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(Circulation. 2004;109:1172-1179.)
© 2004 American Heart Association, Inc.

Basic Science Reports

Three-Dimensional Reconstruction of the Rabbit Atrioventricular Conduction Axis by Combining Histological, Desmin, and Connexin Mapping Data

Yu-Shien Ko, MD, PhD; Hung-I Yeh, MD, PhD; Yu-Lin Ko, MD, PhD; Yu-Chun Hsu, MFA; Chin-Fen Chen, BS; Semon Wu, MS; Ying-Shiung Lee, MD; Nicholas J. Severs, PhD, DSc

From the First Cardiovascular Division (Y.-S.K., Y.-L.K., C.-F.C., S.W., Y.-S.L.), Chang Gung Memorial Hospital; Department of Industrial Design (Y.-C.H.), Chang Gung University, and Department of Internal Medicine (H.-I.Y.), Mackay Memorial Hospital, Mackay Junior College of Nursing, and Taipei Medical University, Taipei, Taiwan, Republic of China; and National Heart and Lung Institute (N.J.S), Imperial College, London, England.

Correspondence to Yu-Shien Ko, MD, PhD, First Cardiovascular Division, Chang Gung Memorial Hospital, Tung-Hwa North Road, Taipei, Taiwan, Republic of China. E-mail c12037{at}adm.cgmh.org.tw

Received May 23, 2003; de novo received August 12, 2003; revision received October 24, 2003; accepted October 28, 2003.

Background— The 3D structure of the atrioventricular conduction axis incorporating detailed cellular and molecular composition, especially that relating to gap-junctional proteins, is still unclear, impeding mechanistic understanding of cardiac rhythmic disorders.

Methods and Results— A 3D model of the rabbit atrioventricular conduction axis was reconstructed by combining histological and immunofluorescence staining on serial sections. The exact cellular boundaries, especially those between transitional cells and atrial myocardium, were demarcated by a dense and irregular desmin-labeling pattern in conductive myocardium. The model demonstrates that the atrioventricular conduction axis is segregated into 2 connecting compartments, 1 predominantly expressing connexin45 (compact node and transitional cells) and the other predominantly coexpressing connexin43 and connexin45 (His bundle, lower nodal cells, and posterior nodal extension). The transitional zone shows unique features of spatial complexity, including a bridging bilayer structure (a deep transitional zone connecting with a superficial atrial-transitional overlay) and asymmetrical continuity (wider atrial-transitional interfaces and shorter atrial-axial distances in the hisian portion than in the ostial portion). In the latter compartment, the His bundle, lower nodal cells, and posterior nodal extension form a continual axis and longitudinal transitional-axial interface.

Conclusions— Key findings of the present study are the demonstration of a distinct anatomical border between transitional and atrial cells, connection between transitional cells and both lower nodal cells and posterior nodal extension, and distinctive connexin expression patterns in different compartments of the rabbit atrioventricular conduction axis. These features, synthesized in a novel 3D model, provide a structural framework for the interpretation of nodal function.

Key Words: myocardium • immunohistochemistry • atrioventricular node • conduction

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