Implications of structure and geometry on cardiac electrical activity.

Electrical activity in the heart is dependent on the structure of the cellular components and their appositional geometry. The cells of the conduction system in mammals have a structure favoring faster conduction vis a vis the common working cells of the ventricles, which is further enhanced in large mammals and, significantly, in birds by an increase in cell diameters and tight packing of the component cells into large bundles. Tight packing also generates very narrow intracellular clefts that because of accumulation and depletion phenomena may contribute significantly to the measured electrical activity. Conduction cells may exist in mammalian atria analogous to their presence in bird atria, their electrical activity being possibly influenced by their diffuse anatomical integration with the common atrial working cells. Cell and bundle connections appear to be frequent within one length constant.