Background: Inter-atrial conduction disturbance is associated with the presence of atrial fibrillation (AF), although little is known about the anatomy of the inter-atrial connections.
Methods and results: Twenty-seven hearts from in-hospital deaths were examined and stratified in two groups with regard to their history of AF. Measurements of atrial weight were performed after excising the atria at the level of the atrioventricular valve plane and separation from the inter-atrial septum (IAS). In addition, in 15 of 27 hearts (seven AF, eight non-AF) the IAS was sliced into 10 microm thick parallel histological sections at intervals of 1 mm starting at the valve plane and ending at the atrial roof. The sections were stained with van Gieson's stain. The variable morphology of the anterior and posterior inter-atrial connective muscle bundles is described. The total number of inter-atrial connections varied from 1 to 5. The anterior route (Bachmann's bundle) was not found in seven of 15 specimens.
Conclusion: Inter-atrial connections are characterized by substantial variability in morphology and in the distribution of bundles. This may account for part of the variable susceptibility to AF.