct) were measured (2). All patients after implantation had a complete electronic control of leadless pacemaker to assess A4 wave amplitude.

Results
We found that A4 wave amplitude was inversely correlated to 2D-LA volume (Spearman's coefficient rho=-0.96; p=0.003), while it was positively related to LAsr (rho=0.81; p=0.05) and LAsct absolute value (Figure B). In the last years, in addition to the traditional echocardiographic parameters, LA was studied with a new functional parameter, LAs (3). The MARVEL2 study showed that A4 amplitude is fundamental to ensure a high AVS percentage; it was directly related to a parameter defined generically "atrial strain" (4). It is known that LAs is a complex parameter that indicates how the left atrium works overall. Today, thanks to the technological developments of the new echocardiographic software, it can be evaluated more precisely in its components. According to our preliminary data the components that predict A4 amplitude are specifically LAsr and LAsct: we found higher value of A4 in patients that have grater absolute value of these LAs parameters. LAsr is related to the atrial filling and depends on atrial stiffness and fibrosis, LAsct is an indicator of LA ability to empty, thus contributing to the final stage of ventricular diastolic filling. These are simple measurable parameters of LA functional capacity and they seem capable of predicting the possibility of a good AVS in LCPM pacing.

Conclusion
Patient selection is crucial to obtain good clinical outcomes. In this context, echocardiographic parameters and particularly the LAs study look promising to make a correct choice.