Katsuaki Yokoyama

Novel Contact Force Sensor Incorporated in Irrigated Radiofrequency Ablation Catheter Predicts Lesion Size and Incidence of Steam Pop and Thrombus

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.

Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop

Background— Electrode cooling by circulating fluid within the electrode (closed loop) or open irrigation facilitates radiofrequency (RF) ablation. This study compared lesion parameters between closed loop and open irrigation with the use of a canine model. Methods and Results— In 8 anesthetized dogs, the skin over the thigh muscle was incised and raised, forming a cradle superfused with heparinized blood (activated clotting time >350 seconds) at 37°C. A 7F 4-mm closed loop electrode (irrigation 36 mL/min) and 7.5F 3.5-mm open irrigation electrode (irrigation 17 mL/min) were positioned perpendicular to the thigh muscle at 10 g contact weight. RF was applied (n=121) at 20 or 30 W for 60 seconds in low (0.1 m/s) or high (0.5 m/s) pulsatile blood flow. Temperatures were measured in the electrode, electrode-tissue interface, and within the tissue at 3- and 7-mm depths. After each RF, the cradle was emptied to examine the electrode and interface for thrombus. There was no difference between closed loop and open irrigation in impedance, lesion depth, or tissue temperature at 20 or 30 W. Interface temperature and electrode temperature were greater in the closed loop application. Thrombus occurred in 32 of 63 closed loop versus 0 of 58 open irrigation RF applications (P<0.05) with interface temperature ≥80°C in all 32 (electrode temperature <40°C in 1, 40°C to 50°C in 26, and >50°C in 5). With closed loop, interface temperature and thrombus incidence were greater at 30 W and low blood flow. With open irrigation, interface temperature remained low (≤71°C) with no difference between 20 and 30 W or between low and high blood flow. Steam pop occurred at 20 W in 4 of 35 closed loop and 0 of 30 open irrigation and at 30 W in 15 of 28 closed loop and 4 of 28 open irrigation applications (P<0.05). Conclusions— Lower interface temperature, thrombus, and steam pop, especially in low blood flow, indicate greater interface cooling with open irrigation.

Initial Experience Using a Forward Directed, High-Intensity Focused Ultrasound Balloon Catheter for Pulmonary Vein Antrum Isolation in Patients with Atrial Fibrillation

Background: A high‐intensity‐focused ultrasound balloon catheter (HIFU‐BC) is designed to isolate pulmonary veins (PV) outside the ostia (PV antrum). This catheter uses a parabolic CO2 balloon (behind water balloon) to focus a 20‐, 25‐, or 30‐mm diameter ring of ultrasound forward of the balloon (parallel to catheter shaft). The purpose of this study is to test the safety and efficacy of the HIFU‐BC for PV antrum isolation in patients with atrial fibrillation (AF).

Comparison of Cryothermia and Radiofrequency Current in Safety and Efficacy of Catheter Ablation within the Canine Coronary Sinus Close to the Left Circumflex Coronary Artery

Introduction: A canine model was used to compare cryoablation and radiofrequency ablation (RFA) within the coronary sinus (CS) in the ability to create a transmural CS myocardial (Trans‐CSM) lesion and risk of coronary artery stenosis.

Canine Model of Esophageal Injury and Atrial-Esophageal Fistula After Applications of Forward-Firing High-Intensity Focused Ultrasound and Side-Firing Unfocused Ultrasound in the Left Atrium and Inside the Pulmonary Vein

Background—Left atrial–esophageal fistula is a serious and poorly understood complication of catheter ablation of atrial fibrillation. The purpose of this study was to (1) develop a canine model of esophageal injury and left atrial-esophageal fistula after applications of forward-firing high-intensity focused ultrasound (HIFU) and side-firing unfocused ultrasound (SFU); (2) examine the relationship to esophageal temperature (Eso-temp); and (3) study the evolution of injury/healing. Methods and Results—Twenty dogs were studied. After transeptal puncture, HIFU catheter (ProRhythm Inc; 13 dogs) was positioned close to the esophagus, either outside (n=6) or inside (n=7) the inferior pulmonary vein (PV). In 7 other dogs, an SFU catheter was placed deep inside the PV, close to the esophagus. A balloon (20- to 25-mm diameter) with 7 thermocouples (2-mm separation) was positioned in the esophagus (Eso-balloon). Variable air filling of the Eso-balloon controlled the distance from the esophagus to the sonication source, pressing the esophagus against left atrium/PV. One to 9 (median, 5) HIFU (35 W) and 5 to 7 (median, 5) SFU (40 W) sonications were delivered for 40 seconds. Maximum luminal Eso-temp was closely related to HIFU Eso-balloon distance. For HIFU outside PV, Eso-temp ≥50°C occurred only for HIFU Eso-balloon distance ≤2 mm. For HIFU/SFU inside the PV, Eso-temp was ≥50°C, with HIFU Eso-balloon distance up to 6.8 mm. Endoscopy identified esophageal ulcer immediately after ablation in 11 of 13 HIFU dogs and 7 of 7 SFU dogs, all with Eso-temp ≥50°C. Endoscopy at 2 weeks showed ulcer healing in 5 of 11 chronic dogs and ulcer size progression with relaxation of the lower esophageal sphincter and esophagitis in 6 dogs. Two dogs developed left atrial-esophageal fistula and died at 2 weeks. Conclusions—This model produces esophageal ulcer when Eso-temp is ≥50°C. Eso-temp is higher with HIFU/SFU applications closer to the esophagus and with HIFU/SFU applications inside the PV. Ulcer progression and left atrial-esophageal fistula were associated with reflux esophagitis.

Novel Balloon Catheter Technologies for Pulmonary Vein/Antrum Isolation

We describe novel balloon catheter technologies for pulmonary vein (PV)/antrum isolation using three different energy sources (high-intensity focused ultrasound, laser energy and cryothermia). 1) A High-intensity focused ultrasound (HIFU) balloon catheter is designed to focus HIFU energy circumferentially outside the PV (PV antrum). The catheter has two non-compliant balloons and a 9MHz ultrasound crystal is located with the distal bal loon filled with contrast and water. The proximal balloon, filled with carbon dioxide, forma a parabolic reflecting interface to focus the ultrasound energy 2–6 mm in front of the distal balloon surface. 2) An endoscopic laser balloon catheter (ELBC) is designed to visualize the balloon-tissue interface using an endoscopic fiber in the balloon (filled with deuterium dioxide), combined with an adjustable focus for the laser energy (980 nm infrared diode laser) for PV ostial isolation. The laser application is delivered in 90 degree or 150 degree arcs and the arc is rotated in sequential laser applications to cover the entire circumference of the PV ostium. 3) A cryothermal balloon ablation system consists of a 10.5 Fr catheter shaft with double inner-outer cooling balloons to prevent refrigerant leakage (balloon diameter 23 mm or 28 mm), is advanced over a guidewire through a 12 Fr deflectable sheath. The refrigerant (N2O) is delivered under pressure from the console into the inner balloon chamber, where it undergoes a liquid-to gas phase change, resulting in balloon cooling to − 80 °C.

Response to Letter Regarding Article “Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop”

We thank Drs Saul and Haemmerich for their comments regarding our article,1 but we respectfully disagree. Using the open-irrigation electrode in clinical practice in the “temperature control” mode with an adequate irrigation flow rate (17 mL/min at ≤30 W and 30 mL/min at 31 to 50 W) infrequently results in reaching the target electrode temperature (ET, 40°C to 45°C). Therefore, radiofrequency (RF) energy is delivered continuously at the power limit (ie, 30 W). This is essentially “power control.” Thrombus did not occur when the closed-loop electrode was used in the 8 RF applications with ET ≤40°C in high blood flow. However, in low blood flow, thrombus …