Radiofrequency catheter ablation using cooled electrodes: impact of irrigation flow rate and catheter contact pressure on lesion dimensions.

Irrigation of radiofrequency current (RF) ablation reduces the risk of thrombus formation. The aim of this study was to investigate the impact of different irrigation catheter flow rates and contact pressures from the catheter on the development of lesion dimension and thrombus formation. A thigh muscle preparation was achieved in six sheep to create a cradle that was filled and perfused with heparinized blood (250 mL/min, 37 C degrees). RF ablation (30 s, 30 W) was initially performed with three different irrigation flow rates (5 mL/min, 10 mL/min, and 20 mL/min) and a perpendicular position (0.1 N contact pressure) of the irrigated ablation catheter ("Sprinklr," Medtronic, Inc., Minneapolis, MN, USA). The next lesions were induced with constant contact pressure of 0.05 Newton (N); 0.1 N; 0.3 and 0.5 N and a parallel or perpendicular orientation of the catheter, respectively. A constant irrigation flow of 10 mL/min was maintained during these RF applications. Cross sections of the lesions were investigated with regard to maximal depth and maximal diameter at and below the surface. During high flow irrigation (20 mL/min) the surface diameter was significantly smaller (0.63 +/- 0.1 cm) compared to irrigation flowrates of 5 mL/min (0.88 +/- 0.2 cm) and 10 mL/min (1 +/- 0.1 cm). Thrombus formation was not observed during any RF application. Only in perpendicular catheter orientations with a contact pressure of 0.5 N were significantly deeper lesions (0.85 +/- 0.12 cm) induced compared to 0.05 N (0.55 +/- 0.02 cm), 0.1 N (0.7 +/- 0.01 cm) and 0.3 N (0.67 +/- 0.01 cm) contact pressure. There was no significant difference in lesion depth with different flow rates. Irrigated RF ablation even with low flow rates and high catheter contact pressure prevented thrombus formation at the electrode. Smaller lesion diameters have been created with high irrigation flow rates. The deeper lesion created with high catheter contact pressure might be caused by a greater power transmission to the tissue.