High Incidence of Thrombus Formation Without Impedance Rise During Radiofrequency Ablation Using Electrode Temperature Control

Abstract

The authors hypothesized that during RF ablation, the electrode to tissue interface temperature may significantly exceed electrode temperature in the presence of cooling blood flow and produce thrombus. In 12 anesthetized dogs, the skin over the thigh muscle was incised and raised to form a cradle that was superfused with heparinized canine blood (ACT > 350 s) at 37 degrees C. A 7 Fr, 4-mm or 8-mm ablation electrode containing a thermocouple was held perpendicular to the thigh muscle at 10-g contact weight. Interface temperature was measured at opposite sides of the electrode using tiny optical probes. RF applications (n = 157) were delivered at an electrode temperature of 45 degrees C, 55 degrees C, 65 degrees C, and 75 degrees C for 60 seconds, with or without pulsatile blood flow (150 mL/min). Without blood flow, the interface temperature was similar to the electrode temperature. With blood flow, the interface temperature (side opposite blood flow) was up to 36 degrees C and 57 degrees C higher than the electrode temperature using the 4- and 8-mm electrodes, respectively. After each RF, the cradle was emptied and the electrode and interface were examined. Thrombus developed without impedance rise at an interface temperature as low as 73 degrees C without blood flow and 80 degrees C with blood flow (11/16 RFs at 65 degrees C electrode temperature using 4 mm and 13/13 RFs at an electrode temperature of 55 degrees C using an 8-mm electrode with blood flow). With blood flow, interface temperature markedly exceeded the electrode temperature and the difference was greater with an 8-mm electrode (due to greater electrode cooling). In the presence of blood flow, thrombus occurred without an impedance rise at an electrode temperature as low as 65 degrees C with a 4-mm electrode and 55 degrees C with an 8-mm electrode.

Comparative Analysis of Different Methods of Modeling the Thermal Effect of Circulating Blood Flow During RF Cardiac Ablation

“…In the case of constant temperature, Matsudaira et al [37] found experimentally that temperature distribution in the blood was clearly non symmetrical around the electrode axis, with higher values on the side opposite the blood flow. They also found that the maximal temperature in the blood was 68.3±4.3ºC with a 4-mm electrode after 60 seconds of ablation, 55ºC target temperature, and high blood flow condition.…”

Analysis of Catheter-Tip (8-mm) and Actual Tissue Temperatures Achieved During Radiofrequency Ablation at the Orifice of the Pulmonary Vein

“…As demonstrated previously, in high-blood-flow states, there is an increased tissue-tocatheter-tip temperature discrepancy in a tissue-bath model in comparison with low-blood-flow states. 9 In the canine model, a perpendicular tip/tissue orientation in the right superior PV is difficult to achieve because of the angle created in the small left atrium. Furthermore, a parallel position is difficult to achieve in the right superior PV without entering the PV.…”

“…It is unclear whether the temperature recorded at the catheter tip accurately reflects tissue temperature at times or if an extensive "cooled-tip" effect is present near the PV orifice. 9 Therefore, the purposes of this study were to (1) determine the catheter-tip versus tissue temperature profile during ablation with an 8-mm tipped catheter, (2) determine the clinical factors that may result in inaccurate catheter-tip reflection of actual tissue temperatures, and (3) evaluate the impact of repetitive burns at a single site on the dynamics of tissue heating.…”

Lesion Formation by Ventricular Septal Ablation With Irrigated Electrodes - Comparison of Bipolar and Sequential Unipolar Ablation -

“…However, the high incidence of thrombus formation without impedance rise during RF ablation using electrode temperature control (69% with a catheter-tip temperature of 65°C) using 4-mm tip conventional ablation catheter was reported previously. 15 Thus, an irrigation catheter might be safer conventional ablation catheter when higher power ablation is expected.…”