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Funding Acknowledgements Type of funding sources: None. Background Bipolar radiofrequency catheter ablation (BA) is an important therapeutic option for therapy refractory ventricular arrhythmias. BA approaches may frequently include titration of energy from lower to higher levels and target epicardial sites with overlying fat tissue. However, the actual effect on lesion formation has not been evaluated.  Purpose Investigating lesion modalities during BA (a) using low-to-high energy titration, (b) conducting prior sequential unipolar ablation additional to BA and (c) in epicardial fat tissue.  Methods  An ex-vivo model consisting of freshly explanted swine hearts positioned in a circulating temperature-controlled saline bath was established. An irrigated active and ground ablation catheter with a 3.5mm tip connected to a novel single generator capable of performing BA were positioned on both sides of the left ventricular/ventricular septal myocardium orthogonal to respective swine tissue. Radiofrequency energy was applied with a fixed force of 10 g for 60 s using different approaches: (1) Titration group, BA of 30 W following BA of 50W; (2) sequential group, ablating unipolar from both catheters using 30 W; (3) epicardial fat group (fat thickness &amp;gt;1 cm) with BA of 50W; (4) sequential + BA group, applying unipolar energy of 30 W first on both catheters with consecutive BA of 50W; (5) control group, with BA of 30, 40 or 50 W only. Dimensions of set lesion as well as bipolar generator impedance during ablation were assessed.  Results A total of 65 ablation lesions were analyzed. The mean tissue thickness was 18 ± 3 mm (range 11-23 mm), with a mean fat thickness of 3.5 ± 1.1 mm in the epicardial fat group. Overall, transmurality was observed in 17 lesions (26%) with the highest rates in the titration and sequential + BA group (75 / 100%), while no difference to the control group applying 50 W was detected (Kruskal-Wallis test, p = 0.30/0.19) and no lesion displaying transmurality in the epicardial fat group (p &amp;lt; 0.001). The maximum impedance drop during ablation was highest in the control group applying 50 W and lowest in the epicardial fat group (51 ± 24 vs 23 ± 12 Ω, p = 0.02). The lesion volume did not differ between titration and control group applying 50 W (455 ± 230 vs 426 ± 268 mm3, p &amp;gt; 0.99), whereas being significantly larger than in the epicardial fat group [median 59 (interquartile range 41-92 mm3), p = 0.02/0.01]. The sequential + BA group showed significantly increased lesion volume compared with both titration and control group [1401 (1093-1728) mm3, p = 0.004, Figure]. Eleven steam pops (17%) were registered with similar distribution between groups (p = 0.24). Conclusion Lesion dimensions were similar between the BA titration approach and BA solely applying 50 W. Prior sequential unipolar ablation may significantly increase ablation lesion volumes during BA. The effect of BA at sites of significant epicardial fat tissue &amp;gt;1 cm may be severely limited, which should be considered during procedure planning. Abstract Figure. Lesion dimensions in BA approaches

Biophysical evaluation of clinical bipolar radiofrequency ablation approaches in a porcine ex-vivo model