Effect of Saline Irrigation Flow Rate on Temperature Profile during Cooled Radiofrequency Ablation

Introduction: Cooled radiofrequency ablation has been developed clinically for the treatment of ventricular tachycardia. Although clinical studies employ a constant saline flow rate for cooling, we hypothesized that varying the flow rates might optimize the temperature profile at depth.Methods: In excised ovine left ventricle, we compared the temperature profile from a catheter tip electrode thermocouple to those placed at depths of 0.0mm, 1.0mm, and 2.0mm. We compared the following settings: 20Watts without flow, 20Watts with 0.3cc/sec flow, 20Watts with 0.5cc/sec flow, and 70°C surface temperature without flow (temperature control).Results: The temperatures decreased from 77.5±10.5°C, 91.7±6.3°C, 65.5±11.8°C, and 52.5±11.8°C at 20W without saline irrigation at the tip, 0.0mm, 1.0mm, and 2.0mm, respectively, to 33.0±1.4°C*, 63.4±7.0°C*, 57.1±5.8°C*, 49.9±5.8°C+ at 20W with 0.5ml/sec flow (*P<0.01, +P=0.09). The lesion volumes were 79.6mm³ for 20W without flow, 64.1mm³ for 20W with 0.3ml/sec flow, 47.5mm³ for 20W with 0.5ml/sec flow, and 28.6mm³ for temperature control.Conclusions: We conclude that 1) the temperature profile greatly depends upon the rate of saline flow for cooling; 2) at high flow rates, the 0.0mm and 1.0mm temperatures are similar; 3) even at high irrigation rates, lesion size is greater than for temperature control; 4) the tip temperature significantly underestimates the surface temperature and improved methods of measuring temperature are needed.