Spectral analysis of optical maps in isolated rabbit hearts during ventricular fibrillation and spontaneous termination
Ventricular fibrillation (VF) is the leading cause of death in the western world. Within a few minutes of onset of VF, irreversible damage to the brain and heart occurs leading to death. The only effective treatment for VF at present is defibrillation and unfortunately it is not always successful. Only 1 in 20 out of hospital VF patients are defibrillated successfully but patients do not survive. Hence, it is crucial to understand the basic mechanism of VF to improve defibrillation efficacy and explore alternative treatment options. An optical mapping technique employs imaging of voltage dependent fluorescent dye to visualize electrical activity in isolated animal hearts allowing the study of electrophysiologic properties during fibrillation.
The N-point fast Fourier transform (FFT) has been widely used to analyze optical map data to study activation rates and patterns during fibrillation. Dominant frequency (DF) was extracted from each pixel of the optical map by peak detection of the frequency spectrum obtained using the N-point FFT method. The values in the DF maps were representative of the rate of activation for the corresponding regions and displayed several domains of uniform DF values with distinct boundaries between the domains. Results indicate that spectral peak detection precision is improved when continuous Fourier transform (CFT) was used rather than the N-point FFT method. Possible errors while using N-point FFT are shown in comparison with CFT. DF maps obtained using CFT revealed nuances that went unnoticed in DF maps obtained using N-point FFT. Specifically, gradients between some DF domains were observed and the conduction pattern along such gradients has not been studied previously. Time-space plots and apparent conduction velocity changes studied along these gradients revealed patterns similar to classic Wenckebach type conduction block. However, the gradient patterns are speculated to be due to a Doppler effect of rotor drift during fibrillation. This drift causes apparent conduction velocity changes and may lead to wavebreak due to wavefront-wavetail interaction and play an important role in maintenance of fibrillation.
Typically VF leads to death unless defibrillated. In rare cases, VF reverts back to normal sinus rhythm spontaneously in humans. However, spontaneous reversion to normal sinus rhythm is commonly observed in small, young animals. (Abstract shortened by UMI.)
Anatomy & physiology;
0433: Anatomy & physiology