Interatrial electrical connections: the precise location and preferential conduction.

The atria are assumed to be connected electrically to each other at the level of the Bachmann's bundle, coronary sinus (CS) musculature, and interatrial septum, and these connections may have an important role in the interatrial conduction and perpetuation of various types of atrial tachyarrhythmias. However, the number, location, and preferential connections of the interatrial conduction related to the site of activation have not been examined yet. The endocardium of both atria and the CS were mapped during continuous pacing from the left superior and inferior pulmonary veins, right pulmonary veins, upper and lower right atrium, or right atrial septum at various paced cycle lengths in 14 canines. The electrograms were recorded by custom-made form-fitted electrodes mounted on a specially designed device that allowed the septal aspects of the electrode forms to be spatially fixed to each other accurately. Four distinct interatrial electrical connections were identified at the Bachmann's bundle, CS, and antero-superior and postero-inferior septa. Decremental conduction was not seen in any of the connections. Bachmann's bundle was the most preferential connection during pacing from any epicardial site. The transseptal connections were evident only during pacing from the interatrial septum. The preference among the four connections was determined by the site of stimulation and the propagation of the activation related to the myocardial architecture. These unique preferential connections may play a significant role in the interatrial conduction and perpetuation of atrial tachyarrhythmias.