Mechanism Of Atrial Tachycardia Research Articles

Abstract 13049: Electrophysiological Mechanism of Potassium Channel KCNQ1 p.V162M Mutation Induced Atrial Tachycardia and Epilepsy

Objective: Arrhythmia and epilepsy are the causes of syncope and sudden death. Both of them are associated with abnormal function of potassium ion channels. Delayed rectified potassium current (IKs) is generated by combining the α subunit of potassium ion channel encoded by KCNQ1 gene with the β subunit encoded by KCNE1 gene. It plays an important role in electrical excitation and K+ circulation of nerve cells. In this study, a patient with atrial arrhythmia and epilepsy with a history of syncope was identified by genetic testing as having a mutation in the KCNQ1 p.V162M gene. The purpose of this study was to investigate the effect of KCNQ1 p.V162M mutation on the structure and function of potassium ion channels. Methods: The mutant plasmid KCNQ1-p.V162M was constructed for cell transfection. The expression of protein and mRNA were analyzed by western blotting and real-time quantitative PCR. The IKs of the two groups were detected by whole-cell patch clamp technique. Results: Whole exon gene sequencing revealed that the patient carried the KCNQ1 p.V162M mutation. The results of molecular biology experiment showed that mRNA, KCNQ1 total protein and membrane protein expressions in mutant group were significantly lower than those in wild group. Whole-cell patch clamp results showed that the peak current density and tail current of IKs in the mutant group were significantly decreased compared with those in the wild group, indicating that the mutation of KCNQ1 p.V162M could lead to decreased function of potassium ion channels. Conclusions: KCNQ1 p.V162M mutation can lead to decreased expression of KCNQ1 protein and decreased function of potassium ion channel, which may be the potential mechanism of atrial tachycardia and epilepsy induced by this mutation.

The Use of Local Activation Timing Histogram in Ablation of Focal and Re-Entrant Atrial Tachycardias

BackgroundActivation mapping is often used to differentiate focal from re-entrant arrhythmias. This can be challenging but is critical to ablation success. The local activation time (LAT) histogram, which depicts point distribution over isochronal segments, may help characterize arrhythmia mechanisms and identify an optimal ablation strategy. ObjectivesThis study aimed to investigate features of the LAT histogram associated with the focal vs re-entrant mechanism of atrial tachycardias (ATs) and the use of the LAT histogram in the identification of target ablation sites. MethodsWe retrospectively evaluated cases of focal and re-entrant ATs performed at a single academic tertiary care center for which activation mapping was performed using CARTO 3 version 7 software (Biosense Webster). Baseline patient, arrhythmia, and procedural characteristics as well as LAT histogram features were evaluated for each case. LAT histogram–guided ablation targets were also compared against actual ablation sites. ResultsAmong 52 ATs assessed, 17 were focal, and 35 were re-entrant. Tachycardia cycle length was significantly shorter in re-entrant than in focal ATs (288.2 milliseconds [Q1-Q3: 250-306.5 milliseconds] vs 370 milliseconds [Q1-Q3: 285-400 milliseconds], respectively; P = 0.006). LAT histograms contained more “valleys” in re-entrant than in focal ATs (3 [Q1-Q3: 2-4] vs 1 [Q1-Q3: 1-1]; P < 0.001). No focal ATs contained >2 and no re-entrant ATs contained <1 LAT valley(s). All successful ablation sites correlated with LAT histogram–suggested sites. ConclusionsLAT histograms can help distinguish focal from re-entrant Ats and identify effective ablation sites.

Detailed Analysis of Tachycardia Cycle Length Aids Diagnosis of the Mechanism And Location of Atrial Tachycardias.

Although the mechanism of an AT can usually be elucidated using modern high-resolution mapping systems, it would be helpful if the AT mechanism and circuit could be predicted before initiating mapping. We examined if information gathered from the cycle length (CL) of the tachycardia can help predict AT-mechanism and its localization. 138 activation maps of ATs including 8 focal-ATs, 94 macroreentrant-ATs and 36 localized-ATs in 95 patients were retrospectively reviewed. Maximal CL (MCL) and minimal CL (mCL) over a minute period were measured via a decapolar catheter in the coronary sinus. CL-variation and beat-by-beat CL-alternation were examined. Additionally, CL-respiration correlation was analyzed by the RhythmiaTM system. Both MCL and mCL were significantly shorter in macroreentrant-ATs (MCL = 288[253-348]ms, p = 0.0001; mCL = 283[243-341]ms, p = 0.0012), and also shorter in localized-ATs (MCL = 314[261-349]ms, p = 0.0016; mCL = 295[248-340]ms, p = 0.0047) compared to focal-ATs (MCL = 506[421-555]ms, mCL = 427[347-508]ms). An absolute CL-variation (MCL-mCL) < 24 ms significantly differentiated reentrant ATs from focal-ATs with a sensitivity = 96.9%, specificity = 100%, positive predictive value (PPV) = 100% and negative predictive value (NPV) = 66.7%. The beat-by-beat CL-alternation was observed in 10/138 (7.2%), all of which showed the reentrant mechanism, meaning that beat-by-beat CL-alternation was the strong sign of reentrant mechanism (PPV = 100%). Although the CL-respiration correlation was observed in 28/138 (20.3%) of ATs, this was predominantly in right-atrium (RA)-ATs (24/41, 85.7%), rather than left atrium (LA)-ATs (4/97, 4.1%). A positive CL-respiration correlation highly predicted RA-ATs (PPV = 85.7%), and negative CL-respiration correlation probably suggested LA-ATs (NPV = 84.5%). Detailed analysis of the tachycardia CL helps predict the AT-mechanism and the active AT chamber before an initial mapping.

Unique topological classification of complex reentrant atrial tachycardias enables optimal ablation strategy

Abstract Funding Acknowledgements: Type of funding sources: Public grant(s) – EU funding. Main funding source(s): ERC starting grant - SMARTHEART (Nele Vandersickel) B Reentry is a common underlying mechanism of atrial tachycardia (AT). Reentry loops form around anatomical or functional 'holes' in the electrophysiological substrate and dominate the atrial cycle. Terminating a 'full' loop may cause previously 'suppressed' loops around another hole to become dominant. Interpretation of electroanatomical maps can thus be tedious: a full loop may be easily identified, but predicting suppressed loops is complex. We propose that topological classification may aid identification of suppressed loops in complex AT and improve ablation procedures. O Given a map of reentrant clinical AT, we aim to unambiguously classify the AT and suggest an operator-independent optimal ablation strategy. M The left atrium can be described topologically as a closed surface with three ‘holes’: mitral valve, left and right pulmonary veins (similar for the right atrium). Non-conductive tissue may constitute additional topological holes in the substrate. Anatomical reentry can occur around any of the holes described above. Therefore, we uniquely categorize an AT by identifying the number of holes in combination with the presence of full and suppressed loops. Fig. 1-2 shows the finite number of possible combinations for 3 and 4 holes. An optimal ablation strategy should terminate both full and suppressed loops, by connecting their corresponding holes. Directed graph mapping (DGM) is a method and software implementation to analyze arrhythmia by constructing a directed network from local activation time maps. We extended DGM to perform topological classification of AT. We hypothesize that the full reentry loops will correspond to the cycles detected by DGM in the network, while suppressed loops are characterized by activity propagating around a hole for at least 60% of its circumference. To test our algorithms, we generated &amp;gt; 1000 simulations corresponding to 5 different scenarios of Fig. 1-2 whereby the circumference of the suppressed loop was varied between 50% and 90% by adding slow conductive tissue. We also classified 110 clinical cases of mapped AT retrospectively and compared our suggested ablation strategy with the clinical ablation lines which ended the AT. R Terminating solely the full loops by an ablation line led to the suppressed loops creating a slower AT in 95% of simulations. Further ablation to terminate the suppressed loop ended the AT. Following our suggested ablation strategy directly terminated the AT. The ablation strategy suggested by DGM was topologically equivalent to clinically successful ablations in 90% of clinical cases. In 5 cases, DGM correctly predicted that the chosen ablation lead to a suppressed loop becoming dominant, resulting in slower AT. C We presented a unique topological classification of AT. We showed that suppressed loops play a pivotal role as not ablating them leads to slower AT. Benefits include preventing redo maps, shorter and operator independent procedures, and possibly reducing AT recurrence.

Utility and limitations of coherent mapping algorithm utilizing vectors and global propagation patterns in atrial tachycardia.

A novel mapping algorithm utilizing vectors and global patterns of propagation (Coherent™, Biosense Webster) has been developed to help identify the mechanism of atrial tachycardia (AT). We aimed to determine the diagnostic accuracy of coherent mapping compared with that of ripple mapping. This study included 41 consecutive patients with 84 ATs (47 reentrant and 37 focal ATs). Two independent electrophysiologists confirmed the diagnoses using coherent mapping before the ripple map-guided ablation. AT termination was achieved in 75 of 84 ATs (89%) at first ablation lesion set. Four of the remaining nine ATs, which were terminated before an index radiofrequency (RF) application, were non-inducible after RF delivery at the first lesion set, whereas the other five ATs were terminated at the second lesion set. Diagnostic agreement between coherent and ripple maps was achieved in 51 of 84 ATs (61%): 28 of the 47 macroreentrant ATs (60%) and 23 of the 37 focal ATs (62%; P=0.826). In typical macroreentrant ATs, including left atrial roof, perimitral, and cavotricuspid isthmus-dependent ATs, coherent maps achieved diagnostic agreement in 23 of 29 ATs (79%), which was higher than that in other ATs (51%, P=0.018): 13 of 26 macroreentrant ATs (50%) and 15 of 29 focal ATs (52%, P=1.000). Ripple map-guided AT ablation achieved a high termination rate in the first lesion set. Coherent mapping yielded a favorable diagnostic accuracy for typical macroreentrant ATs, though its value for diagnosing other ATs was limited.

Artificial intelligence-enabled electrocardiogram to distinguish cavotricuspid isthmus dependence from other atrial tachycardia mechanisms.

Accurately determining atrial arrhythmia mechanisms from a 12-lead electrocardiogram (ECG) can be challenging. Given the high success rate of cavotricuspid isthmus (CTI) ablation, identification of CTI-dependent typical atrial flutter (AFL) is important for treatment decisions and procedure planning. We sought to train a convolutional neural network (CNN) to classify CTI-dependent AFL vs. non-CTI dependent atrial tachycardia (AT), using data from the invasive electrophysiology (EP) study as the gold standard. We trained a CNN on data from 231 patients undergoing EP studies for atrial tachyarrhythmia. A total of 13 500 five-second 12-lead ECG segments were used for training. Each case was labelled CTI-dependent AFL or non-CTI-dependent AT based on the findings of the EP study. The model performance was evaluated against a test set of 57 patients. A survey of electrophysiologists in Europe was undertaken on the same 57 ECGs. The model had an accuracy of 86% (95% CI 0.77-0.95) compared to median expert electrophysiologist accuracy of 79% (range 70-84%). In the two thirds of test set cases (38/57) where both the model and electrophysiologist consensus were in agreement, the prediction accuracy was 100%. Saliency mapping demonstrated atrial activation was the most important segment of the ECG for determining model output. We describe the first CNN trained to differentiate CTI-dependent AFL from other AT using the ECG. Our model matched and complemented expert electrophysiologist performance. Automated artificial intelligence-enhanced ECG analysis could help guide treatment decisions and plan ablation procedures for patients with organized atrial arrhythmias.

Left Atrial Anterior Wall Scar-Related Atrial Tachycardia in Patients after Catheter Ablation or Cardiac Surgery: Electrophysiological Characteristics and Ablation Strategy.

Background: The mechanisms of atrial tachycardia (AT) related to the left atrial anterior wall (LAAW) are complex and can be challenging to map in patients after catheter ablation for atrial fibrillation (AF) or cardiac surgery. We aimed to investigate the electrophysiological characteristics AT and to devise an ablation strategy. Methods and Results: We identified 31 scar-related LAAW reentrant ATs in 22 patients after catheter ablation for AF or cardiac surgery. Activation maps of the left atrium (LA) or both atria were obtained using a high-density mapping system, and the precise mechanism and critical area for each AT were analyzed. Patients were followed up regularly in a clinic. After analyzing the activation and propagation of each AT, the scar-related LAAW ATs were classified into three types, based on mechanisms related to: (1) LAAW conduction gap(s) in 19 LA macro-reentrant ATs; (2) LAAW epicardial connection(s) in 11 LA or bi-atrial ATs; and (3) LAAW local micro-reentry in 1 LAAW AT. Multiple ATs were identified in seven patients. Effective ablation (termination or circuit change of AT) was obtained in 30 ATs by targeting the critical area identified by the mapping system. During 16.0 ± 7.6 months follow-up, recurrent AT occurred in two patients. Conclusions: Three mechanisms of scar-related AT of LAAW were identified, most of which were related to LAAW conduction gaps. Notably, epicardial AT or bi-atrial AT comprised a nonnegligible proportion. A high-density mapping system could make it possible to determine the accurate mechanism of AT and serve as a guide following ablation.

PO-694-02 UTILITY AND LIMITATION OF A NOVEL MAPPING ALGORITHM UTILIZING VECTORS AND GLOBAL PATTERN OF PROPAGATION IN ATRIAL TACHYCARDIA

A novel mapping algorithm utilizing vectors and global pattern of propagation has been described to help identifying the mechanism of atrial tachycardia (AT, Coherent™, BiosenseWebster). However, the utility and limitation of coherent mapping in comparison with ripple mapping remains uncertain.

Intuitive diagnosis of complex atrial tachycardia mechanisms using a novel histogram module of an ultra-high-resolution mapping system.

The LUMIPOINT™ software module was developed to aid the physician in determining the mechanism of individual atrial tachycardias (ATs). The purpose of this study was to assess the clinical utility of the SKYLINE™ histogram that is a part of LUMIPOINT™. This study included consecutive patients with iatrogenic sustained AT who underwent catheter ablation using conventional mapping (RHYTHMIA™). SKYLINE™ patterns were analyzed offline and classified into two types: (1) focal type (type-F) exhibiting a low-amplitude (relative activating surface area < 10%) plateau period and (2) reentrant type (type-R) showing no plateau period. How well the two patterns distinguished between focal and macroreentrant ATs as determined by conventional mapping was evaluated. We studied 101 iatrogenic ATs in 91 patients (female: 24, mean age: 67.3 ± 9.1years). Activation mapping revealed 79 (78.2%) macroreentrant, 6 (5.9%) localized reentrant, and 16 (15.8%) focal ATs. Among the 72 type-R ATs, the mechanism was truly a macroreentry in 70 ATs. However, one focal AT and one localized reentrant AT displayed a type-R pattern (pseudo-reentry pattern). In the 29 type-F ATs, nine macroreentrant ATs were recognized (pseudo-focal pattern). Using SKYLINE™ type-R to differentiate macroreentrant AT from AT with centrifugal activation (focal or localized reentry), the sensitivity and specificity were 88.6% and 90.9%, respectively. Even when the SKYLINE™ type did not match the mapping-based AT mechanism, all discrepancies were electrophysiologically explicable using the SKYLINE™ histograms. SKYLINE™ histograms are a useful tool for the intuitive diagnosis of AT mechanisms.

Use of high-density activation and voltage mapping in combination with entrainment to delineate gap-related atrial tachycardias post atrial fibrillation ablation.

An incomplete understanding of the mechanism of atrial tachycardia (AT) is a major determinant of ablation failure. We systematically evaluated the mechanisms of AT using ultra-high-resolution mapping in a large cohort of patients. We included 107 consecutive patients (mean age: 65.7 ± 9.2 years, males: 81 patients) with documented endocardial gap-related AT after left atrial ablation for persistent atrial fibrillation (AF). We analysed the mechanism of 134 AT (94 macro-re-entries and 40 localized re-entries) using high-resolution activation mapping in combination with high-density voltage and entrainment mapping. Voltage in the conducting channels may be extremely low, even <0.1 mV (0.14 ± 0.095 mV, 51 of 134 AT, 41%), and almost always <0.5 mV (0.03-0.5 mV, 133 of 134 AT, 99.3%). The use of multipolar Orion, HDGrid, and Pentaray catheters improved our accuracy in delineating ultra-low-voltage areas critical for maintenance of the circuit of endocardial gap-related AT. Conventional ablation catheters often do not detect any signal (noise level) even using adequate contact force, and only multipolar catheters of small electrodes and shorter interelectrode space can detect clear fractionated low-amplitude and high frequency signals, critical for re-entry maintenance. We performed a diagnosis in 112 out of 134 AT (83.6%) using only activation mapping and in 134 out of 134 AT (100%) using the combination of activation and entrainment mapping. High-resolution activation mapping in combination with high-density voltage and entrainment mapping is the ideal strategy to delineate the critical part of the circuit in endocardial gap-related re-entrant AT after AF ablation.

Characterization of Complex Atrial Tachycardia in Patients With Previous Atrial Interventions Using High-Resolution Mapping.

This study systematically evaluated mechanisms of atrial tachycardia (AT) by using ultra-high-resolution mapping in a large cohort of patients. An incomplete understanding of the mechanism of AT is a major determinant of ablation failure. Consecutive patients with≥1 AT (excluding cavotricuspid isthmus-dependent flutter) were included. Mapping was performed with a 64-pole mapping catheter. The AT mechanism was defined based on activation mapping and confirmed by entrainment in selected cases. A total of 132 patients were included (60 ± 12 years; 31 [23%] female; 111 [84%] previous atrial fibrillation [AF] ablation; 5 [4%] previous left atriotomy). One hundred four (94%) of the 111 post-AF ablation AT patients had substrate-based ablation during the index AF ablation. A total of 214 ATs were mapped, with complete definition of the AT mechanism in 206 (96%). A total of 129 (60%) had anatomic macro-re-entry (circuit diameter 44.2 ± 9.6mm), 57 (27%) had scar-related localized re-entry (circuit diameter 25.8 ± 12.2mm), and 20 (9%) had focal AT. Fifty-eight (45%) patients had multiple ATs (27 [20%] dual-loop re-entry; 60 [43%] sequential AT) with complex and highly variable transitions between AT circuits. A total of 116 (90%) of 129 macro-re-entrant ATs, 56 (98%) of 57 localized AT, and 20 (100%) of 20 focal ATs terminated after radiofrequency ablation. After a mean follow-up of 13 ± 9months, 57 (46%) patients experienced recurrence of AT. Among patients with AT in the context of previous atrial interventions, particularly post-AF ablation patients, multiple complex AT circuits are common. Despite complete delineation of arrhythmia circuits using ultra-high-resolution mapping and high acute ablation success rates, long-term freedom from AT is modest.

Multi-electrode mapping of complex macroreentry atrial tachycardia

BackgroundMulti-electrode mapping (MEM) is increasingly applied in ablation of complex atrial arrhythmias. This study aimed to evaluate MEM for analysis and treatment of complex macroreentry atrial tachycardia (MAT). MethodsPatients with MAT related to scarring, history of heart surgery or atrial linear ablation were studied. Patients were mapped with conventional activation mapping (CAM) or MEM. After characterizing the mechanism of atrial tachycardia (AT), the ablation was performed. ResultsThe study consisted of 114 eligible patients, 74 in the CAM and 40 in MEM. Compared with CAM, MEM had a shorter procedure duration (156.7 ± 59.1 ms vs. 127.3 ± 59.3 ms, P = 0.003) and mapping duration (62.6 ± 35.7 ms vs. 30.5 ± 15.3 ms, P < 0.001) and more mapping points (1364.9 ± 828.7 points vs. 148.3 ± 79.6 points, P < 0.001). There were no significant differences between CAM and MEM in acute ablation success rate, complication, postoperative AADs, and ablation duration. The mean disease-free survival time in CAM versus MEM was 20.8 (95% CI: 17.6–24.1) months versus 26.6 (95% CI: 22.7–30.4) months. The median disease-free survival time in the CAM versus MEM was 20.0 (95% CI: 13.9–26.1) months versus 30.0 (95% CI: 26.7–36.3) months. The AT recurrence risk of MEM was 0.522 times that of CAM (HR 95% CI: 0.282–0.968; P = 0.039). ConclusionMEM is strongly recommended in ablation of complex MAT.

Useful Electrocardiographic Features to Help Identify the Mechanism of Atrial Tachycardia Occurring After Persistent Atrial Fibrillation Ablation

The purpose of this study was to describe and identify useful electrocardiographic characteristics to helpidentify the mechanism of atrial tachycardia (AT) occurring after persistent atrial fibrillation (PsAF) ablation. Electrocardiographic analysis to help identify the mechanism of AT after PsAF ablation is much limitedby the fact that remodeling and ablation alter the normal activation pattern. All consecutive patients who underwent mapping and ablation of AT after PsAF ablation were included.Surface P waves were analyzed during higher (>2:1) grades of atrioventricular block. One hundred ninety-six ATs with visible P waves were identified in 127 patients (macro-re-entry in 57%, centrifugal AT in 43%). One-third displayed low-voltage P waves (≤0.1 mV). An isoelectric line >80 ms was more common in centrifugal compared with macro-re-entrant AT (47% vs. 24%; p< 0.001), but its positive predictive value was limited (60%). A minority of peritricuspid ATs displayed the classic saw-tooth pattern (27% [n= 22]). However, the "precordial transition" (a gradual transition from an upright component in lead V1 to a negative component with progression across the precordium) remained often observed and specifically identified peritricuspid AT (specificity, 98%; sensitivity, 59%). Only 2 unique features could help identify perimitral AT (n= 60). First, the presence of a negative or negative-positive P-wave in any of leads V2 to V6 identified perimitral AT with 97% specificity and 30% sensitivity. Second, a "notched" negative component at the beginning of a positive P-wave in the inferior leads specifically identified clockwise perimitral AT (specificity, 98%; sensitivity, 25%). Only few unique electrocardiographic characteristics help identify the mechanism of AT afterPsAFablation.Knowledge of these characteristics may aid in planning and performing ablation.

P386Relationship between scar and atrial tachycardia mechanisms: insight from registered magnetic resonance and ultra-high density activation mapping using the Rhythmia system

P386Relationship between scar and atrial tachycardia mechanisms: insight from registered magnetic resonance and ultra-high density activation mapping using the Rhythmia system

37 * Optimized local activation time sampling density for left atrial electroanatomic mapping

Introduction: Local activation time (LAT) mapping using electroanatomic mapping systems forms the cornerstone of diagnosis of complex atrial arrhythmias. Whilst new and emerging technologies exist to create higher-density LAT maps the end goal of LAT mapping (to identify the tachycardia mechanism and appropriate ablation site) remains unchanged. Here we identify the optimum point density for a variety of atrial tachycardia mechanisms, based on systematic analysis of in silico and in vivo LAT mapping data. Methods: Optimal sampling density for atrial tachyarrhythmias was determined in silico and in vivo. A variety of tachycardia mechanisms (focal, linear, re-entrant and spiral wave) were re-created on a 4×4 cm atrial monolayer model. Resulting isochronal activation maps were re-sampled at random locations with point-densities ranging from 0.25 to 10 points/cm2 and ‘downsampled' isochronal maps were re-interpolated across the monolayer. Error in the downsampled activation maps was quantified as the sum of squared differences between the original and re-interpolated LAT map activation times. Optimal sampling density was thereafter defined as the lowest point sampling density that resulted in an error reduction rate of less than 0.05 ms per mesh node per additional point sampled. Once validated, this technique was applied in vivo using high density left atrial maps (n=6) collected using point-by-point sampling (original sampling density 2.5±0.8 points/cm2). Result: Figure A shows the method applied to a simulated focal tachycardia with optimal sampling density identified at the point where the error reduction rate curve crosses the 0.05ms/node/point line. In silico, the optimum sampling density for focal, spiral-wave and re-entrant activation patterns was 1.2, 1.6 and 1.7 points/cm2. Linear activation in a 2-dimensional domain represents a special case where map accuracy is independent of sampling density. Figure B shows the same method applied to a clinical focal tachycardia. In vivo, the optimum sampling density for focal, macro-re-entry and localized re-entry was 0.9-1.0, 0.9-1.6 and 1.1-1.7 points/cm2. Conclusion: Optimal sampling densities can be identified for a variety of tachycardia mechanisms to maximize the diagnostic yield of interpolated LAT maps. Greater sampling density is required to correctly reveal more complex activation patterns (e.g. macro-re-entry and spiral-wave activation). For both focal and re-entrant left atrial tachycardias there appears to be no additional benefit in performing LAT sampling at a density greater than 1.7points/cm2. ![Graphic][1] [1]: /embed/inline-graphic-1.gif

Understanding atrial arrhythmia mechanisms by mapping and ablation

strate for the arrhythmia. It is perhaps pertinent to note the limitations of the electrocardiogram diagnosis. The term ‘flutter’ is used to describe rapid atrial tachycardias (AT) with an undulating waveform without isoelectric baseline; however, this has been overlooked by many groups reporting left AT that, as in Coffey’s paper, show rather long cycle lengths, around 300 ms, and longer isoelectric baselines between P-waves. Since the term ‘flutter’ is so closely related to typical flutter, depending on the cavotricuspid isthmus, it tends to suggest a macroreentrant mechanism, and the term ‘atrial tachycardia’ would appear more appropriate, as it does not pre-judge the mechanism. 2 In fact, around one-third of the mechanisms described in this study were focal discharges. The mapping technique, leading to ablation of the critical isthmus or the focus responsible for the arrhythmia, is remarkable because it creates excellent activation maps on the virtual atrial anatomy and allows, with some limitations, better understanding of the arrhythmia mechanism. Reduction of pacing manoeuvres to the minimum necessary to confirm the role of critical areas of the circuit minimizes the chances of altering activation sequences, a significant concern in left atrial macroreentrant AT, in which complex combinations of anatomic and functional obstacles can support multiple reentrant circuits and/or focal mechanisms. The average number of AT mechanisms encountered was 1.9 per patient, and 21 patients had three or more AT mechanisms, underlining the importance of this method. Another point of interest is the extremely low voltage recorded at some of the critical isthmuses that would suggest that activation could course over thin epicardial layers of atrial myocardium over endocardial scars. The interpretation of these local electrograms would be very difficult in the absence of the full activation maps supported with critical entrainment runs to confirm participation of adjacent areas in the circuit. The complexity and low amplitude of the electrograms would make quite impossible to reliably measure local post-pacing intervals at these critical isthmuses. Atrial tachycardia mechanisms were based in both atria and one-third were called septal. Two-thirds of the AT had a macroreentrant mechanism, and about one-third were focal. It is not clear from the paper if combinations of focal and macroreentrant mechanisms were found in the same patient and if more than one AT could be localized at distant sites in the same patient, but the report does give the general impression of dealing with severely diseased (remodelled? injured?) atria. The worse performance with ‘septal’ AT raises questions about the ability to precisely locate foci or critical isthmuses in this anatomically complex area. This seems particularly relevant because fragmented electrograms are often recorded from the septal atrial walls 3 and this

Clinical Approach to Atrial Tachycardia and Atrial Flutter From an Understanding of the Mechanisms. Electrophysiology Based on Anatomy

In 2009, 2343 catheter ablation procedures were performed in Spain for focal atrial tachycardia or atrial flutter (typical and atypical), with a yearly growth rate of 8%, indicating the clinical importance of these arrhythmias. The classic categorization of atrial tachycardia and atrial flutter based on rate and morphological criteria has become almost irrelevant at a time when clinical electrophysiology may lead to curative intervention based on a definition of the mechanism, making it necessary to bring laboratory experience closer to clinical practice. In this review we outline our present understanding of atrial tachycardia mechanisms, both focal and macroreentrant, and attempt to establish the conceptual links with classic concepts that may help the clinician to make a differential diagnosis and establish therapeutic indications, including that of an electrophysiologic study. Some of the concepts may seem complex, but we thought it important to provide an overview of the electrophysiological methods that may eventually lead to the description of the anatomic bases of the arrhythmias; currently, these are easier to understand thanks to the virtual anatomic casts built using computerized navigation systems.

Enfoque clínico de la taquicardia y el aleteo auricular desde su mecanismo: electrofisiología basada en la anatomía

In 2009, 2343 catheter ablation procedures were performed in Spain for focal atrial tachycardia or atrial flutter (typical and atypical), with a yearly growth rate of 8%, indicating the clinical importance of these arrhythmias. The classic categorization of atrial tachycardia and atrial flutter based on rate and morphological criteria has become almost irrelevant at a time when clinical electrophysiology may lead to curative intervention based on a definition of the mechanism, making it necessary to bring laboratory experience closer to clinical practice. In this review we outline our present understanding of atrial tachycardia mechanisms, both focal and macroreentrant, and attempt to establish the conceptual links with classic concepts that may help the clinician to make a differential diagnosis and establish therapeutic indications, including that of an electrophysiologic study. Some of the concepts may seem complex, but we thought it important to provide an overview of the electrophysiological methods that may eventually lead to the description of the anatomic bases of the arrhythmias; currently, these are easier to understand thanks to the virtual anatomic casts built using computerized navigation systems.Full English text available from:www.revespcardiol.org

The Electroanatomic Mechanisms of Atrial Tachycardia in Patients with Tetralogy of Fallot and Double Outlet Right Ventricle

Atrial tachycardias (AT) are common after palliation or repair of congenital heart disease. The electroanatomic mechanism of AT in postoperative tetralogy of Fallot (TOF) and double outlet right ventricle (DORV) patients has not been fully explored. Retrospective analysis of TOF or DORV patients was performed in the electrophysiology (EP) lab from January 1997 to March 2010. Sustained ATs were mapped using the Carto system (Biosense Webster, Diamond Bar, CA, USA). Fifty-eight patients were identified with 82 EP studies performed and 127 ATs identified. The first EP study for AT was performed at a median age of 35 years (2-58 years). Ninety-five IART circuits were identified, 5 in a figure-of-8 pattern. There were 13 focal ATs, 4 ectopic ATs, and 15 presentations of atrial fibrillation (AF). The cavotricuspid isthmus (CTI) was the critical area for ablation in the majority of TOF and DORV patients (53%). The CTI, along with the lateral RA wall, made up 85% of IART circuits. Excluding AF, the acute success rate for ablation was 90%. Of the 58 patients, 20 had additional ablation attempts, 19 within 3 years of their first ablation. The CTI and lateral RA wall are critical corridors of conduction in 85% of IART circuits in TOF and DORV patients. The acute success rate for AT ablations is high, but a substantial number of patients have required additional ablation procedures. Recurrences may be reduced if both the CTI and lateral RA wall are targeted and blocked, even if the mapped circuit points only to 1 region.

Mechanism of Atrial Tachycardia Induced by Atrial Pacing after Extensive Encircling Pulmonary Vein Isolation

Objective: Our objective was to evaluate the mechanism of atrial tachycardia (AT) induced by atrial pacing using EnSite NavX multi-electrode mapping system after extensive encircling pulmonary vein isolation (EEPVI) for the paroxysmal atrial fibrillation (AF). Methods: We evaluated 100 consecutive paroxysmal AF patients undergoing EEPVI (all were first procedures, age 60±11 years, 66 males, LA diameter 34±5 mm). Rapid atrial pacing up to 170 ms was performed to induce AF or AT after EEPVI. Activation mapping of induced AT was performed using EnSite NavX. Results: EEPVI was completed in all patients. After EEPVI, AF was induced in 13 patients and AT was induced in 31 patients (34 AT). Atrial activation sequences of 27 AT were evaluated. In the 27 AT, 22 (81%) were macro-reentrant AT and 5 (19%) were focal AT. In the 22 macro-reentrant AT, 11 were peri-mitral AT with a cycle length (CL) of 200±25 ms, 5 were roof-dependent AT (CL 202±56 ms, 3 around left PV and 2 around right PV) and 6 were atrial flutter around tricuspid annulus (CL 212±22 ms). Conclusions: Majority of AT induced by atrial pacing after the completion of EEPVI are macro-reentrant AT. Three reentrant circuits, i.e., around mitral valve, tricuspid valve and pulmonary vein, relate with maintenance of the macro-reentrant AT.