Right Coronary Artery Occlusion During RF Ablation of Typical Atrial Flutter

RCA Occlusion During RF Ablation . Right coronary artery (RCA) occlusion and acute myocardial infarction are rare during radiofrequency (RF) ablation of the cavotricuspid isthmus. Ventricular fibrillation (VF) or cardiac arrest in the periprocedural period may be the initial or only clinical manifestation. Septal or lateral RF delivery may increase the risk. We report 2 cases of RCA occlusion during ablation of typical atrial flutter (AFL). Angiographic and anatomical correlations are illustrated. One patient was ablated with a septal approach, the other with a lateral approach, and in each instance the RCA occluded near the ablative lesions. If septal or lateral ablation lines are contemplated during ablation of isthmus‐dependent atrial flutter, fluoroscopic or electroanatomic confirmation of catheter position is pivotal. Smaller tipped catheters, energy titration (to minimally effective dose), saline irrigation, or cryoablation should also be considered to help avoid this serious complication. (J Cardiovasc Electrophysiol, Vol. pp. 818‐821, July 2010)     

Tracking dynamic conduction recovery across the cavotricuspid isthmus

OBJECTIVES: We sought to assess the dynamic temporal course of conduction recovery during and after radiofrequency (RF) catheter ablation of the cavotricuspid isthmus. BACKGROUND: Although cavotricuspid isthmus block is accepted as the best end point of ablation for typical flutter, conduction recovery is thought to underlie many eventual recurrences. Its time course and frequency have not been determined. METHODS: In a prospective group of 30 patients (26 men and 4 women, age 64 +/- 12 years) undergoing ablation of typical flutter in the cavotricuspid isthmus, the morphology of the P wave during pacing from the low lateral right atrium after achievement of complete isthmus block was identified as a reference. Regression of this morphologic P wave change was confirmed to be associated with intracardiac evidence of the recovery of cavotricuspid isthmus conduction and was observed throughout the procedure both during ablation in sinus rhythm (n = 15, group B) and just after flutter termination (n = 15, group A). RESULTS: Stable complete isthmus block was achieved in all patients; 29 had a terminal positivity of the paced P wave. Flutter termination resulted in stable block and terminal P wave positivity in three patients, transient terminal P wave positivity and transient block despite continuing RF at the same site in five patients and no block in the remaining seven patients. Conduction recovery identified by recovery of P wave changes was nearly as common (48%) during ablation in sinus rhythm. Multiple recoveries were noted in some patients, and 72% of all recoveries occurred within 1 min. Conduction recovery was only rarely associated with coagulum, impedance elevation or pops. CONCLUSIONS: Conduction recovery in the cavotricuspid isthmus is common during and after ablation and can be accurately, dynamically and continuously observed by monitoring the recovery of the low lateral right atrial paced P wave change.     

单导管标测在心房扑动射频消融中的意义

目的:探讨单导管标测法在心房扑动(房扑)射频消融中的应用方法和效果。方法:阵发性心房颤动并发房扑患者行肺静脉电隔离术时采用单导管标测法消融房扑30例。所有患者行肺静脉电隔离术后,将10极冠状静脉窦(CS)导管远端2对电极放置于CS内,余位于CS外,并使之有一定的张力,使导管贴靠于三尖瓣环和低右房。用冷盐水灌注消融导管线性消融三尖瓣峡部,房扑发作患者在房扑下消融,窦律患者在CS远端电极起搏下消融,可在术中随时把大头消融导管置于希氏束部位,用于评价是否已完全达双向阻滞,即:起搏CS远端电极,刺激信号至CS近端电极A波的距离大于至希氏束A波的距离,则CS口至低右房单向阻滞;CS近端电极起搏,刺激信号至CS远端电极A波的距离大于至希氏束A波的距离,则低右房至CS口单向阻滞,从而达双向阻滞,CS近端电极起搏所需电压较高,有的患者可达24mA。结果:所用阵发性心房颤动并发房扑患者均成功行三尖瓣峡部线性射频消融,达到双向阻滞,无手术相关并发症,随访4个月～2年,无房扑复发。结论:单导管标测法对房扑患者行三尖瓣峡部线性射频消融操作简单、快速,可完全用于评价消融结果,成功率高,并且节省手术费用。     

三尖瓣峡部线性消融在心房颤动治疗中的效果

三尖瓣峡部是典型房扑折返环中的缓慢传导区域,对这一解剖结构进行线性消融以达到双向传导阻滞是典型房扑的一线治疗方法。房颤与典型房扑内在关系密切,一方面房颤与典型房扑往往共存于同一患者,另一方面房颤患者在电生理检查中常可见到典型房扑的诱发。因此在房颤射频消融术中常常补充三尖瓣峡部线性消融,以期病人获得更好的远期预后。但最近的研究对这一术式的疗效提出了质疑。本文以两种心律失常的内在联系为切入点,就三尖瓣峡部消融在房颤射频消融术中的疗效进行综述。     

射频消融治疗心房扑动

目的总结典型心房扑动的射频消融治疗经验。方法56例因反复心悸的住院患者,男性38例,女性18例,平均年龄(54.2±6.2)岁。体表心电图及动态心电图记录阵发心房扑动34例,持续心房扑动22例,口服胺碘酮治疗效果差。全部病例常规取右股静脉途径插入20极环状Halo电极记录心房激动顺序,4极电极送至冠状窦供起搏标测使用。结果全部手术成功。其中36例心房扑动于射频发放过程中终止,20例于窦性心律下放电消融。所有病例于消融结束后分别起搏冠状窦近端和低位右心房,证实峡部双相传导阻滞作为消融终点,即刻成功率100%。平均随访(6±2.6)个月,3例于术后2个月复发,复发率5.4%,经再次射频消融治疗成功,随访6个月,未再复发。结论以温控射频导管不间断放电线性消融治疗典型心房扑动疗效肯定,成功率高。     

Identification and ablation of atypical atrial flutter. Entrainment pacing combined with electroanatomic mapping

Differentiation between typical and atypical atrial flutter solely based upon surface ECG pattern may be limited. However, successful ablation of atrial flutter depends on the exact identification of the responsible re-entrant circuit and its critical isthmus. Between August 2001 and June 2003, we performed conventional entrainment pacing within the cavotricuspid isthmus in 71 patients with sustained atrial flutter. In patients with positive entrainment we considered the arrhythmia as typical flutter and treated them with conventional ablation of the cavotricuspid isthmus. As a consequence of negative entrainment we performed 3D-electroanatomic activation mapping (CARTO trade mark ). Conventional ablation of the right atrial isthmus was successful in all patients (n = 54) with positive entrainment. We performed electroanatomic mapping in the remaining 17 patients (14 male; age 60.9 +/- 16 years) resulting in the identification of 6 cases with typical and 11 cases with atypical flutter. Therefore, entrainment pacing was able to predict the true presence of typical atrial flutter in 91.5%. Atypical flutter was right sided in 4 patients and left sided in 7 cases. Electrically silent ("low voltage") areas probably demonstrating atrial myopathy were identified in all cases with left sided and in 2 patients with right sided flutter. In these patients targets for ablation lines were located between silent areas and anatomic barriers (inferior pulmonary veins, mitral respectively tricuspid annulus, or vena cava inferior). In 1 patient, the investigation was stopped due to variable ECG pattern and atrial cycle lengths. In the remaining cases, ablation was acutely successful. One patient, after surgical closure of a ventricular septal defect, demonstrated a dual-loop intra-atrial reentry tachycardia dependent on two different isthmuses. This arrhythmia required ablation of those distinct isthmuses to be interrupted. After a mean follow-up of 8.8 +/- 3.4 months, there was one patient with a recurrence of left-sided atrial flutter. Another patient developed permanent atrial fibrillation shortly after the procedure. Mean duration time of the procedure was 235.6 +/- 56.4 min (right atrium: 196 +/- 17.3 min; left atrium: 267.2 +/- 59.5 min), and average fluoroscopy time was 21.8 +/- 11.7 min (right atrium: 9.5 +/- 6 min; left atrium: 28.9 +/- 7 min). There was no incidence of serious complications associated with these procedures. In conclusion, conventional pacing in the cavotricuspid isthmus combined with electroanatomic mapping was an effective method to differentiate between typical and atypical atrial flutter. Electroanatomic mapping was a powerful tool both for identification of different atrial re-entrant circuits including their critical isthmuses as well as for effective application of individual ablation line strategies.     

Transvenous catheter–based microwave ablation for atrial flutter

We report a case of successful transvenous, catheter-based, cavotricuspid isthmus ablation for treatment of atrial flutter using microwave energy. Microwave energy was delivered at 900–930 MHz using 21 W of power. Bidirectional cavotricuspid isthmus conduction block was achieved by microwave ablation without any patient discomfort or complication during the procedure. Our initial experience suggests that transcatheter microwave ablation is feasible for the cure of typical atrial flutter.     

Macroscopic and microscopic study of the right coronary artery after radiofrequency catheter ablation of cavotricuspid isthmus in an experimental model]

INTRODUCTION AND OBJECTIVES: The right coronary artery (RCA) is found in the AV groove, just below the ablation target of atrial flutter, the cavotricuspid isthmus (ICT). After radiofrequency (RF) ablation with standard catheters, there have been no reports of complications, but it may not be successful in 10% of the cases. However, the use of irrigated tip catheters, which create deeper lesions, might potentially damage the coronary tree. METHODS: We analyzed the effects of ICT RF ablation on the coronary tree, with macroscopic and microscopic anatomopathological study. Ablation on ICT was performed using an irrigated tip catheter in 16 pigs and was randomly compared with a standard ablation catheter. There were no clinical problems, modifications of ST or new arrhythmias during the ablation. The heart was extracted at 1 week. RESULTS: The macroscopic study demonstrated that the right coronary artery was preserved, along the ICT, surrounded by the epicardial fat. The microscopic study showed an inflammatory reaction in the epicardial fat that reached the adventitia of the coronary artery, but never produced necrosis in 14 cases. The muscular wall of the artery had signs of focal inflammation without endothelium involvement in 2 cases. However, we found a subepicardial vein completely damaged by the radiofrequency. CONCLUSIONS: Although the right coronary artery is located just below the isthmus, no necrosis was observed in any case. However, there was an inflammatory reaction that focally reached the muscular wall. The veins may be damaged in RF ablation, perhaps due to the different blood flow of each vessel.     

射频消融心房扑动拖带刺激的电生理特征

探讨射频消融心房扑动 (简称房扑 )拖带刺激的电生理特征 ,更好的理解房扑机制 ,以期提高消融成功率、减少复发率。 5例阵发性典型房扑患者 ,诱发房扑后 ,在高位、低位右房 ,冠状窦口 (CSO)及右房下部的峡部分别进行拖带刺激 ,分析心房激动顺序 ,然后进行三尖瓣环至下腔静脉之间的线性消融。 5例房扑折返环均为逆钟向旋转 ,峡部 ,高位、低位右房及CSO呈现隐匿拖带 ,左房和卵圆窝呈现显性拖带 ,平均放电 9± 6次 ,均达到右房峡部双向阻滞。CSO起搏时体表心电图Ⅱ、Ⅲ、aVF导联P波形态发生改变。结论 :隐匿、显性拖带对判断峡部依赖性逆钟向房扑有较高价值 ,CSO起搏时心内电图激动顺序和体表心电图P波改变可做为判断峡部消融达到双向阻滞的标志     

Recording of double atrial potentials as a marker for isthmus block during ablation of atrial flutter

Radiofrequency ablation is an established method for treatment of type I atrial flutter. The assessment of creation of complete bidirectional isthmus block following linear ablation of the isthmus is an integral part of ablation procedure. Conventionally, bidirectional isthmus block is tested by pacing on either side of ablation line and looking for reversal of activation sequence in the right atrium. We looked at the feasibility of recording double potentials, separated by an isoelectric interval along the ablation line as an alternative method to demonstrate bidirectional isthmus block. An attempt was made to record the double potentials following linear ablation of the cavotricuspid isthmus. Following ablation, bidirectional isthmus block was also tested by pacing from the coronary sinus os and the low-lateral right atrium. We could demonstrate double potentials in 9 of the 11 patients in whom we attempted to record them following linear ablation of flutter. The presence of bidirectional block by pacing from coronary sinus os and low lateral right atrium could be demonstrated in 10 (91%) patients. Thus, double atrial potentials, separated by an isoelectric interval can be demonstrated following ablation of atrial flutter. Double potentials, if demonstrable on coronary sinus os and low lateral right atrium pacing, could serve as an alternative marker of isthmus block.     

Right ventricular pacing to assess transisthmus conduction in patients undergoing isthmus-dependent atrial flutter ablation: a new useful technique?

BACKGROUND: Successful radiofrequency (RF) ablation of typical, isthmus-dependent atrial flutter requires establishment and confirmation of bidirectional conduction block across the cavotricuspid isthmus. Low atrial pacing usually is performed from the bipoles of the 20-pole Halo catheter, septal and lateral to the cavotricuspid isthmus ablation line. However, occasionally this is difficult because of high pacing thresholds and/or saturation of the atrial electrograms recorded near the pacing catheter. OBJECTIVES: The purpose of this study was to assess if right ventricular (RV) pacing and resulting retrograde atrial activation can be used to assess conduction block from the septum to the lateral wall in a clockwise direction. METHODS: Thirty-five consecutive male patients (mean age 64 +/- 10 years; mean ejection fraction 42 +/- 13%; mean left atrial dimension 44 +/- 6 mm) with typical isthmus-dependent atrial flutter were studied. The following electrophysiology catheters were used: 20-pole catheter along the tricuspid annulus, quadripolar catheters at the His and/or RV apex, and 8-mm ablation catheter. Following RF ablation of the cavotricuspid isthmus, bidirectional conduction block was confirmed in all 35 patients by pacing at a cycle length of 600 ms from bipoles septal and lateral to the cavotricuspid isthmus ablation line. Conduction times from pacing artifact to adjacent bipolar atrial electrograms and reversal of atrial activation pattern were analyzed. RV pacing was performed and retrograde atrial activation pattern assessed. If retrograde AV nodal conduction was absent, isoproterenol was infused intravenously at 2 microg/min, and RV pacing was repeated. The conduction time between the double potentials across the cavotricuspid isthmus ablation line was measured. RESULTS: Mean conduction times across the isthmus during septal (S), lateral (L), and RV pacing were 145 +/- 21 ms, 144 +/- 24 ms, and 129 +/- 20 ms, respectively. Retrograde AV nodal conduction was present in 34 of 35 patients (isoproterenol 8 patients). Evidence of conduction block by a clear change in activation pattern across the isthmus was seen during RV pacing in 33 of 35 patients with bidirectional conduction block. CONCLUSION: RV pacing is a simple and easy maneuver that can be performed to assess isthmus conduction in most patients.     

Invasive Elektrophysiologie: Komplikationen, Alpträume und deren Management

Most minor side effects of ablation in the right atrium and right ventricle relate to femoral venous catheterization but there is a small risk of severe complications including atrioventricular (AV) block, damage of surrounding structures and thromboembolic events. Impairment of AV conduction can occur during ablation of atrioventricular re-entrant tachycardia, ablation of anteroseptal, mid-septal and parahisian accessory pathways, ablation of ectopic atrial tachycardia originating from the vicinity of the atrioventricular node and when ablating the septal isthmus for typical atrial flutter. Damage of the right coronary artery is a very rare complication after inferior isthmus ablation with high energy. The thromboembolic risk during and after cardioversion and ablation of atrial flutter is higher than previously recognized and anticoagulation therapy decreases this risk. The risk of perforation and tamponade during ablation in the right atrium and right ventricle is very low but particular caution is necessary in thin-walled structures such as the coronary sinus and the upper right ventricular outflow tract. Phrenic nerve injury can be avoided by pacing from the mapping electrode before application of radiofrequency energy at the right atrial free wall. Limitation of power output depending on the site of ablation and titration of energy application with continuous control of temperature and impedance should be considered to minimize the risk of complications.     

三尖瓣峡部消融对心房颤动导管消融术后复发的影响

目的:评估三尖瓣峡部消融对伴有典型心房扑动(房扑)和不伴典型房扑发作的心房颤动(房颤)患者术后复发的影响.方法:连续入选房颤射频消融治疗患者113例,根据有无典型房扑分为三尖瓣峡部消融组(CTI组)和未行三尖瓣峡部消融组(Non-CTI组),比较临床特征及手术特点,并随访术后典型房扑和房颤发生率.结果:Non-CTI组左房内径更大,持续性和永久性房颤的比例、左房线性消融的比例更高.而CTI组射频消融时间较Non-CTI组更长.术后典型房扑和房颤发生率2组无显著区别.结论:无典型房扑发作的房颤患者,不行三尖瓣峡部消融,不会升高术后典型房扑发生率和房颤复发率,同时射频消融时间缩短.     

Ventricular location of a part of the right atrial isthmus after tricuspid valve replacement for Ebstein’s anomaly: a challenge for atrial flutter ablation

We report the case of a patient with atrial flutter late after tricuspid valve replacement for Ebstein’s anomaly. Computed tomographic angiography revealed that coronary sinus ostium and part of the right atrial isthmus were located on the ventricular side of the valve ring due to the specific surgical approach in this condition. Based on the results of electroanatomic mapping and entrainment, the arrhythmia was found to be cavotricuspid isthmus dependent clockwise atrial flutter. Completion of the isthmus line required ablation lesions across the artificial valve. When these were delivered the arrhythmia terminated and isthmus block was achieved. Due to arrhythmia recurrence a redo procedure was performed which demonstrated conduction recovery in the ventricular part of the cavotricuspid isthmus. Intracardiac ultrasound-guided ablation successfully eliminated conduction across the isthmus with subsequent freedom from arrhythmia on follow up.     

Radiofrequency ablation for cure of atrial flutter

Abstract Background: Atrial flutter is a common arrhythmia which frequently recurs after cardioversion and is relatively difficult to control with antiarrhythmic agents.
Aims: To evaluate the success rate, recurrence rate and safety of radiofrequency (RF) ablation for atrial flutter in a consecutive series of patients with drug refractory chronic or paroxysmal forms of the arrhythmia.
Methods: Electrophysiologic evaluation of atrial flutter included activation mapping with a 20 electrode halo cadieter placed around the tricuspid annulus and entrainment mapping from within the low right atrial isthmus. After confirmation of the arrhythmia mechanism with these techniques, an anatomic approach was used to create a linear lesion between the inferior tricuspid annulus and the eustachian ridge at the anterior margin of the inferior vena cava. In order to demonstrate successful ablation, mapping techniques were employed to show that bi-directional conduction block was present in the low right atrial isthmus.
Results: Successful ablation was achieved in 26/27 patients (96%). In one patient with a grossly enlarged right atrium, isthmus block could not be achieved. Of the 26 patients with successful ablation, mere has been one recurrence of typical flutter (4%) during a mean follow-up period of 5.5±2.7 months. This patient underwent a successful repeat ablation procedure. Of eight patients with documented clinical atrial fibrillation (in addition to atrial flutter) prior to the procedure, five continued to have atrial fibrillation following the ablation. There were no procedural complications and all patients had normal AV conduction at the completion of the ablation.
Conclusions: RF ablation is a highly effective and safe procedure for cure of atrial flutter. In patients with chronic or recurrent forms of atrial flutter RF ablation should be considered as a first line therapeutic option.     

Correlation of atrial electrocardiographic amplitude with radiofrequency energy required to ablate cavotricuspid isthmus-dependent atrial flutter

OBJECTIVES: The purpose of this study was to evaluate a possible correlation between atrial ECG amplitude in common atrial flutter (AFL) and radiofrequency (RF) energy required to achieve cavotricuspid isthmus block. BACKGROUND: The amount of RF delivery required for ablation of typical AFL is variable. This variation has been attributed to the cavotricuspid isthmus anatomy. Atrial ECG amplitude can be a marker of atrial anatomic variations and therefore may correlate with RF duration required to achieve cavotricuspid isthmus block. METHODS: Seventy consecutive patients were prospectively studied. Ablation of the cavotricuspid isthmus was performed by creating a line of block between the inferior tricuspid annulus and the inferior caval vein using 8-mm-tip electrode catheters. If more than 20 minutes of RF time was required to achieve conduction block, the catheter was changed to an irrigated-tip catheter. Atrial ECG amplitude was assessed in leads II, III, aVF, and aVL. RESULTS: A total of 14 +/- 11 minutes of RF energy was delivered to achieve block in all patients; 12 patients (8%) required more than 20 minutes. Atrial ECG amplitude showed highly significant correlations with cumulative RF energy (F and P waves in lead II: r = 0.703 and r = 0.737, P < .001). P-wave amplitude <0.2 mV and/or flutter wave amplitude <0.35 mV in lead II have a high negative predictive value to predict <20 min RF delivery (96% and 89% respectively). CONCLUSIONS: A significant correlation exists between atrial ECG amplitude and amount of RF required to ablate typical AFL. Atrial ECG amplitude may be a surrogate marker of characteristics of isthmus anatomy. These findings may influence the choice of catheter used for cavotricuspid isthmus ablation.     

Changing coronary sinus activation during catheter ablation of isthmus-dependent right atrial flutter: what is the mechanism?

A 69-year-old woman was referred for cavotricuspid isthmus ablation due to typical isthmus-dependent right atrial flutter. During ablation, intracardiac activation sequence in coronary sinus (CS) changed without altering the cycle length or the P-wave morphology. This suggests that interatrial connection via CS was blocked and left atrium (LA) was activated from Bachmann's bundle or/and connections between fossa ovalis and LA.     

Correlation between electrogram morphology and standard criteria to validate bidirectional cavotricuspid block in common atrial flutter ablation.

AIM: Assessment of a bidirectional conduction block within the cavotricuspid isthmus (CTI) is critical during radiofrequency (RF) atrial flutter (AF) ablation. We investigated the use of bipolar atrial electrogram (BAE) morphology as an additional criterion identifying CTI block and tested it against two recognized criteria: differential pacing and reversal of the right atrial depolarization sequence during coronary sinus (CS) pacing. METHODS AND RESULTS: An RF ablation procedure was performed during 600 ms CS pacing in 100 consecutive patients with a common AF. BAE recorded along the CTI were continuously monitored. CTI conduction block was achieved by RF ablation in all patients and a clear change in BAE polarity in the Electrogram recorded by the dipoles located on the CTI and immediately lateral to the intended line of block (RS to QR pattern) associated with a confirmed CTI conduction block was observed in all cases. BAE morphology changes predicted bidirectional CTI conduction blocks with a 100% positive and a 100% negative predictive value. At a mean follow-up of 33 +/- 11 months, there was a 5% AF recurrence rate. CONCLUSIONS: Our study suggests that morphological changes in BAE recorded at sites lateral and adjacent to the target line of block may be used as a unique and robust criterion to validate CTI conduction block during AF ablation procedure.     

Assessment of the maximum voltage-guided technique for cavotricuspid isthmus ablation during ongoing atrial flutter

Objectives We aimed to test the maximum voltage-guided cavotricuspid isthmus (CTI) ablation technique during ongoing atrial flutter. Background Former pathological and electrophysiological studies clarified that the cavotricuspid isthmus is composed of distinct muscular bundles, which are responsible for the conduction of electrical activation. Based on this observation, a maximum voltage-guided ablation technique (MVGT) was developed. This technique was assessed during pacing from the coronary sinus and was reported to be a feasible method to reach bidirectional isthmus block without the need for a complete anatomic ablation line. Methods This was a prospective, randomized single center study. Twenty patients underwent CTI ablation during atrial flutter. In group I (10 pts) CTI ablation was performed with complete anatomical ablation line. In group II (10 pts) ablation was guided by the highest amplitude potentials on the CTI sequentially until bidirectional isthmus block was reached. The following parameters were compared: acute success rate, procedure time, fluoroscopy time, number of radiofrequency (RF) applications and total RF duration. Results In all patients, atrial flutter terminated during ablation. Bidirectional isthmus block could be achieved in all pts. Procedure time was shorter in group II (107 ± 40 vs 68 ± 19 min, p < 0.01). Significantly less fluoroscopy was used in group II (22.6 ± 10.6 vs 12.1 ± 3.8 min, p < 0.01). There were less RF applications in group II (27.1 ± 21.5 vs 5.9 ± 2.4, p < 0.001). Conclusions (1) The major finding of this study is that MVGT is a feasible method even during ongoing atrial flutter. (2) Our data confirm that MVGT is an effective technique for CTI ablation with considerable decrease in procedure and fluoroscopy times.     

Electrogram polarity and cavotricuspid isthmus block during ablation of typical atrial flutter

INTRODUCTION: The atrial activation sequence around the tricuspid annulus has been used to assess whether complete block has been achieved across the cavotricuspid isthmus during radiofrequency ablation of typical atrial flutter. However, sometimes the atrial activation sequence does not clearly establish the presence or absence of complete block. The purpose of this study was to determine whether a change in the polarity of atrial electrograms recorded near the ablation line is an accurate indicator of complete isthmus block. METHODS AND RESULTS: Radiofrequency ablation was performed in 34 men and 10 women (age 60 +/- 13 years [mean +/- SD]) with isthmus-dependent, counterclockwise atrial flutter. Electrograms were recorded around the tricuspid annulus using a duodecapolar halo catheter. Electrograms recorded from two distal electrode pairs (E1 and E2) positioned just anterior to the ablation line were analyzed during atrial flutter and during coronary sinus pacing, before and after ablation. Complete isthmus block was verified by the presence of widely split double electrograms along the entire ablation line. Complete bidirectional isthmus block was achieved in 39 (89%) of 44 patients. Before ablation, the initial polarity of E1 and E2 was predominantly negative during atrial flutter and predominantly positive during coronary sinus pacing. During incomplete isthmus block, the electrogram polarity became reversed either only at E2, or at neither E1 nor E2. In every patient, the polarity of E1 and E2 became negative during coronary sinus pacing only after complete isthmus block was achieved. In 4 patients (10%), the atrial activation sequence recorded with the halo catheter was consistent with complete isthmus block, but the presence of incomplete block was accurately detected by inspection of the polarity of E1 and E2. CONCLUSION: Reversal of polarity in bipolar electrograms recorded just anterior to the line of isthmus block during coronary sinus pacing after ablation of atrial flutter is a simple, quick, and accurate indicator of complete isthmus block.