Anatomic, Histologic and Mechanical Features of the Right Atrium: Implications for Leadless Atrial Pacemaker Implantation.

BACKGROUND: Leadless pacemakers (LP) may mitigate the risk of lead failure and pocket infection related to conventional transvenous pacemakers. Atrial LP are currently being investigated. However, the optimal and safest implant site is not known.

OBJECTIVES: We aimed to evaluate the right atrial (RA) anatomy and the adjacent structures using complementary analytic models (gross anatomy, cardiac MRI, and computer simulation), to identify the optimal safest location to implant an atrial LP human.

METHODS: Wall thickness and anatomic relationships of the RA was studied in 45 formalin-preserved human hearts. In-vivo RA anatomy was assessed in 100 cardiac MRI scans. Finally, 3D collision modelling was undertaken assessing for mechanical device interaction.

RESULTS: Three potential locations for an atrial LP were identified; the right atrial appendage (RAA) base, apex and RA lateral wall. The RAA base had a wall thickness of 2.7 ± 1.6 mm, with a low incidence of collision in virtual implants. The anteromedial recess of the RAA apex had a wall thickness of only 1.3 ± 0.4 mm and minimal interaction in the collision modelling. The RA lateral wall thickness was 2.6 ± 0.9 mm, but is in close proximity to the phrenic nerve and sinoatrial artery.

CONCLUSIONS: Based on anatomical review and 3D modelling the best compromise for an atrial LP implantation may be the RAA base (low incidence of collision, relatively thick myocardial tissue and without proximity to relevant epicardial structures); the anteromedial recess of the RAA apex and lateral wall are alternate sites. The mid-RAA, RA/SVC junction and septum appear to be sub-optimal fixation locations.