Impact of transisthmus linear ablation of typical atrial flutter on coronary sinus activation time

Complete or incomplete bidirectional isthmus conduction block after linear ablation of atrial flutter is difficult to interpret without detailed multiple electrodes mapping along the tricuspid annulus and the low right atrial isthmus area. The influence of isthmus block on the intraatrial septal and coronary sinus activation has not been assessed by endocardial mapping. This study was designed to analyze the intraartial and interatrial activation times in a retrospective fashion to investigate (1) whether isthmus conduction block can change the coronary sinus activation sequence during low lateral right atrial pacing, and (2) the correlation between change of coronary sinus activation time and isthmus conduction block. Sixty-five consecutive patients (mean age, 57 +/- 18 years) with clinically documented typical atrial flutter were studied. A 20-pole "Halo" catheter was placed around the tricuspid annulus including the entire low right atrial isthmus to verify complete bidirectional isthmus block. Activation time from ostium to distal coronary sinus (OCS-->DCS), and interatrial septum and isthmus activation times during right atrial pacing were analyzed and compared before and after incomplete or complete isthmus block. Complete bidirectional isthmus block was achieved in 50 (77%) patients. During low lateral right atrial pacing, linear ablation at low right atrial isthmus results in a significant delay of activation in all coronary sinus recording sites with greater extent at the ostium area without influence on interatrial septum activation in complete and incomplete isthmus conduction block. The difference of the OCS-->DCS interval before and after ablation, delta (OCS-->DCS), was well correlated with results of isthmus conduction block and significantly longer in patients with complete than those with incomplete isthmus block (34 +/- 11 vs 11 +/- 8 ms, P < 0.001), thereby allowing a value of 20 ms as a discriminative parameter to differentiate incomplete (< 20 ms) from complete (> or = 20 ms) isthmus counterclockwise conduction block with a sensitivity of 96% and a specificity of 88%. In conclusion, creation of a line of block at the inferior vena cava-tricuspid annulus isthmus could change coronary sinus activation sequence during low lateral right atrial pacing in sinus rhythm. The change of coronary sinus activation time after linear ablation, delta (OCS-->DCS), was well correlated with isthmus conduction block by using a value > or = 20 ms to discern complete counterclockwise isthmus block.     

Impact of the ECG for detection of intraatrial conduction block after atrial flutter ablation

Induction of complete bidirectional conduction block via the posterior isthmus of the right atrium is introduced as a standard endpoint for catheter ablation of atrial flutter. The present study sought to investigate the impact of changes in P wave duration and morphology detected by the surface ECG during coronary sinus and posterolateral right atrial stimulation as a marker for conduction block. Morphology and duration changes of the paced P wave before and after radiofrequency catheter (RFC) ablation were estimated in 22 patients referred for ablation of atrial flutter. We looked for a morphology change of the terminal portion in the 12-lead ECG and an increment of P wave duration. In 16 of 22 patients in whom atrial flutter ablation resulted in a complete bidirectional block, the conduction block was unidirectional in 4 patients and conduction times remained unchanged in 2 patients. After induction of complete bidirectional block a change of the terminal portion of the P wave towards a more positive morphology in one or more inferior leads was detected in 14 (88%) of 16 patients during coronary sinus stimulation and in 15 (94%) of 16 patients during posterolateral right atrial stimulation. These changes were predominantly observed in the inferior leads. Positive morphology changes of the terminal P wave portion in the inferior leads indicating conduction block with a sensitivity of 86% and a specificity of 100% were observed. An increment of 10 ms or more in P wave duration indicates conduction block with a specificity of 100% and a sensitivity of 67%. There was a significantly larger increment of P wave duration during coronary sinus (CS) stimulation compared to posterolateral right atrial stimulation (38 +/- 21 vs 16 +/- 21 ms). The analysis of P wave duration and morphology in the inferior leads of the surface ECG is a reliable tool to assess the intraatrial conduction after atrial flutter ablation. Different conduction during coronary sinus and posterolateral right atrial pacing may cause a different P wave duration after ablation.     

Radiofrequency ablation of atrial flutter: a randomized controlled study of two anatomic approaches

Atrial flutter often results from a macroreentrant circuit that uses anatomic structures within the right atrium as its borders. RF ablation at the site of an obligatory isthmus can eliminate the atrial flutter circuit. The aim of this study was to compare two approaches to atrial flutter ablation: the septal (septal aspect of the tricuspid valve annulus to coronary sinus ostium and Eustachian ridge) approach versus the posterior (inferior vena cava to tricuspid valve annulus) approach. Twenty patients were randomized to either the "septal" or "posterior" approach. Entrainment mapping and/or confirmation of bidirectional isthmus conduction at baseline were performed in those patients in atrial flutter and normal sinus rhythm, respectively. RF ablation was performed with standard catheters and techniques. Crossover was permitted after two lines of RF lesions. Endpoints included acute success rates and fluoroscopy times. There was no statistically significant difference in the success rate between the two approaches using intention-to-treat analysis. Fluoroscopy times in the septal versus posterior approaches were 58.4 +/- 30.3 versus 70.8 +/- 31.1 minutes, respectively (P = 0.7). There was more frequent crossover in patients assigned to the septal approach and the one major complication, atrioventricular block, also occurred using this approach. There was no statistically significant difference in the success rate or fluoroscopy times between the septal and posterior approaches to atrial flutter ablation. However, given the risk of atrioventricular block with the septal approach, the posterior approach should be the preferred initial choice.     

Progressive isthmus delay during atrial flutter ablation: the critical importance of isthmus spanning electrodes for distinguishing pseudoblock from block

Bidirectional isthmus block is associated with successful atrial flutter ablation, whereas creation of increased isthmus conduction delay without block can be proarrhythmic. Often, halo catheter electrodes fail to provide adequate sub-Eustachian isthmus recordings. The aim of this study was to determine if progressive isthmus conduction delay results in the false appearance of block during atrialflutter ablation. A 20-pole deflectable catheter was prospectively positioned across the sub-Eustachian isthmus (from the coronary sinus os [CSO] to 7:00 on the tricuspid valve annulus [TVA] clock face in the left anterior oblique [LAO] projection) in nine patients undergoing atrial flutter ablation. During sinus rhythm, conduction time was measured from the CSO to the 7:00 position while pacing the CSO. Measurements were repeated after each linear lesion and after conduction block was achieved. Transisthmus conduction time at baseline, just prior to success, and after the presence of complete block was 54 +/- 9, 123 +/- 39, and 155 +/- 30 ms, respectively (P < or = 0.01). The marked delay prior to complete block resulted in reversal of the activation sequence in electrodes at TVA 7:00, creating the false appearance of isthmus block; the isthmus electrodes clearly distinguished delay from block. Catheter ablation results in progressive isthmus conduction delay prior to the creation of complete block. Electrodes spanning the isthmus and line of block are critical for distinguishing conduction delay (and pseudoisthmus block) from block.     

Catheter Inversion:

Cure of typical atrial flutter (AFL) by catheter ablation to produce bidirectional block across the tricuspid annulus-inferior vena cava isthmus (IS) is highly effective, but failures may occur. We describe a technique that may allow creation of bidirectional block where a conventional strategy has failed.AFL ablation was performed using the conventional approach with a mapping/ablation (ablation) catheter introduced via the right femoral vein (RFV) to create a line of bidirectional block across the IS. If this was not achieved after five passes of the ablation catheter from the tricuspid annulus to the inferior vena cava (IVC) a catheter inversion technique was used. This allowed stable positioning of the ablation catheter at the IVC end of the isthmus. In 11 patients, a mean of 17 (range 3 to 45) radiofrequency (RF) applications was given before the catheter inversion technique was applied. Following catheter inversion a mean of 4 (1 to 14) further RF applications achieved bidirectional isthmus block in every patient. No complications occurred. Catheter inversion provides a simple, safe, and effective means of achieving bidirectional isthmus conduction block in cases where a conventional ablation strategy might have failed. (PACE 2004; 27[Pt. I]:775–778)     

Use of a Three-Dimensional, Nonfluoroscopic Mapping System for Catheter Ablation of Typical Atrial Flutter

Recent studies have shown that typical atrial flutter (AFL) results from right atrial reentry around the tricuspid annulus (TA), constrained between the TA and crista terminalis (CT) on the free-wall and the TA and eustachian ridge (ER) on the septum. Creation of a complete line of conduction block across the subeustachian isthmus, between the TA and ER, elminates AFL. The accuracy of fluoroscopy in localizing the anatomical boundaries and previous radiofrequency application sites is limited. This article describes an approach for utilizing a new three-dimensional nonfluoroscopic electroanatomical mapping system (CARTO) to examine the global right atrial activation pattern in patients during AFL, localize the anatomical boundaries, and create a complete line of conduction block by ablation across the subeustachian isthmus. During AFL, the locations of CT and ER are identified by double atrial potentials recorded along the intercaval region and between the inferior vena cava and coronary sinus ostium, respectively. Radiofrequency ablation across the subeustachian isthmus is performed during coronary sinus pacing. Beginning at TA, the ablation electrode is moved toward ER in 2–3 mm increments. Each movement is marked on the right atrial map to visualize the ablation line. In the event of residual conduction across the ablation line, defects in the ablation line are located by mapping along the previous ablation sites guided by CARTO system to locate the transition from the double atrial potentials (indicating block) to a single atrial potential (indicating conduction). Radiofrequency ablation to the site showing the single atrial potential along the ablation line produces complete conduction block across the subeustachian isthmus. In conclusion, the new electroanatomical mapping system allows precise 3-D localization of the anatomical boundaries of the AFL reentrant circuit, and facilitates ablation by accurately locating defects in the ablation line.(PACE 1998; 21:1279–1286)     

A very narrow preexisting isthmus in a case with typical atrial flutter

A 61-year-old woman with typical atrial flutter underwent an electrophysiologic study and radiofrequency catheter ablation. The electroanatomic mapping revealed two contiguous lines of distinct double potentials (DPs) extending anteriorly/posteriorly from the coronary sinus ostium to the inferior vena cava (IVC) border. A large part of the anterior line of the DPs was close and parallel to the tricuspid annulus (TA). An initial discrete radiofrequency application at the very narrow preexisting isthmus between the TA and anterior line of the DPs completed the IVC-TA isthmus conduction block.     

Escape mapping to achieve bidirectional block: A case series

Escape mapping is a novel technique that can be used to locate sites of persistent conduction and achieve exit block during an atrial fibrillation ablation. This method allows for mapping solely with the ablation catheter in the left atrium by annotating to a catheter in the coronary sinus. We illustrate the utility escape mapping during an atrial fibrillation ablation where entrance block is achieved without exit block. We further expand upon this technique by describing the first reported case of escape mapping being used to achieve bidirectional block during an atrial flutter ablation.     

Site specificity of transverse crista terminalis conduction in patients with atrial flutter

INTRODUCTION: The causes of transcristal conduction (TC) in patients with atrial flutter (AFL) are unknown. METHODS AND RESULTS: In two groups of patients referred for AFL ablation, 36 had cavotricuspid isthmus (CTI) dependent flutter (Group I) and 24 had lower (n = 21) or upper loop reentry (n = 5) (Group II). After ablation, isthmus block was evaluated by pacing from the coronary sinus (CS) and low lateral right atrium and by alternative techniques, including mapping with electrodes spanning the CTI or electroanatomic mapping. After bidirectional CTI block was verified, 21/36 (58%) in Group I showed TC with CS pacing, including low TC in 16 (including 11 showing "pseudo" CTI conduction), higher TC in 6 and multiple breaks in 3. However, 8 with low TC during CS pacing showed unidirectional block by pacing outside of the CS os. Twelve (50%) in Group II had TC during CS pacing after bidirectional CTI block, with low TC in 5 (2 mimicking residual CTI conduction) and higher breaks in 9. There was no significant difference in the incidence of TC during CS pacing after CTI block between groups. In seven autopsied hearts, the muscle orientation between the proximal CS musculature and Eustachian ridge were examined. Muscular connections between the CS and Eustachian ridge coursing toward the orifice of inferior vena cava were found in one of the hearts. CONCLUSIONS: It is concluded that in patients with bidirectional CTI block, pacing from the CS may be associated with TC mimicking a conduction leak through the isthmus. Pacing just outside the CS os helps distinguish pseudo from true isthmus block.     

Atrial Flutter Mapping and Ablation I

Endocardial mapping has led to a detailed knowledge of reentry mechanisms in atrial flutter. Multipolar and deflecting tip catheters allow recording local electrograms from multiple areas of the right atrium, and from the coronary sinus. In common flutter, with the typical "sawtooth" pattern, there is circular activation of the right atrium in a "counterclockwise" direction, descending in the anterior and lateral walls, and ascending in the septum and posterior wall. Superior and inferior vena cava, linked by a "line" of functional block in the posterolateral wall, make the central obstacle for circular activation. The cranial and caudal turning points are the atrial "roof," and the isthmus between the inferior vena cava and the tricuspid valve. Complex conduction patterns, probably including slow conduction are detectable in the low septal area, around the coronary sinus. Atypical flutter, without the sharp negative deflections of common flutter, sometimes shows circular activation in the right atrium, rotating in the opposite direction of common flutter (clockwise). Other atypical flutters show no circular right atrial activation, and only partial data from coronary sinus activation, combined with the response to atrial stimulation (entrainment) allow the diagnosis of left atrial reentry, without a precise delimitation of the circuits. In patients having undergone cardiac surgery, atypical flutter may be based on reentry around surgical scars. To our knowledge, the mechanism of type II flutter has not been disclosed in humans.     

Prospective randomized comparison of cooled radiofrequency versus standard radiofrequency energy for ablation of typical atrial flutter

In patients with atrial flutter, conventional RF ablation may not result in complete isthmus block. This prospective, randomized study tested the hypothesis that the cooled RF ablation is safe and facilitates the achievement of isthmus block with fewer RF applications than with standard ablation for typical atrial flutter. Isthmus ablation was performed in 59 patients (40 men, 64 +/- 14 years) with type I atrial flutter using standard RF (n = 31) or cooled RF (n = 28) catheters with crossover after 12 unsuccessful RF applications. The endpoint was bidirectional isthmus block or a total of 24 unsuccessful RF applications. After the first 12 RF applications, 17 (55%) of 31 standard RF and 22 (79%) of 28 cooled RF patients had bidirectional isthmus block (P < 0.05). After the remaining patients crossed over to the alternate RF ablation system and underwent up to 12 more RF applications, bidirectional isthmus block had been demonstrated in 27 (87%) of 31 standard RF and 25 (89%) of 28 cooled RF patients (P = NS). Isthmus block was not achieved within 24 RF applications in four standard and three cooled RF patients. Mean measured tip temperatures for cooled RF were lower than for standard RF (38.5 degrees C +/- 6.98 degrees C vs 57.2 degrees C +/- 7.42 degrees C, P < 0.0001). Peak temperatures were also lower for cooled RF compared to standard RF (45.7 degrees C +/- 22.7 degrees C vs 63.4 degrees C +/- 9.87 degrees C, P < 0.0001). Importantly, mean power delivered was significantly higher for cooled than for standard RF (42.3 +/- 9.48 vs 34.0 +/- 14.0 W, P < 0.0001). There were no serious complications for either ablation system. During a 12.8 +/- 3.76-month follow-up, there were two atrial flutter recurrences in the cooled RF group and four in the standard RF group (P = NS). In patients with type I atrial flutter, ablation with the cooled RF catheter is as safe as, and facilitates creation of bidirectional isthmus block more rapidly than, standard RF ablation.     

Diagnosis and ablation of atrial flutter using a high resolution, noncontact mapping system

The ablation of atrial flutter can sometimes be time consuming and unsuccessful using conventional catheter techniques especially in patients with recurrences after previous ablation procedures. Simultaneous high resolution mapping from multiple sites may overcome some of the limitations. Therefore, a new high resolution noncontact mapping system was used for diagnosis and ablation of atrial flutter in 15 patients. The mapping system consists of a catheter-mounted multielectrode array, an amplifier, and a computer workstation. Far-field potentials recorded by the multielectrode catheter are amplified, digitized, and sampled at 1.2 kHz, and digitally filtered to construct high resolution activation maps during tachycardia. Ablation catheters can be steered to target sites without fluoroscopy. In 12 of the 15 patients the analysis of the activation sequence during tachycardia showed a counter-clockwise, and in 1 of 15 patients a clockwise, rotating wavefront using the isthmus as part of the reentrant circuit. In two patients no tachycardia could be induced. In 3 of the 15 patients with previous conventional ablation procedures the gap in the line of block in the isthmus region was identified and marked on the animation model. The isthmus in the right atrium was ablated and isthmus block verified by the mapping system in all patients. No complications were observed. No recurrences of atrial flutter occurred during follow-up of 4 +/- 1.7 months. The total procedure and fluoroscopy time was 171 +/- 50.0 minutes and 24 +/- 12.7 minutes, respectively. In conclusion, the use of the new high resolution noncontact mapping system in patients with right atrial flutter is safe and highly effective. In patients with previously failed conventional ablation procedures the use of a noncontact mapping system may facilitate the identification of the gap in the line of block in the isthmus region and reablation of atrial flutter.     

Using Intracardiac Catheter Recordings from the His and Proximal Coronary Sinus to Distinguish Isthmus Conduction Block During Catheter Ablation of Type I Atrial Flutter

Isthmus conduction block, demonstrated with the use of multipolar catheter recordings, is considered the preferred endpoint for ablation of type I atrial flutter. This study investigated the feasibility of using recordings from the His and coronary sinus (CS) to document isthmus conduction block. Isthmus conduction block was produced with linear radiofrequency (RF) ablation in 27 patients with type I atrial flutter. In 13 patients (group I), RF was delivered until bidirectional isthmus conduction block was demonstrated with multipolar Halo catheter recordings. In 14 patients (group II), RF was delivered during pacing from the lateral isthmus at 600 ms until a reversal in activation of the proximal CS and His occurred. At this point, data from the Halo recordings were reviewed to see if reversal correlated with conduction block; if not, further ablation was performed until block was demonstrated. The initial reversal in His and CS activation during RF energy delivery correlated with isthmus block in only 4 (28.6%) of 14 patients in group II. Additional RF delivery produced isthmus block in the other ten patients resulting in a further increase in the St-CS interval of 35 ± 20 ms. A His-CS interval of at least -40 ms signified isthmus block with a sensitivity and specificity of 48% and 100%, respectively. Reversal in His-CS activation during pacing from the lateral margin of the isthmus is not specific for the creation of isthmus block. While activation of the proximal CS bipole > 40 ms after activation of the His appears specific for isthmus block, the low sensitivity of this finding limits its clinical use.     

Site-specific influence of transversal conduction across crista terminalis on recognition of isthmus block

BACKGROUND: Transversal conduction across crista terminalis (CT) is commonly observed during low-rate coronary sinus (CS) pacing after isthmus ablation and sometimes mimics incomplete clockwise isthmus block (IB). Site-specific influence of trans-cristal conduction gap on recognition of clockwise IB has been poorly understood. METHODS: Forty-five patients with common-type atrial flutter underwent mapping of CT and free wall lateral to CT during CS pacing of 100 ppm using CARTO after verification of IB, while duodecapolar catheter was positioned along tricuspid annulus to map periannular activation. RESULTS: A total of 43 gaps were demonstrated at upper (n = 15, 35%), middle (n = 17, 40%), and lower one-thirds of CT (n = 11, 25%) in 36 of 45 patients (80%). Gaps were single in 31 (69%) and multiple in 5 patients (11%). Activation patterns of free wall lateral to CT in CARTO maps were descending pattern without gaps (n = 9, 20%), collision pattern with a single gap (n = 31, 69%), and simultaneous pattern with multiple gaps (n = 5, 11%). Activation sequence of duodecapolar catheter was complete block pattern in 41 (91%) and incomplete block pattern in 4 patients (9%), masquerading as persistent clockwise isthmus conduction. The incomplete block pattern in duodecapolar catheter was exclusively associated with a gap at the lower CT (0/15, 0/17, and 4/11 gaps at upper, middle, and lower CT, respectively; P < 0.01) and was attributable to faster conduction across CT gaps than in complete block pattern. CONCLUSIONS: Trans-cristal conduction was commonly observed during low-rate CS pacing. Rapid transversal conduction exclusively across lower CT masqueraded as incomplete clockwise IB.     

Three-dimensional mapping of atypical right atrial flutter late after chest stabbing

We present the case of a female patient who previously underwent cardiac surgery for traumatic anterior right atrial perforation after a stabbing attack. Four years later the patient presented with right atrial common type flutter and isthmus ablation was performed subsequently. However, three years after isthmus ablation the patient was readmitted with atypical right atrial flutter. Electrophysiological study revealed persistent bidirectional isthmus block. Three-dimensional mapping (NavX, St. Jude Medical, St. Paul, MN, USA) demonstrated an incisional tachycardia with the critical isthmus at the border of the anterior area of scar in a close proximity to the superior tricuspid annulus. After ablation of this isthmus the patient was arrhythmia free after a follow-up of 9 months. This case illustrates that three-dimensional scar mapping may help to identify unusual isthmus sites that may be simultaneously responsible for both typical and atypical atrial flutter.     

Basket catheter-guided three-dimensional activation patterns construction and ablation of common type atrial flutter

Construction of three-dimensional activation maps and evaluation of ablation-created bidirectional block in the tricuspid valve-inferior vena caval (TV-IVC) isthmus in patients with atrial flutter (AF) are difficult with conventional mapping technique. In 36 patients with type I AF (25 men, 11 women; mean age 62 +/- 10.5 years) a multielectrode basket catheter (BC) was deployed in the right atrium (RA). Out of 64 BC electrodes, 56 bipolar electrograms were derived. Three-dimensional activation patterns were constructed with a software program. Stable electrograms of satisfactory quality were obtained in 49 +/- 2 electrode pairs. Capture was possible in 36 +/- 3 of bipoles. In counterclockwise AF (CCW-AF) and clockwise AF (CW-AF) episodes, cycle lengths and TV-IVC isthmus conduction times were 248 +/- 26 ms and 251 +/- 23 ms, (P = 0.74) and 105 +/- 28 ms and 106 +/- 33 ms (P = 0.92), respectively. Conduction velocity in the TV-IVC isthmus was lower than in the anterior or septal limbs of the circuit, in counterclockwise or clockwise episodes. Double potentials were recorded in 94% of patients. Three-dimensional activation patterns were delineated and displayed as isochronal maps. The reentry circuit involved the TV-IVC isthmus, septal, and anterior walls and a part of the RA roof anterior to superior vena cava. Postablation isthmus conduction was evaluated through the sequence criteria, local electrogram-based criteria, and the analysis of three-dimensional activation patterns of the paced rhythms. The complete isthmus block was associated with a significant increase of the low anterior low septal conduction interval (152 +/- 29 vs 104 +/- 32 ms, P = 0.001) and the low septal-low anterior conduction interval (150 +/- 31 vs 107 +/- 33 ms, P = 0.001). Radiofrequency ablation was successful in 32 (90%) of 36 patients. In conclusion, the current mapping system enables construction of three-dimensional activation patterns and facilitates evaluation of the postablation TV-IVC isthmus block in patients with AF.     

Mechanism of atrial flutter occurring late after orthotopic heart transplantation with atrio-atrial anastomosis

OBJECTIVE: We sought to better define the electrophysiologic mechanism of atrial flutter in patients after heart transplantation. BACKGROUND: Atrial flutter is a recognized problem in the post-cardiac transplant population. The electrophysiologic basis of atrial flutter in this patient population is not completely understood. METHODS: Six patients with cardiac allografts and symptoms related to recurrent atrial flutter underwent diagnostic electrophysiologic study with electroanatomic mapping and radiofrequency catheter ablation. Comparison was made with a control non-transplant population of 11 patients with typical counterclockwise right atrial flutter. RESULTS: In each case, mapping showed typical counterclockwise activation of the donor-derived portion of the right atrium, with concealed entrainment shown upon pacing in the cavotricuspid isthmus (CTI). The anastomotic suture line of the atrio-atrial anastomosis formed the posterior barrier of the reentrant circuit. Ablation of the electrically active, donor-derived portion of the CTI was sufficient to terminate atrial flutter and render it noninducible. Comparison with the control population showed that the electrically active portion of the CTI was significantly shorter in patients with transplant-associated flutter and that ablation was accomplished with the same or fewer radiofrequency lesions. CONCLUSIONS: Atrial flutter in cardiac transplant recipients is a form of typical counterclockwise, isthmus-dependent flutter in which the atrio-atrial anastomotic suture line forms the posterior barrier of the reentrant circuit. Ablation in the donor-derived portion of the CTI is sufficient to create bidirectional conduction block and eliminate this arrhythmia. Ablation or surgical division of the donor CTI at the time of transplantation could prevent this arrhythmia.     

Protected circumferential conduction in the posterior atrioventricular vestibule of the left atrium: electrophysiologic and anatomic correlates

BACKGROUND: The anatomic substrate for protected isthmus conduction in the right atrium has been well defined. Little is known of similar substrates in the left atrium (LA). METHODS: Patients (pts) with reentrant tachycardia (AVRT) supported by a single left-sided accessory pathway were studied retrospectively (n = 64) and prospectively (n = 31). Intracardiac electrograms were recorded from the His bundle position and coronary sinus (CS). The LA was mapped with a steerable catheter using the transseptal approach. LA anatomy was examined grossly and histologically in six cadaver hearts after removal of endocardium. RESULTS: A distal-to-proximal CS activation sequence during AVRT was seen in all patients with a left lateral accessory pathway before ablation. After one to three radiofrequency (RF) energy deliveries that did not interrupt accessory pathway conduction, the CS activation sequence was reversed in three patients in the retrospective group and bidirectional conduction block in the posterior atrioventricular vestibule of the LA (PAVV) was demonstrated in nine patients in the prospective group. Four of the six cadaver hearts showed a distinct circumferential inferoposterior myocardial bundle that coursed parallel to the CS in the PAVV. CONCLUSIONS: We described evidence of bidirectional intraatrial block in the PAVV after application of RF energy during accessory pathway ablation. Such conduction block may mimic the presence of a second accessory pathway. Our data suggest that circumferential conduction in the PAVV may be poorly coupled to the rest of the LA and may be involved in the macro-reentrant circuit around the mitral annulus. The circumferential inferoposterior myocardial bundle may serve as the underlying anatomic substrate.     

Electroanatomic Mapping to Identify Breakthrough Sites in Recurrent Typical Human Flutter

SRA, J., et al. : Electroanatomic Mapping to Identify Breakthrough Sites in Recurrent Typical Human Flutter. The accuracy of conventional techniques in localizing previous radiofrequency (RF) ablation sites and thus breakthrough sites of recurrent atrial flutter is somewhat limited. We investigated the role of electroanatomic mapping for identifying breakthrough sites or "gaps" at the tricuspid annulus and inferior vena cava (IVC)/eustachian ridge isthmus to help RF ablation in patients with recurrent typical flutter. Twelve patients (  8 men, 4 women, age 63 ± 10 years  ) with recurrent typical atrial flutter were included in the study. An electroanatomic mapping system (CARTO) was used to create a voltage map and activation and propagation patterns in the right atrium. Detailed voltage, activation, and propagation mapping of the tricuspid annulus and IVC/eustachian ridge isthmus allowed precise identification of gaps in all 12 patients at the tricuspid annulus (eight sites), IVC ridges (two sites), mid-isthmus region (one site), and tricuspid annulus and IVC ridges (one site). Radiofrequency energy directed at these sites eliminated atrial flutter in all 12 patients, confirmed by noninducibility of atrial flutter and demonstration of conduction block during atrial pacing on either side of the lesion lines. During a mean follow-up of  14.8 ± 3.5 months  (  range 8–19 months  ), paroxysmal atrial flutter recurred in only one patient and was subsequently treated with amiodarone, although this had been ineffective prior to ablation. Electroanatomic mapping can precisely identify gaps in the lesion line responsible for breakthrough of recurrent typical atrial flutter at the tricuspid annulus and at the IVC/eustachian ridge isthmus. These sites can be targeted with RF ablation with a high degree of success.     

Detour conduction can mimic complete conduction block at the cavo-tricuspid isthmus

A 54-year-old man with typical atrial flutter underwent linear ablation at the cavo-tricuspid isthmus. Though standard tricuspid annulus (TA) mapping and differential pacing suggested complete isthmus conduction block, electroanatomic mapping revealed that detoured conduction through a residual conduction gap around the inferior vena cava far from the TA mimicked complete conduction block. Though the double potential interval along the block line was not long enough to guarantee a complete line of block after eliminating the conduction gap, electroanatomic remapping accurately confirmed a complete block line, suggesting electroanatomic mapping may be the most reliable method to confirm complete isthmus conduction block.