Abstract 3102: Translesion Myocardial Impedance as an Indicator of Lesion Production by RF Ablation
Most studies of impedance changes by RF ablation report a rise in the impedance of the ablation system. The impedance of cardiac tissue itself may change due to intercellular uncoupling or vascular effects within the lesion. Thus translesion tissue impedance may provide an intraoperative indicator of lesion production. Also since impedance represents passive properties, it may be independent of the electrophysiological state of the tissue, allowing measurements during arrhythmias or regular rhythm. Here, we measured translesion AC impedance of myocardial tissue before and after producing lesions (n=26) in isolated perfused rabbit hearts with epicardial RF ablation (480 kHz, 1800–3600 J/cm2). The 4-electrode method for impedance measurement, which is independent of the RF delivery system, was used with 1 kHz subthreshold (1 μA) current applied across the lesion while recording translesion voltage. Magnitudes and phase of impedance were determined using spectral analysis of the voltage. Lesions were then examined histologically with tetrazolium chloride. Results show that magnitudes of AC impedance of the tissue increased during the 10 minutes after RF ablation (Figure⇓). No significant changes in the phase angle were observed. In all lesions, the rise of impedance in 1–5 minutes was 29 ± 11 Ω(a 14% increase) or 42 ± 9 Ω (a 23% increase) for lesions that contained an epicardial gap or were complete, respectively (p<0.05). Rises in impedance after ablation are consistent with progressive uncoupling of cells at gap junctions. Since the impedance is a direct indicator of changes in the passive tissue properties, it may be useful as an indicator of lesion production during procedures.