Clinical use of cooled radiofrequency ablation

Irrigated (cooled) radiofrequency (RF) ablation has become our primary ablation tool for treating atrial fibrillation, macroreentrant atrial tachycardias, and scar-related ventricular tachycardias. As with any technology that increases ablation lesion size, there is the potential for increased risk. The methods described are a cautious approach to power titration that considers the risks of excessive heating and the lesion size needed for a particular site. Future methods of assessing lesion creation will hopefully refine energy titration to improve safety and efficacy of cooled RF ablation.     

Time course of esophageal lesions after catheter ablation with cryothermal and radiofrequency ablation: implication for atrio-esophageal fistula formation after catheter ablation for atrial fibrillation

Background: Atrio-esophageal fistulas have been described as a consequence of radiofrequency (RF) ablation for the treatment of atrial fibrillation (AF). However, whether cryoablation can avoid this potential fatal complication remains unclear.
Methods and Results: We studied the effects of direct application of RF and cryoablation on the cervical esophagus in 16 calves. Cryoablation was performed with a 6.5-mm catheter probe using a single 5-minute freeze at <−80°C, and RF ablation was delivered with an 8-mm catheter electrode at 50 W and 50°C for 45–60 seconds. Histopathologic assessments were performed at 1, 4, 7, and 14 day(s) after completion of the ablation protocol: four animals were examined each day. A total of 85 direct esophageal ablations were performed: 41 with RF and 44 with cryoablation. There were no significant differences in lesion width, depth, or volume between cryoablation and RF ablation at Day 1, 4, and 14 after the procedure (P > 0.05). However, lesion width and volume were significantly larger with RF than with cryoablation at Day 7. Although acute (Day 1) and chronic (Day 14) RF and cryoablation lesions were of comparable size, histologic evidence of partial- to full-wall esophageal lesion ulceration was observed in 0 of 44 (0%) lesions with cryoablation, compared with 9 of 41 (22%) lesions with RF ablation (P = 0.0025).
Conclusions: Direct application of cryoablation and RF ablation created similar acute and chronic lesion dimensions on the esophagus. However, cryoablation was associated with a significantly lower risk of esophageal ulceration, compared with RF ablation.     

Comparison of lesion sizes produced by cryoablation and open irrigation radiofrequency ablation catheters

Introduction: The relative lesion sizes created by large electrode cryoablation catheter and irrigated radiofrequency (RF) ablation are not known. The purpose of this study was to directly compare lesion sizes created by cryoablation and irrigated RF under controlled conditions.
Methods and Results : Ablation lesions were created in freshly harvested porcine left ventricular myocardium in a blood-filled tissue bath using an 8-mm-tip cryoablation catheter and a 3.5-mm-tip open-irrigated RF ablation catheter. Lesions were created under all permutations of the following conditions: electrode orientation vertical (perpendicular) or horizontal (parallel) to the tissue, electrode contact pressure at 6 or 20 g, and blood flow at 0.2 or 0.4 m/s over the electrode-tissue interface. The largest lesion volumes created with cryoablation were 961 ± 103 mm³, compared with the largest lesions volumes created with RF of 680 ± 48 mm³ (P < 0.001). The 3-way interactions among electrode orientation, contact pressure, and superfusate blood velocity accounted for the variation in lesion volumes for both catheters (both r²= 0.97, both P < 0.0001). The greater contact pressure increased lesion size for both cryoablation and RF. For cryoablation, lesion sizes were increased by the horizontal orientation and by the lower blood flow velocity. For open-irrigated RF, lesion sizes were significantly reduced by the horizontal orientation, however.
Conclusions : Depending on conditions of electrode orientation, contact pressure, and blood velocity, either 8-mm-tip cryoablation or open-irrigated RF may produce the larger lesion volumes. Open-irrigated RF lesion sizes are reduced in the horizontal catheter orientation.     

Comparison of epicardial cryoablation and irrigated radiofrequency ablation in a Swine infarct model

Epicardial Cryoablation in Swine. Introduction: Cryoablation is an alternative to radiofrequency (RF) energy used in some ablation procedures. Its role and effectiveness compared to irrigated RF in epicardial tissue and epicardial substrates is not yet fully established. Methods and Results: Using a swine chronic infarct model, we compared RF lesions produced by an open‐irrigated 3.5 mm tip catheter with those produced by an 8 mm tip cryocatheter in epicardial infarct border zone, epicardial normal tissue, and normal endocardium. In the infarct border zone, cryolesions were larger than RF lesions in maximum diameter (9.3 ± 2.9 mm vs 6.2 ± 2 mm, P < 0.001) and volume (171.7 ± 173.1 mm³ vs 77 ± 53.5 mm³, P = 0.021). In normal epicardial tissue, cryolesions were larger in maximum diameter (11.2 ± 4.3 mm vs 7.7 ± 3.1 mm, P = 0.012), depth (5.8 ± 1.6 mm vs 4.7 ± 1.4 mm, P = 0.034), and volume (274.7 ± 242.2 mm³ vs 112 ± 102.9 mm³, P = 0.002). In normal endocardium, no significant differences were found. Conclusions: Epicardial cryoablation with an 8 mm tip cryocatheter led to larger lesion volume in infarcted myocardium compared to a 3.5 mm irrigated RF catheter. This is likely related to a combination of cryoadherence, more efficient energy delivery with horizontal orientation, and lack of warming by circulating blood. Cryoablation merits further investigation as a modality for treating ventricular tachycardia of epicardial origin in humans. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1016‐1023, September 2012)     

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.     

Tako-tsubo cardiomyopathy following transcatheter radiofrequency ablation of the atrioventricular node.

A 66-year-old woman with atrial fibrillation and hypertension developed tako-tsubo cardiomyopathy following acutely uneventful radiofrequency catheter ablation of the atrioventricular (AV) node. We speculate that the increase in sympathetic activity that accompanies AV node ablation contributed to the pathophysiological process, which involves increased catecholamines and/or apical adrenoreceptor density and responsiveness.     

Efficacy and safety of cryoenergy in the ablation of atrioventricular reentrant tachycardia substrates in children and adolescents

INTRODUCTION: Cryoenergy has evolved as a safe and effective alternative for ablation of arrhythmia substrates in adult patients. Due to two specific features, cryomapping and cryoadhesion, this technique appears very attractive for pediatric patients minimizing complications and fluoroscopy time. The aim of the study was to investigate efficacy and safety of cryoenergy in the ablation of supraventricular tachycardia (SVT) substrates in pediatric patients. PATIENTS AND METHODS: Thirty-two patients (mean age: 10.1 +/- 3.5 years) with SVT (accessory pathways: n = 19; atrioventricular nodal reentrant tachycardia (AVNRT): n = 13) underwent electrophysiological study under the guidance of the LocaLisa system. Cryomapping at -30 degrees C was performed to predict cryoablation outcome and to ascertain AV conduction. Cryoenergy was delivered subsequently at the same spot (cryoablation at -70 degrees C) as verified by the LocaLisa system. RESULTS: Successful cryoablation was achieved in 24 of 32 patients (75%). A median of two (1-10) cryoablations were delivered. In the remaining 8 patients, radiofrequency (RF) current application was effective in 5 resulting in an overall success rate of 90.6%. In 4 patients with an accessory pathway cryomapping was not predictive for successful cryoablation (negative predictive value 66.6%). In 3 additional patients with AVNRT transient high-grade AV block occurred during cryoablation despite previous "safe" cryomapping at the same location. No other major complications were noted. CONCLUSION: Cryoablation of SVT substrates in pediatric patients was associated with a lower success rate compared to RF catheter ablation. Cryomapping decreased the number of permanent lesions but did not predict cryoablation outcome in all tachycardia substrates.     

射频消蚀术前后血清心肌酶变化的研究

对３３例患者射频消蚀术（简称ＲＦＣＡ）前后的血清心肌酶（ＣＫ、ＣＫ－ＭＢ．ＡＳＴ、ＬＤＨ、ＬＤＨ１）进行动态观察。结果表明：ＲＦＣＡ后血清心肌酶活性均有不同程度的升高（Ｐ＜０．０１）；ＣＫ及ＣＫ－ＭＢ于术后６小时达到峰值，２４小时恢复至正常水平，ＡＳＴ于术后１２小时达峰值、时达峰值，７２小时恢复正常，ＬＤＨ及ＬＤＨ，的达峰及恢复时间分别为２４小时和１２０小时；多元线性相关分析显示心肌酶活性的升高程度与消蚀靶点个数呈高度正相关（ｒ＝０．８１３６，Ｐ＜０．００１）．揭示ＲＦＣＡ对心肌组织有不同程度的损伤，影响心肌损伤范围的主要因素是消蚀靶点的多少。因此，在ＲＦＣＡ中，应力求标测定位准确，尽量减少试探性放电，以最大限度地减少心肌损伤。     

特发性心房颤动射频消融术后左心功能心脏超声评价及预后的研究

目的研究导管射频消融术对特发性心房颤动(AF)患者左心功能及预后的影响。方法入选2007年10月至2009年11月在贵州省人民医院心内科成功行射频消融术后未复发的特发性AF患者28例。包括持续性AF组(SAF)13例,阵发性AF组(PAF)15例。于术前、术后1个月、半年、1年时随访超声心动图检查,分别测量二尖瓣血流频谱、左心房射血力(LAEF)及左心室射血分数(LVEF),同时行生存质量问卷调查。结果射频消融术成功治疗AF后,3例SAF组患者二尖瓣血流频谱A峰未出现,其余A峰流速较术前明显增加(P<0.05);术后半年PAF组患者LAEF基本恢复正常(P<0.05),术后1年SAF组患者LAEF有所升高,但和术前相比差异无统计学意义(P>0.05);术后各组左心室射血分数较术前增加[SAF组(55.79±8.96)%对(48.13±5.18)%,P<0.05;PAF组(64.59±7.41)%对(51.09±5.63)%,P<0.01];各组总生存质量评分显著改善(P<0.05);PAF患者左心功能较SAF组恢复更为明显(P<0.05)。结论射频消融术后PAF患者左心功能恢复较SAF更加显著及迅速,预后更好,提示SAF患者射频消融术后须长期随访及相应治疗。     

国产可调节输出功率的双极射频消融装置的离体动物实验

目的 研究不同输出功率下,双极射频消融装置对不同厚度离体心房组织消融至透壁所需的时间及使用阻抗指标评价透壁性时的病理学检验,从而确定国产消融装置的合理输出功率.方法 20头猪屠宰后马上获取猪心,立即浸入4℃的生理盐水溶液中,清洗后制备离体心房组织.使用自行研制的输出功率可调式双极射频消融装置及消融钳,分别使用25 W、30 W及35 W的输出功率对离体心房组织进行消融.消融线间隔约5mm,彼此间平行.消融透壁的指标是消融时该处同时测定的电阻抗大于100 Ω.依次使用相同的输出功率,记录对不同厚度心房组织完成消融所需时间.消融完成后,沿两条消融线中点依次剪开心房组织,肉眼检查消融效果,测量消融线处组织厚度.按消融组织厚度,将心房组织分成＜2 mm、2～4 mm（≥2 mm,＜4 mm）、4～6 mm（≥4 mm,＜6 mm）及≥6mm4组.对应于不同输出功率和厚度,将心房组织分为12个区组.分别随机挑选每个区组的心房组织10块,将心房组织浸入多聚甲醛溶液,固定后心房组织使用石蜡切片,Mason三色法染色,显微镜下检验是否透壁.结果 实验共有350条消融线到达透壁指标.4～6 mm及＞6 mm组的心房组织消融完成时间明显长于＜2 mm组心房组织[（12.4±0.9）s比（24.3±0.3）s,P=0.042;（12.4±0.9）s比（35.9±0.3）s,P=0.001].消融完成时间在输出功率25 W与35 W间有显著差异[（28.9±0.5）s比（16.9±0.5）s,P=0.010].心房组织厚度与消融完成时间呈正相关.单次消融到达消融透壁指标时的病理透壁率为0～60％,随心房厚度增厚而降低,随输出功率增加而升高.结论 心房组织的消融完成时间随射频输出功率增加而缩短,并与心房组织厚度呈正相关.单次射频消融的透壁率较低.综合考虑消融所需时间、透壁率及安全性,输出功率在30～35 W是国产消融仪较为合理的射频输出功率.     

射频消融治疗快速性心律失常的体会

临床安全应用射频导管消融（ＲＦＣＡ）治疗各类快速性心律失常７８０例，总成功率９７．８％。其中房室折返性心动过速（ＡＶＲＴ）５５４例；房室结折返性心动过速（ＡＶＮＲＴ）１８２例；房扑１５例；房颤５例；特发性室速８例；右室流出道室速、室早１４例；致心律失常性右室心肌病（ＡＲＶＣ）２例。本组患者无一例发生血胸、气胸、心包填塞、动脉拴塞、３°房室传导阻滞、室颤等严重并发症。本文特别强调了术前充分准备、术中精确标测定位、细心轻巧操作、严谨控制消融能量和时间，术中与术后严密监护，可以最大程度地降低并发症的发生率。