Atrial Excitation Sequence during Ectopic Atrial Beats in the Rabbit

The propagation process of the atrial excitation was investigated during ectopic atrial rhythms evoked by electrical pacing through stimulation at several sites in 35 isolated rabbit atria using intracellular microelectrodes. Excitation sequences was correlated with the atrial deflections in a distant bipolar electrogram representing a cranio-caudal atrial activation. The conduction velocity was faster along the crista terminalis but slower across the coronary sinus ostium than in the ordinary atrial muscle. These differences in conduction velocity resulted in the upward artial deflection on the distant bipolar electrogram in the rhythm which was produced by stimulation at the right side of the lower interatrial septum. On a function as a preferential conduction pathway in the case of left to right direction of excitation, as in left atrial rhythm. On stimulation of the postero-inferior region of the left atrium, the region around the coronary sinus ostium was the first area in the right atrium to be activated. Inversely, the impulse originating from the coronary sinus ostium wasconducted relatively fast to the postero-inferior region of the left atrium. These findings suggested that there might be a preferential conduction pathway along the coronary sinus vein or its neighbouring tissues.