Modeling fibroblast-mediated conduction in the ventricle

This study used a model of a cardiac muscle fiber composed of myocytes (M) and a centrally located insert of fibroblasts (F). Myocytes were represented with the Luo-Rudy model with physical dimensions of cultured neonatal mouse cardiac myocytes. Fibroblasts were represented as passive cells with negligible transmembrane currents. Gap functional conductance values were set to 15, 4.7 and 4 nS for MM, MF, and FF junctions respectively. Conduction delay, velocity, and changes in dV/dt max were studied for inserts composed of 1-4 cells, with varying fibroblast length. Results showed that propagation is sustained for inserts of up to 3 cells with significant conduction delays and depressed conduction velocities. Action potentials from myocytes distal to the insert had depressed dV/dt max and long foot potentials. Fibroblasts intercalated in a cardiac muscle fiber may allow propagation of the electrical activity through electrotonic interactions, introducing long propagation delays and changes in conduction velocity. These electrical interactions may explain phenomena such as fractionated electrograms and microreentry.