Anatomic, histologic, and mechanical features of the right atrium: implications for leadless atrial pacemaker implantation

Figure 1. Endocardial right atrial anatomical relations: (A) diagram of right atrial appendage from an right anterior oblique (RAO) perspective. (B) Representative specimen of the RA demonstrating the CT [large (blue) dots] and its bifurcation with the SB [small (red) dots]. (C) Representative specimen of the RAA viewed in left anterior oblique (LAO). (D) Histological section through the RAA showing the thin wall (arrows) between pectinate muscles. BB, Bachmann’s bundle; CT, crista terminalis; L, posterolateral recess; LA, left atrium; M, anteromedial recess; PM, pectinate muscles; RAA, right atrial appendage; SB, sagittal bundle, SVC, superior vena cava. (D and C) reproduced with permission.8 CS, coronary sinus; CT, crista terminalis; IVC, inferior vena cava; RAA, right atrial appendage; SB, sagittal bundle; SVC, superior vena cava; TV, tricuspid valve.

Figure 2. Epicardial right atrial anatomical relationships: anterior view of the heart demonstrating the right atrial appendage (RAA) and its relationship to the aorta and right ventricular outflow tract (RVOT). The RAA is divided into a posterolateral (PL) and anteromedial (AM) recess by the sagittal bundle [samll (red) dots] and the crista terminalis [large (blue) dots]. The epicardial fat pad overlying the RVOT and RCA can be seen just below the AM. RCA, right coronary artery.

Figure 3. Cardiac MRI dimensions analysed. Representative MRI images demonstrating the measurements taken and the resultant mean measurement; (A) two-chamber view. (B) Four-chamber view. Measurements noted: A—RAA ostium, B—RAA depth to CT, C—RAA depth to mid-point of RAA ostium, D—CT to lateral TVA, E—RA diameter (2Ch view) perpendicular to TV annulus, F—RA diameter (2Ch view) perpendicular to RAA ostium, G—TVA diameter (2Ch view). BSA, body surface area; CT, crista terminalis; MRI, magnetic resonance imaging; RA, right atrium; RAA, right atrial appendage; TVA, tricuspid valve annulus.

Figure 4. 3D collision analysis: representative images from four patients of the collision analysis from 3D modelling in a right lateral (top) and superior (bottom) view demonstrating the incidence of collision of the virtual device implant throughout the cardiac cycle. A 0% incidence of contact throughout the cardiac cycle is represented in blue with a continuous scale to 100% contact throughout the cardiac cycle in dark red. (The three suggested implant locations for an atrial leadless pacemaker in this collision model are shown in supplementary material online, Figure S2.) IVC, inferior vena cava; RAA, right atrial appendage; SVC, superior vena cava; TV, tricuspid valve.