Tissue-specific determinants of anisotropic conduction velocity in canine atrial and ventricular myocardium

Abstract

Electrical conduction is very rapid and highly anisotropic in atrial fiber bundles, such as the crista terminalis. In contrast to left ventricular myocardium in which the ratio of longitudinal to transverse conduction velocities is ≃3, propagation velocity in the crista terminalis is ≃10 times greater in the longitudinal than in the transverse direction. To elucidate potential determinants of these distinct conduction properties, we characterized structural and molecular features of intercellular coupling in the crista terminalis and left ventricular myocardium of the canine heart. Analysis of the number and spatial orientation of myocyte interconnections at gap junctions revealed that a typical left ventricular myocyte was connected to 11.3±2.2 other myocytes. Approximately equal numbers of connections occurred between ventricular myocytes juxtaposed in side-to-side and end-to- end orientation. In contrast, a typical myocyte of the crista terminalis was connected to only 6.4±1.7 other cells (P