Relationship between Maximal Upstroke Velocity of Transmembrane Voltage and Minimum Time Derivative of Extracellular Potential

The purpose of this computational study was to test the pertinence of the magnitude of the minimum time derivative of the extracellular potential, |dVes /dtmin |, measured in a thin, conducting solution layer adjacent to the tissue, as an index of cardiac excitability. For this purpose, we performed computational studies characterizing the relationship between |dVes /dtmin | and the maximum upstroke velocity of transmembrane voltage, dVm /dtmax , which has been used in previous studies as an index of excitability. A three-dimensional bidomain model of electrical conduction in cardiac tissue was used based on the Noble-Varghese-Kohl-Noble model of ventricular myocytes. The spatial domain included a slab of cardiac tissue with intra- and extracellular anisotropic conductivities surrounded by a layer of solution. The simulations showed linear relationships between |dVes /dtmin | and dVm /dtmax for reduction of maximum sodium current conductance (G Na ) from 100% to 20%. The relationship was dependent on location and propagation direction. However, when both parameters were normalized, those dependencies disappeared. In summary, our study demonstrated that normalized |dVes /dtmin | is linearly related to normalized dVm /dtmax . The results support our hypothesis that normalized |dVes /dtmin | can be used as an index of cardiac excitability.

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