High-resolution fluorescent imaging in rabbit hearts demonstrates that fast pathway conduction during sinus rhythm results from a broad posterior wavefront rather than a distinct anterior input channel.
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Questions distinct anterior AV nodal input in sinus rhythm; leaves open relevance to human dual-pathway physiology.
INTRODUCTION: We sought to determine the precise pathways of engagement of the AV node during sinus rhythm. METHODS AND RESULTS: Langendorff-perfused rabbit hearts were stained with 20 microM of the voltage-sensitive dye di-4-ANEPPS. Preparations containing the right atrium, sinoatrial (SA) and AV nodes, and interatrial septum were subsequently dissected and mapped in vitro using a 16 X 16 photodiode array with an adjustable resolution of 150 to 750 microns per diode. 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 using the triangulation method. In all preparations, spontaneous activation began at the SA node, rapidly spread along the crista terminalis (CrT), entered the AV nodal region via the posterior "slow" pathway, and 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. Notably, there was no evidence for the presence of a distinct anterior entrance into the AV node. CONCLUSIONS: Fast pathway conduction during sinus rhythm results from a broad posterior wavefront that envelops the AV node with subsequent retrograde atrial septal activation.
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Efimov et al. (1997) studied this question.
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