Background— An open-irrigated radiofrequency (RF) ablation catheter was developed to measure contact force (CF). Three optical fibers measure microdeformation of the catheter tip. The purpose of this study was to (1) validate the accuracy of CF sensor (CFS) (bench test); and (2) determine the relationship between CF and tissue temperatures, lesion size, steam pop, and thrombus during RF ablation using a canine thigh muscle preparation. Methods and Results— CFS measurements (total 1409) from 2 catheters in 3 angles (perpendicular, parallel, and 45°) were compared with a certified balance (range, 0 to 50 g). CFS measurements correlated highly (R2≥0.988; mean error, ≤1.0 g). In 10 anesthetized dogs, a skin cradle over the thigh muscle was superfused with heparinized blood at 37°C. A 7F catheter with 3.5-mm saline-irrigated electrode and CFS (Endosense) was held perpendicular to the muscle at CF of 2, 10, 20, 30, and 40 g. RF was delivered (n=100) for 60 seconds at 30 or 50 W (irrigation 17 or 30 mL/min). Tissue temperature (3 and 7 mm depths), lesion size, thrombus, and steam pop increased significantly with increasing CF at each RF power. Lesion size was greater with applications of lower power (30 W) and greater CF (30 to 40 g) than at high power (50 W) with lower CF (2 to 10 g). Conclusions— This novel ablation catheter, which accurately measures CF, confirmed CF is a major determinant of RF lesion size. Steam pop and thrombus incidence also increases with CF. CFS in an open-irrigated ablation catheter that may optimize the selection of RF power and application time to maximize lesion formation and reduce the risk of steam pop and thrombus

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Background - With short radiofrequency (RF) applications, tissue temperature continues to rise after RF-termination ("thermal latency"), which may result in lesion growth after RF-termination. The purpose was to compare in-vivo tissue temperature profile (thermal latency), lesion size and the incidence of steam pop and thrombus between RF-ablation with very-high-power-very-short-RF(90W/4s), high-power-short-RF(50W/10s) and moderate-power-moderate-RF(30W/30s) in a canine thigh muscle preparation and beating heart. Methods - In the thigh muscle preparation (5dogs), a 3.5mm ablation-electrode with 66 or 56 small irrigation holes (QDOT-Micro or ThermoCoolSmartTouch-SF, respectively) was held perpendicular or parallel to the muscle at 10 or 30g contact force (CF). Total of 120RFs were delivered at 90W/4s(QDOT-catheter), 50W/10s or 30W/30s(SF-catheter). Electrode temperature, electrode-tissue-interface temperature and tissue temperatures at 3mm and 7mm-depths were measured. In 6 closed-chest dogs, total of 72RFs were delivered in the ventricle at 90W/4s, 50W/10s or 30W/30s. Results - In the thigh muscle preparation, tissue temperatures and lesion size (depth, diameter and volume) were lowest/smallest for RFs at 90W/4s, followed by 50W/10s and greatest for 30W/30s. Thermal latency (Δtemperature and duration) was greatest for RFs at 90W/4s, followed by 50W/10s and smallest for 30W/30s ( p <0.01). Effective tissue heating (area under curve≥50°C at 3mm-depth) was observed after RF-termination in 88.0±7.6% with 90W/4s, 57.7±14.6% with 50W/10s, and only 31.9±8.5% with 30W/30s ( p <0.01). In beating hearts, lesion size was also smallest with 90W/4s and greatest with 30W/30s RFs. Increasing CF significantly increased lesion depth in all three groups. There was no significant difference in the incidence of steam pop or thrombus between three groups. Conclusions - Tissue temperatures and lesion size (depth, diameter and volume) were lowest/smallest for RF-applications at 90W/4s, followed by 50W/10s and greatest for 30W/30s. The greater thermal latency for 90W/4s RF-applications suggests that a significant portion of lesion is created after RF-termination due to conductive tissue heating.

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Background— Electrode-tissue contact force (CF) is believed to be a major factor in radiofrequency lesion size. The purpose of this study was to determine, in the beating canine heart, the relationship between CF and radiofrequency lesion size and the accuracy of predicting CF and lesion size by measuring electrogram amplitude, impedance, and electrode temperature. Methods and Results— Eight dogs were studied closed chest. Using a 7F catheter with a 3.5 mm irrigated electrode and CF sensor (TactiCath, St. Jude Medical), radiofrequency applications were delivered to 3 separate sites in the right ventricle (30 W, 60 seconds, 17 mL/min irrigation) and 3 sites in the left ventricle (40 W, 60 seconds, 30 mL/min irrigation) at (1) low CF (median 8 g); (2) moderate CF (median 21 g); and (3) high CF (median 60 g). Dogs were euthanized and lesion size was measured. At constant radiofrequency and time, lesion size increased significantly with increasing CF ( P <0.01). The incidence of a steam pop increased with both increasing CF and higher power. Peak electrode temperature correlated poorly with lesion size. The decrease in impedance during the radiofrequency application correlated well with lesion size for lesions in the left ventricle but less well for lesions in the right ventricle. There was a poor relationship between CF and the amplitude of the bipolar or unipolar ventricular electrogram, unipolar injury current, and impedance. Conclusions— Radiofrequencylesion size and the incidence of steam pop increase strikingly with increasing CF. Electrogram parameters and initial impedance are poor predictors of CF for radiofrequency ablation.