Internal Cardioversion of Atrial Fibrillation in Sheep

Background. The cardioversion efficacy of multiple defibrillation waveforms and electrode systems was compared in a sheep model of atrial fibrillation. Methods and Results. Sustained atrial fibrillation couldbe induced with rapid atrial pacing in 23 (55%) of the animals. This study was performed in four parts. Six sheep with sustained atrial fibrillation were used for data analysis for each part, except in part 4 where five sheep without sustained atrial fibrillation were used. In part 1, four lead systems and four single capacitor truncated exponential defibrillation waveforms (two monophasic and two biphasic) were tested. In part 2, two transvenous lead systems were compared; one was a right-to-left system with one electrode located in the right side of the heart and the other electrode located in the left side of the heart, and the other was a totally right-sided system with both electrodes located in the right side of the heart. Eight (four monophasic and four biphasic) waveforms were tested with each lead system. In part 3, eight transvenous lead systems were compared, and two waveforms (one monophasic and one biphasic) were tested with each lead system. For parts 1-3, probability of success curves were determined for each waveform/lead system configuration using an up-down technique with 15 shocks per configuration. In part 4, shocks were synchronized to the QRS and given through two lead configurations during sinus rhythm in 20-V steps starting with 40 and ending with 500 V, and two waveforms were tested with each lead syste