Dimensional analysis of the electrical activity in fibrillating isolated hearts

The dynamical behavior of the electrophysiological response at the epicardium of isolated Langendorff-perfused rabbit heart during different induced arrhythmic conditions is studied with the use of the correlation dimension D₂ and Lyapunov exponents. Different conditions are investigated: normal sinus rhythm (NSR), normal sinus rhythm after ischemia (NSRI), and ventricular fibrillation with and without perfusion (VFWP and VF, respectively). Both single lead and simultaneous recordings from four leads are analyzed. The correlation dimensions during VF and VFWP are significantly higher than during NSR or NSRI, although low-dimensional attractors could not be clearly observed in VF and VFWP. Our conclusions are (a) that isolated hearts behave periodically during NSR, probably because the heart does not have to cope with time-varying demands either from the nervous system or from the metabolism; (b) during NSRI, spatially different regions of the heart show periodicities or chaotic behavior with low-dimensions, possibly due to electrophysiological inhomogeneity of the heart tissue; (c) during VF and VFWP, an intrinsic change in the dynamics seems to occur, and the heart behaves as a high-dimensional system, wherein VFWP signals show a greater spatial homogeneity than do VF signals. We propose a possible interpretation of the results in terms of the synchronization of cells by a pacemaker and desynchronization as a result of malignant arrhythmias.