Temperature-Controlled Irrigated Tip Radiofrequency Catheter Ablation:

Temperature-Controlled Irrigated Tip Ablation. Introduction : In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures < 60% partly due to the limited lesion size after conventional radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion size, hut has increased risk of cratering. The present study explores irrigated tip catheter ablation in temperature- controlled mode, target temperature 60°C, using an irrigation rate of 1 mL/min, comparing this to conventional catheter technique, target temperature 80°C.
Methods and Results : In vivo anesthetized pigs were ablated in the left ventricle. In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Lesion volume was significantly larger after irrigated tip ablation both in vivo (544 ± 218 vs 325 ± 194 mm³, P < 0.01) and in vitro (286 ± 113 vs 179 ± 23 mm³, P < 0.01). The incidence of cratering was not significantly different between the two groups. In vivo, no coagulum formation on part of the catheter tip was seen after irrigated tip ablation as opposed to 52% of the applications with conventional ablation (P < 0.05).
Conclusion : We conclude that temperature-controlled radiofrequency ablation with irrigated tip catheters using low target temperature and low infusion rate enlarges lesion size without increasing the incidence of cratering and reduces coagulum formation of the tip.     

双大头电极间放电成功消融后间隔旁道(附一例报告)

报道１例采用在双大头电极之间放电成功消融后间隔旁道的病例。该例有心动过速病史８年，特殊检查未见心脏结构异常。心电图示显性Ｂ型预激。心内标测为连接左房与右室的后间隔旁道。采用常规单大头电极分别在三尖瓣环右房侧、二尖瓣环左室侧及左房侧反复放电均未成功。改用与单大头电极放电相同位置的三尖瓣环右房侧与二尖瓣环左室侧的双大头电极之间放电，功率１５Ｗ、阻抗９８Ω，放电３ｓ后ｄｅｌｔａ波消失，巩固放电至９９ｓ而获得成功。此例说明，在单大头电极放电失败后采用在双大头电极之间放电可以进一步提高导管射频消融后间隔旁道的成功率     

射频消融源于三尖瓣环的房性心动过速

目的:报道起源于三尖瓣环上的房性心动过速(房速)的电生理特点和射频消融结果。方法:根据成功靶点影像位置和靶点图A:V比值,5例房速起源于三尖瓣环。结果:5例房速心动过速平均周长(340.2±30.5)ms,心房刺激可以诱发和终止心动过速,3例心室刺激可以诱发, 三磷酸腺苷可以终止所有心动过速。成功靶点图的A:V之比为0.7±0.9,3例位于右侧游离壁,2例为右后游离壁,5 例均消融成功。结论:部分房速可以起源于三尖瓣环并可以被成功地消融。     

Intracardiac Echocardiographic Imaging in Guiding and Monitoring Radiofrequency Catheter Ablation at the Tricuspid Annulus

Intracardiac echocardiography (ICE) with lower frequency is a new imaging modality. We present the case of a patient with dilated cardiomyopathy and recurrent supraventricular tachycardia due to a right posterolateral accessory pathway. ICE imaging was performed using a 9-MHz (9-Fr) catheter positioned in the right atrium and guided precise catheter localization at the lateral tri-cuspid annulus where the bypass tract was located, which facilitated successful radiofrequency ablation. In addition, ICE imaging detected anatomic abnormalities, including localized pericar-dial effusion and torn tricuspid chordae tendineae, which were all identified at the onset of the procedure. The effusions remained stable during imaging monitoring throughout the procedure, which helped reassure us that these abnormalities were not procedure related. In summary, ICE imaging may significantly improve procedural efficacy in selected catheter ablation procedure and help detect anatomic abnormalities, procedural complications, or both.     

Counter Intuitive Relations Between in vivo RF Lesion Size, Power, and Tip Temperature

Background: Radiofrequency (RF) lesion size in vitro is positively correlated with applied power and catheter tip temperature. However, the relation between RF lesion size, power, and tip temperature in vivo remains unclear. We hypothesized that due to flow, anatomy and tip contact effects in vivo, increased tip temperature would be inversely related to applied power and RF lesion size. Methods: RF lesions were created on the endocardium of 16 pigs using 5, 6, and 7 Fr catheters. The ablation generator was set to achieve a temperature of 70°C. RF lesions were created in different regions of the heart so as to encompass a wide range of blood flow and catheter movement conditions. RF lesions were measured acutely (DIMEN, mm) and correlated with average power applied (POWER, W), and average tip temperature (TEMP, °C). The POWER and TEMP relation was also examined. Results: For TEMPs below 55°C, the power output from the generator was typically maximized at 50 W. At TEMPs above 55°C, POWER decreased exponentially with increasing TEMP {POWER = 50 – exp(-((41-TEMP)/7)), r = 0.98, p < 0.05}. Further, DIMEN tended to be inversely related to TEMP (Slope: –0.07 ± 0.04, r = –0.15, p = 0.07); but, was positively related to POWER (Slope: 0.04 ± 0.02, r = 0.23, p < 0.05). These relations varied by tip size and estimated local blood flow characteristics. Conclusion: In vivo, variable tissue contact and flow yield DIMEN-POWER-TEMP relations opposite to those found in vitro. These counterintuitive results suggest that maximum in vivo RF lesion size is achieved when power is maximized at tip temperatures between 50 and 60°C.     

Comparison of Standard and Irrigated Radiofrequency Ablation in the Canine Ventricle

Standard and Irrigated RF Ablation Lesions. Introduction : radiofrequency ablation is successful for treating some arrhythmias but not for CAD-VT, possibly due to insufficient lesion size. Irrigated electrodes were developed to apply higher power for longer duration to create larger lesions. Our objective was to characterize and compare irrigated and standard ablation in terms of lesion size, crater, and coagulum formation. Additionally, a method is proposed for creating large irrigated lesions without craters.
Methods and Results : Three ablation protocols were conducted in canine ventricles. Protocol I: standard ablation was performed in power mode at 10, 20, 30, and 50 W, and electrode-temperature mode at 70° and 90°C (120 sec). Protocol II: irrigated ablation was conducted with 30 and 50 W (30 and 120 sec). Protocol III: to create large lesions without craters, irrigated ablation was performed at 20 W (5 and 10 min). With a standard electrode, the largest lesions were created using 20 W (358 ± 194 mm³) and using 90°C (301 ± 130 mm²). Ablation duration decreased with power for the power mode standard ablations. The largest irrigated lesions were formed using 50 W (986 ± 357 mm²). Large lesions without craters were created with irrigation using 20 W for 10 minutes (602 ± 175 mm²). Coagulum was seen for most standard ablations but infrequently for irrigated ablations. Craters were observed with 30 and 50 W irrigated ablation but were not observed with 20 W irrigated ablation.
Conclusion : Irrigated ablation created larger lesions than standard; large lesions may be created without craters using moderate power and long duration.     

Effect of Saline Irrigation Flow Rate on Temperature Profile during Cooled Radiofrequency Ablation

Introduction: 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.Methods: In excised ovine left ventricle, we compared the temperature profile from a catheter tip electrode thermocouple to those placed at depths of 0.0mm, 1.0mm, and 2.0mm. We compared the following settings: 20Watts without flow, 20Watts with 0.3cc/sec flow, 20Watts with 0.5cc/sec flow, and 70°C surface temperature without flow (temperature control).Results: The temperatures decreased from 77.5±10.5°C, 91.7±6.3°C, 65.5±11.8°C, and 52.5±11.8°C at 20W without saline irrigation at the tip, 0.0mm, 1.0mm, and 2.0mm, respectively, to 33.0±1.4°C*, 63.4±7.0°C*, 57.1±5.8°C*, 49.9±5.8°C+ at 20W with 0.5ml/sec flow (*P<0.01, +P=0.09). The lesion volumes were 79.6mm³ for 20W without flow, 64.1mm³ for 20W with 0.3ml/sec flow, 47.5mm³ for 20W with 0.5ml/sec flow, and 28.6mm³ for temperature control.Conclusions: We conclude that 1) the temperature profile greatly depends upon the rate of saline flow for cooling; 2) at high flow rates, the 0.0mm and 1.0mm 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.     

Catheter Ablation of Ventricular Endocardium Using Radiofrequency Energy: Determinants of Lesion Volume and Shape

Radiofrequency energy was delivered at varying powers and durations to excised portions of canine left ventricle that were mounted in a tank of saline at room temperature. A radiofrequenciy generator delivered alternating current in a sine wave pattern at a frequency of 500 kHz, at variable voltage. In each of five excised ventricles, 49 lesions were created, at delivered RMS voltages from 18 to 40 V and durations of ablation from 5 to 180 seconds. Lesion diameter and depth were measured grossly, and lesion volume and shape (ratio of radius/depth) were calculated. Lesion diameter, depth, and volume increased with increasing power and duration of energy delivery, and the relation of delivered energy (joules) to calculated lesion volume (mm³) was linear (r = 0.88, P < 0.001). Shallower lesions were produced by shorter duration of energy delivery at all power levels, and similar volume but deeper, more symmetric lesions by lower power and longer duration of energy delivery. Radiofrequency energy in vitro thus produces reproducible lesions whose volume is proportional to delivered energy, and whose shape can be altered by delivering similar total energies, but varying the power and duration of energy delivery     

Temperature Monitoring in Radiofrequency Catheter Ablation of Atrial Flutter Using the Linear Ablation Technique

Temperature Monitoring of Ablation. Introduction: Information about temperature and impedance monitoring during radiofrequency catheter linear ablation of atrial flutter bas not been reported. We proposed that a radiofrequency catheter ablation system using a closed-loop temperature control model could decrease the incidence of coagulum formation and shorten the radiation exposure and procedure times compared with those found in a power control model.
Methods and Results: Forty patients (8 women and 32 men; mean age 64 ± 7 years) with atrial flutter were referred for radiofrequency ablation. The patients were randomized into two groups: group I patients underwent radiofrequency catheter linear ablation of atrial flutter using a power control of energy output model; and group II patients underwent the closed-loop temperature control model with a target electrode temperature of 70°C. As compared with group II, group I patients bad a higher incidence of coagulum formation (12% vs 2%, P < 0.05), temperature shutdown (11% vs 0%, P < 0.01), and impedance shutdown (16% vs 3%, P < 0.01), more radiofrequency applications (7 ± 3 vs 4 ± 2, P < 0.01), and longer procedure time (100 ± 25 vs 75 ± 23 minutes, P < 0.05) and radiation exposure time (31 ± 10 vs 20 ± 7 minutes, P < 0.05) required for successful ablation. Larger deviations of temperature (9.0°± 2.4°C vs 5.0°± 1.2°C, P < 0.0001) and impedance (9.2 ± 2.6 ω vs 5.3 ± 1.6 ω, P < 0.0001) were also found in group I patients compared with those in group II.
Conclusions : This study demonstrated that a closed-loop temperature control model could facilitate the effects of radiofrequency catheter ablation of the atrial flutter circuit by decreasing coagulum formation, temperature and impedance shutdown, and procedure and radiation exposure times.     

Effect of Electrode Orientation on Lesion Sizes Produced by Irrigated Radiofrequency Ablation Catheters

Background: Irrigated radiofrequency (RF) ablation catheters may produce different lesion sizes dependent upon the electrode orientation to the tissue. This study examined the effect of irrigated electrode orientation on the lesion size and explores a potential mechanism for this effect.
Methods and Results: Lesions were created in isolated porcine myocardium using an open irrigation, closed irrigation, and nonirrigated RF catheter (all 3.5–4 mm tips). Lesions were created with the electrodes with all permutations of electrode orientation (vertical or horizontal), contact pressure (6 or 20 g), and saline superfusate flow (0.2 or 0.4 m/sec) over tissue interface. The effect of electrode irrigation without RF delivery on tissue temperature was assessed with intramyocardial temperature probes and infrared thermal imaging. For both irrigated catheters, the horizontal orientation produced 25–30% smaller lesion volumes than the vertical orientation despite equal or greater power deliveries. The horizontal orientation produced larger lesion volumes for the nonirrigated catheter. Higher superfusate flow rates were associated with decreased lesion volumes for the irrigated catheters but greater lesion volumes for the nonirrigated catheter. Catheter irrigation alone without RF delivery reduced intramyocardial temperatures up to 4.9°C and the horizontal orientation produced a 2-fold greater area of tissue cooling than the vertical orientation.
Conclusion: Horizontal electrode orientations reduce lesion volumes for irrigated RF catheters. This effect may be in part due to greater areas of active tissue cooling in the horizontal orientation.     

Comparison of Ventricular Radiofrequency Lesions in Sheep Using Standard Irrigated Tip Catheter versus Catheter Ablation Enabling Direct Visualization

Comparison of Ventricular Radiofrequency Lesions in Sheep. Introduction: In vivo assessment of RF ablation lesions is limited. Improved feedback could affect procedural outcome. A novel catheter, IRIS? Cardiac Ablation Catheter (IRIS), enabling direct tissue visualization during ablation, was compared to a 3.5 mm open‐irrigated tip ThermoCool? Catheter (THERM) for endocardial ventricular RF ablation in sheep. Methods: Sixteen anesthetized sheep (6 ± 1 years old, 60 ± 10 kg) underwent ventricular RF applications with either the THERM (Biosense Webster) or IRIS (Voyage Medical) ablation catheter. In the THERM group, RF was delivered (30 W, 60 seconds) when electrode contact was achieved as assessed by recording high‐amplitude electrogram, tactile feedback, and x‐ray. In the IRIS group, direct visualization was used to confirm tissue contact and to guide energy delivery (10–25 W for 60 seconds) depending on visual feedback during lesion formation. Results: A total of 160 RF applications were delivered (80 with THERM; 80 with IRIS). Average power delivery was significantly higher in the THERM group than in the IRIS group (30 ± 2 W [25–30 W] for 57 ± 14 seconds vs 21 ± 4 W [10–25 W] for 57 ± 27 seconds; P<0.001). At necropsy, 62/80 (78%) lesions created with THERM were identified versus 79/80 (99%) with IRIS (P<0.001). The lesion dimensions were not significantly different between THERM and IRIS. Conclusion: Despite best efforts using standard clinical assessments of catheter contact, 22% of RF applications in the ventricles using a standard open‐irrigated catheter could not be identified on necropsy. In vivo assessment of catheter contact by direct visualization of the tissue undergoing RF ablation with the IRIS? catheter was more reliable by allowing creation of 99% prescribed target lesions without significant complications. (J Cardiovasc Electrophysiol, Vol. 23, pp. 869‐873, August 2012)     

Cooled-Tip Ablation Results in Increased Radiofrequency Power Delivery and Lesion Size in the Canine Heart: Importance of Catheter-Tip Temperature Monitoring for Prevention of Popping and Impedance Rise

Since myocardial lesion size during radio-frequency (RF) ablation is limited at high power by impedance rise when electrode tip temperature exceed 100 °C, controlling tip temperature by continuous intraelectrode saline infusion could permit generation of larger lesion. (1) Two dogs randomly received either standard or cooled tip RF ablation at 4 to 6 separate LV sites. Power output of 30 W was delivered via modified 7 Fr deflectable catheter with 4 mm tip for up to 120 sec or until impedance rise occurred. (2) Six dogs randomly received cooled tip RF ablation at power output of 20, 30, 40 W for 120 sec. (3) Three dogs randomly received cooled tip RF ablation using room temperature saline (21–25 °C) or chilled saline (1–4 °C) infusion. Results: Overall, peak tip temperature was lower for cooled vs standard RF deliveries (97±17 °C vs. 42±8 °C). Lesion depth and volume were significantly larger for cooled burns. Lesion depth and volume and the incidence of abrupt impedance rise/popping did not differ between room temperature saline and chilled saline infusion. The catheter-tip temperature at the onset of popping and abrupt impedance rise was 54±5 °C(48–60 °C) and 59±10 °C(50–75 °C). Conclusion: Cooled tip RF current delivery at high power is associated with increased myocardial lesion size which may facilitate successful ablation of ventricular tachycardia associated with acquired structural heart disease. Catheter-tip temperature should be maintained below 45 °C to prevent popping and abrupt impedance rise during RF energy delivery.     

射频导管消融中温度场模型的建立

通过了解射频导管消融心肌形成损伤斑的过程，探讨一些主要因素（功率、消融时间、血流等）与形成损伤斑的关系以及对损伤深度的影响，提出了建立在射频电流组织加热和热传导基础上的射频导管消融中温度场的一维理论模型，初步分析了血流对温度场分布的影响，得出：稳定后的温度场在径向的分布基本上与距离的四次方及血流速度成反比；近场温度场建立过程的时间常数与血流速度成反比，与径向距离的平方成反比，即离导管端电极越近，温度升高得越快，达到稳定的时间越短。仿真计算的结果提示要加深有效消融的深度而又不致在导管端电极头引起凝血与炭化，可以考虑加大电极头的面积或用电极矩阵来进行射频消融的加热，同时也可以考虑“冷却导管端电极”（如将低温生理盐水引入导管内，再从电极头部喷出）的方式。     

Radiofrequency Delivery Through a Cooled Catheter Tip Allows the Creation of Larger Endomyocardial Lesions in the Ovine Heart

RF Lesions From Cooled Electrode. Introduction: The delivery of radiofrequency (RF) energy through conventional catheter electrodes is often associated with coagulation necrosis at the tissue-electrode interface, with resultant impedance rise and limited lesion size. This study was performed to examine the effects of catheter tip cooling during RF delivery, to test the hypothesis that such cooling would decrease the likelihood of impedance rise and allow the creation of larger endomyocardial lesions. Methods and Results: The experiments were performed in eight open chest, anesthetized sheep. RF lesions were created within both ventricular chambers of each animal through a catheter tip that could he cooled with a saline perfusate. Assignment of cooled versus non-cooled RF delivery to either ventricle was alternated from one animal to the next. In each set of experiments, lesion volumes relative to the mode of RF delivery were compared. The mean power delivered via the cooled electrode (22.04 ± 4.51 W) was significantly higher than that delivered via the noncooled electrode (6.10 ± 2.47 W; P < 0.001). The mean duration of RF delivery was 42.7 ± 11.2 sec for noncooled lesions versus 49.2 ± 6.8 sec for cooled lesions (P < 0.01). Mean lesion volume was 436.07 ± 177.00 mm³ for noncooled RF delivery versus 1247.78 ± 520.51 mm³ for cooled RF delivery (P < 0.001). This significantly larger lesion size with cooled RF delivery was associated with no instance of impedance rise in 27 attempts versus 11 impedance rises in 28 attempts with noncooled RF (P < 0.001). Conclusions: Delivery of RF energy through a cooled catheter tip allows the creation of larger endomyocardial lesions by limiting the occurrence of impedance rise despite the delivery of greater energy. These observations suggest that, under certain conditions, resistive tissue heating at a distance from the site of current delivery may play an important role in RF ablation therapy.     

Radiofrequency Catheter Ablation of the Left Bundle Branch in a Canine Model

Left Bundle Branch Ablation. Introduction: Transcatheter ablation of the left bundle branch may be considered for management of selected macroreentrant ventricular tachycardias. Left bundle ablation can also change the sequence of left ventricular contraction and may simulate pacing in hypertrophic obstructive cardiomyopathy. The purpose of this study was to determine electrophysiologic and anatomic parameters for successful selective transcatheter left bundle ablation in a canine model. Methods and Results: A catheter was advanced to the left ventricular apex and the tip deflected toward the septum, until a discrete left bundle potential (LBP) was found. Radiofrequency (RF) energy was then applied until left bundle branch block or complete AV block occurred. In 29 (85%) dogs, an LBP (mean LBP-V 16 ± 3 msec; range 10 to 20 msec) was identified resulting in successful left bundle ablation. In 5 (15%) dogs, a similar potential (mean potential-V 28 ± 4 msec; P = 0.001 vs LBP-V) was identified, but RF energy application produced complete AV block. The A:V electrogram ratio at the successful LBP ablation site was < 1:10 in all 29 dogs successfully ablated, but only 2 (40%) of 5 dogs in the unsuccessful group (P = 0.0017). In 4 successfully ablated dogs, the right bundle potential was mapped and complete AV block was created by RF energy application, confirming that the left bundle was completely ablated. In 9 dogs, the left bundle and AV junction were sequentially ablated with 1 lesion at each site. Postmortem examination showed 2 discrete lesions 1.2 ± 0.7 cm apart. Conclusions: Selective transcatheter left bundle ablation was successfully guided by the LBP. The distance between the AV junction and the main left bundle was 1.2 cm in this canine model. An A:V ratio < 1:10 and an LBP-V time < 20 msec appear to minimize the risk of AV block. Prudent use of similar techniques may cure macroreentrant ventricular tachycardias and reduce the need for permanent pacing in hypertrophic obstructive cardiomyopathy.     

Temperature-controlled Radiofrequency Ablation of Cardiac Tissue: An In Vitro Study of the Impact of Electrode Orientation, Electrode Tissue Contact Pressure and External Convective Cooling

Background: A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size.Methods and Results: In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Temperature-controlled ablation at 80 °C for 60 s was performed using a 7F 4 mm tip electrode in either perpendicular or parallel contact with the endocardium at a pressure of 10 or 20 g. Increased flow around the electrode was induced by circulating the saline in the tissue bath at a flow-velocity of 0.1 m/s. Lesion volume was determined by cutting lesions in 1 mm thick slices, staining with nitroblue tetrazolium and planimetering. A total of 107 lesions was created. Lesion size was significantly larger for perpendicular electrode orientation compared to parallel for both pressure-settings and both levels of flow around the electrode (p < 0.05). Increased flow around the electrode enlarged lesion size (p < 0.005). Electrode-tissue contact pressure had no significant impact on lesion size.Conclusions: During temperature-controlled radiofrequency ablation increased external cooling of the electrode tip due to either flow of the surrounding liquid or poor electrode tissue contact, as exemplified by perpendicular versus parallel electrode orientation, increases lesion size significantly. This is in contrast to the impact of these factors during power-controlled ablation due to the lack of increased power-delivery in the latter situation.     

Determinants of Lesion Size During Radiofrequency Catheter Ablation: The Role of Electrode-Tissue Contact Pressure and Duration of Energy Delivery

Determinants of Radiofrequency Lesion Size. Introduction: Radiofrequency (RF) catheter ablation is a promising modality in the management of cardiac arrhythmias, but the optimum protocol for energy delivery has not yet been determined. The purpose of this study was to examine the effects of varying electrode-tissue contact pressure and varying duration of RF energy delivery on the size of the resultant lesion in an in vitro model of isolated perfused and superfused canine myocardium. Methods and Results: RF power (500 kHz) was delivered through the tip of a specially-designed thermistor-tipped 1.6-mm diameter electrode mounted on an adjustable fulcrum so that contact force could be varied. RF power was adjusted to maintain a constant electrode-tissue interface temperature of 80°C during lesion production. Seventy-nine lesions were created with a 90-second RF energy delivery, and a contact force that was varied between 0 and 400 newtons (N) (0-41 g). Lesions produced with a small contact force (10 N) were significantly larger than those with a contact force of zero (width 5.5 mm vs 3.8 mm, P <0.0002), but not significantly different from those produced with the maximum contact force of 400 N (width 6.5 mm, P = NS). However, the greater contact force significantly decreased the power required to maintain a constant electrode-tissue interface temperature. Ninety-six lesions were then created using a constant contact force, but duration of energy delivery was varied from 10 to 600 seconds. Lesion size grew monoexponentially with time. The t_1/2 of lesion growth was 7.6 and 9.6 seconds for depth and width, respectively. Conclusion: Thus, close electrode-tissue contact is essential for adequate lesion formation during RF ablation of myocardium, but increasing contact force does not significantly increase lesion size if power is adjusted to maintain a constant electrode-tissue interface temperature. In order to approach steady-state and maximize lesion size, duration of RF energy delivery should be at least 40 seconds.