Defibrillation: Mechanisms, waveforms, energy levels, transthoracic impedance and automated external defibrillators

Cardiac arrest still remains a daunting medical emergency in Western societies and is the cause of approximately 250,000-600,000 deaths annually in the United States, with ventricular fibrillation being the initial rhythm in 20-38% of cases. Defibrillation is the only treatment available to terminate this life-threatening arrhythmia. This chapter deals initially with the mechanisms of defibrillation, the waveforms and the recommended energy levels of defibrillation. Furthermore, factors influencing transthoracic impedance, which is a major determinant of successful defibrillation, are analysed. Finally, this chapter discusses the use of automated external defibrillators and the early access to defibrillation by lay personnel in out-of-hospital cardiac arrest.;