Conduction through a Narrow Isthmus in Isolated Canine Atrial Tissue

Isolated blocks of dog atrial tissue were dissected to provide a narrow isthmus connecting two broader areas. Unidirectional block was readily demonstrable at the junctions of the narrow band with the larger areas. Transmembrane action potentials just proximal to the blocked junction were abbreviated, while only local electronic potentials were recorded beyond. Acetylcholine restored 1:1 propagation in blocked preparations. The model may explain some of the features of intermittent preexcitation.