Investigation of myocardial bioimpedance at multiple frequencies for cardiac radiofrequency ablation: Ex-vivo experiments

Abstract

BACKGROUND: Bioimpedance method is used clinically as a surrogate measure of effective tissue heating during cardiac ablation. It does not, however provide information regarding thermal cellular destruction which is the goal of ablation procedures. OBJECTIVES: This study investigated myocardial impedance (resistance and reactance) at different frequencies in response to the thermal effect and across temperatures where tissue necrosis occurs during ablation. METHODS: An ex-vivo experiment bench was designed to heat heart muscle tissue blocks uniformly to different targeted temperatures. Tissue resistance and reactance were recorded at three frequencies of 5 k, 50 k and 250 kHz. Impedance was measured in 3 phases (1) the relationship of tissue impedance with thermal effect at temperatures < 50 �C, (2) impedance change at 55 �C to 85 �C at which cellular necrosis occurs, and (3) post-ablation impedance during restitution back to 37 �C$.$ Results: Myocardial resistance and reactance demonstrated a strong linear relationship with temperature effect within the tissue (-1.3%/ �C and -1.96%/ �C on average respectively, frequency dependent). At ? 65 �C, the reactance was almost abolished (?0?) and stayed flat during the restitution back to 37 �C, potentially indicative of complete necrosis. Time to reactance abolishment was a few seconds for ? 75 �C, 17 seconds for 65 �C and few minutes for 55 �C. CONCLUSIONS: Myocardial impedance behaviour thermal and necrotic effects were straightforward and observable. Changes in reactance can be used as a potential indicator of cellular necrosis. SIGNIFICANCE: Data provided can be used to develop better models and solutions for monitoring the efficacy of cardiac ablation procedures, thus enhancing clinical outcomes.