Focal atrial tachycardias arising from the right atrial appendage: electrocardiographic and electrophysiologic characteristics and radiofrequency ablation

Objective: To characterize the electrocardiographic and electrophysiological features and frequency of focal atrial tachycardia (AT) originating from the right atrial appendage (RAA).
Background: The RAA has been described as a site of origin of AT, but detailed characterization of these tachycardias is limited.
Methods: Ten patients (3.8%) of 261 undergoing radiofrequency ablation (RFA) for focal AT are reported. Endocardial activation maps (EAM) were recorded from catheters at the CS (10 pole), tricuspid annulus (20 pole Halo catheter), and His positions. P waves were classified as negative, positive, isoelectric, or biphasic.
Results: The mean age was 39 ± 20 years, nine males, with symptoms for 4.1 ± 5.1 years. Tachycardia was incessant in seven patients, spontaneous in one patient, and induced by programmed extrastimuli in two patients. These foci had a characteristic P wave morphology. The P wave was negative in lead V₁ in all patients, becoming progressively positive across the precordial leads. The P waves in the inferior leads were low amplitude positive in the majority of patients. Earliest EAM activity occurred on the Halo catheter in all patients. Mean activation time at the successful RFA site =−38 ± 15 msec. Irrigated catheters were used in six patients, due to difficulty achieving adequate power. RFA was acutely successful in all patients. Long-term success was achieved in all patients over a mean follow up of 8 ± 7 months.
Conclusions: The RAA is an uncommon site of origin for focal AT (3.8%). It can be suspected as a potential anatomic site of AT origin from the characteristic P wave and activation timing. Irrigated ablation catheters are often required for successful ablation. Long-term success was achieved with focal ablation in all patients.     

High-resolution mapping and histologic examination of long radiofrequency lesions in canine atria

INTRODUCTION: Catheter ablation may prevent conduction of multiple atrial wavefronts and/or reduce the critical mass of atrial myocardium required to sustain fibrillation. The purpose of this study was to examine the effect of radiofrequency (RF) energy application on conduction in canine atria by performing high-density epicardial mapping and careful histologic examination of the ablation zone. METHODS AND RESULTS: RF energy was applied to the right atrial endocardium in nine anesthetized mongrel dogs in an attempt to create a line of conduction block spanning the vertical length of a 504-channel epicardial mapping plaque. The mean length and width of the histologically determined ablation zone was 34 +/- 4 and 7.3 +/- 2.6 mm, respectively. No thrombus was present. Conduction block that spanned the mapping plaque in 6 of 9 animals was matched histologically by continuous transmural necrosis in five. In one, only a portion of the ablation zone was transmural; the remainder was wide but nontransmural. In 2 of 3 animals with conduction, a narrow region was present where continuous transmural necrosis was absent. In the other animal, conduction was present despite continuous transmural necrosis. CONCLUSION: Conduction block usually occurred when continuous transmural necrosis was present, and conduction usually persisted when continuous transmural necrosis was absent. However, important exceptions were observed, including block when the ablation zone was wide but nontransmural, and conduction despite a thin line of continuous transmural necrosis.     

A novel hybrid transcatheter ablation system that combines radiofrequency and cryoenergy

Introduction: Radiofrequency (RF) and cryoenergy are largely considered independent modalities for the transcatheter ablation of cardiac arrhythmias. There are numerous theoretical advantages to engineering a system capable of delivering both energy forms.
Methods and Results: We designed a hybrid steerable catheter capable of delivering RF and cryoenergy independently, sequentially, and simultaneously. The novel catheter system was tested pre-clinically by creating a total of 180 ablation lesions in 20 mongrel dogs. Right atrial and right and left ventricular sites were preselected by a randomized factorial design devised to compare sequential and simultaneous RF and cryoenergy applications to standard RF, irrigated RF, and standard cryoablation. A steerable 4-mm electrode-tip hybrid catheter ("Fire and Ice") was created by modifying a 7 F cryocatheter (Freezor™, CryoCath Technologies, Montreal, Canada). RF energy was injected via a copper wire, thermocouples were isolated to reduce RF interference, and 100 KHz band pass filters and RF chokes were added. Sequential low-dose RF (20 W, 60 seconds) preceding or following cryoablation resulted in larger lesions (P = 0.0010). The addition of RF energy did, however, produce more thrombus than cryoenergy alone, with clot detected on 82.4% versus 12.1% of ablation lesions, P < 0.0001. Simultaneously applying the two energy modalities (45 W, 10 or 30°C, 60 seconds) created more voluminous lesions than standard RF ablation (median 288.1 vs 126.1 mm³, P = 0.0333) of similar dimension to irrigated RF ablation.
Conclusion: A versatile catheter system was fashioned capable of creating standard cryoablation lesions, standard RF lesions, and simultaneous lesions of similar dimension to irrigated RF.     

Acute coronary occlusion during radiofrequency catheter ablation of typical atrial flutter

We report the first case of acute right coronary artery occlusion in an adult patient during radiofrequency catheter ablation of typical atrial flutter. ST segment elevation rapidly resolved with antithrombotic therapy. This complication was thought to be due to the short distance between the endocardium and the right coronary artery at the ablation site, the high-wattage output from the radiofrequency generator, and the lack of sufficient cooling effect related to a severe upstream coronary stenosis. In patients with known right coronary artery stenosis who are suffering from typical atrial flutter, evaluation of the significance of the stenosis would be reasonable.     

Avoiding microbubbles formation during radiofrequency left atrial ablation versus continuous microbubbles formation and standard radiofrequency ablation protocols: comparison of energy profiles and chronic lesion characteristics

BACKGROUND: Radiofrequency (RF) energy parameters and chronic lesion characteristics associated with the microbubbles formation have not been yet fully elucidated. OBJECTIVES: The objective of this study was to compare the energy profiles and chronic lesion characteristics associated with RF ablation of the pulmonary vein antrum using three different ablation protocols: (1) avoiding microbubbles; (2) continuous microbubble formation; (3) temperature-guided ablation. METHODS: A 4-mm tip ablation catheter was used for creating RF ablation lesions in 15 adult mongrel dogs. All ablation lesions were created at the posterior aspect of the PV antrum in each animal. Avoiding microbubbles (group 1, n = 5 dogs, 23 lesions), continuous microbubble formation (group 2, n = 5 dogs, 22 lesions), and temperature-guided (group 3, n = 5 dogs, 19 lesions, target temperature 60 degrees C/power limit 50 W) ablation lesions were analyzed. RESULTS: Group 1 showed significantly lower power (19 +/- 8.6 W), lower temperature (50 +/- 4.8 degrees C), higher efficiency-of-heating index (2.9 +/- 0.8 degrees C/W), and lower impedance (109 +/- 24.4 Omega) than groups 2 (38 +/- 8.4 W; 63 +/- 10 degrees C; 1.8 +/- 0.8 degrees C/W; 148 +/- 34.4 Omega) and 3 (44 +/- 12 W; 57 +/- 2.4 degrees C; 1.4 +/- 0.5 degrees C/W; 139 +/- 23.1 Omega) (P < 0.001 vs groups 2 and 3). During ablation, no significant events were detected in group 1, but 11 cases of audible pop, 11 cases of catheter tip charring, and 1 case of fatal myocardial perforation were observed in groups 2 and 3. Transmural lesions were more frequently created in group 1. CONCLUSION: RF energy delivery applying "avoiding microbubbles" protocol seems to be associated with higher degree of safety and efficacy when compared to temperature-guided and continuous microbubble-formation ablation protocols.     

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。     

舒张期电位在左后分支室性心动过速射频消融中的作用

目的:分析舒张期电位与左后分支室性心动过速(室速)的相互关系及其对射频消融成功率的影响,探讨左后分支室速有效的消融部位。方法:选择我院2008-04-2010-01收治的28例无器质性心脏病的左后分支室速患者,心电图呈右束支传导阻滞,下壁导联QRS波为负向,电轴左偏,静脉注射维拉帕米可终止室速,心房快速刺激及心室程控刺激均可诱发出心动过速。于窦性心律时在左室后间隔标测到提前的浦肯野电位(P电位),如消融后未出现舒张期电位则重新寻找靶点,直至该部位消融后出现舒张期电位。结果:28例患者于窦性心律时在靶点处消融后均出现舒张期电位,心房及心室刺激均未能诱发室速,且随访6个月后均无复发。结论:舒张期电位的出现提示左后分支室速折返环的阻断,如消融后出现该电位可明显提高手术成功率。     

Atypical left atrial flutter after intraoperative radiofrequency ablation of chronic atrial fibrillation: successful ablation using three-dimensional electroanatomic mapping

Curative treatment of chronic atrial fibrillation (AF) remains a challenging task for electrophysiologists. Eliminating the initiating triggers by focal radiofrequency ablation in a subset of patients with paroxysmal AF and modifying the maintaining substrate by performing linear lesions within the left atrium in patients with prolonged episodes of AF are among the alternative approaches for management of these patients. Recently, a new intraoperative treatment procedure aimed at eliminating left atrial anatomic "anchor" reentrant circuits by induction of contiguous lesions using radiofrequency energy under direct vision was introduced. However, atypical left atrial flutter may occur during follow-up after intraoperative ablation of AF. These arrhythmias most likely are due to discontinuities in linear lesions; therefore, they can be successfully mapped and ablated in a subsequent percutaneous catheter ablation procedure. We report and discuss the case of a patient who underwent successful intraoperative ablation of chronic AF, but who developed atypical left atrial flutter postoperatively. Three-dimensional nonfluoroscopic electroanatomic mapping revealed a gap in the linear lesion line connecting the left upper and right upper pulmonary vein orifices. Ablation at the exit site of the breakthrough was successful.     

Acute effects of left atrial radiofrequency ablation on atrial fibrillation

INTRODUCTION: Acutely, when left atrial ablation is performed during atrial fibrillation (AF), the AF may persist and require cardioversion, or it may convert to sinus rhythm or to atrial tachycardia/flutter. The prevalence of these acute outcomes has not been described. METHODS AND RESULTS: Left atrial ablation, usually including encirclement of the pulmonary veins, was performed during AF in 144 patients with drug-refractory AF. Conversion to sinus rhythm occurred in 19 patients (13%), to left atrial tachycardia in 6 (4%), and to atrial flutter in 6 (4%). In the 6 patients with a focal atrial tachycardia, the mean cycle length was 294 +/- 45 ms. The tachycardia arose in the left atrial roof in 3 patients, the left atrial appendage in 2, and the anterior left atrium in 1. In 3 of 6 patients, the focal atrial tachycardia originated in an area that displayed a relatively short cycle length during AF. In 6 patients, AF converted to macroreentrant atrial flutter with a mean cycle length of 253 +/- 47 ms, involving the mitral isthmus in 5 patients and the septum in 1 patient. All atrial tachycardias and flutters were successfully ablated with 1 to 15 applications of radiofrequency energy. CONCLUSION: When left atrial ablation is performed during AF, the AF may convert to atrial tachycardia or flutter in approximately 10% of patients. Focal atrial tachycardias that occur during ablation of AF may be attributable to driving mechanisms that persist after AF has been eliminated, whereas atrial flutter results from incomplete ablation lines.     

Change in the retrograde atrial activation sequence following radiofrequency modification of the atrioventricular node: implications for the electrophysiologic circuit of a variant of atrioventricular nodal reentrant tachycardia

INTRODUCTION: Despite the great success in treating AV nodal reentrant tachycardia (AVNRT) with radiofrequency modification of the AV node, the dimensions of the electrophysiologic circuit of this arrhythmia remain unclear, and simple models fail to explain all tachycardia-related phenomena. METHODS AND RESULTS: We describe three unusual cases of supraventricular tachycardia (SVT). In all three cases, retrograde atrial activation during ventricular pacing or during SVT manifested local left atrial electrograms recorded from the coronary sinus preceding the septal atrial electrograms (eccentric activation), with earliest atrial activity at the lateral or posterolateral mitral annulus. Electrophysiologic maneuvers and observations were consistent with AVNRT as the mechanism in each case. In all cases, radiofrequency modification of the AV node eliminated inducible SVT and abolished dual pathway AV nodal physiology. The retrograde atrial activation sequence during ventricular pacing changed after ablation in each case, with septal atrial electrograms preceding left atrial electrograms recorded from the coronary sinus (concentric activation). CONCLUSION: The observations in these cases cannot be explained by the traditional model of slow, fast, and intermediate AV nodal pathways. A model incorporating a circuit close to the AV node with left atrial and coronary sinus connections is proposed.     

Acute coronary occlusion secondary to radiofrequency catheter ablation of a left lateral accessory pathway

A case of asymptomatic acute coronary occlusion secondary toradiofrequency catheter ablation of a left lateral accessorypathway is reported. Due to post-procedural ST modificationsof the surface ECG, a coronary angiography was performed whichdisclosed total occlusion of the first marginal branch of theleft circumflex coronary artery. A cute myocardial infarctionwas confirmed by moderate cardiac enzyme release, abnormal myocardialperfusion scan and mild lateral hypokinesia at echocardiographv.This rare but potentially harmful complication of interventionalelectrophysiology should be kept in mind and coronary angiographyperformed immediately when coronary occlusion related to radiofrequencyapplication is suspected.     

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。     

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.     

Junctional rhythm during slow pathway radiofrequency ablation in patients with atrioventricular nodal reentrant tachycardia: beat-to-beat analysis and its prognostic value in relation to electrophysiologic and anatomic parameters

INTRODUCTION: Junctional rhythm usually is considered a sensitive but nonspecific marker of successful ablation of the slow pathway in AV nodal reentrant tachycardia. Nevertheless, this junctional rhythm has been little studied, and its relations to recognized predictors of successful radiofrequency (RF) application were never established in any study. METHODS AND RESULTS: Thirty-nine patients underwent RF ablation of the slow pathway for AV nodal reentrant tachycardia. Ninety RF applications were delivered, and each ablation site was determined using three different fluoroscopic projections. Six anatomic zones were defined from low posterior septum to the site of distal His-bundle recording (P1, P2, M1, M2, A1, and A2). Characteristics of junctional rhythm during RF applications were analyzed. Atrial electrogram characteristics at the ablation sites also were studied. All patients had successful slow pathway ablation, without any complication. The ablation sites were located as follows: 41 at P1, 26 at P2, 20 at M1, and 3 in M2. Forty RF applications were successful: 14 of 41 attempts at P1, 7 of 26 at P2, 16 of 20 at M1, and 3 of 3 at M2. Mid-septal ablation site (M1 and M2) was associated with higher occurrence of junctional rhythm (P < 0.0001), earlier first junctional beat (P = 0.008), and earlier occurrence of the longest junctional burst (P = 0.03) compared with posterior ablation site (P1 and P2). The combination of a mid-septal ablation site and a first junctional beat occurring < or = 3 seconds after onset of RF application identified successful RF application with 100% accuracy. Using multivariate analysis, the ablation site, duration of atrial electrogram (including slow pathway potential when present), and occurrence of junctional rhythm were independent predictors of success. CONCLUSION: Successful slow pathway ablation depends on many factors. Junctional rhythm characteristics are related to the site of RF delivery and can be helpful in assessing successful slow pathway ablation.     

Percutaneous microwave and radiofrequency ablation for hepatocellular carcinoma: a retrospective comparative study

Background Percutaneous microwave ablation and radiofrequency ablation are two commonly used modalities for the treatment of hepatocellular carcinoma; however, comparisons of them have not been documented adequately. Methods Of 102 patients with biopsy-proved hepatocellular carcinoma, 49 (98 nodules) were treated percutaneously with microwave ablation and 53 (72 nodules) with radiofrequency ablation. The local tumor control, complications related to treatment, and long-term results of the two modalities were compared retrospectively. Results The complete ablation rates were 94.9% (93/98) using microwave ablation vs 93.1% (67/72) using radiofrequency ablation (P = 0.75), and no significant differences were found either in the ablation of tumors of 3.0 cm or less (P = 1.00) or in those of more than 3.0 cm (P = 1.00) between the two modalities. The local recurrence rates were 11.8% (11/93) using microwave ablation vs 20.9% (14/67) using radiofrequency ablation (P = 0.12), and there were no significant differences between the two modalities either in tumors of 3.0 cm or less (P = 0.36) or in those of more than 3.0 cm (P = 0.82). The rates of major complications associated with microwave ablation and radiofrequency ablation were 8.2% (4/49) vs 5.7% (3/53; P = 0.71). The disease-free survival rates in the microwave ablation group were 45.9%, 26.9%, 26.9%, and 13.4% at 1, 2, 3, and 4 years, respectively, and those in the radiofrequency ablation group were 37.2%, 20.7%, and 15.5% at 1, 2 and 3 years, respectively (P = 0.53). The 1-, 2-, 3-, and 4-year cumulative survival rates for patients who underwent microwave ablation were 81.6%, 61.2%, 50.5%, and 36.8%, respectively, and for patients who underwent radiofrequency ablation the rates were 71.7%, 47.2%, 37.6%, and 24.2%, respectively (P = 0.12). Conclusions Percutaneous microwave ablation and radiofrequency ablation are both effective methods in treating hepatocellular carcinomas. The local tumor control, complications related to treatment, and long-term survivals were equivalent for the two modalities.     

Change in size of lesions over 3 weeks after radiofrequency ablation of left ventricle

INTRODUCTION: The initial success or failure of radiofrequency ablation (RFA) does not always reflect the long-term outcome that can lead to complications such as late atrioventricular block or recurrence of accessory pathways. We hypothesize that these occurrences may be due to a change in lesion size over time. METHODS AND RESULTS: Intramural RFAs were performed on five greyhounds at thoracotomy using an epicardial approach into the left ventricular (LV) wall. Twenty-one gauge needle electrode ablations were created in the anterior aspect of the left ventricle. Radiofrequency energy was delivered at 600 Hz for 60 seconds and at an electrode temperature of 90 degrees C. Eight ablations were created in each greyhound and the chest was closed. After 3 weeks, a further eight ablations were created under the same conditions in the lateral aspect of the LV, ensuring they were well away from the chronic lesions, and the dogs were sacrificed an hour later. All lesions were removed, stained with Gomori Trichrome and measured. There was no significant difference in lesion size detected in the 1-hour-old lesions compared with 3-week-old lesions. Acute lesions were well demarcated by an area of fibrous scar and a central necrotic region. Chronic lesions showed chronic inflammatory cells and strands of collagen. CONCLUSIONS: This study shows no change in lesion dimension over time and hence a change in size may not contribute to a change in RFA outcome over time.