A Quantitative Measurement of Spatial Orderin Ventricular Fibrillation

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Abstract
Quantifying Spatial Order in Fibrillation. Introduction: The degree of organization in ventricular fibrillation (V F) is not known. As an objective measurement of spatial order, spatial correlation functions and their characteristic lengths were estimated from epicardial electrograms of pigs in VF. Methods and Results: VF was induced by premature stimulation in five pigs, EIectroj;raniswere simultaneously recorded with a 22 × 23 array of unipolar electrodes spaced 1.12 mmapart, Data were obtained by sampling the signals at 2000 Hz for 20 minutes immediately afterthe initiation of VF. Correlations between all pairs of signals were computed at various times.Correlation lengths were estimated from the decay of average correlation as a function of electrode separation. The correlation length of the VF in pigs was found to be approximately 4 to 10 mM. varying as fihrillation progressed. The degree of correlation decreased in the first 4 seconds after fibrillation then increased over the next minute. Conclusion: The correlation length is much smaller than the scale of the heart, suggestingthat many independent regions of activity exist on the epicardium at any one time. On theother hand, the correlation length is 4 to 10 times the interelectrode spacing, indicating thatsome coherence is present. These results imply that the heart behaves during VF as a highdimensional, but not random, system involving many spatial degrees of freedom, which mayexplain the lack of convergence of fractal dimension estimates reported in the literature.Changes in the correlation length also suggest that VF reorganizes slightly in the first minuteafter an initial breakdown in structure.