Figure 1. Recordings from an array placed over the His bundle of an isolated rabbit heart.

A) Strong ventricular, His, and atrial signals were recorded during sinus rhythm from the 3 regions of the 8×8 array, 300 µm spaced electrodes, shown in red, green, and blue, respectively. Electrograms at sites 1, 2, and 3 are shown in B) A pseudo ECG, unipolar electrogram (from site 2 in A), and 3 Laplacian recordings (from sites 1, 2, and 3 in A) during sinus and VF. Each recording was 500 ms in duration. The unipole at site 2 shows ventricular (red arrows), His (green arrows), and atrial (blue arrows) deflection, while the Laplacians isolate the strongest local signal and eliminate far field signals. During VF, it is difficult to distinguish different activation types with the unipolar signal, but the different Laplacians facilitate waveform identification.