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Transthoracic impedance and current flow are determinants of defibrillation success with monophasic shocks. Whether transthoracic impedance, either independently or via its association with body weight, is a determinant of biphasic waveform shock success has not been determined.We studied 22 swine, weighing 18-41 kg. After 15 s of ventricular fibrillation, each pig received transthoracic truncated exponential biphasic shocks (5/5 ms), 70-360 J. Shock success was strongly associated individually with body weight, leading-edge transthoracic impedance and current at low energy levels (70 and 100 J, all P0.001). Multiple logistic regression analysis showed a significant association of body weight with shock success after adjusting for the effect of leading-edge impedance (odds ratio of success for 1 kg decrease in weight at 70 J was 1.29, 95% CI: 1.05-1.59, P=0.02; and at 100 J was 1.30, 95% CI: 1.14-1.49, P0.0001). The same result was observed after adjusting for the effect of leading-edge current. At 150 J or higher energy levels, no significant association was observed.Body weight is a determinant of shock success with biphasic waveforms at low energy levels in this swine model.

Our purpose was to compare biphasic versus monophasic shock success for VF termination in a porcine model of acute left ventricular (LV) dysfunction.For the termination of ventricular fibrillation (VF), transthoracic biphasic waveform shocks achieve higher success rates than monophasic shocks. However, the effectiveness of biphasic versus monophasic defibrillation in a setting of left ventricular dysfunction has not been reported.In 23 open-chest adult swine (15-25 kg), LV dysfunction [or =25% decline in cardiac output (CO)] was induced by continuous inhalation of halothane (1-1.75%). Each pig randomly received transthoracic biphasic and monophasic shocks at three energy levels (30, 50 and 100 J) in two conditions: baseline and LV dysfunction. Halothane effect on left ventricular size and contraction was measured by echocardiography in three additional swine.With halothane, pigs demonstrated a decline in CO (baseline 4.16+/-0.19, halothane 2.72+/-0.19 l/min, P0.01), mean arterial pressure (baseline 107.2+/-3.5, halothane 80.1+/-3.4 mmHg, P0.01) and increased left ventricular end-diastolic pressure (baseline 6.4+/-0.9, halothane 12.7+/-0.8 mmHg, P0.01). LV diameters increased and fractional shortening fell. During baseline, biphasic shocks achieved significantly greater success (termination of VF) compared to monophasic waveforms (100 J: biphasic 83.3+/-9.5 versus monophasic 38.9+/-9.5%, P0.01; 50 J: biphasic 67.1+/-8.8 versus monophasic 11.8+/-5.7%, P0.01; 30 J: biphasic: 31.9+/-6.4 versus monophasic 0+/-0%, P0.01). The superiority of the biphasic waveform to terminate VF was retained during LV dysfunction at all energy levels (100 J: biphasic 78.3+/-7.3 versus monophasic 37.5+/-8.1%, P0.01; 50 J: biphasic 65.5+/-11.5 versus monophasic 11.7+/-5.9%, P0.01; 30 J: biphasic: 40.6+/-8.0 versus monophasic 3.1+/-3.1%, P0.01). Within both waveforms, there were no significant differences in percent shock success at any energy level comparing baseline with LV dysfunction.In this porcine model of acute LV dysfunction, biphasic waveform shocks were not only superior to monophasic waveform shocks for termination of VF during baseline, but retained superiority to monophasic waveform shocks when LV dysfunction was present.

The purpose of this study was to compare truncated exponential biphasic waveform versus truncated exponential monophasic waveform shocks for transthoracic defibrillation over a wide range of energies. Biphasic waveforms are more effective than monophasic shocks for defibrillation at energies of 150-200 Joules (J) but there are few data available comparing efficacy and safety of biphasic versus monophasic defibrillation at energies of150 J or200 J. Thirteen adult swine (weighing 18-26 kg, mean 20 kg) were deeply anesthetized and intubated. After 15 s of electrically-induced ventricular fibrillation (VF), each pig received truncated exponential monophasic shocks (10 ms) and truncated exponential biphasic shocks (5/5 ms) in random order. Energy doses ranged from 70 to 360 J. Success was defined as termination of VF at 5 s post-shock. For both biphasic and monophasic waveforms success rate rose as energy was increased. Biphasic waveform shocks (5/5 ms) were superior to 10 ms monophasic waveform shocks at the very low energy levels (at 70 J, biphasic: 80+/-9%, monophasic; 32+/-11% and at 100 J, biphasic; 96+/-3% and monophasic 39+/-11%, both P0.01). No significant differences in shock success were seen between biphasic and monophasic waveform shocks at 200 J or higher energy levels. Shock success of75% was achieved with 200 J (10 J/kg) for both waveforms. Pulseless electrical activity (PEA) or ventricular asystole occurred in 4 animals receiving monophasic shocks and 1 animal receiving biphasic shocks. Biphasic waveform shocks (5/5 ms) for transthoracic defibrillation were superior to monophasic shocks (10 ms) at low energy levels. Percent success increased with increasing energies. PEA occurred infrequently with either waveform.

Background: Electrode polarity may alter the success of biphasic shocks from implantable systems. Whether the electrode polarity influences the success of transthoracic biphasic defibrillation is unknown. We determined the effect of electrode polarity on biphasic transthoracic defibrillation in a porcine model. Method: In ten anesthetized adult pigs, 16–28 kg, electrode pads were placed in two different orientations on the chest wall; apex-right parasternal and sternal-vertebral column. Ventricular fibrillation (VF) was electrically induced and allowed to persist for 30 s. Truncated exponential biphasic shocks (5/3 ms) were delivered at 20, 30, 50, 70 and 100 J. Four shocks at each energy level were delivered to construct energy vs. % success curves for VF termination. Electrode polarity for the first pulse was varied so that the first pulse cathode was either the apex (for apex-parasternal) or sternum (for sternum-vertebral column), or the reverse. The second pulse polarity was always the opposite of the first. Results: VF termination success rose from 0 to 86% as energy increased from 20 to 100 J. Varying the electrode polarity did not alter success rates at any energy level with either electrode pad placement. Conclusion: In this porcine model of transthoracic defibrillation, varying the biphasic shock electrode polarity did not alter transthoracic defibrillation success. Positional labeling of transthoracic biphasic defibrillation electrode pads may be unnecessary.

Objectives: The purpose of this study was to determine and compare the efficacy of biphasic and monophasic waveforms in a porcine model of pediatric defibrillation. Background: The efficacy and safety of biphasic waveforms in children has not been established. Methods: We initially studied 27 piglets: 12 weighed 3–6 kg (‘infants’), and 15 weighed 7–12 kg (‘children’). Ventricular fibrillation (VF) was induced by rapid right ventricular pacing and maintained for 15 s. Transthoracic shocks of 7–100 J energy were given using monophasic (5 ms truncated exponential) and biphasic (5 ms positive, 5 ms negative pulse, truncated exponential) waveforms. A second study of four ‘infant’ and four ‘child’ piglets utilized the same protocol but with a 10 ms instead of 5 ms monophasic truncated exponential shock waveform compared with the 10 ms biphasic waveform. Results: For both biphasic and monophasic waveforms, shock success rate (termination of VF) rose steadily as energy was increased. In the first study in the ‘infant’ 3–6 kg group, the 10 ms biphasic waveforms were superior to 5 ms monophasic waveforms at 10, 20, and 30 J energies, and in the ‘child’ 7–12 kg group at 20 and 30 J energies ( P 80%) were achieved by 20 J (4 J/kg) biphasic waveform shocks in the ‘infant’ piglets and 30 J (3 J/kg) biphasic waveform shocks in the ‘child’ piglets. In the second study using a 10 ms monophasic waveform, we found similar results. Pulseless electrical activity occurred in two animals following biphasic shocks and in two animals following monophasic shocks. Conclusions: Biphasic waveforms proved superior to monophasic waveforms in both infant and child models. High success rates were achieved with low-energy biphasic shocks. Biphasic waveform defibrillation is a promising advance in pediatric resuscitation.