Effect of saline irrigation flow rate on temperature profile during cooled radiofrequency ablation

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.

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 0.5cc/sec flow, and 70C surface temperature without flow (temperature control).

The temperatures decreased from 77.5 +/-10.5 degrees C, 91.7+/-6.3 degrees C, 65.5 +/- 11.8 degrees C, and 52.5 +/- 11.8 degrees C at 20W without saline irrigation at the tip, 0.0mm, 1.0mm, and 2.0 mm, respectively, to 33.0+/-1.4 degrees C, 63.4 +/- 7.0 degrees C, 57.1+/-5.8 degrees C, 49.9+/-5.8 degrees C+ at 20W with 0.5 ml/sec flow (*p<0.01, +p = 0.09). The lesion volumes were 79.6mm3 for 20W without flow, 64.1 mm3 for 20W with 0.3 ml/sec flow, 47.5 mm3 for 20W with 0.5 ml/sec flow, and 28.6 mm3 for temperature control.

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.