Epicardial Ablation With Irrigated Electrodes - Effect of Bipolar vs. Unipolar Ablation on Lesion Formation

Background: Ablation of ventricular tachycardia originating from the left ventricular (LV) epicardium is often limited by the radiofrequency power delivery. We compared the effect of bipolar vs. unipolar epicardial ablation on lesion size. Methods and Results: Eleven excised pig hearts were superfused with saline (2L/min). Unipolar ablation (25 or 30W for 120s) was performed between the LV epicardial saline-irrigated electrode and an indifferent electrode (n=33 lesions). Bipolar ablation (25 or 30W for 120s) was performed between a 4-mm saline-irrigated-tip (20 ml/min) electrode on the LV epicardium and an opposing 10-mm non-irrigated-tip electrode on the LV endocarcium (n=38 lesions). Wall thickness did not differ between experiments (15.4 +/- 2.4 vs. 15.3 +/- 2.1 mm). Impedance was lower at the beginning and end of unipolar ablation than at the beginning and end of bipolar ablation (163.2 +/- 20.3 Omega and 109.9 +/- 16.0 Omega vs. 194.6 +/- 23.3 Omega and 127.1 +/- 16.4 Omega respectively) (P<0.001). Epicardial lesion width dic not differ between unipolar and bipolar ablation (10.1 +/- 2.7 vs. 10.2 +/- 2.4 mm), but lesion depth was greater with bipolar ablation (10.6 +/- 2.7 vs. 7.5 +/- 1.0 mm) (P<0.001). Unipolar ablation produced no transmural lesion, but bipolar ablation produced 15 (46%) (P<0.001). Steam pop occurred in 11(29%) and 3 (9%) cases, respectively (P=0.036). Conclusions: Bipolar ablation of the LV free wall is highly effective at creating an appropriately deep epicardial lesion. (Circ J 2012; 76: 322-327)