Transthoracic defibrillation of dogs with Edmark, biphasic, and quadriphasic waveforms

Patients with high transthoracic impedance are reported to be at higher risk of poor outcomes when treated by present defibrillators. This study evaluates the defibrillation efficacy of biphasic truncated exponential (BTE), quadriphasic truncated exponential (QTE), and Edmark waveforms at simulated low, average, and high impedance levels. Waveforms were tested at 2 energy levels in random order in anesthetized dogs (n = 15, 16.9 +/- 1.2 kg), and a supplemental study estimated the ED50 peak current for BTE and QTE at a simulated high impedance level. Overall, BTE and QTE were equivalent, and both were superior to Edmark at equal delivered energies (P<.0001). However, in simulated high impedance patients at 24 J, QTE was superior to BTE (71% vs. 49%, P =.011 (borderline significance-see text)). Supplemental study, QTE mean ED50 peak current was lower than BTE (7.9 vs. 8.9 A, P =.0049). QTE and BTE waveforms were superior to Edmark at all studied conditions, but QTE appears to be superior to BTE in simulated high impedance patients.