导管微波消融兔心外膜和犬心内膜房室环部位对心肌损伤的病理学观察

目的 通过经导管途径对兔左室心外膜和犬心内膜房窀环部位的微波消融,观察微波消融对心肌琥珀酸脱氢酶(SDH)活性的影响及对消融位点心肌组织面积和体积的损伤程度.方法 ①日本健康大白兔21只.按体质量随机分为10,20,30 W组,每组7只.采用20%乌拉坦(4 ml/kg)静脉麻醉后暴露心脏,将微波电极轻置于左室前壁心外膜,高压盐水冲注下分别以10,20,30 W消融30 s.取心室肌,按免疫组化法显示SDH,光镜下观察结果 ,用千分尺测量损伤范围,计算损伤面积.②健康杂种犬32只,雌雄不限,按体质量分40,50,60,80 W组,每组8只,设2个时间点,每个时间点4只.采用戊巴比妥钠,按30 mg/kg静脉麻醉,气管插管接呼吸机及心电监护.将消融导管固定于左右心室前/后壁近间隔的房室环处,40,50 W组同时消融左右心室前壁,60,80 W组同时消融左右心室后壁,消融时间分别60,120 s.实验结束后取出心脏,用千分尺测量损伤范围,计算损伤体积,观察是否形成透壁性损伤并进行病理学检查.结果 光镜下,消融区SDH活性产物消失,细胞结构不清晰,呈淡蓝色,与周围组织界限清楚.消融中心酶缺损区损伤直径和损伤面积随消融功率(10,20,30 W)增加而明显扩大,分别为(3.99±0.41),(5.20±0.25),(6.31±0.37)mm和(12.53±2.56),(21.19±3.14),(30.96±3.76)mm2,组间比较差异有统计学意义(F值分别为76.8,58.5,P＜0.01或＜0.05).犬消融后,光镜下可见损伤区心肌呈凝同性坏死,心内膜可见少量附壁血栓形成.在消融的116个消融点中,发生透壁性损伤16个,有5个损伤累及到肺组织,可见心室穿孔的发生.心肌损伤体积随消融功率(40,50,60,80 W)增大而增加,在消融60,120 s时损伤体积分别为(46.7±2.5),(51.1±2.7),(133.2±3.4),(141.8±3.9),(248.5±6.2),(260.3±6.5),(313.7±9.5),(327.4±10.5)mm3,组间比较差异有统计学意义(F值分别为31.16,27.85,P＜0.01),相同功率,消融时间延长,损伤体积加大.结论 微波可经心内膜消融房室环部位接近心外膜的深病灶,微波输出功率增加,消融时间延长,对心肌组织损伤程度增大.     

通过动物实验评价射频能量对冠状动脉的急性损伤

目的通过动物实验观察射频消融术(RFCA)是否会导致冠状动脉(简称冠脉)的急性损伤,对比不同的消融方法对冠脉的影响。方法取成年犬21只,雌雄不限,随机分三组,第一组消融电极为4mm,能量级别设定为60℃/120s,分别消融左房室环、右房室环、冠状静脉窦内和心外膜的近冠脉处;第二组能量级别设定为80℃/120s,分别消融除心外膜外的其它三处;第三组消融电极为8mm,能量级别设定为60℃/120s,仅消融左右房室环。术毕观察消融点附近冠脉损伤情况,并取消融点及附近冠脉作病理检查,光镜下观察心肌和冠脉的变化。结果大体下观察,没有发现冠脉管腔的狭窄及管腔内血栓形成。对63处消融点附近的冠脉进行光镜检查时,3例冠脉或其分支出现明显变化,动脉壁破裂、壁结构消失、平滑肌溃疡、变性坏死,溃疡内有大量白细胞浸润;9例冠脉内皮细胞出现肿胀、脱落甚至消失;其余冠脉未有任何变化。结论常规RFCA是安全可靠的,但特殊部位、高能量射频消融时,应注意冠脉的损伤。     

功率、时间和间距对离体猪心双极射频消融的影响

目的 研究临床条件下多参数双极射频消融在离体猪心上形成的消融灶的形态大小,评价双极射频消融的有效性和安全性.方法 在预设功率(30 W和40 W)和灌注条件(1250m l/h)下用4 mm的大头双极消融电极对新鲜离体猪心进行消融,电极间距离从12～ 17 mm,时间从20～90 s,测定交汇消融灶的长度、深度、连接率和爆破率.结果 时间增加时,长度、深度、连接率、爆破率都增加;间距增加时,长度增加,深度、连接率、爆破率下降;功率增加时,长度、连接率、爆破率增加,深度减小.12 mm、20 s、30 W,有盐水灌注(1250 ml/h)时双击消融有效性和安全性最好,长度均值为19.89 mm,深度均值为3.94 mm,连接率100％,爆破率6％.结论 双极消融可以在电极间距离12 mm、20 s、30 W、有灌流(1250 ml/h)时形成稳定的交汇消融灶.     

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。     

^99mTc—MIBI心肌显像评价射频消融对儿童心肌的损伤

采用99mTc-甲氧基异丁基异腈(99mTc-MIBI)心肌灌注单光子发射型计算机断层显像(SPECT)方法观察射频导管消融(RFCA)对儿童心肌的损伤情况,旨在评价RFCA在儿童应用的安全性.8例快速型心律失常患儿,男7例,女1例,年龄8.5±3.0(5～13)岁.反复发作心动过速6个月～3年,发作时心电图6例示阵发性室上性心动过速(PSVT),2例为特发性室性心动过速(IVT).全部病例RFCA治疗前经体检、X线胸片、超声心动图及心肌酶学检查未发现器质性心脏病.全部患儿于术前1～2天及术后1天行99mTc-MIBI心肌灌注SPECT检查.评价标准为在至少两个不同轴面断层图像上同一部位出现放射性减低(>20%)、灶性缺损或花斑样改变为异常.若RFCA术前正常部位在术后出现上述改变,判定为消融致心肌损伤.全部病例均消融成功,未出现任何并发症.其中左侧房室旁道3例,消融部位为左室前侧壁;右侧房室旁道2例,消融部位为右室游离壁;房室结双径路1例,消融部位为冠状窦口下缘与His束电极之间;IVT 2例,消融部位为右室流出道.输出功率:左侧房室旁道15～20 W,右侧房室旁道25～40 W,房室结双径路15 W,右室流出道IVT 25 W.平均放电时间157±33 (120～195)s.8例患儿经99mTc-MIBI心肌灌注SPECT检查,其中7例RFCA前后无异常改变,1例RFCA术前及术后在短轴和垂直长轴断面均可见左室前壁(非放电部位)放射性减低.     

超声导管心室肌消融的实验研究

评估超声消融损伤灶的组织学改变 ,探讨各种物理因素对超声损伤范围的影响。使用自行研制的超声导管消融系统 ,在冠状动脉灌注及表面灌流的犬离体右室或左室游离壁热动力学模型上 ,以不同的电功率及辐照时间进行心室肌消融。结果 :持续 45s的超声消融能造成均一的、边界清楚的心肌坏死灶。电功率与损伤灶深度呈线性相关 (Y =2 .81+ 0 .4X ,r2 =0 .745 ) ,电功率 2 3.81W、超声辐照 6 0s产生的损伤灶最深 ,达 12 .2 7± 1.75mm。损伤面积与辐照时间呈正相关关系 (Y =17.94+ 0 .2 8X ,r2 =0 .5 8)。结论 :超声能量可能成为心内消融的能源。与射频消融相比 ,超声消融可造成更深的心肌损伤灶 ,提示超声消融有可能消除位于较深层心肌中的致心律失常病灶 ,这对于心肌梗死后室性心动过速的消融有较大的意义     

射频消融后组织学损伤和电学损伤范围的对比研究

目的：为确定射频消融后心动过速复发的原因，本文对射频消融犬右心室肌造成的电学损伤与组织学损伤范围进行了对比实验研究：方法：17只犬随机分成4组，实验组分别用20W10s、20W30s、20W60s的射频电流经心外膜消融犬右心室肌。实验前和实验后即刻、30、60min用单相动作电位电极导管在消融中心点及距中心点2、4、6、8即处死动物并取组织标本，测量组织学损伤范围：10、15和20mm处分别记录单相动作电位。术后立。结果；射频消融后，各时间点上动作电位幅度明显降低。消融中心部位电学损伤最严重，随远离中心点，损伤程度逐渐减轻。距中心点15mm左右，动作电位幅度基本恢复正常。消融后动作电位时间变化不明显。结论：本实验第一次提出了射频消融后电学损伤范围的概念，并发现电学损伤范围明显大于组织学损伤范围。临床上当消融治疗靶点定位不准确时，房室旁路则可能位于仅有电学损伤的部位。异常传导活动因电学损伤而暂时受抑制，造成成功的假象。这可能是射频消融成功后心动过速复发的主要原因。     

三维标测指导下冷盐水灌注导管在右侧房室旁路患者射频消融治疗中的有效性和安全性

目的 比较三维标测指导下冷盐水灌注导管与普通消融导管在右侧房室旁路患者射频消融治疗中的安全性和有效性。方法 对2018年1月至2022年6月在西安交通大学第二附属医院心内科行三维标测指导下射频消融治疗的112例右侧房室旁路患者进行回顾性研究,其中43例接受冷盐水灌注导管消融治疗（冷盐水组）,69例接受普通导管消融治疗（普通导管组）。比较两组患者的放电消融时间、放电次数、X线曝光量、即刻成功率、手术并发症、复发率的差别。结果 冷盐水组患者的手术时间、放电消融时间、X线曝光时间和辐射剂量,均低于普通导管组,差异均有统计学意义（P<0.05）。两组患者的即刻成功率（97.7% vs. 94.2%,P>0.05）和并发症发生率比较,差异无统计学意义（2.3% vs. 4.3%,P>0.05）。随访（32.3±17.7）个月,两组患者的复发率比较,差异无统计学意义（4.7% vs. 5.8%,P>0.05）。然而,冷盐水组有8例患者既往曾有消融失败或复发（8/43;18.6%）,普通导管组有3例既往消融失败或复发（3/69;4.3%）,两组间比较差异有统计学意义（P<...     

经导管微波消融房室环部位及心外膜病灶可行性的实验研究

目的旨在寻找一种可控制经导管途径心内膜非随机部位的微波消融方法。观察释放不同微波功率、时间对房室环部位心肌损伤范围和血流动力学、心电学的影响。了解导致房室环部位透壁性损伤的微波输出功率和放电时间及其安全性。方法选用实验用犬32只利用射频电极导管的可操控性，结合X线影像，将外周介入用8F长鞘管导入并固定于左、右心室前、后壁近间隔的房室环处。快速交换送入自制的微波消融导管并记录到小A大V波。微波输出能量设定为8个级别组，共消融126个位点，其中40W×60s／120s、50W×60s／120s4组消融左、右心室前壁；60W×60s／120s、80W×60s／120s4组消融左、右心室后壁。除40W×60s、50W×60s两组各7个消融点外，其余级别组均为16个消融点（左、右各8点）。实验结束后取出心脏，以1／6π×长×宽×深计算损伤体积，观察是否形成透壁性损伤，并进行光镜病理学检查。结果消融前后心电学及血流动力学指标差异无统计学意义（P〉0．05）。房室环部位损伤体积随微波输出能量级别的递增而明显扩大，左侧损伤体积由（47．0±26．1）mm^3增加到（326．7±109．0）mm^3，右侧损伤体积由（48．6±29．1）mm^3增加到（289．9±79．9）mm^3，各自组间比较差异有统计学意义（PL〈0．01，Pr〈0．01），损伤体积与输出功率呈正相关（rL=0．83，rR=0．87）；而恒定功率时随时间的延长，损伤体积呈平行增加（P〈0．05，r=0．85）；与损伤体积相比，损伤深度与放电时间相关性更强（r=0．91）。16个消融点发生透壁性损伤，其中5个消融点的透壁性损伤累及肺组织。微波消融产生的心肌损伤范围成椭圆体，显微镜下为均匀凝固性坏死，与周围的心肌组织间存在着非常清晰的界限，可见少量附壁血栓。结论利用微波消融房室环部位及心外膜下病灶是可行的，引起的损伤可以深至犬心肌厚度的4／5至心外膜，但应高度警惕走行于心外膜房室环部的冠状动脉和心脏静脉的损伤。恰到好处的能量选择和得心应手的微波消融电极，还需更加精细的研究工作。     

射频消融冠状窦的实验研究

对16条犬进行射频导管消融冠状静脉窦的作用及安全性研究.射频于冠状窦内电极导管和胸部片状电极间释放,能量为1229±711焦耳.13条犬于消融后半小时处死,3条犬于3～4周后处死.消融部位损伤长3.2±1.8mm,宽2.2±1.7mm,深2.±1.0mm,镜下所见为边界清晰的凝固性坏死(急性期)与纤维化(慢性期).冠状动脉、二尖瓣及心内膜均未受累.除二条犬偶发房性早搏或室性早搏外无心律失常发生,无血流动力学改变,无1例发生冠状静脉窦破裂.表明高能射频消融冠状静脉窦安全,就其损伤部位而论可能对破坏病人的左侧房室旁道有效.     

Epicardial radiofrequency ablation of ventricular myocardium: Factors affecting lesion formation and damage to adjacent structures

We evaluated the factors affecting epicardial radiofrequency (RF) lesion formation in normal ventricular myocardium. In 16 dogs, a minithoracotomy was made and a sheath was placed in the pericardial space. Standard ablation lesions (4-mm tip catheter; 70 ( composite function) C/60 seconds) were created in each ventricle under fluoroscopy guidance (n = 7) or hand-held with direct visualization of the catheter to assure optimal electrode-tissue contact (n = 6). In the latter, thermally-shielded (TS) electrodes (50% tip surface along its 4 mm length) were used in 3/6 dogs. Catheter tip (4 mm) irrigation (13 mL/minutes; 40 ( composite function) C/60 seconds) was employed with conventional techniques in 3 additional dogs. RESULTS: With optimal electrode-tissue contact (11 lesions), power (3.4 +/- 2.3 W vs. 16 +/- 13 W; p < 0.001) and pacing thresholds (0.2 +/- 0.0 mA vs. 3.6 +/- 5.7 mA; p = 0.004) were lower than standard RF (25 lesions). However, lesion dimensions were similar and transmural lesions did not occur (depth 2.8 +/- 1.1 mm vs. 3.0 +/- 1.5 mm). Catheter irrigation allowed high power outputs (43 +/- 6.1 W; p < 0.001) generating transmural lesions, 5/9 (55%), depth 6.4 +/- 2.1 mm. At constant power (2 W), catheter-tip temperature (52 +/- 5.2( composite function) C vs. 57 +/- 6.6( composite function) C; p = NS) and lesion (10 in each group) dimensions were similar for conventional and TS electrodes, but damage to parietal pericardium and lungs occurred with conventional electrodes only (70% vs. 0% p = 0.02). CONCLUSION: Standard epicardial RF ablation does not produce deep lesions and exhibits a significant energy loss probably due to poor electrode-tissue contact. Catheter irrigation allows delivery of high power outputs to the epicardium consistently creating deeper lesions than standard ablation. TS electrodes may reduce damage to neighboring structures during epicardial RF ablation.     

Cooled needle catheter ablation creates deeper and wider lesions than irrigated tip catheter ablation

OBJECTIVES: To design and test a catheter that could create deeper ablation lesions. BACKGROUND: Endocardial radiofrequency (RF) ablation is unable to reliably create transmural ventricular lesions. We designed an intramural needle ablation catheter with an internally cooled 1.1-mm diameter straight needle that could be advanced up to 14 mm into the myocardium. The prototype catheter was compared with an irrigated tip ablation catheter. METHODS: Ablation lesions were created under general anesthesia in 14 male sheep (weight 44 +/- 7.3 kg) with fluoroscopic guidance. Each of the catheters was used to create two ablation lesions at randomly allocated positions within the left ventricle. The irrigation rate, target temperature, and maximum power were: 20 mL/min, 85 degrees C, 50 W for the intramural needle catheter and 20 mL/min, 50 degrees C, 50 W for the irrigated tip catheter, respectively. All ablations were performed for 2 minutes. After the last ablation, blue tetrazolium (12.5 mg/kg) was infused intravenously. The heart was removed via a left thoracotomy after monitoring the sheep for one hour. RESULTS: There was no evidence of cardiac tamponade in any sheep. The intramural needle catheter lesions were significantly wider (10.9 +/- 2.8 mm vs 10.1 +/- 2.4 mm, P = 0.01), deeper (9.6 +/- 2.0 mm vs 7.0 +/- 1.3 mm, P = 0.01), and more likely to be transmural (38% vs 0%, P = 0.03). CONCLUSIONS: Cooled intramural needle ablation creates lesions that are significantly deeper and wider than endocardial RF ablation using an irrigated tip catheter in sheep hearts. This technology may be useful in treating ventricular tachycardia resistant to conventional ablation techniques.     

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.     

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.     

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.     

Direct visualization of epicardial structures and ablation utilizing a visually guided laser balloon catheter: preliminary findings

Epicardial Laser Balloon Ablation. Background: Intrapericardial mapping and ablation can be utilized to target epicardial arrhythmic circuits. Current epicardial ablation strategies are associated with risk of damage to adjacent structures, including the coronary vasculature and phrenic nerves. Objectives: The purpose of this study was to evaluate the feasibility of an investigational, visually guided laser balloon catheter for manipulation within the pericardial space, visualization of epicardial structures, and delivery of laser ablation lesions to the ventricular myocardium. Methods: Pericardial access was obtained in 4 anesthetized swine by subxyphoid puncture. The laser balloon catheter was introduced into the pericardial space via a deflectable sheath, and was manipulated to predefined regions in all animals. Visually guided laser ablation was performed on the ventricular myocardium, with post mortem examination of lesion size and depth. Results: The laser ablation catheter could be manipulated to all targeted regions in all animals. Associated structures, including epicardial coronary arteries and veins as well as an endocardial catheter in the left atrial appendage, were easily visualized. A total of 9 laser energy applications at varying power/time settings were performed. Ablation utilizing moderate (7–8.5 W) power produced relatively uniform lesions (diameter 5–12 mm, depth 6–9 mm), while high (14 W) power produced a visible “steam pop” with a large, hemorrhagic lesion (22 × 11 × 11 mm). Conclusions: The investigational laser balloon catheter can be manipulated within the epicardial space, allowing for direct visualization of surrounding structures during ablation. Titration of laser power can be utilized to create moderate‐sized ablation lesions while avoiding steam pops . (J Cardiovasc Electrophysiol, Vol. 22, pp. 808‐812, July 2011)     

A comparison of open irrigated and non-irrigated tip catheter ablation for pulmonary vein isolation.

AIMS: The relative efficacy and safety of open irrigated tip catheters compared with conventional non-irrigated catheters for pulmonary vein isolation (PVI) is unknown. METHODS: Forty-eight patients undergoing PVI using an open irrigated tip ablation catheter (Group 1) were compared with a group of 31 historical controls (Group 2). The control group underwent similar procedures using a standard, 4 mm tip, temperature controlled ablation catheter. Electrical mapping with a circular catheter was used to guide segmental radiofrequency ablation at the vein ostia. RESULTS: At follow-up (3.5+/-3.5 months) after a single procedure 35/48 (73%) patients in Group 1 and 14/31 (45%) in Group 2 were in sinus rhythm (p=0.03). Antiarrhythmic drug use was lower among those in Group 1 maintained in sinus rhythm (9/35 (26%) vs 8/14 (57%), p=0.002). Recurrent atrial fibrillation was more common in Group 2 (28/31 (90%) vs 28/48 (58%) p=0.004). Serious complications were uncommon in both groups. CONCLUSIONS: Compared with an historical control group, pulmonary vein isolation using open irrigated tip catheters was superior to ablation with conventional 4 mm tip catheters. Patients undergoing ablation with an irrigated tip catheter were less likely to experience symptomatic recurrences of atrial fibrillation or require further therapy for post-procedural arrhythmias.     

Mechanisms for Enlarging Lesion Size During Irrigated Tip Radiofrequency Ablation:

INTRODUCTION: Irrigated tip radiofrequency ablation of cardiac arrhythmias was developed to increase the size of the radiofrequency-induced lesion, since cooling of the electrode tip allows use of higher power settings. The purpose of this study was to determine if the increased lesion size during irrigated tip ablation is caused by the cooling effect solely or if increased electrical conductivity around the tip also contributes by increasing the "current-delivering size" of the tip: the so-called "virtual electrode effect." METHODS AND RESULTS: In vitro strips of left ventricular porcine myocardium and in vivo canine left ventricles were ablated. In vitro closed loop tip and showerhead irrigated tip catheters were compared. In vitro and in vivo showerhead tip catheters irrigated with solutions having different ionic content were compared. We found no difference in lesion size for closed loop and showerhead-type catheters (998 +/- 345 vs. 811 +/- 313 mm(3) during power-controlled ablation and 227 +/- 76 vs 318 +/- 127 mm(3) during temperature-controlled ablation). For irrigation with liquids having increasing ionic strength we found a decrease in lesion volume in vitro (361 +/- 249 vs. 812 +/- 229 mm(3) (P < 0.001) for power-controlled and 156 +/- 78 vs. 318 +/- 127 mm(3) (P < 0.05) for temperature-controlled ablation and nonsignificant differences in vivo. CONCLUSIONS: The mechanism for enlarging lesion size during radiofrequency irrigated-tip ablation is that higher power levels can be used. There is no virtual electrode effect caused by the highly conductive surroundings of the tip during irrigation. In vitro this effect is shown to be opposite: it decreases lesion size.