Abstract 40: A Percutaneous Catheter-based System for the Measurement of Defibrillation Potential Gradients Applicable to Closed-Chest Resuscitation Research
Background: Local electric (E) field produced by a shock more reliably predicts VF termination than shock strength (joules). In this study we evaluated a multiple electrode catheter device for closed-chest 3-D measurements of E field from transthoracic shocks and assessed the relationship between the measured E field and defibrillation (DF) outcome.
Methods: Electrode-tipped catheters were placed in intracardiac locations. An empirically derived calibration matrix was used to transform simultaneously measured voltages into orthogonal E field vector components using a custom microprocessor. E fields produced by 30 J and 300 J biphasic shocks were compared (n = 5 swine). Correlations were determined for measured current and E field at various shock strengths at two different transthoracic impedances (n = 5 swine). VF was induced in 12 animals and E field measured during DF attempts undertaken 7 min later.
Results: E field measured at intracardiac sites are shown in the table⇓. Within animals, the variability of the measurement at each site ranged from 2.8 ± 1.6% to 5.7 ± 4.5%. Significant correlations (p < 0.001) between E field and peak current were observed at native impedance (34 ± 4 ohms, r = 0.73) and adjusted impedance (76 ± 4 ohms, r = 0.70) with shocks of 200, 300, and 360 J. In VF studies, E field closely fit a typical sigmoidal dose response curve with a minimal value of 4.72 V/cm and 50% success at 9.35 V/cm.
Conclusions: 1.The catheter E field measurement demonstrated a fairly uniform energy distribution across the heart, confirming finite element model data. 2. There was small variability of the measurement within animals and significant correlation with current. 3. When evaluated as a predictor of shock success, values were consistent with previously reported critical fields of 5 V/cm and showed a sigmoidal dose response. This technique may be of value in evaluating waveforms for transthoracic defibrillation as well as electrode size, placement, and composition.