ARCHITECTURE OF THE ATRIAL MUSCULATURE IN AND AROUND THE TRIANGLE OF KOCH - ITS POTENTIAL RELEVANCE TO ATRIOVENTRICULAR NODAL REENTRY

Introduction: Recent studies suggest that atrial fibers in the approac hes to the AV node form part of the dual pathways recognized electroph ysiologically in patients with AV nodal reentrant tachycardia (AVNRT). Our aim was to determine, by gross dissection, the arrangement of the superficial musculature in the area of the triangle of Koch in normal hearts and in hearts with documented AVNRT, hoping to ascertain anato mic features that might contribute to the debate, Methods and Results: We used blunt dissection to study the architecture of the superficial atrial musculature in 16 autopsied hearts from adults who died of non cardiac disease, A well-defined pattern of architecture of muscle fibe rs was found in the region of the triangle of Koch, showing marked var iations in 7 of the 16 specimens, The relationship of these fibers to the histologically specialized AV node was confirmed by histology in t hree cases, Two hearts from patients with known AVNRT, treated by abla tion in one, were examined further histologically. These sections show ed that the site of ablation was well distant from the histologically discrete AV node, Conclusion: The variability in the arrangement of th e superficial atrial muscle fibers in the area of the triangle of Koch may be one of the factors influencing the route for impulses entering the AV node, Lesions that ablate nodal reentry are within these atria l fibers rather than the histologically specialized AV node.