New Conduction Pathways from the Left Atrium to the Right Atrium and to the Ventricle Along the Anterior and Posterior Portions of the Left A-V Ring

By employing electrographic electrodes, suction electrodes and microelectrodes, 2 conduction pathways were discovered in the anteromedial portion and in the posteromedial portion along the AV ring at the lower margin of the left atrium in the isolated rabbit heart. They were found to conduct the left atrial impulses to the right atrium and separately through the AV node to the ventricle. The one in the posteromedial portion was found to be different from the inferior interatrial pathway reported recently by Scherlag et al. Histological examination after functional studies revealed that each pathway was embedded in the fibrofatty tissues at the site of the attachment of the mitral valve to the left atrium. The anterior pathway encircled the anterior portion of the mitral ring and entered the anterosuperior portion of the AV node. The posterior pathway encircled the posterior portion of the mitral ring and entered the posteroinferior portion of the AV node. They can be regarded as interatrial pathways and in a sense as accessory AV conduction pathways from the left atrium.