Modifications on regularity and spectrum of ventricular fibrillation signal induced by physical training

The objective of this work is to study the modifications on cardiac response during ventricular fibrillation (VF) induced by physical training. The analysis was performed in the frequency domain of VF, and the regularity of the signal was also considered. Two sets of records were acquired: control (G1: without physical training, N=10), and trained (G2, N=9). Cardiac registers were obtained using a 240-electrodes matrix located on left ventricle of isolated rabbit heart. A Langendorff system was used to maintain the heart perfusion. VF was induced by increased frequencies. To analyze the time course of VF, records were processed in 4-second segments. For every segment and channel, Welch periodogram with Hanning window, two non-overlapped sections and zero padding, was computed. Parameters considered in frequency domain are: dominant frequency (DF) and normalized energy (NE: spectral energy in the window DF±1Hz, normalized by spectral energy in 5-35Hz band). For every segment and channel, a regularity analysis of VF was performed, obtaining the regularity index (RI), which is a measure of similarity among local activation waves present in every channel. Mean values for the parameters (DF, NE and RI) of the whole set of electrodes were computed for every segment. Obtained results show that DF is lower for trained rabbits (G1: 18.234±1, 241Hz; G2: 14.370±0, 866Hz; p<0.001). NE is greater for this group (G1: 0.140±0.006; G2: 0.263±0.017; p<0.001), suggesting a greater spectral concentration around DF. Finally, a greater regularity has been observed in the fibrillation signal for trained group (IR, G1: 0.756±0.026; G2: 0.834±0.014; p<0.001). As a summary, the results suggest that both spectral characteristics and regularity of VF signal are clearly different for G1 and G2 groups. The trained group (G2) shows greater regularity, lower DF and spectral dispersion. These factors should be interpreted as a more stable cardiac response to VF