Local multifrequency impedance to characterize the myocardial tissue in patients submitted to pulmonary vein isolation procedures

Abstract Introduction Precise characterization of the anatomical substrate using voltage mapping is essential for successful catheter ablation of atrial arrhythmias, but local voltage can be affected by edema or by local alterations in the myocardial tissue. Local multifrequency impedance (LMI) is a passive property of the myocardium that encompasses the intra- and extracellular resistances and cell membrane capacitance and may overcome these limitations. Purpose The objective of this study was to characterize the LMI magnitude and phase angle of pre- and post-ablated myocardium in patients. Methods Eleven patients were submitted to a standard pulmonary vein (PV) isolation procedure. The left atrium was accessed through a single transseptal puncture and a 3D high density electroanatomical map constructed (CARTO 3 system) with a multipolar catheter (Pentarray, Biosense Webster). Afterwards, we used an irrigated ablation catheter (QDOT, Biosense Webster, USA) to measure the LMI from 1 to 1,000 kHz at fifty sites per patient in the antral region of all the PV with a custom-made impedance recording system (CARDIO-Z system) adapted to the navigation system. A wide antral isolation of the PV was performed using a high-power short-duration radiofrequency protocol (4 seconds @ 90W). After confirming PV isolation, we performed fifty additional LMI recordings at the previous sites over the ablation line. The study conformed to the principles of the Declaration of Helsinki of the World Medical Association and was approved by the local ethical committee. Results Figure 1 shows that the LMI magnitude of pre-ablated myocardium was significantly higher than of post-ablated myocardium and of blood pool, from 1 to 371 kHz (LMI magnitude @ 41kHz: |ZPRE|=110±15 Ω vs. |ZPOST|=90±10 Ω vs. |ZBLOOD|=90±8 Ω; ANOVA p<0.001). LMI of blood pool vs. post-ablated myocardium did not show differences. The LMI phase angle of pre-ablated myocardium was lower than of post-ablated myocardium and blood pool, at high frequencies (LMI phase angle @ 307kHz: ΦPRE=-10±3° vs. ΦPOST=-7±4°vs. ΦBLOOD=-6±2°; ANOVA p<0.001). The current frequency range that better discriminated pre-ablated from post-ablated regions was 1–371 kHz for the LMI magnitude and 173–1,000 kHz for the LMI phase angle. The cyclic changes of the LMI magnitude showed an inverse relationship with the contact force, with maximum values during the systole that correlated well with the lower values of contact force and with the EGM. These cyclic changes during the cardiac cycle were more attenuated in the post-ablated tissue (Figure 2). Conclusions Mapping of local myocardial electrical impedance can discriminate between healthy and post-ablated tissue in patients submitted to PV isolation procedures. This information could be useful to create new metrics to correctly characterize the anatomical substrate and robustly assess a correct pulmonary vein isolation.Fig1.LMI of blood, pre & post-ablation. Fig2.LMI@5kHz, force, EGM and ECGs (V1)