Abstract 9064: The Increase of Tissue Echogenicity as the Pre-State of Steam Pops During Radiofrequency Catheter Ablation

Introduction: Steam pops (SPs) during radiofrequency catheter ablation (RFA) using force sensing catheters are infrequent but represent a potential severe complication such as embolic stroke, cardiac perforation. SPs remains unpredictable, and unclear in detailed phenomenon. Methods: In an ex vivo, we set the bovine myocardium to 36 °C in a constant temperature bath and performed an experiment in a water tank that generated a non-pulsatile flow. RFA using irrigation catheter was applied at catheter-tissue contact force (CF) 5, 10, 20g, 30g, 40g, and 50g for 30sec. The increase of tissue echogenicity (increased echo brightness) observed by intracardiac echocardiographic images using ViewFlex™ Xtra and impedance during RFA were evaluated with and without SPs. Results: SPs phenomenon appeared in 48 out of 137 sites (35%), and the increased echo brightness during RFA was observed in 89 lesions (65%). All lesions with SPs showed increased echo brightness before SPs (6.4±6.1sec before SPs). Sites with SPs showed stronger CF (30.8±14.8g vs. 22.9±15.9g, p=0.0047), higher initial impedance (78±12Ω vs. 73±9Ω, p=0.0063), greater impedance drops in 5 seconds after the beginning of RFA (13±7Ω, vs. 6±5Ω, p<0.0001), and earlier appearance of increased echo brightness (9.7±6.2 vs 17.4±6.3 sec, p<0.0001). Among 89 lesions with increased echo brightness, sites with SPs showed greater impedance drops in 5 seconds after the beginning of RFA (13±7Ω, vs. 7±6Ω, P<0.0001). In ROC curve analysis of the impedance drops in 5 seconds after the beginning of RFA (AUC, 0.81; sensitivity, 85%; specificity, 71%), optimal cut-off value of SPs was 7.6Ω, and SPs were not observed in lesions with the impedance drops of 3Ω or less. (Figure) Conclusions: The increase of tissue echogenicity observed by ICE images show the pre-state of all steam pops during RFA. Steam pops could be avoided by checking the impedance drop at the initial stage of RFA under ICE monitoring.