A sensitivity study of the safety factor for conduction in the myocardium

The safety factor (SF) is an indicator of the safeness of electrical conduction in the myocardium. In the present work, we have studied the sensitivity of the SF defined by Shaw and Rudy to the integration interval (II) using computer simulations, and then defined and evaluated a new and simplified method to calculate SF (SF_m). Our results reveal that the sensitivity of the SF to the II is negligible outside the depolarization phase, delimited by the instant when membrane potential derivative (dV/dt) reaches 1% of its maximum (t_1%) and the instant when membrane potential is maximum ( t_Vmax ), so we have computed the SF considering this II. Our SF_m shows a desirable behaviour as a) it drops below unity when propagation failure occurs and b) the SF_m registered during normoxia decreases when membrane excitability is reduced, and increases when high cell uncoupling is forced. This computational simplification could facilitate the use of the SF in heterogeneous 2D and 3D tissues