Effects of anodal cardiac stimulation on Vm and Cai2+ distributions: a bidomain study

The aim of this work is to study make and break excitation mechanisms elicited by anodal pulses at different coupling intervals using 2D and 3D anisotropic Bidomain simulations. Two different S1-S2 stimulation protocols are considered, one with the S2 pulse delivered at the same location of the S1 pulse and the other at a distant location. Anodal strength-interval (S-I) curves are computed for both S1-S2 protocols showing results consistent with experimental S-I curves, both in terms of stimulus threshold amplitude and depth of the anodal dip during the break phase. The intracellular calcium concentration (Cai2+) distribution presents virtual electrode patterns similar to the transmembrane potential ( Vm) distribution. Cai2+ displays a weak negative change within the virtual anode area, while a strong positive change is observed within the virtual cathode areas. The results show that with both S1-S2 protocols Vm and Cai2+ exhibit the same make and break excitation mechanisms, but with a delayed Cai2+ response.