HIGH-RESOLUTION FLUORESCENT IMAGING DOES NOT REVEAL A DISTINCT ATRIOVENTRICULAR NODAL ANTERIOR INPUT CHANNEL (FAST PATHWAY) IN THE RABBIT HEART DURING SINUS RHYTHM

Fluorescent Imaging of AVN. Introduction: We sought to determine the p recise pathways of engagement of the AV node during sinus rhythm, Meth ods and Results: Langendorff-perfused rabbit hearts were stained with 20 mu M of the voltage-sensitive dye di-4-ANEPPS. Preparations contain ing the right atrium, sinoatrial (SA) and AV nodes, and interatrial se ptum were subsequently dissected and mapped in vitro using a 16 x 16 p hotodiode array with an adjustable resolution of 150 to 750 mu m per d iode, Motion artifacts were eliminated by using 15 mM 2,3-butanedione monoxime (BDM), Activation time-points were defined as (-dF/dt)(max), where F = fluorescence, Isochronal maps of activation were plotted usi ng the triangulation method, In all preparations, spontaneous activati on began at the SA node, rapidly spread along the crista terminalis (C rT), entered the AV nodal region via the posterior ''slow'' pathway, a nd retrogradely spread to the septal region with a smaller conduction velocity compared to that along the CrT, Collision of anterograde and retrograde wavefronts was frequently observed in the mid-septum. Notab ly, there was no evidence for the presence of a distinct anterior entr ance into the AV node, Conclusion: Fast pathway conduction during sinu s rhythm results from a broad posterior wavefront that envelops the AV node with subsequent retrograde atrial septal activation.