Averaging over depth during optical mapping of electroporation

During defibrillation, strong electric shocks applied to the heart can cause electroporation: the formation of large, nonselective pores in the cell membrane. Experiments using optical mapping indicate that electroporation occurs in cardiac tissue when the transmembrane potential, V/sub m/, is significantly less than /spl plusmn/400 mV. Our hypothesis, which we test by numerical simulation, is that V/sub m/ is greater than /spl plusmn/400 mV at the tissue surface, but optical mapping underestimates V/sub m/ because it averages over depth.