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 0.0 mm, 1.0 mm, and 2.0 mm. We compared the following settings: 20 Watts without flow, 20 Watts with 0.3 cc/sec flow, 20 Watts with 0.5 cc/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 20 W without saline irrigation at the tip, 0.0 mm, 1.0 mm, and 2.0 mm, respectively, to 33.0 ± 1.4°C*, 63.4 ± 7.0°C*, 57.1 ± 5.8°C*, 49.9 ± 5.8°C + at 20 W with 0.5 ml/sec flow (*p <0.01, +p = 0.09). The lesion volumes were 79.6 mm³ for 20 W without flow, 64.1 mm³ for 20 W with 0.3 ml/sec flow, 47.5 mm³ for 20 W with 0.5 ml/sec flow, and 28.6 mm³ 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 0.0 mm and 1.0 mm 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.