EFFICIENT ELECTRODE SPACING FOR EXAMINING SPATIAL-ORGANIZATION DURINGVENTRICULAR-FIBRILLATION

Spatial organization has been observed during episodes of ventricular fibrillation (VF) by recording epicardial unipolar electrograms on a g rid of electrodes. In such studies, the choice of spacing between elec trodes is an important decision, affecting the resolution and the size of the domain to be studied. A basic tenet of sampling theory, the Ny quist criterion, states that an electrode spacing smaller than half th e smallest significant wavelength is required to capture the important details of a spatially sampled process. In this paper, we suggest a m ethod to choose a practical interelectrode spacing by examining wavenu mber power spectra of high-resolution VF data recorded from a square 1 1 x 11 array of electrodes spaced 0.28 mm apart. The plaque was suture d on the epicardium near the left ventricular apex in seven anesthetiz ed pigs. VF was induced with ac simulation. Unipolar extracellular ele ctrograms were simultaneously recorded from each channel for 2 s after the induction of VF. Each signal was sampled in time at 1000 Hz. Wave number power spectra were calculated for 100 ms segments using the zer o-delay wavenumber spectrum method, for a total of 140 power spectra. All spectra had dominant peaks at the origin and fell off rapidly with increasing wavenumber (decreasing wavelength). In all the spectra, ev ery wavelength shorter than 1.4 mm contributed insignificant power. Fu rthermore, in 134 of 140 spectra (96%), insignificant power levels wer e associated with every wavelength shorter than 2.8 mm. These results suggest that, for unipolar extracellular electrodes, an intersensor sp acing on the order of 1 mm is appropriate to study organization during early VF.