Energy, current, and success in defibrillation and cardioversion: clinical studies using an automated impedance-based method of energy adjustment

The purposes of this study were two. First, we wanted to evaluate in patients a technique for automated adjustment of selected energy for defibrillation or cardioversion based on transthoracic impedance. Second, we wanted to define the relationship of peak current and shock success in various arrhythmias. Applying a previously validated method of predicting transthoracic impedance in advance of any shock, we modified defibrillators to automatically double the operator-selected energy if the predicted impedance exceeded 70 omega. Success rates of shocks given for ventricular and atrial arrhythmias from these modified energy-adjusting defibrillators were compared with success rates for shocks given from standard defibrillators. We prospectively collected data on 347 patients who received a total of 1009 shocks. Low-energy (100 J) shocks given to high-impedance (greater than or equal to 70 omega) patients had a poor success rate; in such high-impedance patients significant improvement in shock success rate was achieved by the energy-adjusting defibrillators. For example, when 100 J shocks were selected for high-impedance patients in ventricular fibrillation the energy-adjusting defibrillators achieved a shock success rate of 75%, whereas standard defibrillators achieved a shock success rate of only 36% (p less than .01). Similar improvements were seen for ventricular tachycardia and atrial fibrillation. Thus, automated energy adjustment based on transthoracic impedance is a beneficial approach to defibrillation and cardioversion. For ventricular fibrillation, atrial fibrillation, and atrial flutter there was a clear relationship between peak current and shock success.