EFFECT OF A PERFUSING BATH ON THE RATE OF RISE OF AN ACTION-POTENTIALPROPAGATING THROUGH A SLAB OF CARDIAC TISSUE

Experiments show that the rate of rise of the action potential depends on the direction of propagation in cardiac tissue. Two interpretation s of these experiments have been presented: (i) the data are evidence of discrete propagation in cardiac tissue, and (ii) the data are an ef fect of the perfusing bath. In this paper we present a mathematical mo del that supports the second interpretation. We use the bidomain model to simulate action potential propagation through a slab of cardiac ti ssue perfused by a bath. We assume an intracellular potential distribu tion and solve the bidomain equations analytically for the transmembra ne and extracellular potentials. The key assumption in our model is th at the intracellular potential is independent of depth within the tiss ue. This assumption ensures that all three boundary conditions at the surface of a bidomain are satisfied simultaneously. One advantage of t his model over previous numerical calculations is that we obtain an an alytical solution for the transmembrane potential. The model predicts that the bath reduces the rate of rise of the transmembrane action pot ential at the tissue surface, and that this reduction depends on the d irection of propagation. The model is consistent with the hypothesis t hat the perfusing bath causes the observed dependence of the action-po tential rate of rise on the direction of propagation, and that this de pendence has nothing to do with discrete properties of cardiac tissue.