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.
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.


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.
Koura
Takahiro
T
Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine, Tokyo, Japan.
Hara
Motoki
M
Takeuchi
Susumu
S
Ota
Kenichi
K
Okada
Yasumasa
Y
Miyoshi
Shunichiro
S
Watanabe
Atsushi
A
Shiraiwa
Kazumi
K
Mitamura
Hideo
H
Kodama
Itsuo
I
Ogawa
Satoshi
S
D000200:Action Potentials; D000375:Aging / Q000502:physiology*; D000818:Animals; D016880:Anisotropy; D016275:Atrial Function; D018780:Body Surface Potential Mapping / Q000379:methods; D002304:Cardiac Pacing, Artificial; D018031:Connexin 43 / Q000032:analysis / Q000276:immunology; D046508:Culture Techniques; D004285:Dogs; D004553:Electric Conductivity; D017629:Gap Junctions / Q000737:chemistry; D006325:Heart Atria / Q000737:chemistry / Q000166:cytology; D006327:Heart Block / Q000503:physiopathology; D007150:Immunohistochemistry; D007700:Kinetics; D008856:Microscopy, Fluorescence / Q000379:methods; D012680:Sensitivity and Specificity
D018031:Connexin 43