Abstract 3: Current-Based Impedance Compensation Outperformed Duration-Based Technique in Defibrillation Efficacy in a High Impedance Pig Model
Purpose Transthoracic impedance (TI) for defibrillation varies widely in patients with a median value of approximately 95–100 ohms. High impedance patients are more difficult to defibrillate. The modern generation of external defibrillators therefore adjusts defibrillation output based on patient impedance measurement prior to shock delivery (impedance compensation). Commercial external defibrillators use different impedance compensation methods (ICM). Defibrillator A (DefA, rectilinear biphasic waveform) controls current with maximum E=200 Joules; Defibrillator B (DefB, truncated exponential waveform) increases shock duration with maximum E=360 Joules. The purpose of the study is to assess the effect of two ICM on defibrillation success for TI>100ohms.
Materials and Methods In 10 domestic pigs (17–28kg), ventricular fibrillation (VF) was electrically induced and untreated for 15 seconds. Animals were randomized to receive defibrillations with either DefA or DefB, at maximum energy settings of which were 200 J for the DefA and 360 J for the DefB. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate between the two defibrillators. A variable resistance, ranging of 80 –200 ohms was placed in series with the defibrillation pads. After 5 minutes recovery, the sequence was repeated for 60 shocks total for each animal, (30 each DefA and DefB).
Results TI was in a range of 108 –278 ohms. The aggregate success rate was 49.5% for the two defibrillators for 600 test shocks. Success rate was significantly higher for DefA vs. DefB (63%vs.36%, p=0.0001, OR=2.8, 95% CI=2.04 –3.85). The DefA (200J) delivered more current and less energy to the animals compared with the DefB (360J).
Conclusions For TI greater than average, the current-based compensation technique was much more efficient than the duration-based technique; higher defibrillation current, not higher energy from extending shock duration resulted in higher defibrillation success.