Factors Affecting the Size and Shape of Electrograms
(Top left) Effect of increasing axial resistivity on extracellular waveform. Computed extracellular waveforms (1 to 5) demonstrate a marked reduction in conduction velocity and electrogram (EGM) amplitude distal to an imposed 10-fold increase in internal axial resistivity between sites 2 and 3. Adapted with permission from Spach et al. (30). (Top right) Effect of directional differences of wavefront of activation in branching fibers with interstitial fibrosis on extracellular electrograms. Wavefront of activation is shown by arrows. Electrograms are shown at numbered sites. Adapted with permission from Spach et al. (30). (Lower left) Effect of impedance mismatch on electrogram. Conduction from small fiber to larger fiber is markedly impaired due to source-sink mismatch (courtesy of Dr. Andrew Wit). (Lower right) Connexin-43 (Cx43) disarray following infarction. Connexins are no longer at the longitudinal ends of muscle fibers but are lateralized. This is associated with zig-zag conduction and fractionated electrograms.