Use of surface Laplacian to extract local activation from epicardial electrograms

Electrocardiograms were recorded overlying a region of injury on the epicardial surface of a canine heart in a four day infarct model. Electrograms were recorded simultaneously from 121 sites with an electrode array with interelectrode spacing of 1 mm. The surface Laplacian, L, of the electrograms was calculated using the four neighboring sites. Propagation in the border zone was modeled by a planar wave of finite thickness moving with uniform velocity. The source region was simulated with use of the bidomain model for the heart. Computer model results showed that the amplitude of L, diminished as electrode spacing became larger than 0.1 mm. The amplitude also fell as the distance of the wave from the surface increased, decreasing by 40% for a depth of 0.1 mm. The surface Laplacian determined from recorded electrograms showed a sharp deflection with a substantial reduction in the QS wave arising from distant sources. Hence the surface Laplacian may be useful as a spatial filter to extract local activity from epicardial electrograms.