Fig. 1.

Identification of the atrial pacemaker complex. (a) Photograph of a typical SA nodal preparation as viewed from the endocardium with relevant structures labeled. (b) Typical atrial activation map of normal sinus rhythm from the same SAN preparation as shown in panel A. The white ellipsoid represents the area of earliest activation of the atria. (c) Typical histology slide of the SAN with its approximate borders outlined by the dotted black line. (d) Typical immunofluorescent slide of the SAN with its approximate border outlined by the dotted white line. Connexin 43 is absent within the borders of the SAN. Abbreviations: SAN, sinoatrial node; SVC, superior vena cava; IVC, inferior vena cava; RAA, right atrial appendage; IAS, interatrial septum; Cx43, connexin 43. Modified and reproduced with permission from Fedorov, et al. Structural and functional evidence for discrete exit pathways that connect the canine sinoatrial node and atria. Circ Res. 104(7), 915-923 (2009).