Transthoracic Ventricular Defibrillation in the 100 kg Calf with Untruncated and Truncated Exponential Stimuli

The effectiveness in reversing ventricular fibrillation of 30 s duration of 50 untruncated and truncated exponential waveforms was studied in 6000 fibrillation-defibrillation episodes in 100 kg calves. The study employed waveforms which could be generated with nominal stored energy levels (in the basic capacitor-switch sense) of 220, 440, and 660 J and initial current levels of 50, 70, 100, 140, and 200 A. Fifty A waveforms having a time constant of decay of 10 ms were truncated at 15 and 30 A while those having time constants of 20 and 30 ms were truncated at 15, 30, and 45 A. Seventy A waveforms having time constants of 5, 10, and 15 ms were untruncated or truncated at 15, 30, and 45 A. One hundred A waveforms having time constants of 2.5, 5.0, and 7.5 ms were untruncated or truncated at 15, 30, and 45 A. One hundred forty A waveforms having time constants of 1.25, 2.50, and 3.75 ms were untruncated or truncated at 15, 30, and 45 A. Two hundred A waveforms having time constants of 0.63, 1.25, and 1.88 ms were untruncated or truncated at 45 A. We used 75 animals in the study.