Chronic incomplete atrioventricular block induced by radiofrequency catheter ablation

To determine if catheter ablation of the atrioventricular (AV) junction with radiofrequency energy can induce chronic incomplete (first- and second-degree) AV block to avoid the need for a permanent pacemaker, 20 closed-chest dogs were studied. Group 1 (10 dogs) received radiofrequency energy (750 kHz) with a fixed power setting (5 or 10 W) while increasing the pulse duration from 10 to 50 seconds for each application. Group 2 (10 dogs) received energy with a fixed pulse duration (20 or 30 seconds) while increasing the power setting from 5 to 10 W or from 10 to 20 W during each energy delivery. Radiofrequency energy was delivered between a chest-patch electrode and the distal electrode of a regular 7F tripolar His bundle catheter. For each application, the energy delivery was interrupted when 1) the PR interval prolonged (greater than 50%) or 2) second-degree or complete AV block occurred and persisted up to 5 seconds. The ablation procedure ended when there was 1) persistent PR prolongation (greater than 50%) or persistent second-degree AV block (lasting greater than 30 minutes) after ablation, 2) occurrence of two consecutive transient (less than 1 minute) complete AV blocks after each energy delivery, or 3) complete AV block (lasting greater than 2 minutes) after ablation. Of seven dogs in group 1 and five dogs in group 2 in which incomplete AV block was achieved 1 hour after the procedure, six in group 1 and five in group 2 remained in incomplete AV block 2-3 months after ablation. One dog in group 1 progressed into complete AV block. Of the remaining three dogs in group 1 and five dogs in group 2 in which complete AV block was initially achieved 1 hour after ablation, two in group 1 and four in group 2 continued to have complete AV block, whereas one in each group had AV conduction returned to incomplete at 1-2 months of follow-up. Thus, a total of 13 dogs had chronic incomplete AV block induced by radiofrequency catheter ablation. Pathologic examination of the conduction system in two dogs with first-degree AV block, two dogs with second-degree AV block, and one dog with complete AV block showed discrete scars involving the approaches to the AV node and the AV node itself. It is concluded that, in most dogs studied, chronic incomplete AV block could be achieved by careful titration of the dosage of radiofrequency energy and by regulation of the ablation end points.     

Radiofrequency ablation of ventricular myocardium using active fixation and passive contact catheter delivery systems

This study examined the qualitative and quantitative effects of radiofrequency energy using active fixation and passive contact catheter delivery systems on normal bovine atrium and ventricle and diseased human ventricle in vitro. Two active fixation (custom screw-in or suction electrode) catheters and two passive contact (custom ring or standard electrode) catheters were used with a 500 kHz radiofrequency current generator. Linear regression analysis between lesion dimensions and power output showed excellent correlation coefficients for all catheter delivery systems except the suction catheter. Lesion sizes also increased with duration of radiofrequency energy delivery at low power using the USCI quadripolar catheter. Lesion size in diseased human ventricle was considerably smaller than in the normal ventricle. Comparison of induced lesion dimensions using pulsed and continuous delivery modes showed only minor differences. Tissue impedance was relatively constant during energy delivery. Arcing was associated with a sudden increase in voltage and impedance and a sudden decline in current. This was most frequently observed at high power and with the suction electrode catheter. The use of high (50 W) power output and prolonged application (up to 180 seconds) in atrium and ventricle did not induce perforation. We conclude that a variety of catheter delivery systems can be used for effective radiofrequency energy delivery and ablation in atrial and ventricular myocardium in the pulsed or continuous mode. Impedance changes during radiofrequency ablation cannot be used to guide the extent of ablation but do detect arcing during the procedure.     

Is radiofrequency catheter ablation available for treatment of ventricular tachycardias?--Effects of sequential unipolar applications using multiple electrode catheter]

The purpose of this study was to examine the effects of radiofrequency energy delivered to the canine endocardium in sequential unipolar applications using multipolar electrode catheter for treatment of ventricular tachycardias. Radiofrequency energy generated by the newly designed device (500 kHz) was delivered to the ventricular myocardium by a quadripolar electrode catheter. The device could indicate output and voltage and could calculate myocardial impedance. In order to determine the power of the ablation in vivo, sequential unipolar application was performed with various output in vitro. A continuous endocardial ablation was achieved with output beyond 15 W and with duration of 5 sec per one pole. According to our measurement, the myocardial impedance in vivo was about three times as large as that in vitro. Therefore, minimal output of 45 W in vivo was applied in the same manner in vitro, which resulted in continuous belt-shaped endocardial ablated lesion. Ventricular stimuli after sequential unipolar applications did not induce ventricular tachycardia in any of the dogs. We conclude that radiofrequency sequential unipolar application using the newly designed device produces a large ablated area and may be suitable for ablation of the foci of ventricular tachycardias.     

Esophageal imaging and strategies for avoiding injury during left atrial ablation for atrial fibrillation

BACKGROUND: Part of the esophagus is contiguous to the posterior wall (PW) of the left atrium (LA). Esophageal injury has occurred during LA ablation for atrial fibrillation (AF). The ability to identify the esophagus and monitor LAPW lesions with intracardiac echocardiography (ICE) has not been documented. METHODS: We report an index case of atrioesphageal fistula as a complication of transcatheter ablation of AF. After the index case, we retrospectively reviewed morphologic changes with radiofrequency (RF) delivered at LAPW during pulmonary vein (PV) electrical isolation using an 8-mm tip electrode (up to 70 W at a maximum of 50-52 degrees C for 60 seconds) or Chilli catheter (up to 50 W at a maximum of 40 degrees C for 60 seconds). ICE did not influence lesion application. After the index case, RF power was reduced at areas adjacent to the esophagus (8 mm/30-50 W at 50 degrees C or Chilli/40 W at a maximum of 38 degrees C). Duration of RF, 10-30 seconds, was titrated based on accelerated bubble formation or early echogenic lesion formation. RESULTS: The longitudinal extent of the contiguous LAPW-esophageal wall (length 18-59 mm) was identified in all 152 patients (ages 56 +/- 10 years, 117 men). Preablation LAPW (2.8 +/- 0.7 mm) and contiguous anterior esophageal wall (3.0 +/- 0.8 mm) thickness were noted. A total of 6 +/- 4.9 lesions/patient were delivered to the LAPW contiguous to the esophagus. Echogenic LAPW thickness increased to 7.5 +/- 2.1 mm (vs. 2.8 +/- 0.5 mm preablation) before the index case (n = 70 patients) and 4.7 +/- 1.6 mm (vs. 2.9 +/- 0.6 mm) after the index case (n = 67), with power reduction and titration of duration of energy delivery RF (P <.01) and PV isolation in all. CONCLUSIONS: The LAPW-esophageal region can be identified and monitored with ICE imaging during ablation procedures. RF lesions to the LAPW in PV isolation can produce dramatic morphologic changes immediately adjacent to the anterior esophageal wall. A reduction in power amount and duration as described coupled with online lesion monitoring to further titrate duration (<30 seconds) of power delivery decreases the depth of lesion formation and limits the risk of esophageal involvement.     

Ablation of the atrioventricular junction with radiofrequency energy using a new electrode catheter

Percutaneous catheter ablation using radiofrequency energy can be used to interrupt atrioventricular (AV) conduction in patients with supraventricular tachycardia refractory to drugs. Results of radiofrequency ablation of the AV junction using a custom-designed catheter with a large, 3-mm-long distal electrode, 2-mm interelectrode spacing, and a shaft with increased torsional rigidity were compared with those using a standard quadripolar electrode catheter (Bard EP). An electrocoagulator (Microvasive Bicap 4005) supplied unmodulated radiofrequency current at 550 kHz, which was applied between the distal electrode of the ablation catheter and a large skin electrode. With use of the modified catheter, 12 of 13 patients (92%) had persistent complete AV block induced with 7 +/- 5 applications of 18 +/- 6 W of radiofrequency power. In contrast, complete AV block was produced in only 9 of 18 (50%) historical control patients treated with the standard catheter, despite a similar number of applications (7 +/- 5) and power output (16 +/- 4 W). A rise in impedance, due to desiccation of tissue and coagulum formation, occurred earlier (28 +/- 18 vs 52 +/- 24 seconds, p less than 0.001) and more frequently (54 vs 40% of applications, p = 0.047) in patients treated with the standard catheter than in patients treated with the modified catheter. The use of a catheter designed to increase the surface area of electrode-tissue contact allows more radiofrequency energy to be delivered before a rise in impedance occurs and appears to increase the effectiveness of radiofrequency ablation of the AV junction.     

Microwave Ablation of Myocardial Tissue

Microwave Ablation of Myocardial Tissue. Introduction: The biophysical properties of microwave electromagnetic radiation suggest that it may be an alternative to radiofrequency (RF) energy for ablation of arrhythmias resistant to treatment using RF ablation.
Methods and Results: The aim of this study was to characterize lesions produced using simple element designs in a blood super fused ovine tissue model to simulate endocardial ablation. The effect of tissue bath flow, duration of microwave exposure, and changes in forward power on lesion size were examined using a modified monopole element. Lesion size increased with increasing duration of exposure and increasing forward power (P ≤ 0.05). Lesion depth was 0.7 ± (1.7 mm after 30 seconds and n.5 ± L9 mm after 360 seconds. Lesion depths at 61. 71, and 80 W were 6.4 ± 3.7, 8.9 ±±2.0, and 11.9 ± 1.2 mm, respectively. Altering flow within the bath from 3 to 5 L/min did not significantly change lesion size.
Conclusion: Simple element designs can be used to produce a range of lesions from very small sizes to lesions that are transmural in the ventricle. The temperature half-time for microwave ablation is far greater than that of RF ablation. Like RF lesions, the lesions produced by microwave ablation have greater width than depth. Deep penetration of lesions into the ventricular myocardium can (only be achieved with these elements by producing lesions of perhaps unnecessarily large volume.     

Catheter ablation of atrioventricular junction using radiofrequency current in 17 patients. Comparison of standard and large-tip catheter electrodes

BACKGROUND. Two catheter electrode systems were compared for delivering radiofrequency current for ablation of the atrioventricular junction. Seventeen patients with drug-resistant supraventricular tachyarrhythmias were studied. METHODS AND RESULTS. A 6F or 7F catheter with six or eight standard electrodes (1.25 mm wide, 2.5-mm spacing) was used in the first seven patients (group 1). A 7F quadripolar catheter with a large-tip electrode (4 mm long; surface area, 27 mm2) was used in the final 10 patients (group 2). Both ablation catheters were positioned to record a large atrial potential and a small but sharp His bundle potential from the distal bipolar electrode pair. Radiofrequency current was applied between a large skin electrode on the left posterior chest and either 1) each individual electrode on the standard-tip electrode catheter at 40 V (group 1) or 2) the large-tip electrode at 50-60 V (group 2). Radiofrequency current was limited to 40 V in group patients because of the strong potential for an early impedance rise when higher voltage is applied through standard electrodes. Complete atrioventricular block was achieved in six of seven group 1 patients and all 10 group 2 patients. A junctional escape rhythm followed ablation in five or six group 1 patients (mean cycle length, 1,066 +/- 162 msec) and eight of 10 group 2 patients (mean cycle length, 1,281 +/- 231 msec). Atrioventricular block was produced in a mean of 4.7 +/- 4.6 radiofrequency current applications delivered over a period of 42 +/- 45 minutes using the large-tip electrode (group 2) compared with 46 +/- 22 applications using standard electrodes (15.9 +/- 10.2 applications delivered through the standard-tip electrode) over a period of 147 +/- 59 minutes (group 1). For the application producing atrioventricular block, the large-tip electrode used higher voltage (58 +/- 17 versus 38 +/- 5 V, p less than 0.03) and had lower impedance (103 +/- 22 versus 148 +/- 40 omega, p less than 0.01), resulting in greater power (33.0 +/- 13.0 versus 10.2 +/- 0.6 W, p less than 0.003) and shorter time to block (8 +/- 3 versus 22 +/- 3 seconds, p less than 0.001). Current delivery through standard electrodes was limited by an impedance rise occurring 7 +/- 7 seconds after the onset of one or more radiofrequency current applications at 10 +/- 1 W in six of seven patients. Using the large-tip electrode, an impedance rise occurred in five of 10 patients, but at 25 +/- 10 W and after 21 +/- 9 seconds. Atrioventricular block occurred before the impedance rise in three of these five patients. Complete atrioventricular block persisted in 15 of 16 patients at a mean follow-up of 8.7 months. Atrioventricular conduction returned at 1 month in one group 2 patient and was successfully ablated by a second procedure. Three group 1 patients died 0.5-2 months after ablation, and a fourth patient underwent cardiac transplantation after 10 months. Pathological examination of the heart in two of these patients showed necrosis of the atrioventricular node and origin of the His bundle, without injury to the middle or distal His bundle. All 10 group 2 patients are alive and subjectively improved after ablation. CONCLUSIONS. We conclude that catheter-delivered radiofrequency current effectively produces complete atrioventricular block (94%) without requiring general anesthesia or the risk of ventricular dysfunction or cardiac perforation. The large-tip electrode allows a threefold increase in delivered power and markedly decreases the number of pulses and time required to produce atrioventricular block.     

The LETR-Principle: A Novel Method to Assess Electrode-Tissue Contact in Radiofrequency Ablation

Minimal Power RF Application. Introduction: Stable electrode-tissue contact is crucial for successful radiofrequency ablation of cardiac tachyarrhythmias. In this in vitro study, a custom-made radiofrequency generator was used to evaluate the correlation between tip temperature response to a minimal radiofrequency power delivery (Low Energy Temperature Response: LETR-Principle) and electrode-tissue contact as well as lesion size.
Methods and Results : A battery-powered radiofrequency generator (LETR-Box, 500 kHz, 0.1 to 0.3 W) could measure the temperature increase at the tip electrode with 0.01°C accuracy. The device was tested in vitro using isolated porcine ventricular tissue. For various electrode-tissue settings (i.e., 0 to 0.89 N contact force), the temperature increase (δT) due to 0.1-W power delivery for 10 seconds was recorded. Subsequently, for the same electrode-tissue contact, a temperature-controlled radiofrequency ablation was performed (70°C target temperature. 50-W maximum output, 30 sec). Thereafter, the lesion size was measured histologically. To prove the safety of the applied LETR-Principle, the tissue was inspected microscopically after continuous radiofrequency power delivery of 0.3 W for 1 hour with high contact pressure (1.33 N). The delivery of 0.1-W radiofrequency power resulted in an average δT of 0.18° plusmn; 0.13°C. During temperature-controlled radiofrequency ablation, the tip temperature was 59° 8.5°C, resulting in a lesion depth of 4.8 ± 0.6 mm. The correlation coefficient between δT and contact force was 0.97 and 0.81. respectively, for lesion depth. No lesion was microscopically visible after power delivery of 0.3 W for 1 hour with 1.33 N contact pressure.
Conclusion : The LETR-Principle safely indicates electrode-tissue contact and lesion depth under in vitro conditions and can be useful for catheter positioning during radiofrequency ablation procedures.     

Indication of the radiofrequency induced lesion size by pre-ablation measurements.

BACKGROUND: During radiofrequency ablation of arrhythmias tissue heating and hence lesion size depend on electrode-tissue contact and cooling of the electrode tip caused by cavitary blood flow. These factors are unique and unknown for each catheter placement in the beating heart. A tool for assessing these factors prior to ablation may indicate the lesion size which will be obtained for any given catheter position. METHODS AND RESULTS: Radiofrequency ablation was performed in vitro on strips of left ventricular porcine myocardium during two different levels of convective cooling (0 or 0.1 m/s), two different contact pressures (10 or 30 g) and parallel or perpendicular electrode-tissue orientation using 7F 4 mm tip catheters. Prior to ablation the impedance rise (DeltaIMP) caused by the obtained contact and the temperature rise with a 0.6 W 5 s test pulse (DeltaT) were measured. Subsequently, during unchanged conditions, radiofrequency ablation was performed as either temperature-controlled, power-controlled or irrigated tip ablation and lesion size was determined. DeltaIMP increased significantly (P < 0.05) by improved contact, whereas it was not affected by convective cooling. DeltaT was significantly increased by increasing contact pressure (P < 0.05) and significantly decreased by increased cooling (P < 0.001). DeltaT was not systematically affected by electrode orientation. The product of DeltaT and DeltaIMP showed a significant correlation between the obtained lesion size and power output for temperature-controlled and between lesion size and tip temperature for power-controlled ablation (P < 0.001). CONCLUSIONS: Pre-ablation measurement of DeltaIMP and DeltaT can indicate the lesion size resulting after ablation in temperature-controlled, power-controlled and irrigated ablation in vitro, since DeltaT reflects cavitary cooling and to a smaller extent electrode-tissue contact, and DeltaIMP reflects only electrode-tissue contact.     

A rewarming maneuver demonstrates the contribution of blood flow to electrode cooling during internally irrigated RF ablation

Introduction: Titration of radiofrequency (RF) ablation energy to avoid steam pops while maximizing lesion size is difficult because of disparities between electrode and tissue temperature. We hypothesized that the variable contribution of local blood flow to electrode cooling contributes to electrode-tissue temperature disparity, even with an irrigated RF catheter.
Methods and Results: Forty RF lesions were made in the atria of live swine with an internally irrigated cooled RF catheter. Prior to RF delivery, the catheter tip was cooled and then allowed to rewarm to body temperature by stopping irrigant flow. The rewarming time (RT) was noted. The catheter was again cooled and RF energy delivered, with power titrated to achieve electrode temperature of 40°C, which was previously defined as the approximate upper limit of safety. Lesion formation and steam pops were observed with intracardiac echocardiography. The RT ranged from 10 to 47 seconds. Nine steam pops were seen. The mean RT for lesions with pops was faster than those without (20 vs. 33 seconds, P = 0.003). The 20 lesions with faster RT required more power to achieve target temperature than the 20 lesions with slower RT (P = 0.01). Eight of nine steam pops occurred in the group with faster RT.
Conclusions: RT quantifies convective heating by blood prior to RF. Faster RT predicts greater cooling by blood during irrigated RF, a greater power requirement to reach target electrode temperature, and a higher risk of steam pops during fixed-temperature ablation. RT therefore can demonstrate the variation in blood cooling with each lesion and can be used to tailor energy delivery to maximize efficacy and safety.     

Radiofrequency ablation of hepatic tissue: a new experimental animal model

BACKGROUND/AIMS: Experimental radiofrequency ablation has already been performed in healthy livers of porcine models, but not in less expensive and easy-to-manage rats, with devices capable of delivering radiofrequency ablation in the 20-30 g liver of such small animals being so far unavailable. METHODOLOGY: We experimented with a modified system of radiofrequency ablation of liver tissue in rat models developing a custom-made needle-microelectrode of very small dimensions (0.3x2 mm) and an electrode-tip cooling technique, based on saline solution infusion. We adjusted duration (seconds) and power (watts) of radiofrequency ablation letting them range between 5-50 seconds and 5-25 W, respectively, to obtain the greatest lesions with the least side effects. After sacrificing the animals, an accurate histological examination of the liver was made. RESULTS: It is possible to establish beforehand the diameter of thermal liver lesion on the basis of joules of applied energy. The greatest increase of liver thermal lesion diameter (8 mm) is obtained with a 250-joule (10 W for 25 seconds) thermal energy cooling the electrode-tissue interface. CONCLUSIONS: Experimental radiofrequency ablation in rat liver is an effective and cheap way to study its effects on healthy hepatic tissues. It might be the first step to treat experimentally caused liver tumors.     

Transmembraneous Irrigation of Multipolar Radiofrequency Ablation Catheters: Induction of Linear Lesions Encircling the Pulmonary Vein Ostium Without the Risk of Coagulum Formation?

INTRODUCTION: Pulmonary vein (PV) isolation for the curative treatment of atrial fibrillation using conventional radiofrequency ablation (RF) catheters with the point by point technique is time consuming and carries a remaining risk for thrombembolic complications. AIMS OF THE STUDY: Aim of the present in vivo study was to evaluate feasibility and safety of a novel multipolar irrigated ablation catheter designed to create contiguous lesions encircling the PV ostium in a single ablation position. METHODS: The entire ablation section (tripolar, length of each electrode 22 mm, interelectrode distance 2 mm, helix radius: 9 and 10 mm) of the 7F RF catheter (Encirclr, Medtronic, MN, USA) was covered by a porous membrane (pore size 30 micron) providing continuous irrigation. The helical formed catheter was used in two different experimental settings. Initially, a thigh muscle preparation has been performed in 7 anesthetized sheep in order to evaluate the development of lesions at different power level (40-80 W) and RF duration (30-90 sec). The ablation catheter was placed at the surface of the thigh muscle in a perpendicular position (0.1 N contact pressure) and perfused with heparinized blood (250 ml/min, 37C degrees ). Irrigation was provided with a flow rate of 10 ml/min. The resulted lesion morphology was evaluated with regard to coagulum or crater formation and lesion depth and diameter. Subsequently in 9 anesthetized sheep intracardiac ablation has been achieved with 50 W and an irrigation flow of 10 ml/min. Transseptal puncture and RF ablations were guided using fluoroscopy and intracardiac echocardiography (ICE, Acuson, USA). Endpoint of the intracardiac RF applications was the reduction of local electrogram amplitude >50%. RF applications were achieved at both atrial appendages and in the orifices of the coronary sinus (CS), the vena cava inferior (VCI) and PV. Following RF ablation all animals were sacrificed and following in vivo staining (2% TTC) macroscopically and histologically investigations of the lesions were performed. RESULTS: At the thigh muscle preparation 57 RF applications have been performed. The lesion depth was homogeneous without gaps between the ablation electrodes. There was a significant increase comparing 30 with 90 sec of RF duration for 40, 50 and 60 W applications respectively: 40 W: 1.1 +/- 0.4 vs. 3.6 +/- 0.5; 50 W: 1.2 +/- 0.3 vs. 4.6 +/- 0.4 mm and 60 W: 2.6 +/- 0.6 vs. 4.8 +/- 0.5 mm. All applications with 80 W (n = 3) had to be terminated due to immediate increase of impedance >150 omega. Late impedance rises (>60 sec) without occurrence of coagulum formation have been observed in 1 out of 4 RF applications with 60 W.A total of 85 RF applications could be achieved intracardiacally in the right atrium (right atrial appendage n = 18, ostium of the coronary sinus n = 12, ostium of the inferior caval vein: n = 12) and in the left atrium (left atrial appendage: n = 15, ostium of the PV: n = 28). ICE guided positioning of the catheter and showed during all applications no coagulum formation at the electrode or impedance rise (>150 Omega). Reduction of local electrograms (>50%) were observed following 48 out 85 (56%) RF applications. The lesions showed a homogeneous depth of 4 +/- 2 mm and a width 5 +/- 2 mm at the surface. No charring or crater formation could be observed in any of the lesions. CONCLUSIONS: In the present in vivo studies it could be demonstrated that long irrigated ablation electrodes induce continuous lesions without the risk of thrombus formation at the electrode. Increase of RF duration from 30 to 90 seconds with power setting of 40-60 W, respectively, created deeper lesions without the risk of thrombus formation. Thus, the helical formed irrigated ablation catheter appears to be appropriate for simplified PV isolation.     

Gold‐Tip Electrodes—A New “Deep Lesion” Technology for Catheter Ablation? In Vitro Comparison of a Gold Alloy Versus Platinum–Iridium Tip Electrode Ablation Catheter

Gold-tip electrodes. Radiofrequency (RF) catheter ablation is widely used to induce focal myocardial necrosis using the effect of resistive heating through high-frequency current delivery. It is current standard to limit the target tissue-electrode interface temperature to a maximum of 60-70 degrees C to avoid char formation. Gold (Au) exhibits a thermal conductivity of nearly four times greater than platinum (Pt-Ir) (3.17 W/cm Kelvin vs 0.716 W/cm Kelvin), it was therefore hypothesized that RF ablation using a gold electrode would create broader and deeper lesions as a result of a better heat conduction from the tissue-electrode interface and additional cooling of the gold electrode by "heat loss" to the intracardiac blood. Both mechanisms would allow applying more RF power to the tissue before the electrode-tissue interface temperature limit is reached. To test this hypothesis, we performed in vitro isolated liver and pig heart investigations comparing lesion depths of a new Au-alloy-tip electrode to standard Pt-Ir electrode material. Mean lesion depth in liver tissue for Pt-Ir was 4.33+/-0.45 mm (n=60) whereas Au electrode was able to achieve significantly deeper lesions (5.86+/-0.37 mm [n=60; P<0.001]). The mean power delivered using Pt-Ir was 6.95+/-2.41 W whereas Au tip electrode delivered 9.64+/-3.78 W indicating a statistically significant difference (P<0.05). In vitro pig heart tissue Au ablation (n=20) increased significantly the lesion depth (Au: 4.85+/-1.01 mm, Pt-Ir: 2.96+/-0.81 mm, n=20; P<0.001). Au tip electrode again applied significantly more power (P<0.001). Gold-tip electrode catheters were able to induce deeper lesions using RF ablation in vitro as compared to Pt-Ir tip electrode material. In liver and in pig heart tissue, the increase in lesion depth was associated with a significant increase in the average power applied with the gold electrode at the same level of electrode-tissue temperature as compared to platinum material.     

利用射频消融法拔出起搏电极导线的实验研究

探索利用起搏电极导线直接释放射频能量到心肌组织是否可拔出起搏电极 ,多少能量合适。取新鲜猪心脏 ,切成条状心肌组织块 ,放置于盛有 37～ 38℃生理盐水的不锈钢碗中 ,碗底接射频背部电极 ,将单极导线(MedtronicCapsureSP 4 0 2 3)顶端压在心肌组织上 ,释放射频能量 ,方案为 1,2 ,3,4 ,5W ,时间为 3,6 ,9…… 2 1s,双极导线的顶端电极消融方案同单极电极。双极导线 (MedtronicCapsureSP 4 0 92 ,4 5 92 )的环圈电极放电为 8,10 ,12W ,时间为 5 ,10 ,15 ,2 0s消融后测损伤范围。结果 :单极导线放电 1W、12s,损伤范围是 2 .0± 0 .5mm× 1.7± 0 .6mm ,2W、6s,3W、3s其损伤范围分别是 2 .6± 0 .4mm× 2 .2± 0 .3mm ,2 .3± 0 .3mm× 2 .2± 0 .6mm ,4W、5W ,3s可引起明显心肌损伤。双极导线的顶端电极消融损伤范围与单极导线相比无统计学差异 (P >0 .0 5 )。心室双极导线的环圈电极放电 8W、2 0s ,10W、10s ,其损伤范围分别是 6 .3± 0 .6mm× 5 .0± 0 .0mm ,5 .5± 1.3mm× 4 .3± 0 .6mm。心房双极导线的环圈电极消融损伤范围与心室双极导线相比有统计学差异 (P <0 .0 5 )。结论 :利用起搏电极导线直接释放射频能量到心肌组织体外实验是可行的 ,这有可能成为拔除永久起搏导线的一种简单实用方法。     

An experimental study of determining the appropriate frequency of radiofrequency catheter ablation in vitro and in vivo for ventricular tachycardias]

The purpose of this study was to examine the appropriate frequency of radiofrequency catheter ablation (RFA) for ventricular tachycardia. Radiofrequency energy generated by a device in which the frequency could be changed, was delivered from an electrode catheter with an electrode tip-width of 4 mm. RFA was performed for 10 seconds with 20W (50V x 0.4A) using 7 different frequencies from 10 to 500 kHz on ventricular myocardium in vitro and in anesthetized dogs. The ablated lesion was significantly larger with RFA of 200-300 kHz in both surface area and depth (p less than 0.05). The appearance of ventricular arrhythmia during RFA increased as the frequency decreased, and one dog applied with RFA of 100 kHz had spontaneous ventricular fibrillation resulting in death. All dogs with frequency less than 100 kHz had a muscle cramp during RFA. We conclude that appropriate frequency seems to be 200-300 kHz to obtain a large ablated lesion, and a frequency higher than 300 kHz seems suitable to avoid arrhythmia. We also conclude that a frequency under 100 kHz should not be used.     

应用特制电极消融实验性心房颤动的研究

为使迷宫手术治疗心房颤动（简称房颤）时出血少、损伤小和缩短手术时间，制备了特殊射频消融电极。并将其物理学参数、形成心房透壁性消融灶所需的能量（经心内外膜消融分别为２０Ｗ×３０ｓ和１５Ｗ×３０ｓ）和消融灶的病理变化与Ｗｅｂｓｔｅｒ导管消融结果进行比较，各参数均基本一致，且该电极用于房颤消融可以减少消融次数，更有利于形成比较均匀一致的心房线性消融灶，对心房本身的大小、形态影响较小。应用该电极在心房、腔静脉等部位按一定的路径作连续性、透壁性线性消融可明显地减少犬实验性房颤的诱发次数和持续时间。     

Safety profiles and lesion size of different radiofrequency ablation technologies: a comparison of large tip, open and closed irrigation catheters

INTRODUCTION: Different technologies have been developed for radiofrequency ablation (RFA), which include increasing electrode (tip) size and cooling the tip through irrigation either internally (closed-loop) with D5W or externally (open-loop) with saline. Although these catheters are widely used clinically, the propensity for adverse events and the lesion profiles of each of these catheter technologies have not been directly compared under a wide range of controlled conditions. METHODS AND RESULTS: Freshly excised canine thigh muscle was placed in a chamber filled with circulating, heparinized blood heated to 37 degrees C. Five different catheters were tested: 4 mm tip, 10 mm tip single thermistor, 10 mm tip multitemperature sensor, 4 mm closed-loop irrigated cooled-tip, and 4 mm open-loop irrigated cooled tip at several different contact and power settings. The catheter and tissue interface was continuously monitored with intracardiac echocardiography (echo) (Acuson). During the RFA, any bubbling generated from the tip and/or popping seen on echo was noted, and after each RFA, the catheter and lesion were examined for the presence of thrombus. For all of the catheters, complications correlated to the electrode tip temperature and power setting. All of the catheters experienced complications at any lesion size except for the open-irrigated catheter, which only had complications at the largest lesions. Overall, the cooled tip catheters experienced an at least sixfold greater odds of popping, bubbling, and impedance rises than the 4 mm, but the majority occurred at power levels greater than 20 W. The open-irrigated catheters created eccentric lesions that extended away from the tissue-catheter interface, in the direction of blood flow. In addition, it produced saline filled blisters at the lesion site in 16.7% of the burns. The 10 mm catheter had an at least twofold greater odds of thrombus, charring, and bubbling, but larger lesions than the 10 mm multitemperature sensor catheter. CONCLUSIONS: Catheter type, contact conditions, and power settings all play a role in lesion size and in the frequency of complications that occur during an RFA. Cooling the electrode tip, either internally or externally, does not prevent complications from occurring, especially at the higher power control settings. Adding more temperature sensors to the 10 mm seems to reduce the amount of complications that can occur.     

In vivo evaluation of virtual electrode mapping and ablation utilizing a direct endocardial visualization ablation catheter

Visualization Catheter with Virtual Electrode Ablation. Background: Radiofrequency (RF) ablation utilizing direct endocardial visualization (DEV) requires a “virtual electrode” to deliver RF energy while preserving visualization. This study aimed to: (1) examine the virtual electrode RF ablation efficacy; (2) determine the optimal power and duration settings; and (3) evaluate the utility of virtual electrode unipolar electrograms. Methods and Results: The DEV catheter lesions were compared to lesions formed using a 3.5 mm open irrigated tip catheter within the right atria of 12 sheep. Generator power settings for DEV were titrated from 12W, 14W and 16W for 20, 30 and 40 seconds duration with 25 mL/min saline irrigation. Standard irrigated tip catheter settings of 30W, 50°C for 30 seconds and 30 mL/min were used. The DEV lesions were significantly greater in surface area and both major and minor axes compared to irrigated tip lesions (surface area 19.43 ± 9.09 vs 10.88 ± 4.72 mm, P<0.01) with no difference in transmurality (93/94 vs 46/47) or depth (1.86 ± 0.75 vs 1.85 ± 0.57 mm). Absolute electrogram amplitude reduction was greater for DEV lesions (1.89 ± 1.31 vs 1.49 ± 0.78 mV, P = 0.04), but no difference in percentage reduction. Pre‐ablation pacing thresholds were not different between DEV (0.79 ± 0.36 mA) and irrigated tip (0.73 ± 0.25 mA) lesions. There were no complications noted during ablation with either catheter. Conclusions: Virtual electrode ablation consistently created wider lesions at lower power compared to irrigated tip ablation. Virtual electrode electrograms showed a comparable pacing and sensing efficacy in detecting local myocardial electrophysiological changes. (J Cardiovasc Electrophysiol, Vol. 23, pp. 88‐95, January 2012)     

Radiofrequency catheter ablation of the atrioventricular junction from the left ventricle

BACKGROUND. The purpose of this study was to describe a new technique for catheter ablation of the atrioventricular junction using radiofrequency energy delivered in the left ventricle. METHODS AND RESULTS. Catheter ablation of the atrioventricular (AV) junction using a catheter positioned across the tricuspid annulus was unsuccessful in eight patients with a mean +/- SD age of 51 +/- 19 years who had AV nodal reentry tachycardia (three patients), orthodromic tachycardia using a concealed midseptal accessory pathway, atrial tachycardia, atrial flutter (two patients), or atrial fibrillation. Before attempts at catheter ablation of the AV junction, each patient had been refractory to pharmacological therapy, and four had failed attempts at either catheter modification of the AV node using radiofrequency energy or surgical and catheter ablation of the accessory pathway. Conventional right-sided catheter ablation of the AV junction using radiofrequency energy in six patients and both radiofrequency energy and direct current shocks in two patients was ineffective. The mean amplitude of the His bundle potential recorded at the tricuspid annulus at the sites of unsuccessful AV junction ablation was 0.1 +/- 0.08 mV, with a maximum His amplitude of 0.03-0.28 mV. A 7F deflectable-tip quadripolar electrode catheter with a 4-mm distal electrode was positioned against the upper left ventricular septum using a retrograde aortic approach from the femoral artery. Third-degree AV block was induced in each of the eight patients with 20-36 W applied for 15-30 seconds. The His bundle potential at the sites of successful AV junction ablation ranged from 0.06 to 0.99 mV, with a mean of 0.27 +/- 0.32 mV. There was no rise in the creatine kinase-MB fraction and no complications occurred. An intrinsic escape rhythm of 30-60 beats/min was present in seven of the eight patients. Each patient received a permanent pacemaker and has been asymptomatic during 3-13 months of follow-up. CONCLUSIONS. Catheter ablation of the AV junction can be achieved effectively and safely using radiofrequency energy delivered in the left ventricle when the conventional right-sided approach is unsuccessful.     

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.