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(Circulation. 2002;105:2092.)
© 2002 American Heart Association, Inc.

Basic Science Reports

Anisotropic Conduction Properties in Canine Atria Analyzed by High-Resolution Optical Mapping

Preferential Direction of Conduction Block Changes From Longitudinal to Transverse With Increasing Age

Takahiro Koura, MD; Motoki Hara, MD; Susumu Takeuchi, MD; Kenichi Ota, MD; Yasumasa Okada, MD; Shunichiro Miyoshi, MD; Atsushi Watanabe, DVM; Kazumi Shiraiwa, PhD; Hideo Mitamura, MD; Itsuo Kodama, MD; Satoshi Ogawa, MD

From the Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine (T.K., M.H., K.O., S.M., H.M., S.O.); the Department of Circulation, the Research Institute of Environmental Medicine, Nagoya University (S.T., I.K.); the Department of Medicine, Keio Tsukigase Rehabilitation Center (Y.O.); and the Institute for Life Science Research, Asahi Kasei Corporation (A.W., K.S.), Tokyo, Japan.

Correspondence to Motoki Hara, MD, Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. E-mail hara{at}cpnet.med.keio.ac.jp

Background— Anisotropic conduction properties may provide a substrate for reentrant arrhythmias. We investigated the age-dependent changes of structural and functional anisotropy in isolated right atria from infant (1 to 2 months), young (6 to 12 months), and old (6 to 10 years) dogs.

Methods and Results— The histology of the mapped atrial tissues (a small subepicardial area, 2.8x4.2 mm) was characterized by an age-dependent increase of myofiber width and fat cell infiltration between myofibers. Cx43 was distributed homogeneously over the entire cell surface in infant dogs, whereas it progressively polarized to the cell termini with increasing age. The activation sequences were analyzed by high-resolution optical mapping using a voltage-sensitive dye. Activation fronts from the pacing site proceeded more rapidly along fiber orientation (longitudinal) than across it (transverse). Infant dogs showed "elliptical" isochrones with a smooth transition between longitudinal and transverse propagation, whereas old dogs had a "square" pattern with a sharp transition. Conduction block occurred predominantly during longitudinal propagation in infant dogs but during transverse propagation in old dogs. The shape of the wave front and the degree of lateral uncoupling seemed to decide the preferential direction of block. A zigzag activation causing an extremely slow transverse conduction was observed only in old dogs.

Conclusions— Along with the age-dependent structural anisotropy, the preferential direction of block changed from longitudinal to transverse in association with a change in the wave front configuration. A zigzag propagation based on lateral uncoupling would predispose the elderly to multiple reentry and a higher incidence of atrial fibrillation.

Key Words: atrium • anisotropy • heart block • gap junctions

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