Safety and efficacy parameters for bipolar RF ablation is not well defined.

To study the safe range of power, the utility of trans-myocardial bipolar EGM amplitude and circuit impedance in ablation monitoring.

Sixteen beating ex vivo Human and Swine hearts were studied in the Langendorff set up. Ninety-two bipolar ablations using two, 4mm irrigated catheters were performed with the settings of 20-50W, 60s, 30ml/min irrigation in the left ventricle.

For low-power ablations (20 & 30W), transmurality was observed in 29/38 (76%) and 10/28 (36%) ablations for tissue thickness ≤17mm and >17mm, respectively. For high-power ablations (40 & 50W), transmurality was observed in 5/7 (71%) and 7/19 (37%) ablations for tissue thickness ≤17mm and >17mm, respectively. Steam pop occurrence for low and high-power ablations were 11/66 (16%) and 16/26 (62%), (p=0.0001) respectively. Lesion depth (limited by transmurality) was 12.0 ± 5.7 and 12.3 ± 5.8mm, (p=1). Trans-myocardial EGM amplitude decrement >60% strongly predicted transmurality (AUC 0.8) and circuit impedance decrement >26% predicted steam pops (AUC 0.75). Half normal saline did not affect transmurality or incidence of steam pops compared to normal saline irrigation.

Bipolar RF ablation of 20-30W power provided an ideal balance of safety and efficacy, whereas power ≥40W should be used with caution due to the high incidence of steam pops. Lesion transmurality monitoring and steam pop avoidance were best achieved using trans-myocardial bipolar EGM voltage and circuit impedance respectively.