Measuring changing spatial complexity in ventricular fibrillation using the Karhunen-Loeve decomposition of 506-channel epicardial data

The Karhunen-Loeve (K-L) decomposition was used to describe quantitatively changes in spatial organization during extended episodes of ventricular fibrillation (VF). VF was induced by premature stimulation in 5 pigs. Unipolar epicardial electrograms were simultaneously recorded with a 22 × 23 array of electrodes spaced 1.12 mm apart. Data consisting of epicardial potentials during VF, as well as during sinus rhythm, were decomposed into orthogonal spatial modes using the K-L method. In sinus rhythm, 3-4 K-L modes were required to account for 90% of the total variance, compared to 5-28 during VF. As VF progressed from 1 to 3 seconds the number of modes, M, required to reach the 90% threshold increased in every animal. From 3 seconds to 60 seconds M always decreased. These differences were significant with p < 0.05, suggesting that electrically induced VF in pigs increases in organization during the first minute after initiation.