The relationship of shock parameters and defibrillation efficiency

The electrical shock is the only useful method to terminate the ventricular fibrillation (VF). The low energy defibrillation research is very important. The relationship of the shock parameters and the defibrillation efficiency will be investigated in this study. The mechanism of electrical defibrillation is that most of the myocardium cells can be enforced to depolarize and enter to refractory period at the same time when electrical field of the shock interacts with myocardium. The change of trans-membrane potential depends on the trans-membrane current. The defibrillation voltage is only the method to produce the needed current. The voltage needed to defibrillation lies on the defibrillation impedance. Energy is the product of the voltage and current and more easily influenced by the impedance and the current distribution. The effects of pulse duration to defibrillation threshold need to be considered also. Generally, the change of trans-membrane potential to reach the depolarization ΔE is constant. Then I × τ (pulse duration) is a constant too. So cell's depolarization depends on the quantities of charge (the product of current and time) injected to the cell. Totally 7 domestic swine had been used for animal trails and more than 300 times VF had been induced. Defibrillation threshold is the lowest dosage of the shock for successful defibrillation. The animal trails show that the charge threshold varies little when the pulse duration is short but it will increase quickly at an certain pulse duration. We think that electric charge Q is the main parameter to determine the defibrillation result. The energy threshold is diverse because it maybe influenced by many reasons. So the energy threshold can be used to evaluate the ways and means of defibrillation, but not suitable to be used as the defibrillation dosage