Intravenous Adenosine to Predict Conduction Recurrence in Cavotricuspid Isthmus Early After Ablation of Typical Atrial Flutter: Myth or Reality?

Adenosine and Ablation of Typical Atrial Flutter. Introduction: Early recovery of conduction (ER) after cavotricuspid isthmus (CTI) ablation for typical atrial flutter (AFl) occurs in approximately 10% of the patients. If not recognized, ER might lead to AFl recurrences. In this study, we hypothesized that intravenous adenosine (iADO) can be used to predict ER in the CTI immediately after RF ablation and distinguish functional block from the complete destruction of the CTI myocardium. Methods: We prospectively included 68 consecutive patients (age: 65 ± 14 years; male: 78%) referred in our centers for AFl ablation. Immediately after bidirectional isthmus block validation, a bolus of iADO was given during continuous pacing from the proximal coronary sinus. Patients with functional block revealed under iADO (iADO+) and those without (iADO?) were subsequently observed for a 30‐minute waiting period (ER?) or until sustained recovery of the conduction through the CTI (ER+). Results: Seven patients presented a persistent recovery (ER+, 10.3%, mean time to recovery: 14 ± 9 minutes). None of them presented even a transient resumption of conduction under iADO (iADO+: 0). With univariate analysis, we identified a heavy patient weight (>95 kg) as a predictor of ER (sensitivity: 71%). Conclusions: Adenosine does not predict early recovery in the CTI after linear ablation for atrial flutter. We found that a patient weight over 95 kg predicted early recovery of conduction through the CTI with a sensitivity of 71%. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1201–1206, November 2012)     

Evaluation of an individualized strategy of cavotricuspid isthmus ablation as an adjunct to atrial fibrillation ablation

Objectives: To evaluate supplementary cavotricuspid isthmus (CTI) ablation as an adjunct to atrial fibrillation (AF) ablation in selected patients.
Background: It is unclear whether routine CTI ablation is beneficial in all patients undergoing AF ablation.
Methods and Results: In patients undergoing AF ablation, additional CTI block was created only for those with typical atrial flutter (Afl) before or during the ablation. Out of 188 consecutive patients (108 male, 56 ± 9 years), 75 underwent CTI ablation (Group CTI+) and left atrial (LA) ablation (circular mapping-guided extensive pulmonary vein isolation in all and linear LA ablation when required), while 113 underwent LA ablation alone (Group CTI−). Group CTI+ patients had smaller LA and less frequently persistent/permanent AF and linear LA ablation. Over a follow-up of 30 ± 10 months, complications (4% vs 5%, P = NS), typical Afl occurrence (1.3% and 2.6%, P = NS) and AF recurrence (25% and 28%, P = NS) were similar. Atypical Afl was more common in Group CTI− (4 vs 14%, P = 0.026). Eighty-two percent and 79% of patients in Groups CTI+ and CTI−, respectively, remained arrhythmia free in stable sinus rhythm without antiarrhythmic drug treatment (P = NS).
Conclusions: Avoiding supplementary CTI ablation in AF ablation patients without evidence of typical flutter does not result in a higher incidence of typical Afl. Despite more persistent/permanent AF and larger LA in patients without evidence of typical flutter, a strategy of selective supplementary ablation resulted in similar and low AF recurrence rates in the group without CTI ablation compared with the group with CTI ablation.     

Mapping-guided ablation of the cavotricuspid isthmus: A novel simplified approach to radiofrequency catheter ablation of isthmus-dependent atrial flutter

BACKGROUND: Because the anatomic features of the cavotricuspid isthmus (CTI) are complex, radiofrequency (RF) energy requirements for CTI ablation may vary at each point within the CTI. Conventionally, multiple-site mapping has been required for determining CTI conduction block. OBJECTIVES: The purpose of this study was to develop a more efficacious method for ablation of isthmus-dependent atrial flutter. METHODS: Forty consecutive patients underwent CTI ablation using a CTI mapping-guided approach (20 patients) or a conventional approach (20 patients). In the CTI mapping-guided approach, an octapolar catheter was positioned on the CTI parallel to, and downstream from, the intended ablation line in order to map and ablate the breakthrough point. RESULTS: Complete CTI block was achieved in all study patients. CTI mapping of incomplete ablation lines revealed that the site with the shortest interval between double potentials did not always coincide with the conduction gap. Disappearance of a breakthrough pattern on the CTI electrograms corresponded to creation of complete CTI block. During ablation, CTI mapping exhibited pseudo-CTI block in 8% of patients in the clockwise direction and 63% of patients in the counterclockwise direction. The number and total time of RF applications were significantly lower with the CTI mapping-guided approach than with the conventional approach (7.7 +/- 3.9 applications vs 13.8 +/- 8.9 applications and 8.9 +/- 4.4 minutes vs 16.3 +/- 11.9 minutes, respectively, P <.05). In the CTI mapping-guided approach, RF applications were not required along the entire CTI in 7 patients (35%). CONCLUSION: This simplified technique was feasible for creating and determining complete CTI block, with fewer RF applications required.     

Characteristics of virtual unipolar electrograms for detecting isthmus block during radiofrequency ablation of typical atrial flutter

OBJECTIVES: The purpose of this study was to investigate the characteristics of the second component of local virtual unipolar electrograms recorded at the ablation line during coronary sinus (CS) pacing after radiofrequency ablation (RFA) of the cavotricuspid isthmus (CTI) for typical atrial flutter (AFL). BACKGROUND: Radiofrequency ablation of the CTI can produce local double potentials at the ablation line. The second component of unipolar electrograms represents the approaching wavefront in the right atrium opposite the pacing site. We hypothesized that the morphologic characteristics of the second component of double potentials would be useful in detecting complete CTI block. METHODS: Radiofrequency ablation of the CTI was performed in 52 patients (males = 37, females = 15, 62 +/- 12 years) with typical AFL. The noncontact mapping system (Ensite 3000, Endocardial Solutions, St. Paul, Minnesota) was used to guide RFA. Virtual unipolar electrograms along the ablation line during CS pacing after RFA were analyzed. Complete or incomplete CTI block was confirmed by the activation sequence on the halo catheter and noncontact mapping. RESULTS: Three groups were classified after ablation. Group I (n = 37) had complete bidirectional CTI block. During CS pacing, the second component of unipolar electrograms showed an R or Rs pattern. Group II (n = 12) had incomplete CTI block. The second component of unipolar electrograms showed an rS pattern. Group III (n = 3) had complete CTI block with transcristal conduction. The second component of unipolar electrograms showed an rSR pattern. CONCLUSIONS: A predominant R-wave pattern in the second component of unipolar double potentials at the ablation line indicates complete CTI block, even in the presence of transcristal conduction.     

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.     

Concealed Automaticity From an Island of Atrial Myocardium Post Cavotricuspid Ablation

Island of Atrial Myocardium Post Cavotricuspid Ablation. We report the case of a patient with paroxysmal atrial fibrillation in whom 2 previous cavotricuspid isthmus (CTI) ablations were performed for recurrent type I counterclockwise atrial flutter. One year after the last CTI ablation, the patient underwent pulmonary vein isolation for AF and reassessment of conduction block in the CTI was performed during the procedure. While mapping the CTI, activations were documented within the CTI that were dissociated from both right atrial and ventricular activity during sinus rhythm and pacing maneuvers. This dissociated activity was confined to a region delimited by the 2 previous ablation lines, the tricuspid annulus and the inferior vena cava. These findings suggest that an island of atrial myocardium with automatic activity was created within the CTI by previous ablation lines. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1408‐1409, December 2010)     

Further Evidence for the “Muscle Bundle” Hypothesis of Cavotricuspid Isthmus Conduction: Physiological Proof,with Clinical Implications for Ablation

Two Line Flutter Ablation . Introduction: It has been suggested that the cavotricuspid isthmus (CTI) is composed of discrete muscle bundles with preferred paths of conduction. An ablation technique targeting high‐voltage local electrograms (maximum voltage guided or MVG technique) has been described with the aim of preferentially targeting the muscle bundles. We hypothesized that the MVG technique could provide isthmus block even if the high voltage targets were clearly separated on different ablation lines. In contrast, conduction over a continuous sheet of muscle would require a single continuous ablation line. Methods: Twenty‐two consecutive patients (mean age 65 ± 11.7, 5 females) underwent ablation using the MVG technique on 2 noncontiguous lines in the CTI. Ablation lesions were first applied at the septal aspect of the CTI, targeting only the ventricular (anterior) aspect of the annulus. A line distinctly lateral and noncontiguous to the first was then chosen to target high voltage potentials on the atrial (posterior) aspect of the CTI. Results: Complete CTI block was achieved in all study patients without complication. A mean of 7.8 ± 3.7 ablation lesions were required. Mean ablation time was 401.0 ± 414.5 seconds. Conclusion: Two nonoverlapping incomplete lines of ablation in the CTI consistently lead to bidirectional conduction block. This further supports the hypothesis that conduction over the CTI occurs over discrete muscle bundles. These bundles can be targeted individually for ablation without the need to ablate a continuous line over the CTI. (J Cardiovasc Electrophysiol, Vol. 24, pp. 47‐52, January 2013)     

CARTO指导下三尖瓣环峡部解剖特征对线性消融的影响

目的探讨CARTO系统指导下三尖瓣环峡部(CTI)的解剖学特点及其对线性消融的影响。方法接受CTI线性消融的患者,其中典型心房扑动5例、阵发性心房颤动(简称房颤)10例及持续性房颤40例。利用CARTO系统对三尖瓣峡部长度、跨度及最深深度进行测量并根据深度分为囊袋型、凹陷型和平坦型。根据CTI长度将患者分为两组,长组≥35 mm,短组<35 mm。记录CTI消融成功所需时间,同时收集相关临床资料。结果不同类型峡部的长度、跨度、深度及消融所需时间分别为:囊袋型23例(45.5±7.5 mm,38.0±7.4 mm,-9.5±2.8 mm,1707±615 s),凹陷型10例(42.7±9.0 mm,37.2±6.7 mm,-4.2±0.8 mm,1 327±832 s),平坦型22例(36.1±8.9 mm,34.3±8.0 mm,-1.0±3.1 mm,927±404 s)。囊袋型CTI长度、消融时间长于平坦型,囊袋型CTI深度均较平坦型和囊袋型为深(P<0.05)。消融时间与深度正相关(r=0.505,P<0.001)。长组较短组所需消融时间长(1485±681 s vs 803±305 s,P<0.001)。长组以囊袋型为主(48.8%),短组以平坦型为主(78.6%)。结论 CTI线性消融时间与其最深深度相关,峡部越深则消融越费时,囊袋型消融所需时间最多。若CTI长度≥35 mm(更常见于囊袋型CTI),其消融时间则显著延长。     

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.     

Novel Strategies in the Ablation of Typical Atrial Flutter: Role of Intracardiac Echocardiography

Radiofrequency ablation (RFA) of the cavo-tricuspid isthmus (CTI) is one of the most frequently performed procedures in electrophysiology. Despite a high success rate, ablation of the CTI can be unusually difficult in some cases. Multiple tools like angiography, 3D mapping, remote navigation and intracardiac echocardiography (ICE) have been introduced to facilitate typical flutter ablation. This review article summarizes the clinical value of different strategies and tools used for CTI ablation focusing on the importance of approaches utilizing ICE.     

Characteristics of the Cavotricuspid Isthmus in Predicting Recurrent Conduction in the Long-Term Follow-Up

Background: The characteristics of cavotricuspid isthmus (CTI) in patients with atrial fibrillation (AF) and flutter that may predict recurrence of flutter is not known. We aimed to investigate the CTI characteristics in patients who underwent a second ablation procedure for recurrent AF after previous combined pulmonary vein (PV) and CTI ablation.
Methods: Among 196 consecutive patients with drug-refractory symptomatic AF who underwent PV isolation and CTI ablation with bidirectional isthmus block, 49 patients (age 50 ± 12 years, 43 males) had recurrent AF and received a second procedure 291 ± 241 days after the first procedure. Right atrial angiography for the evaluation of the CTI morphology, and the biatrial contact bipolar electrograms were obtained before both procedures.
Results: In the second procedure, 11 (group 1) of the 49 patients demonstrated recovered CTI conduction. Compared with the patients without CTI conduction (group 2, n = 38), group 1 patients had a higher frequency of a pouch-type anatomy (82% vs 13%, P < 0.001), longer CTI (34.0 ± 8.6 vs 25.5 ± 7.5 mm, P = 0.01), longer ablation time, and larger number of radiofrequency applications; furthermore, the preablation bipolar voltage decreased along both the CTI and ablation line in group 2, whereas it remained similar in group 1 in the second procedure.
Conclusions: A high (22%) percentage of CTIs exhibited recurrent conduction in the long-term follow-up. The CTIs with recurrent conduction had a higher incidence of a pouch and longer length compared with those without recurrent conduction.     

Catheter selection for ablation of the cavotricuspid isthmus for treatment of typical atrial flutter

Radiofrequency catheter ablation (RFA) represents the first line therapy of the cavotricuspid isthmus-dependent atrial flutter (CTI-AFL) with a high efficacy and low secondary effects. RFA of CTI-dependent AFL can be performed by using various types of ablation catheters. Recent evaluations comparing externally cooled tip RFA (ecRFA) catheters and large-tip (8 mm) catheters have revealed that these catheters have a higher efficacy for CTI-AFL ablation compared to 4-mm catheters. The reliability of RFA catheters for AFL is variable and an optimal catheter selection may enhance the RFA effectiveness. The main goal of this article is to review the elements that improve the management of CTI RFA. Preliminary examinations of histopathologic and anatomical elements that may interfere with conventional CTI RFA are presented. Experimental studies concerning the electrobiology of large-tip and cooled-tip catheters are compared. The different catheter designs between cooled-tip and 8-mm-tip catheters are examined (size of the deflectable curve, rotation stability, and size of the distal nonsteerable catheter part) because of their critical role in CTI RFA results. A thorough review of clinical trials of each catheter is presented, and comparison of both catheters in this clinical setting is analyzed. In addition, the role of CTI morphology on AFL RF duration is underlined such as the value of right atrial angiography as an adjunct tool for CTI RFA catheter selection. Based on randomized studies, 8-mm-tip catheters seem to be more effective for ablation in case of straight angiographic isthmus morphology. On the other hand, ecRFA catheters appear to be more effective in cases of complex CTI anatomy or difficult CTI RFA. To reduce X-ray exposition and RFA application time, few studies report that CTI angiographic evaluation before RFA allows a catheter selection based on both CTI morphology and length. Moreover, preliminary data of randomized studies showed that an angiographic isthmus evaluation may predict both the effectiveness of a RFA catheter and the risk of an expensive catheter crossover.     

Cavotricuspid isthmus angiography predicts atrial flutter ablation efficacy in 281 patients randomized between 8 mm- and externally irrigated-tip catheter.

AIMS: Radiofrequency ablation (RFA) of cavotricuspid isthmus (CTI)-dependent atrial flutter can be performed using various types of ablation catheters. Recent evaluations comparing externally cooled-tip RFA (ecRFA) catheters and large-tip (8 mm) catheters found that ecRFA catheter may have a higher efficacy for CTI ablation. The aim of this prospective study was to compare both catheters by stratifying on CTI morphology in order to explain, in part, the discrepancies between previous randomized studies, and to validate predictive factors of difficult CTI ablation on clinical, echocardiographic, and angiographic data. METHODS AND RESULTS: Over a period of 24 months, 281 patients were included and stratified on CTI morphology: 'straight', 'concave', and 'pouch-like recess'. In straight CTI (n=150), the duration of application time with a median of 6 min [interquartile range (IQR) 4-9] vs. a median of 12 min (IQR 16-19; P<0.0001) and the duration of X-ray exposure with a median of 6 min (IQR 4.4-9.7) vs. a median of 10.4 min (IQR 7-17; P<0.0001) were significantly lower with an 8 mm-tip when compared with ecRFA catheter. In contrast, in concave CTI (n=95), a trend towards both shorter application time with a median of 12.5 min (IQR 6-23) vs. a median of 19 min (IQR 7-28; P=0.08) and X-ray duration exposure with a median of 10.4 min (IQR 6-20) vs. a median of 13 min (IQR 8-24; P=0.08) with an ecRFA catheter when compared with 8 mm-tip catheter were evidenced. No significant difference was shown between 8 mm-tip and ecRFA catheters in the pouch-like recess group (n=36). Predictive factors of difficult ablation include right CTI length and morphology. CONCLUSION: This study demonstrates that the 8 mm-tip catheter is more effective for ablation in case of a straight angiographic isthmus morphology and that the ecRFA catheter tends to be more effective in case of concave angiographic isthmus morphology. Thus, angiographic isthmus evaluation may predict both the effectiveness of an RF catheter, and the risk of an expensive crossover. These data may explain, in part, the discrepancies of previous studies comparing both catheters.     

Anatomical characteristics of the cavotricuspid isthmus in patients with and without typical atrial flutter: Analysis with two- and three-dimensional intracardiac echocardiography

Introduction The cavotricuspid isthmus (CTI) is crucial in the ablation of typical atrial flutter (AFL), and consequently the CTI anatomy and/or its relation to resistant ablation cases have been widely described in human angiographic studies. Intracardiac echocardiography (ICE) has been shown to be a useful tool for determining detailed anatomical information. Thus, this technology may also allow the visualization of the anatomical characteristics of the CTI, providing an opportunity to further understand the anatomy. Aim We conducted a study to compare the anatomy of the CTI between the patients with and without AFL and to characterize the anatomy of the CTI in the patients with AFL resistant to ablation. Materials and methods Twelve patients with typical AFL and 20 without AFL were enrolled in the study. Two-dimensional (2D) intracardiac echocardiography (ICE) was performed. The recordings were obtained with a 9F, 9-MHz ICE catheter from the right ventricular outflow tract to the inferior vena cava by pulling the catheter back 0.3 mm at a time under guidance with echocardiographic imaging in a respiration-gated manner. Three-dimensional (3D) reconstruction of the images of the CTI were made with a 3D reconstruction system. After the acquisition of the ICE, the CTI ablation was performed in the patients with AFL. Results The 2D and 3D images provided clear visualization of the tricuspid valve, coronary sinus ostium, fossa ovalis and Eustachian valve/ridge (EVR). The CTI was significantly longer in the patients with AFL than in those without AFL (median length 24.6 mm (range 17.0–39.1 mm) versus median length 20.6 mm (range 12.5–28.0 mm), respectively, P < 0.05). However, a deep recess due to a prominent EVR was observed in 9 of 12 (75%) patients with AFL and in 12 of 20 (60%) patients without AFL (N.S.). A deep recess and the relatively long CTI were related to aging in all the study patients, and that relationship was similar in a limited number of patients without AFL. In five patients with AFL resistant to ablation, a deep recess and prominent EVR were observed. Conclusions The 2D and 3D ICE were useful for visualizing the complex anatomy of the CTI and identifying the anatomical characteristics of the CTIs refractory to ablation therapy. The anatomical changes observed in the CTI region may simply be the result of aging and may partially be involved in the development of AFL.     

Atypical Electrocardiographic Features of Cavotricuspid Isthmus‐Dependent Atrial Flutter Occurring during Left Atrial Fibrillation Ablation

Background: Patients who have undergone percutaneous catheter ablation for atrial fibrillation (AF) may develop cavotricuspid isthmus (CTI)‐dependent atrial flutter (AFL), which can occur either spontaneously during left atrial (LA) ablation for AF or by induction from sinus rhythm during the procedure. The electrocardiographic (ECG) characteristics of CTI‐dependent AFL occurring during LA ablation have not been described. The purpose of this study was to describe the ECG features of CTI‐dependent AFL occurring during percutaneous LA catheter ablation for AF. Methods and Results: Of 223 patients presenting for first AF ablation at our institution between May 2004 and February 2008, 20 patients (9%) developed CTI‐dependent AFL during LA ablation for AF. CTI‐dependent AFL developed spontaneously in 4 patients (20%) and was induced in 16 patients (80%). Among these 20 patients, 3 (15%) had typical ECG patterns and 17 (85%) had atypical ECG patterns. Flutter waves in the inferior leads were biphasic in 10 patients (50%), downward in 3 patients (15%), positive in 3 patients (15%), and not fitting the above classifications in 4 patients (20%). There was no statistically significant association between AFL pattern and LA size, left ventricular ejection fraction, total ablation time, duration of prior AF, or type of prior AF. Conclusion: A majority of patients with CTI‐dependent AFL occurring during LA ablation have atypical ECG patterns. Biphasic flutter waves in the inferior leads are common ECG features, occurring in one‐half of patients. Right atrial CTI‐dependent AFL should be suspected even if the ECG appearance is atypical. Ann Noninvasive Electrocardiol 2010;15(3):200–208     

Cavotricuspid isthmus mapping to assess bidirectional block during common atrial flutter radiofrequency ablation

BACKGROUND: We sought to compare published methods to an alternative approach ascertaining cavotricuspid isthmus (CTI) block during atrial flutter ablation. METHODS AND RESULTS: In 39 consecutive patients who underwent an atrial flutter ablation procedure, a 24-pole mapping catheter was positioned so that 2 adjacent dipoles were bracketing the targeted CTI line of block (LOB), with proximal dipoles lateral to the LOB and distal dipoles in the coronary sinus. Two pacing sites were lateral (positions A and B) and 2 were septal (positions C and D) to the LOB, with locations A and D closest to the LOB. A resulting CTI block was accepted when 3 criteria were fulfilled: (1) complete reversal of the right atrial depolarization on the 24-pole catheter when pacing in the coronary sinus, (2) conduction delays from A to D greater than from B to D, and (3) conduction delays from D to A greater than from C to A. A successful CTI block was obtained in all patients. Before CTI block was obtained, a progressive CTI conduction delay was observed in 11 patients (28.2%). During the procedure, the 3 criteria defined above were either all present or all absent. CONCLUSIONS: This study establishes that reversal of the atrial depolarization sequence up to the LOB is a definitive and mandatory criteria of successful atrial flutter ablation.     

Usefulness of the polarity in high-density wide range-filtered bipolar mapping to detect isthmus block during radiofrequency ablation of typical atrial flutter

Background: The atrial activation sequence around the tricuspid annulus (TA) cannot always be used to establish whether complete block has been achieved across the cavotricuspid isthmus (CTI) during radiofrequency ablation (RFCA) for typical counterclockwise atrial flutter (CCW-AFL). Aim: We examined whether a change in the polarity of the atrial high-density wide range-filtered bipolar electrograms recorded near the ablation line is an accurate indicator of complete CTI block. Methods: Nineteen patients with CCW-AFL underwent RFCA. Electrograms were recorded around the TA with duodecapolar conventional (2mm × 8mm × 2mm spacing) and high-density (2-mm spacing) Halo catheters. The bipolar electrograms on the high-density Halo catheter recorded from a series of adjacent electrode pairs positioned just lateral to the ablation line were filtered at a bandpass setting of 0.05–500 Hz. The activation sequence on the conventional Halo catheter during coronary sinus pacing (CSp) and inferolateral TA pacing, and the bipolar electrograms on the high-density Halo catheter during CSp were determined before and after RFCA. The final complete CTI block was verified by the presence of widely split double electrograms ≥100 msec along the ablation line. Results: The final complete CTI block was achieved in all the 19 patients. Before RFCA, the polarity of bipolar electrograms was predominantly negative during CCW-AFL and positive during CSp. In 18 of the 19 patients, the bipolar electrograms exhibited the CCW activation and a negative polarity during CSp only after complete CTI block. In one of those 18 patients, additional applications of RFCA changed the polarity of bipolar electrograms positive to negative although the conventional Halo electrogram activation sequence suggested complete CTI block during CSp. In seven patients, who had transverse conduction across the crista terminalis during CSp, the conventional Halo electrogram activation sequence suggested an incomplete CTI block. However, in six of those seven patients, the CCW activation had a predominantly negative polarity of the bipolar electrograms. In one of those seven patients, complete CTI block was unable to be detected even using the high-density Halo catheter. Conclusions: These data demonstrate that the high-density wide range-filtered mapping can identify the CTI block in undetectable cases of complete CTI block or incomplete CTI block by the conventional method. The polarity of the bipolar electrograms recorded just lateral to the ablation line during CSp after RFCA of AFL may be used as a simple and an accurate indicator of complete CTI block.     

Prospective Observations in the Clinical and Electrophysiological Characteristics of Intra‐Isthmus Reentry

ECG and EGM of IIR. Introduction: Intra‐isthmus reentry (IIR) is a circuit within the cavotricuspid isthmus (CTI). The purpose of this study is to prospectively define the electrogram and surface ECG characteristics of IIR, and its clinical implications. Methods and Results: Fourteen patients underwent electrophysiological studies and were found to have IIR. Detailed electrogram mapping of the CTI was available in all, electroanatomic mapping (EAM) in 8 of 14 (57%) patients. In all, entrainment mapping during tachycardia proved reentry, and showed that the anteroinferior CTI was out of the circuit and the septal CTI was in the circuit in 12 of 14 patients, whereas in 2, the circuit was confined within the mid and/or anteroinferior CTI. Fractionated potentials (FPs) spanning 34–71% of the tachycardia cycle length were recorded within the CTI in all, and double potentials were inscribed in 10 of 14 (71%). Analysis of the tricuspid annulus electrograms showed spontaneous shifts from a counterclockwise (CCW) to clockwise or fusion patterns. Surface ECGs showed either typical CCW pattern (12 patients) or atypical patterns (3 patients). The EAMs showed a focal pattern in 3, a CCW pattern in 5. The successful ablation site always occurred at the area with maximal FP duration. Over the same period, 33 of 384 (9%) patients who underwent ablation for CTI‐dependent flutter had prior successful CTI ablation, 7 of 33 (21%) were found to have IIR during the redo procedure. Conclusions: (1) Electrogram and ECG patterns of IIR frequently show atypical flutter. (2) IIR was successfully ablated in an area of the CTI associated with maximal duration of FPs. (3) IIR is a significant cause of “recurrent flutter” in patients with prior CTI ablation. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1099‐1106)     

Diastolic isthmus length and 'vertical' isthmus angulation identify patients with difficult catheter ablation of typical atrial flutter: a pre-procedural MRI study

Aims: Catheter ablation of isthmus-dependent atrial flutter is technicallydemanding in some patients and extremely simple in others. Theintervention targets a defined anatomical structure, the so-calledcavotricuspid isthmus (CTI). We sought to characterize CTI anatomyin vivo in patients with difficult and simple catheter ablationof atrial flutter. Methods and results: Twenty-six patients were studied. Seven patients with difficult(n = 6) or extremely simple (n = 1) CTI ablation procedureswere retrospectively selected from our catheter ablation database.Thereafter, we prospectively studied 19 patients undergoingCTI ablation in our department. We visualized CTI anatomy byECG- and respiration-gated free precession 1.5 T cardiac magneticresonance imaging (MRI). Magnetic resonance imaging was analysedfor systolic and diastolic CTI length, the angle between thevena cava inferior and CTI, and pouch-like recesses. These parameterswere compared between patients with difficult and simple procedures,split by the median number of energy applications. Patientswith difficult procedures had a longer diastolic CTI length(diastolic isthmus length 20.3 ± 1.8 mm) than those withsimple procedures (diastolic isthmus length 16.6 ± 1.7mm, all data as mean ± SEM, P < 0.05). Cavotricuspidisthmus angulation with respect to inferior vena cava was closerto 90° in patients with difficult procedures (deviationfrom 90°: 15 ± 2°) than those with simple procedures(deviation 23 ± 4°, P < 0.05). Systolic CTI lengthwas not different between groups (32 ± 2 mm in both groups,P > 0.2). Conclusion: Longer diastolic, but not systolic, CTI length and a rectangularangle between CTI and inferior vena cava render CTI catheterablation difficult. Visualization of isthmus anatomy may helpto guide difficult CTI ablation procedures.