Optical Mapping of Multisite Ventricular Fibrillation Synchronization

Defibrillation with strong shocks of several hundred volts is still the most effective way to terminate life-threatening cardiac rhythm abnormalities such as ventricular fibrillation (VF). The standing puzzle that has lasted for several decades is why defibrillate with such a high voltage when the activation threshold of cardiac myocytes is much less than 100mV. Such a conceptual conflict has prompted many theoretical and experimental studies to understand the action of strong shocks. An important goal in defibrillation study is to reduce the shock energy requirement. Because the quality of life in patients carrying implantable cardioverter-defibrillators (ICDs) is significantly affected by the occurrence of shocks, efforts have been made to decrease the shock energy for less pain and battery drain. Major progress came in the 1980s when it was realized that biphasic shocks were far superior to monophasic shocks for defibrillation. Since then, empirical studies of defibrillation waveforms have identified only marginal improvements, suggesting that empirical variation of defibrillation waveform is unlikely to result in conceptual breakthroughs or significant improvements in defibrillation efficacy. Alternatively, defibrillation theories may be used to guide the defibrillation optimization efforts. Although no comprehensive theory of defibrillation presently relates mechanisms, shock timing, and waveform optimization, recent advances in the understanding of electrical stimulation and the initiation and maintenance of VF may serve as a signpost. The bidomain model of both intraand extracellular spaces has provided insights into the mechanism of tissue activation with direct implication for the defibrillation mechanism. Cardiac conduction and activation have been modeled mathematically using complex representations of cardiac cells with detailed ionic currents connected in networks. Predictions of these