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.(ABSTRACT TRUNCATED AT 250 WORDS)