Model studies of infarct zone epicardial electrograms

The authors recorded sets of 124 simultaneous epicardial electrograms using a right-leg reference in a canine model of myocardial infarction. Superimposed on the QRS complexes arising from distant activity are deflections consistent with spread of activity in a thin layer of viable epicardial tissue. To gain insight into the relation of these deflections, which they term local events, to activation isochrones, the authors modeled extracellular potentials associated with an excitation wavefront moving with a velocity of 0.5 mm/ms in a thin layer of isotropic tissue. A realistic upstroke of the transmembrane action potential was used. The excitation front was taken to extend 0.3 mm into the tissue. Model results were obtained for activity passing under or near the electrode, and with excitation which blocks. The half-length (L) of the wavefront was varied as well as its closest approach to the electrode. Maximum amplitude (V_max) and time of zero crossing (T) of the calculated potential were compared with results for the case in which activity passes under the electrode and the case of activity passes to one side of electrode