Excitation spread in cardiac myocyte cultures using paired microelectrode and microelectrode array recordings

Abnormal cell–cell coupling is associated with increased arrhythmic risk, but the detailed electrophysiological understanding of this arrhythmic propensity is still unclear. Therefore, we performed a multiparametric study of excitation spread with cellular resolution in confluent monolayers of cultured cardiomyocytes (CM). Using simultaneous intracellular recordings of action potentials in individual CM pairs, the mean conduction velocity was measured at 30.4±2.2 cm/s (mean±SD). Moreover, in spite of a stable interbeat period and action potential (AP) time parameters, we observed slight periodic spontaneous advances/delays in the interspike time lag, suggesting natural fluctuations in cell coupling and/or in conduction pathway. To check this, synchronous multifocal field potential (FP) recordings were done from CM monolayers grown on substrate-integrated microelectrode arrays (MEA). These multisite FP recordings confirmed that AP parameters (rate, duration, voltage change velocity) were homogenous throughout the recording area. Conversely, the sequential mappings of the delays of activation calculated from the multielectrode matrix revealed for the first time random and iterative cycle-to-cycle changes in the direction of excitation spread. These spontaneous variations in the cardiac impulse propagation pathways may be a safety process protecting from microscopically discontinuous conduction, and abnormality of this natural process could contribute to the genesis of some heart arrhythmias.