Morphometric ablation lesion characteristics comparing 4, 6, and 8 mm electrode-tip cryocatheters

Cryolesion Characteristics. Introduction: Despite widespread clinical use, ablation lesions produced by cryocatheters with 6 and 8 mm electrode-tips have not been fully characterized. We, therefore, sought to quantify and compare lesion dimensions and thrombus formation with 4, 6, and 8 mm electrode-tip cryocatheters. Methods and Results: By means of a randomized factorial design, 72 ablation lesions were created in atrial and ventricular chambers of adult miniature swine at a mean temperature of 79.9 +/- 4.0 degrees C. By histological morphometric analysis, the overall lesion depth was 4.3 +/- 2.1 mm, surface area 61.3 (28.7, 116.0) mm(2), and volume 130.2 (62.7, 231.3) mm(3). Cryolesions produced by all electrode-tip sizes were well circumscribed, with intact endothelial cell layers, and absence of thrombus. Colder temperatures generated lesions of greater surface area (P = 0.0061) and volume (P = 0.0080), but not depth. Depths were similar between the three electrode-tips. However, surface areas produced by 8 mm catheters were 91.7 mm(2) larger on average (176.7% increase, P = 0.0003) than 4 mm and 72.3 mm(2) greater (101.3% increase, P = 0.0144) than 6 mm catheters. The 8 and 6 mm catheters yielded mean lesion volumes 252.6 mm(3) (248.3% increase, P = 0.0041) and 115.9 mm(3) (113.9% increase, P = 0.0670) larger than 4 mm catheters. Greater variability in surface area and volume were observed with 8 mm catheters. Conclusion: Longer electrode-tip cryocatheters produce larger lesions of similar depth, with intact endothelial layers and absence of thrombosis. Surface areas and volumes may be particularly sensitive to catheter tip-to-tissue contact angles with larger electrodes, as reflected by greater variability with 8 mm tips.     

Microwave ablation using a spiral antenna design in a porcine thigh muscle preparation: in vivo assessment of temperature profile and lesion geometry

INTRODUCTION: Theoretical studies have suggested that microwave energy can increase the depth of heating compared with radiofrequency energy. A spiral microwave antenna design may have advantages over previous designs using smaller designs because the resulting power deposition pattern is considerably larger than the catheter diameter. We tested the efficacy of a spiral antenna using microwave energy in a porcine thigh muscle preparation. METHODS AND RESULTS: In five anesthetized pigs, the thigh muscle was exposed and bathed in heparinized bovine blood (36 degrees to 37 degrees C). A helical microwave catheter with a fiberoptic thermometer attached to the distal end was positioned perpendicular to the thigh muscle. The antenna-tissue interface and tissue temperatures at depths of 3.0 and 6.0 mm were measured. A 915-MHz microwave generator delivered energy at one of three power outputs (50, 100, or 150 W) for 60 seconds. Seventy lesions were created: 50 W (n = 23), 100 W (n = 24), and 150 W (n = 23). The mean depths at 50, 100, and 150 W were 4.3 +/- 1.8 mm, 7.2 +/- 1.7 mm, and 9.4 +/- 0.9 mm, respectively. Lesion depth (R = 0.96, P = 0.05), maximum surface dimension (R = 0.99, P = 0.06), and volume (R = 0.99, P = 0.04) were closely correlated to the power applied. CONCLUSION: Power is an important determinant of lesion size using a spiral microwave antenna. A novel, spiral microwave antenna design can create lesions of significant depth that may be applicable for the ablative therapy of ventricular tachycardia.     

Area Under the Real‐Time Contact Force Curve (Force–Time Integral) Predicts Radiofrequency Lesion Size in an In Vitro Contractile Model

FTI Predicts RF Lesion Size in Contractile Model. Introduction: Electrode tissue contact, radiofrequency (RF) power and duration are major determinants of RF lesion size. Since contact forces (CF) vary in the beating heart, we evaluated contact force–time integral (FTI) as a predictor of lesion size at constant RF power in a contractile bench model simulating the beating heart. Methods and Results: An open‐tip irrigated catheter was attached to a movable mount incorporating a dynamic force sensor allowing closed loop control to achieve desired force variations between the catheter tip and bovine skeletal muscle placed on a ground plate. RF energy (20 and 40 W for 60 seconds, 17 cc/min irrigation) was delivered during (1) constant contact (C) at 20 g, (2) variable contact (V) with a 20 g peak and 10 g nadir, and (3) intermittent contact (I) with a 20 g peak and 0 g nadir with loss of contact. V and I protocols were performed at 50 and 100 catheter movements/min and 2 systole:diastole time ratios (50:50 and 30:70). The area under the CF curve was calculated as the FTI. Measured FTI was highest in C, intermediate during V and lowest during I and correlated linearly with lesion volume (P < 0.0001 for 20 and 40 W). Lesion volume was highest in group C, intermediate in V and lowest in group I (P < 0.05 for C vs V, V vs I, and C vs I). Conclusions: Lesion size correlates linearly with measured contact FTI. Constant contact produces the largest and intermittent contact the smallest lesions despite constant RF power and identical peak contact forces. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1038‐1043, September 2010)     

Time to electrode rewarming after cryoablation predicts lesion size

Introduction: There are no methods in clinical use to assess tissue cooling during catheter cryoablation. Cryoablation electrode temperature may be a poor predictor of lesion size. The purpose of this study was to determine whether the time necessary for the cryoablation electrode to cool to target temperature or to rewarm after cryoablation can predict lesion size. Methods and Results: Cryoablation was performed on live porcine left ventricle in a saline bath (37°C) using 8‐mm‐tip catheter. Cryoablation was given for 300 seconds under all permutations of the following conditions: electrode orientation vertical or horizontal, contact pressure 6 or 20 g, superfusate flow over electrode–tissue interface at 0.2 or 0.4 m/s (N = 10 each condition set, total 80 experiments). The time intervals necessary to cool the electrode to the target temperature of ?75°C and to rewarm to + 30°C after termination of cryoablation were recorded. Lesion volume was predicted best by the time necessary to rewarm the elctrode to +30°C (r²= 0.65, P < 0.0001), followed by electrode temperature (r²= 0.28, P < 0.0001) and time to cool the electrode to ?75°C (r²= 0.24, P < 0.0001). Time to +30°C and time to ?75°C were associated with superfusate flow rate, contact pressure, and electrode orientation (r²= 0.80 and 0.61, respectively, both P < 0.0001). Superfusate flow rate, contact pressure, and orientation were also highly predictive of lesion volume (r²= 0.93, P < 0.0001). Conclusions: Time to cryoablation electrode rewarming is a better predictor of cryoablation lesion size than is electrode temperature. Time to cryoablation electrode rewarming reflects important determinants of cryoablation lesion formation—convective warming, contact pressure, and electrode orientation—that are not ascertainable during clinical ablation procedures.     

Temporary esophageal stenting allows healing of esophageal perforations following atrial fibrillation ablation procedures

BACKGROUND: Left atrial catheter ablation (LACA) has emerged as a successful method to eliminate atrial fibrillation (AF). Recent reports have described atrio-esophageal fistulas, often resulting in death, from this procedure. Temporary esophageal stenting is an established therapy for malignant esophageal disease. We describe the first case of successful temporary esophageal stenting for an esophageal perforation following LACA. CASE: A 48-year-old man with symptomatic drug refractory lone AF underwent an uneventful LACA. Fifty-nine ablations with an 8-mm tip ablation catheter (30 seconds, 70 Watts, 55 degrees C), as guided by 3-D NavX mapping, were performed in the left atrium to isolate the pulmonary veins as well as a left atrial flutter and roof ablation line. In addition, complex atrial electrograms in AF and sites of vagal innervation were ablated. Two weeks later, he presented with sub-sternal chest pain, fever, and dysphagia. A chest CT showed a 3-mm esophageal perforation at the level of the left atrium with mediastinal soiling and no pericardial effusion. An urgent upper endoscopy with placement of a PolyFlex removable esophageal stent to seal off the esophago-mediastinal fistula was performed. After 3 weeks of i.v. antibiotics, naso-jejunal tube feedings, and esophageal stenting, the perforation resolved and the stent was removed. Over 18 months of follow-up, there have been no other complications, and he has returned to a physically active life and remains free from AF on previously ineffective anti-arrhythmic drugs. CONCLUSION: Early diagnosis of esophageal perforations following LACA may allow temporary esophageal stenting with successful esophageal healing. Prompt chest CT scans with oral and i.v. contrast should be considered in any patient with sub-sternal chest pain or dysphagia following LACA.     

Echocardiographic lesion characteristics associated with successful ablation of inappropriate sinus tachycardia

INTRODUCTION: Catheter ablation of inappropriate sinus tachycardia has proven difficult. Despite the use of intracardiac echocardiography to help direct radiofrequency (RF) application to the anatomic target of the superolateral crista terminalis (CT), multiple RF lesions often are required. Furthermore, the characteristic echo-anatomic changes with RF application associated with a reduction in heart rate have not been defined. A characteristic echo signature, if present, may facilitate the ablation process. The purpose of this retrospective study was to define the echocardiographic characteristic changes associated with effective RF ablation for inappropriate sinus tachycardia. METHODS AND RESULTS: Detailed intracardiac echocardiographic imaging characterization of the superolateral CT was performed before and at the time of successful heart rate reduction. Using on-line videotape intracardiac echocardiography (9 MHz, 9 French), changes in wall thickness and echodensity at the CT lesion site were assessed at baseline, after each RF lesion, and with the lesion that produced heart rate reduction in 17 patients (age 32 +/- 9 years; 15 women) with inappropriate sinus tachycardia. In all patients, RF ablation was anatomically based and targeted only the superolateral CT. RF lesions were created using 20 to 50 W for up to 2 minutes using an 8-mm tip electrode. Successful heart rate reduction (> or = 20 beats/min) was achieved in 15 of 17 patients and required 41 +/- 31 RF applications (range 5 to 110, median 40). Effective RF (reduced heart rate) was observed starting with the 34th +/- 24th lesion (range 3rd to 86th, median 25th). After effective RF, CT wall thickness was increased (11.4 +/- 3.1 mm vs 7.7 +/- 2.4 mm at baseline) and wall swelling expanded to adjacent superior vena cava, but the degree of thickening was not specific for effective RF associated with heart rate reduction. Importantly, we noted echodensity changes reaching directly to the epicardium with the development of a linear low echodensity or echo-free space at the time of effective RF resulting in heart rate reduction. In two patients without effective heart rate reduction, echodensity changes never reached the epicardium. No complications (superior vena cava-right atrial junction orifice narrowing >50% or pericardial effusion) of RF were identified. CONCLUSION: An echocardiographically guided anatomic approach to RF ablation of inappropriate sinus tachycardia is safe and effective. A characteristic echocardiographic signature suggesting transmural/epicardium damage appears to be present at the time of successful heart rate reduction and may serve as an appropriate guide for directing additional RF when using this anatomic echocardiographically based approach.     

Changes in local wall thickness correlate with pathologic lesion size following radiofrequency catheter ablation: an intracardiac echocardiographic imaging study

INTRODUCTION: High-resolution intracardiac echocardiographic (ICE) imaging can accurately assess wall thickness during radiofrequency (RF) catheter ablation procedures. This study investigated the correlation of changes in wall thickness at the ablation site with pathologic lesion size. METHODS AND RESULTS: ICE image-guided 31 RF applications (30-50 W, up to 120 sec) were performed in five anesthetized closed chest swine (n = 5, body weight 35-60 kg). Twenty-four lesions were delivered in the right and left atria with standard RF; seven lesions were delivered in the left ventricle (LV) with irrigated (30-40 ml/min) RF. Wall thickness and tissue echo density measured by ICE imaging (pre- and 1-minute post-RF delivery) with increased focal echo density following RF deployment in the atria (4.5 +/- 1.5 vs 2.3 +/- 1.0 mm pre-RF) and the LV (9.8 +/- 2.3 vs 6.8 +/- 2.2 mm pre-RF; P < 0.01). The observed changes in wall thickness (DeltaWT) following ablation in the LV were greater than in the atria (3.0 +/- 1.4 vs 2.2 +/- 1.2 mm; P < 0.05). A significant correlation between DeltaWT and lesion depth (ventricular: r = 0.85, P < 0.05; atrial: r = 0.82, P < 0.01) was demonstrated at all ablation sites. Local wall thickness measured post-RF also significantly correlated with lesion depth (r = 0.89, P < 0.01), especially with that of transmural lesions (r = 0.95, n = 23, P < 0.001) at atrial and LV sites. CONCLUSION: Therapeutic RF ablation results in mural swelling and increased echo density. These changes can be detected by ICE imaging and correlate with pathologic lesion size. ICE imaging may be useful in online quantification of lesion size, especially for transmural lesions during clinical catheter ablation procedures.     

50例室性心律失常导管射频消融治疗临床分析

目的:报道不同类型室性心律失常的射频导管消融(RFCA)体会。方法:50例室性心律失常患者中男20例、女30例,年龄14～70(43.21±13.31)岁。除1例为陈旧性心肌梗死冠状动脉旁路移植术(CABG)后持续性室性心动过速(VT)、5例为致心律失常性右室心肌病(ARVC)外,其余44例均为非器质性心脏病室性心律失常。43例非器质性心脏病室性心律失常采用传统的起搏与激动标测。6例器质性心脏病VT及1例多源室性期前收缩(PVC)在非接触标测系统EnSite3000指导下进行消融治疗。结果:①48例消融成功,2例失败,成功率96%,4例复发。②右室流出道(RVOT)起源的VT和PVC具有典型的心电图特征,表现为典型的左束支传导阻滞型伴电轴右偏。RVOT的起源点不同,其12导联心电图特征不同,Ⅰ、Ⅱ、Ⅲ和aVF导联呈RR'型,V1～3具有深S波是游离壁起源的特征。ARVC表现为典型的左束支传导阻滞型伴电轴右偏,窦性心律时V1～3T波浅倒置,心脏核磁或心脏超声心动图见右室心肌运动减弱。③1例ARVC和1例陈旧性心肌梗死CABG术后病例在消融过程中出现心室颤动,经电除颤后继续消融成功。结论:RFCA是一种安全、有效...     

体表QRS电轴与特发性室性心律失常射频导管消融关系的探讨

目的探讨体表QRS电轴与特发性室性心律失常射频导管消融的关系。方法对65例特发性室性心律失常患者采用激动顺序标测和起搏标测法确定室性搏动起源部位并测量其QRS电轴,分析与消融成功的关系。结果65例中室性心动过速24例(左心室源性18例、右心室源性6例),室性期前收缩41例(右心室流出道起源)。其中18例左心室源性室性心动过速,电轴左偏13例,12例(平均-80°)均一次消融成功,另1例出现两种形态室性心动过速,电轴分别为-55°、-30°,为消融失败;电轴右偏5例(平均227°),只有2例(265°、261°)消融成功。电轴左偏者消融成功率(92.3%)与电轴右偏者(40.0%)比较,差异有显著性意义(P<0.05)。6例右心室源性室性心动过速电轴正常(平均84°),且均消融成功。而41例右心室室性期前收缩中,电轴正常37例(64°～90°)消融成功。4例电轴轻度右偏者2例(97°)消融成功,2例(99°、100°)消融失败。电轴正常消融成功率(100%)与右偏者(50.0%)比较,差异有显著性意义(P<0.05)。结论体表室性QRS电轴对术前判断室性心律失常的起源部位、指导标测和缩短标测时间及推断射频导管消融成功的可能性均具有一定的价值。