Scar-related Atrial Tachycardia Research Articles

Automated prediction of isthmus areas in scar-related atrial tachycardias using artificial intelligence.

Ablation of scar-related reentrant atrial tachycardia (SRRAT) involves identification and ablation of a critical isthmus. A graph convolutional network (GCN) is a machine learning structure that is well-suited to analyze the irregularly-structured data obtained in mapping procedures and may be used to identify potential isthmuses. Electroanatomic maps from 29 SRRATs were collected, and custom electrogram features assessing key tissue and wavefront properties were calculated for each point. Isthmuses were labeled off-line. Training data was used to determine the optimal GCN parameters and train the final model. Putative isthmus points were predicted in the training and test populations and grouped into proposed isthmus areas based on density and distance thresholds. The primary outcome was the distance between the centroids of the true and closest proposed isthmus areas. A total of 193 821 points were collected. Thirty isthmuses were detected in 29 tachycardias among 25 patients (median age 65.0, 5 women). The median (IQR) distance between true and the closest proposed isthmus area centroids was 8.2 (3.5, 14.4) mm in the training and 7.3 (2.8, 16.1) mm in the test group. The mean overlap in areas, measured by the Dice coefficient, was 11.5 ± 3.2% in the training group and 13.9 ± 4.6% in the test group. A GCN can be trained to identify isthmus areas in SRRATs and may help identify critical ablation targets.

Ripple AT Plus — isthmus-guided vs conventional ablation in the treatment of scar-related atrial tachycardia: study protocol for a randomised controlled trial

BackgroundCatheter ablation is routinely used to treat scar-related atrial tachycardia (s-AT). Conventional ablation often involves creating anatomical “lines” that transect myocardial tissue supporting reentry. This can be extensive, creating iatrogenic scar as a nidus for future reentry, and may account for arrhythmia recurrence. High-density mapping may identify “narrower isthmuses” requiring less ablation, with ripple mapping proven to be an effective approach in identifying. This trial explores whether ablation of narrower isthmuses in s-AT, defined using ripple mapping, results in greater freedom from arrhythmia recurrence compared to conventional ablation.MethodsThe Ripple-AT-Plus trial (registration ClinicalTrials.gov, NCT03915691) is a prospective, multicentre, single-blinded, randomised controlled trial with 12-month follow-up. Two hundred s-AT patients will be randomised in a 1:1 fashion to either “ripple mapping-guided isthmus ablation” vs conventional ablation on the CARTO3 ConfiDENSE system (Biosense Webster). The primary outcome will compare recurrence of any atrial arrhythmia. Multicentre data will be analysed over a secure web-based cloud-storage and analysis software (CARTONETTM).ConclusionThis is the first trial that considers long-term patient outcomes post s-AT ablation, and whether targeting narrower isthmuses in the era of high density is optimal.

High-density characterization of the sinus rhythm: a new functional substrate map of scar-related atrial tachycardia.

Reentrant atrial tachycardias (ATs) utilize critical isthmus (CI) for the maintenance of the circuit. The electrophysiological characteristics and clinical implications of the targeted CI regions of reentrant ATs during sinus rhythm (SR) were not clear. Therefore, our research aims at studying the electrical properties of the CI sites for scar-related reentrant ATs and the functional substrate mapping identified during SR. Patients mapped with high-density catheters during SR and reentrant ATs were retrospectively analyzed. The CI regions of the reentrant ATs were confirmed by the combination of the activation map and the entrainment. The substrate mapping was analyzed for wavefront propagation, conduction velocity, and electrogram patterns. Twenty patients with 22 reentrant ATs that underwent high-density maps were analyzed at 2 hospitals. Mapping performed during SR identified a scar region of 23.0 ± 13.6% of the left atrium. Regions of the CI in SR were characterized by low voltage (0.3 ± 0.2 mV), conduction slowing (0.4 ± 0.2 m/s), and fractionated electrogram (duration 62.5 ± 13.9 ms). Substrate mapping during SR showed that the regions of the CI located with the low-voltage zone in 16 out of 22 CI (72.7%), the deceleration zone in 15 out of 22 CI (68.2%), and late atrial activation in 12 out of 22 CI (54.5%). Targeting regions of CI achieve 94% of termination or change of the reentrant circuit. At 6.2 ± 7.1 months, there was 75% freedom from atrial arrhythmia. Novel high-density mapping can identify the functional substrates during SR and guide ablation. Low-voltage areas with conduction slowing are putative predictors of the CI for the maintenance of the reentrant ATs.

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.

Safety and feasibility of a novel multilectrode array catheter in mapping atrial and ventricular arrhythmias with high density: results from the multi-center OPTIMUM study

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): This study was funded by Biosense Webster, Inc. Background/Introduction The novel multielectrode array mapping catheter includes 48 electrodes symmetrically distributed across and along 6 splines (Picture), with an additional unipolar reference electrode to reduce far-field signals built in at the tip of the irrigation lumen. Preclinical studies demonstrated its ability to provide high density and high resolution mapping in complex substrates, but its usability and safety in patients with atrial or ventricular arrhythmias have not been investigated. Purpose To assess the safety and mapping performance of the catheter with the electroanatomical navigation system for mapping in the atria and ventricle in patients with a variety of complex arrhythmias. Methods The OPTIMUM study was a prospective, single arm study conducted at 3 European sites. Patients with scar-related atrial tachycardia (AT), PAF and persistent AF (PsAF), ventricular tachycardia (VT), or premature ventricular complexes (PVC) underwent pre-ablation mapping with the study catheter, and subsequent ablation according to institutional standard of care practice; the follow up period was 7 days. The primary safety endpoint was the incidence of device-related serious adverse events (SAE) within 7 days following the procedure. The primary effectiveness endpoint was the completion of protocol-required fast activation and electro anatomical pre-ablation mapping without resort to non-study mapping catheter(s), including fast anatomical mapping, mapping of substrate or any area of interest, and identification of conduction channel(s), gap(s) and critical isthmuses. General procedural characteristics as well as physician feedback (7-point Likert scale: 1 = poor and 7 = excellent) on various aspects of deployment, signal quality, and learning curve were also evaluated. Results Thirty-one patients (mean age: 59.8±14 years, 71.0% male) were enrolled and treated (9 scar-related AT, 12 PAF, and 1 PsAF, 6 VT, and 3 PVC). There was no (0/31) SAE reported, and the primary effectiveness endpoint was achieved in all subjects (31/31). Almost all operators rated highly (≥ 5) on noise reduction in bipolar maps (30/31) and short learning curve (27/31). Bipolar signals and catheter maneuverability were rated highly favorable (≥5) in the left and right atria and met-expectation-and-above (≥4) in the left and right ventricles. Conclusion(s) The first-in-human clinical data demonstrate the safety and effectiveness of the novel microelectrode array mapping catheter to efficiently map various atrial and ventricular complex arrhythmias with good signal quality. Physicians indicated high satisfaction with the learning curve, catheter maneuverability, tissue characterization in all cardiac chambers.

PO-665-07 TIMING OF CRITICAL ISTHMUS AND USEFULNESS OF ACTIVATION MAPPING WITH WINDOW OF INTEREST FROM END TO END OF P WAVE IN COMPLEX SCAR-RELATED ATRIAL TACHYCARDIAS

In activation mapping of scar-related atrial tachycardias, there was no reference of mapping window of interest. We assumed that critical isthmus has the slowest conduction velocity, and thus, may be located in flat area after prominent P wave.

An early multicenter experience of the novel high-density star-shaped mapping catheter in complex arrhythmias.

We aimed to assess the feasibility, safety, and operator feedback of a novel star-shaped high-density mapping catheter containing 48 platinum-iridium mapping electrodes distributed across eight spines. This prospective, single-arm, first-in-human study was conducted at five European sites. Primary endpoints were completion of pre-ablation mapping requirements, obtaining clinically indicated mapping with the new catheter without resorting to non-study mapping catheters, and incidence of serious adverse events (SAEs). Physician feedback survey assessed catheter performance, including deployment, ease of use, and mapping results. The subjects were followed for 7days post-procedure. Of 31 patients enrolled (11 ventricular tachycardia [VT], 10 scar-related atrial tachycardia [AT]/atypical atrial flutter [AFL], and 10 persistent atrial fibrillation [PsAF]), 28 had study catheter inserted for mapping purposes. Pre-ablation mapping was achieved in 23/28 patients (82.1%). Median of total pre-ablation mapping times were 121.0, 72.5, and 31.5min for the VT, scar-related AT/atypical AFL, and PsAF subgroups, respectively. More than two-thirds of mapping points acquired were used to generate CARTO maps relevant for ablation. All 16 patients who had conduction channel(s), gaps(s), or critical isthmus identified had the areas successfully mapped. The ability to deploy, maneuver, and reach the atria and ventricles using the catheter was rated positively for most procedures. Only one SAE (heart failure) was reported, unrelated to the device. The study results demonstrate the feasibility of the OCTARAY catheter to successfully map complex arrhythmias with good safety profile. Operator feedback indicates satisfaction with ease of use and maneuverability of the catheter.

Abstract 12187: Arrhythmia Substrate and Approaches for First-Time and Repeat Catheter Ablation in Patients With D-transposition of the Great Arteries and Atrial Baffles

Introduction: Atrial arrhythmias are common in patients with D-TGA and atrial switch. We sought to analyze the arrhythmia substrate and catheter ablation approaches and outcomes. Methods: We performed a retrospective review of all clinical and procedural data in patients with D-TGA followed at a large tertiary care center. Results: In a cohort of 152 patients (mean age 30±11 years), atrial tachycardia was present in 69(45%) patients. Ablations were performed in 39(26%) patients: macro-reentrant atrial flutter (N=37), atrial fibrillation (N=4), and focal automatic atrial tachycardia (N=3). Detailed electrophysiology study data was available for 34 patients. At first ablation (N=28), cavo-tricuspid isthmus dependent flutter (CTI, 23(82%)) was most common, followed by right atriotomy-related flutter (IART, 16(57%)) and focal atrial tachycardia (FAT, 1(3.5%)). Bidirectional CTI block often required ablation on both sides of the baffle to complete the isthmus line. Access to the pulmonary venous atrium was obtained in 82% of first-time ablations (via retrograde aortic access, 74%, baffle puncture, 6%, or baffle fenestration, 12%) and in 100% of redo procedures. The first ablation was acutely successful in 25 (89%) patients; the other 3 patients had either partial procedural success (1), failed ablation (1), or underwent an empirical ablation (1). Long-term arrhythmia recurrence occurred in 13(46%) after the first ablation and class III antiarrhythmic medications were utilized in 12 patients. At least one long-term recurrence occurred in 11(44%) patients. Importantly, clinical arrhythmia burden was significantly reduced post-ablation, with rare and short-limited episodes amenable to antiarrhythmic drugs or cardioversion. Repeat ablation was required in 3 cases. Long-term arrhythmia recurrence after a previously completed CTI line involved different arrhythmia mechanisms: scar-related reentry (80%) and automatic atrial tachycardia (40%). Conclusions: Atrial arrhythmia in patients with D-TGA often involves the CTI and atriotomy scars. Ablation of the CTI typically requires access to the pulmonary venous atrium to achieve bidirectional block. Despite late recurrence, the clinical arrhythmic burden is substantially improved.

The utility of a novel mapping algorithm utilizing vectors and global pattern of propagation for scar-related atrial tachycardias.

Activation maps of scar-related atrial tachycardias (AT) can be challenging to interpret due to difficulty in inaccurate annotation of electrograms, and an arbitrarily predefined mapping window. A novel mapping software integrating vector data and applying an algorithmic solution taking into consideration global activation pattern has been recently described (Coherent™, Biosense Webster "Investigational"). We aimed to assess the investigational algorithm to determine the mechanism of AT compared with the standard algorithm. This study included patients who underwent ablation of scar-related AT using the Carto 3 and the standard activation algorithm. The mapping data were analyzed retrospectively using the investigational algorithm, and the mechanisms were evaluated by two independent electrophysiologists. A total of 77 scar-related AT activation maps were analyzed (89.6% left atrium, median tachycardia cycle length of 273 ms). Of those, 67 cases with a confirmed mechanism of arrhythmia were used to compare the activation software. The actual mechanism of the arrhythmia was more likely to be identified with the investigational algorithm (67.2% vs. 44.8%, p = .009). In five patients with dual-loop circuits, 3/5 (60%) were correctly identified by the investigational algorithm compared to 0/5 (0%) with the standard software. The reduced atrial voltage was prone to lead to less capable identification of mechanism (p for trend: .05). The investigational algorithm showed higher inter-reviewer agreement (Cohen's kappa .62 vs. .47). In patients with scar-related ATs, activation mapping algorithms integrating vector data and "best-fit" propagation solution may help in identifying the mechanism and the successful site of termination.

Mapping of an atrial tachycardia after Epicor™ high-intensity focused ultrasound ablation: A case report

BackgroundSurgical techniques, such as the application of high-intensity focused ultrasound (HIFU), can be used for pulmonary vein isolation (PVI). Case summaryWe report a case of a 73-year old patient, in whom HIFU failed to achieve PVI but promoted the occurrence of a scar-related atrial tachycardia (AT). Voltage mapping of the left atrium revealed multiple gaps along the ablation line. Coherent mapping with visualization of velocity vectors allowed the correct interpretation and the targeted ablation of the AT. DiscussionCardiac surgery can promote scar-related AT. The coherent mapping function could simplify the mapping of scar-related AT in the future.

The isthmus characteristics of scar-related macroreentrant atrial tachycardia in patients with and without cardiac surgery.

Identifying the critical isthmus (CI) in scar-related macroreentrant atrial tachycardia (AT) is challenging, especially for patients with cardiac surgery. We aimed to investigate the electrophysiological characteristics of scar-related macroreentrant ATs in patients with and without cardiac surgery. A prospective study of 31 patients (mean age 59.4 ± 9.81 years old) with scar-related macroreentrant ATs were enrolled for investigation of substrate properties. Patients were categorized into the nonsurgery (n = 18) and surgery group (n = 13). The CIs were defined by concealed entrainment, conduction velocity less than 0.3 m/s, and the presence of local fractionated electrograms. Among the 31 patients, a total of 65 reentrant circuits and 76 CIs were identified on the coherent map. The scar in the surgical group is larger than the nonsurgical group (18.81 ± 9.22 vs. 10.23 ± 5.34%, p = .016). The CIs in surgical group have longer CI length (15.27 ± 4.89 vs. 11.20 ± 2.96 mm, p = .004), slower conduction velocity (0.46 ± 0.19 vs. 0.69 ± 0.14 m/s, p < .001), and longer total activation time (45.34 ± 9.04 vs. 38.24 ± 8.41%, p = .016) than those in the nonsurgical group. After ablation, 93.54% of patients remained in sinus rhythm during a follow-up of 182 ± 19 days. The characteristics of the isthmus in macroreentrant AT are diverse, especially for surgical scar-related AT. The identification of CIs can facilitate the successful ablation of scar-related ATs.

Ripple mapping-guided atrial tachycardia ablation following open-heart surgery.

Ripple mapping can make the visualization of activation conduction on a 3-dimensional voltage map and is useful tool for scar-related organized atrial tachycardia (AT). This study sought to assess the efficacy of ripple mapping for interpreting reentrant circuits and critical isthmus in postoperative ATs. 34 consecutive patients with a history of mitral valve surgery (mean age, 54.5 ± 12.4years) underwent high density (HD) RM during ATs with CARTO3v4 CONFIDENSE system. The voltage activation threshold was determined by RM over a bipolar voltage map. The identification of underlying mechanisms and ablation setting was based on RM without reviewing activation mapping. A total of 41 ATs (35 spontaneous, 6 induced) were characterized. 39 reentry circuits were successfully mapped (cycle length, 256 ± 43ms). Of the 41 ATs, 28 were confirmed by ripple mapping alone (68%), and 12 (29%) by ripple mapping and entrainment mapping. Of 12 ATs in the left atrium, 9 (75%) needed entrainment to confirm, compared with 5 (17.8%) in the right atrium. Primary endpoint after initial ablation set was achieved in 32 of the 34 patients (94.1%). Freedom from atrial arrhythmias was 79.4% after the follow-up of 12 ± 5months. Of the seven patients with recurrence, three underwent the repeated catheter ablation. Ripple mapping precisely delineated reentrant circuits in post-cardiac surgery AT resulting in a high success rate of ablation. Entrainment maneuvers remain useful for elucidation of complex AT circuits.

Comparison between new confidense HD coloring cartomapping module and new rhythmia mapping system for scar related atrial tachycardia treatment. A prospective randomised study: Preliminary results

Scar-related atrial tachycardias (ATs) are very challenging. Thus far, no comparative studies have been conducted between the up-to-date systems, namely the new confidense HD colouring mapping module (Carto 3 v. 4, Biosense Webster) (HD) and the new rhythmia (Boston Scientific) (RM) mapping system. Our study sought to compare both strategies in terms of: – diagnosis and immediate treatment success; – procedure parameters in AT presenting patients. Overall, 38 patients (68 ± 9 years old) with complete mapping and ablation were randomised (HD = 20, RM = 18). The HD and RM groups displayed similar characteristics and etiologies. The AT mechanisms did not differ between the groups: macro/small loop re-entrant mechanisms were more common in both groups (12/20 [60%] versus 10/18 [56%], P = 0.9), with the remaining diagnosed as multi-loop (5/20 [25%] versus 4/18 [22%]; P = 0.9); focal (1/20 [5%] versus 2/18 [11%], P = 0.9), and localised re-entrant (2/20 [10%] versus 2/18 [11%]). The procedure parameters were as follows: tachycardia cycle length (275 ± 30 vs. 280 ± 50; P = 0.7); number of activation maps per patient (2 ± 1 vs. 2 ± 1; P = 0.9); procedure time (138 ± 90 vs. 139 ± 90 min; P = 0.98); X-ray time exposure (20 ± 11 vs. 24 ± 18 min; P = 0.42); RF application time (39 ± 36 vs. 25 ± 28 min; P = 0.21); and mean number of circuits per patient (1.8 ± 1 vs. 1.6 ± 0.9; 0.6). Acute success was obtained in 15/20 pts (75%) of the HD group and 14/18 (78%) of the RM group (P = 0.9). Two patients who failed to achieve the primary endpoint with the HD colouring were secondly converted to the RM group without success. No crossover was carried out in the RM group. The preliminary results of this prospective monocentre randomised study demonstrate that HD colouring and rhythmia systems exhibit a similar efficacy in achieving acute AT termination.

The Utility of a Novel Mapping Algorithm Utilizing Vectors and Global Pattern for Atrial Tachycardias

Background: Activation maps of scar-related atrial tachycardias (AT) can be challenging to interpret due to difficulty in inaccurate annotation of electrograms, and an arbitrarily predefined mapping window. A novel mapping software integrating vector data and applying an algorithmic solution taking into consideration global activation pattern has been recently described (CoherentTM, Biosense Webster Investigational). Objective: We aimed to assess the investigational algorithm to determine the mechanism of AT compared with the standard algorithm. Methods: This study included patients who underwent ablation of scar-related AT using the Carto 3 and the standard activation algorithm. The mapping data was analyzed retrospectively using the investigational algorithm, and the mechanisms were evaluated by two independent electrophysiologists. Results: A total of 77 scar-related AT activation maps were analyzed (89.6% left atrium, median tachycardia cycle length of 273 milliseconds). Of those, 67 cases with confirmed mechanism of the arrhythmia were used to compare the activation software. The actual mechanism of the arrhythmia was more likely to be identified with the investigational algorithm (67.2% vs 44.8%, P=0.009). In 5 patients with dual-loop circuits, 3/5 (60%) were correctly identified by the investigational algorithm compared to 0/5 (0%) with the standard software. The reduced atrial voltage was prone to lead to less capable identification of mechanism (P for trend: 0.05). The investigational algorithm showed higher inter-reviewer agreement (Cohen's kappa 0.62 vs 0.47). Conclusions: In patients with scar-related ATs, activation mapping algorithms integrating vector data and best-fit propagation solution may help in identifying the mechanism and the successful site of termination.

Outcome after practical isthmus ablation of scar-related atrial tachycardia guided by high-density mapping

Abstract Background High-density mapping (HDM) has been found to precisely identify the practical isthmus of scar-related atrial tachycardia (AT) circuits. Since practical isthmuses have been found to be shorter than the usual anatomical isthmuses targeted ablation has been proposed. However, outcome data are sparse. Here we describe HDM-guided catheter ablation by targeting the practical isthmus in patients with scar-related ATs. Methods and results In 250 consecutive patients with scar-related ATs HDM-guided catheter ablation with the support of a 64-electrode mini-basket catheter has been performed. Most patients underwent a prior catheter ablation (98%) while 13% had a prior cardiac valve surgery and 6% an underlying congenital heart disease. A total of 355 ATs occurred in the index procedure, of which 64% had a macro-, 26% a micro-reentry and 10% a focal mechanism. The ATs had a mean cycle length of 304±4.3 ms and in 237 patients (95%) an acute termination into sinus rhythm was achieved. They were mainly located in the left atrium (72%) but also in the right atrium (25%), bi-atrially (5%) or in the CS (3%) (see figure). Targeting the practical isthmus revealed arrhythmia freedom in 53% of patients after a single procedure during a mid-term follow-up (median 489 days, range 95–1407 days). Freedom from any arrhythmia could be achieved in 74% of patients after multiple procedures and in 93% of patients after multiple procedures and optimal clinical therapy, including pharmaceutical or electrical cardioversion. Conclusions HDM-guided catheter ablation of the practical isthmus in patients with scar-related ATs leads to a high acute success rate. Nevertheless, multiple procedures are necessary in a relevant number of patients resulting in a low recurrence rate. Funding Acknowledgement Type of funding source: None

Scar identification, quantification, and characterization in complex atrial tachycardia: a path to targeted ablation?

Successful catheter ablation of scar-related atrial tachycardia depends on correct identification of the critical isthmus. Often, this is a represented by a small bundle of viable conducting tissue within a low-voltage area. It's identification depends on the magnitude of the signal/noise ratio. Ultra-high density mapping, multipolar catheters with small (eventually unidirectional) and closely-spaced electrodes improves low-voltage electrogram detection. Background noise limitation is also of major importance for improving the signal/noise ratio. Electrophysiological properties of the critical isthmus and the characteristics of the local bipolar electrograms have been recently demonstrated as hallmarks of successful ablation sites in the setting of scar-related atrial tachycardia.

Activation Mapping With Integration of Vector and Velocity Information Improves the Ability to Identify the Mechanism and Location of Complex Scar-Related Atrial Tachycardias

Activation mapping of scar-related atrial tachycardias (ATs) can be difficult to interpret because of inaccurate time annotation of complex electrograms and passive diastolic activity. We examined whether integration of a vector map can help to describe patterns of propagation to better explain the mechanism and location of ATs. The investigational mapping algorithm calculates vectors and applies physiological constraints of electrical excitation in human atrial tissue to determine the arrhythmia source and circuit. Phase I consisted of retrospective evaluation in 35 patients with ATs. Phase II consisted of prospective validation in 20 patients with ATs. Macroreentry was defined as a continuous propagation in a circular path >30 mm; localized reentry was defined as a circular path ≤30 mm; a focal source had a centrifugal spread from a point source. In phase I, standard activation mapping identified 28 of 40 ATs (70%): 25 macroreentry and 3 focal tachycardias. In the remaining 12 ATs, the mechanism and location could not be identified by activation and required entrainment or empirical ablation for termination (radiofrequency time, 17.3±6.6 minutes). In comparison, the investigational algorithm identified 37 of 40 (92.5%) ATs, including 5 macroreentry, 3 localized reentry, and 1 focal AT not identified by standard mapping. It also predicted the successful termination site of all 37 of 40 ATs. In phase II, the investigational algorithm identified 12 macroreentry, 6 localized reentry, and 2 focal tachycardias that all terminated with limited ablation (3.2±1.7 minutes). It identified 3 macroreentry, 3 localized reentry, and 1 focal AT not well characterized by standard mapping. The diagnosis of localized reentry was supported by highly curved vectors, resetting with increasing curve and termination with limited ablation (22±6 s). Activation mapping integrating vectors can help determine the arrhythmia mechanism and identify its critical components. It has particular value for identifying complex macroreentrant circuits and for differentiating a focal source from a localized reentry.

Idiopathic isolated fibrotic atrial cardiomyopathy underlies unexplained scar-related atrial tachycardia in younger patients.

Unexplained scar-related atrial tachycardia (AT) has been frequently encountered in clinical practice. We hypothesized that idiopathic, isolated fibrotic atrial cardiomyopathy (ACM) underlies this rhythm disorder. This study was aimed to characterize the underlying substrate and to explore the aetiology of this unexplained scar-related AT. Twenty-six (11 men, aged 46 ± 13 years) of 52 non-surgical scar-related AT patients identified by three-dimensional voltage mapping were enrolled in this prospective observational study. Multimodality image examinations (echocardiography, cardiac magnetic resonance, 99Tc single-photon emission computed tomography), ventricular voltage mapping, and intracardiac pressure curve recording ruled out ventricular involvement. Catheter ablation was acutely successful for all the patients, and pacemaker implantation was performed in seven patients who presented sinus node dysfunction or atrial standstill after termination of the AT. In three patients with multiple AT recurrences, the diseased areas of the right atrium were resected and dechannelled via mini-invasive surgical interventions. Histological examinations revealed profound fibrosis without amyloidosis or adipose deposition. Viral and familial investigations yielded negative results. Fibrosis progression over a median of 45 (5-109) months of follow-up manifested as atrial arrhythmia recurrence in seven patients and atrial lead non-capture due to newly developed atrial standstill in two patients. Two patients suffered four ischaemic stroke events before receiving anticoagulation treatment. Isolated, fibrotic ACM may underlie the idiopathic scar-related ATs. This novel cardiomyopathy has unique clinical characteristics with high morbidity including stroke and warrants specific therapeutic strategies. Further investigations are required to determine the aetiology and mechanism.

P384Characterization of slow conductions areas in scar-related atrial tachycardia. Insights from high density mapping system

P384Characterization of slow conductions areas in scar-related atrial tachycardia. Insights from high density mapping system

P1464Acute and medium-term outcomes following ablation of complex scar-related atrial tachycardia using a high-resolution mapping system

P1464Acute and medium-term outcomes following ablation of complex scar-related atrial tachycardia using a high-resolution mapping system