A spatial scale factor for electrophysiological models of myocardium

In the United States among males 20-64 years old about 1/3 of deaths are classified as 'sudden cardiac death', and 1/4 had no forewarning, nor did autopsy turn up any visible cause. The heart just switches from its normally periodic pumping to an alternative mode called 'fibrillation' more resembling electrical turbulence. In normal tissue its mechanism is a geometrically re-entrant mode of normal propagation. Everything about this spatial pattern depends upon the magnitude of 'D', the one term with dimension involving space in the pertinent biophysical equations. Explicit or implicit estimates in current literature span orders of magnitude. In this article I argue from a diversity of recent experiments for a narrower range of realistic values. It has an important role in the spatio-temporal evolution of fibrillation and in defibrillation.