Not all irrigated catheters transfer heat similarly. A comparison of 4 open-irrigated catheters

Purpose: There is great diversity of designs in open-irrigated ablation catheters. It is unknown whether they all create similar lesions with the same heat transfer. The purpose of this study was to independently compare, by a thermographic technique, the tissue heat transfer of 4 open-irrigated catheters. Methods: RF applications were performed on bovine LV sections in a heparinized blood bath (37°C) with blood flow circulating at 0.2 m/s. RF was delivered (n=33) for 60s at 20W (irrigation 17 mL/m) using Biosense Thermocool (TC, n=8), SJM CoolFlex (CF, n=8), Boston Scientific Blazer Open-Irrigated (BOI, n=8) and Biosense Surround Flow (SF, n=9). RF was applied perpendicularly to the endocardial surface at the edge of the preparation. Applications were filmed using an infra-red thermal camera (Fluke, Ti-10). Maximum temperature was determined from all pixels and the temperature-depth relation was calculated from 12 equidistant points, 1mm spacing, along a perpendicular line from the electrode-tissue interface. Area of tissue with temperature >50°C (A50) was calculated at 60s. Results: We found no relevant differences comparing maximum temperature or A50 among TC, BOI and CF. However, the SF tended to show lower maximum temperature than the rest (TC: 71±10, BOI: 68±10, CF: 65±7 and SF: 56±11°C; p=0.09). A50 was significantly lower using SF as compared with TC applications (58±90 mm2 Vs 300±204 mm2; p=0.03). This was mainly due to a lower 3 mm-depth temperature with SF (42±6°C) than with the TC (62±14°C; p=0.025) and the BOI (58±13°C; p=0.07). At 7mm-depth no significant differences were found comparing the 4 catheters. In fact, maximum temperature was registered at 5±3.3, 5.3±1.8 and 5.7±3.2mm-depth using TC, BOI, CF (pNS) and significantly deeper with the SF (10.2±2.7mm; p=0.01). Conclusions: Despite technological differences, heat transfer is relatively similar using TC, BOI and CF. However, at 17ml/m, the SF produces a higher surface cooling than the rest of the analyzed catheters, delivering most of the heat to deeper areas. This data supports halving its flow rate for conventional ablation substrates, and may support its use at 17ml/m when lesion depth is needed rather than superficial damage, as in aortic cusps or coronary sinus ablation.