Characteristics of Single-Loop Macroreentrant Biatrial Tachycardia Diagnosed by Ultrahigh-Resolution Mapping System
Background: Biatrial tachycardia (BiAT) is a rare form of atrial macroreentrant tachycardia, in which both atria form a critical part of the circuit. We aimed to identify the characteristics and precise circuits of single-loop macroreentrant BiATs.
Methods and Results: We identified 8 patients (median age, 59.5 years old) with 9 BiATs in a cohort of 336 consecutive patients from 2 institutions who had undergone AT catheter ablation using an automatic ultrahigh-resolution mapping system. Seven of the 8 patients had a history of persistent AF ablation, including septal or anterior left atrium ablation before developing BiAT. One of the 8 patients had a history of an atrial septal patch closure with a massively enlarged right atrium. Nine ATs (median cycle length, 334 ms; median 12 561 points in the left atrium; 8814 points in the right atrium) were diagnosed as single-loop macroreentrant BiATs. We observed 3 types of BiAT (1) BiAT with a perimitral and peritricuspid reentrant circuit (n=3), (2) BiAT using the right atrium septum and a perimitral circuit (n=3), and (3) BiAT using only the left atrium and right atrium septum (n=3). Catheter ablation successfully terminated 8 of the 9 BiATs.
Conclusions: All patients who developed BiAT had an electric obstacle on the anteroseptal left atrium, primarily from prior ablation lesions. In this situation, mapping of both atria should be considered during AT. Because 3 types of single-loop BiAT were observed, ablation strategies should be adjusted to the type of BiAT circuit.
WHAT IS KNOWN?
Biatrial tachycardia (BiAT) is a rare form of atrial macroreentrant tachycardia.
BiAT is often observed in patients with a history of open heart surgery, corrected congenital heart disease, or atrial fibrillation ablation.
WHAT THE STUDY ADDS?
All the patients with BiAT had an electric obstacle located in the septum, which was considered to be the critical component supporting BiAT.
There were 3 types of BiATs classified by the characteristics of the circuit with the detailed evaluation.
Biatrial tachycardia (BiAT) is a rare form of atrial tachyarrhythmia using 2 interatrial bridges and 2 atria, which is most often observed in patients with a history of open heart surgery,1,2 corrected congenital heart disease,3 or atrial fibrillation (AF) ablation.4 Several case reports1–4 with activation maps of BiAT from 3-dimensional (3D) mapping systems have been described, but only 1 detailed mapped case series was reported with a 3D mapping system.4 Thus, the full particulars of BiAT may not have been previously identified.
In the present study, we assessed the characteristics and precise circuit of BiAT by using an ultrahigh-density mapping system.
The data, analytic methods, and study materials will be/have been made available to other researchers for purposes of reproducing the results or replicating the procedure.
In a consecutive series of patients who underwent AT ablation using an automatic high-density mapping system in 2 institutions (Bordeaux and Toulouse) from November 2014 to March 2017, all patients with BiAT were analyzed. In each case, we evaluated the precise circuits in both the left atrium (LA) and right atrium (RA) during BiAT on the high-density activation map. Written informed consent was obtained from all patients. Our institution’s research ethics board approved this study.
Catheter ablation for AT was performed under mild sedation using midazolam and morphine; oral anticoagulation was continued in the patients receiving vitamin K antagonists; in patients with novel oral anticoagulants, they were withheld for at least 1 day before ablation. Antiarrhythmic drugs were discontinued >5 half-lives before ablation with the exception of amiodarone. In all patients, transesophageal echocardiography or an enhanced computed tomographic scan was performed before the procedure to exclude intracardiac thrombus. During the procedure, intracardiac electrograms were continuously recorded and stored at a sweep speed of 100 mm/s on a computer-based digital system (Labsystem Pro, BARD, Boston Scientific, MA). After placement of a deflectable decapolar catheter within the coronary sinus (CS) (Extreme, Sorin/Dynamic XT, Boston Scientific, MA), a transseptal puncture was performed under fluoroscopic guidance; 1 transseptal sheath (Agilis NxT steerable sheath, St Jude Medical) was introduced into the LA. Systemic anticoagulation with a heparin bolus (target activated clotting time >300 s) was performed. Before inserting the mapping multipolar catheter, heparin (100/IU/kg) was administered to achieve an activated clotting time of >300 s. Subsequent boluses of heparin were administered every 20 to 30 minutes if needed. Electroanatomical navigation was performed using the Rhythmia mapping system. During the catheter ablation procedure, a 3.5-mm tip open-irrigated catheter (ThermoCool SF, Biosense Webster, Diamond Bar, CA) was used. Maximum RF energy delivery was set at 30 to 40 W with a temperature limit of 45°C; irrigation was set at 10 to 15 mL/min.
Ultrahigh-Resolution Electroanatomical Mapping
The Rhythmia mapping system (Boston Scientific, MA) uses a 64-pole mini-basket mapping catheter (Orion; Boston Scientific, MA), which incorporates small unidirectional electrodes (0.4 mm2; 2.5 mm spacing) to suppress far-field signals. Detailed electroanatomical mapping of the LA and RA was performed using bidirectional flexion with the basket in variable degrees of deployment (diameter ranging from 3 to 22 mm). The reference electrogram was selected on the decapolar catheter and placed in the CS. An activation map was created under the standard beat acceptance criteria (automatic): (1) cycle length (CL) variation <10 ms, (2) <5 ms activation time difference variations between the CS electrograms, (3) catheter motion <1.0 mm per beat, and (4) catheter tracking uncertainty <3 mm. For fragmented or multiple potential electrocardiogram, the system takes into account the timing in the surrounding area to select the potential to use for timing annotation. In the case of a lack of statistical coherence between neighboring points in an area, no color code is displayed (the area is left gray). Selection of the surface electrocardiogram is based on the projection distance (standard setting was 2 mm): only electrocardiograms recorded within the projection distance from the surface geometry are displayed. After map completion, dense scar thresholding was performed wherever necessary to visualize the entire circuit. The confidence mask parameter was finely tuned for each map and lowered as much as needed for each AT. The confidence mask was nominally established as 0.03 mV.
Diagnosis for BiAT
Activation maps in both LA and RA were studied for each BiAT. A single-loop macroreentrant BiAT was diagnosed if the propagation revealed a reentrant circuit using the LA and RA by a single-loop and RF application on the circuit terminated the BiAT, or preferably, entrainment at points throughout the circuit was followed by a postpacing interval <20 ms greater than the tachycardia CL.
We then classified BiATs into 3 groups according to the circuit, type 1: BiAT using most of the mitral annulus in the LA circuit (including the CS but not the LA septum) and most of the tricuspid annulus in the RA circuit, apart from the RA septum, with 2 interatrial connections (Figure 1; upper); type 2: BiAT using most of the mitral annulus in the LA circuit (including CS) and the RA septum with 2 interatrial connections (Figure 1; upper middle); type 3: BiAT using the LA septum and RA septum with 2 interatrial connections (Figure 1; lower middle). We analyzed the characteristics of all BiATs and the 3 types of BiATs.
Ablation Target and Outcome
Based on the activation map, the narrowest isthmus of the BiAT circuit was chosen as the primary target, and a linear lesion was created across the isthmus connecting scars and anatomic obstacles. Termination of BiAT to sinus rhythm or to another AT during RF application was defined as an AT termination. Noninducibility of the tachycardia after ablation was also defined as an acute success. AT induction was performed by incremental burst pacing to a minimum pacing CL of 200 ms or the local effective refractory period of atrial tissue.
Patients were followed for clinical and asymptomatic recurrences. All patients had regular visits to the referring cardiologist 1, 3, 6, and 12 months after the ablation procedure with a 12-lead ECG and 24-hour Holter monitoring.
Continuous variables are summarized by median±interquartile range (25th–75th percentile). Comparison of continuous variables among 3 groups was performed using the Kruskal–Wallis test. Subsequently, Dunn test was used for post hoc analysis between each group after Kruskal–Wallis test. All reported P values are 2-sided, with a P value of <0.05 considered to indicate statistical significance. Statistical analyses were performed using the Statistical Package for Social Studies, version 24.0 (IBM, Armonk, NY).
In a series of 336 consecutive patients (median age, 59.5 [50.8–69.3] years old) who underwent AT ablation with the Rhythmia system from November 2014 to March 2017 in 2 institutions (Bordeaux and Toulouse), a total of 422 ATs were mapped. Of those, 9 BiATs (9/422, 2.1%) in 8 patients were identified. Of the 265 patients with AT who initially underwent ablation for persistent AF, 7 patients (patients No. 1–7) developed BiAT (2.6%, 7/265). The other patient (patient No. 8) had a history of atrial septal patch closure for an atrial septal defect with an enlarged RA because of Eisenmenger syndrome. Patient characteristics are shown in Table 1. The median number of prior procedures was 2.0 (2–3). Only 1 patient (patient No. 2) had left ventricular systolic dysfunction with a left ventricular ejection fraction of 30%.
Index Ablation Lesions
Only 1 patient had an index procedure limited to pulmonary vein isolation, whereas 6 of the 7 patients with persistent AF had an extensive index procedure with substrate ablation beyond pulmonary vein isolation (Table 2). The remaining patient (patient No. 8) with atrial septal defect patch closure had a history of previous cavotricuspid isthmus linear ablation.
The characteristics of BiATs are shown in Figure 1 and Tables 2 and 3. All of the ECGs of the BiATs are shown in Figure 2. A total of 9 BiATs with high-density maps were observed (Table 3). The median CL was 334 ms (296–406, range, 250–450 ms). All ATs used the right and left atria as a part of the single-loop reentrant circuit. The median activation duration in the LA circuit was 210 (182–226) ms, which was 57.8 (54.5–67.1)% of the tachycardia CL. The median activation duration in the RA circuit was 122 (119–180) ms, which was 42.2 (32.9–45.5)% of the tachycardia CL.
There were 3 BiATs (Table 4) classified as type 1 (BiAT 1–3; Figure 3), 3 BiATs classified as type 2 (BiAT 4–6; Figure 4), and 3 BiATs classified as type 3 (BiAT 7–9; Figure 5). The maps of the remaining BiATs are presented as supplemental files (Figure I through VI in the Data Supplement).
The earliest activation site in the RA was the high-mid septum among the 7 BiATs with counter clockwise rotation (BiAT 1–7, 7/7: 100%), whereas in LA, it was the inferior aspect close to the CS ostium in 6 BiATs (BiAT 1–6, 6/7: 85.7%) and the higher anterior area in BiAT 7 (1/7, 14.3%). However, among the BiATs with clockwise rotation (BiAT 8 and 9), the earliest site was close to the anterior-mid septum in the RA, and the high septum was close to the roof in the LA.
In 7 of 8 cases (patients No. 1, No. 2, No. 4–8), 8 BiATs (88.9%) were successfully terminated by RF application. Six of 8 BiATs were terminated targeting the isthmus identified by the activation map (cavotricuspid isthmus in BiAT 1 and 2; the isthmus between an anteroseptal LA scar and the mitral valve in BiAT 5, 7 and 8; an isthmus between the atrial septal defect patch scar and the superior vena cava in RA BiAT 9). The remaining BiAT were terminated by targeting interatrial connection at the high RA septum (BiAT 4 and 6). After ablation, noninducibility was verified in 7 of 8 cases (87.5%). In patient No. 7, induction was not performed at the end of the procedure.
During a median follow-up period of 12.4 (9.3–20) months, there was 1 recurrence in patient No. 5 (12.5%, 1/8).
The main findings of our study are as follows:
We observed that all the patients with BiAT had an electric obstacle located in the septum, which was considered to be the critical component supporting BiAT.
We have, by using high-density mapping, identified 3 types of BiATs classified by the characteristics of the circuit.
Prevalence of Patients With BiAT
Single-loop macroreentrant BiAT is a rare form of macroreentrant AT, first described in 1998.1–6 In 2015, Mikhaylov et al4 identified 4 patients with BiAT in a cohort of 807 patients who underwent AF ablation guided by a 3D mapping system (4/807, 0.5%). In the present study, we observed 8 patients (2.3%; 8/341 patients) with 9 BiATs (2.1%; 9/422 tachycardias), which was 2.7% (7/263) among patients with prior AF ablation.
Mechanism and Circuits of Single-Loop Macroreentrant BiAT
As has been described in previous reports, BiAT is dependent on an obstacle to conduction in the LA septum.2–4 Prior AF ablation is the commonest cause of such an obstacle in the present study. Mapping of activation in both atria is indicated, therefore, in AT where there is a history of extensive AF ablation or the presence of an anatomic obstacle to conduction. In most present cases, BiAT was considered in the differential diagnosis when there was a history of significant septal anterior ablation and an activation map could not identify a complete AT circuit in a single chamber. Entrainment pacing at the beginning of procedure may be helpful to clarify the involvement of both atria, at the risk of terminating the AT.
The use of high-density mapping in the present study has allowed us to define the course of the activation wavefront and thereby classify BiAT into 3 groups. Activation in each chamber proceeds either around the atrioventricular (AV) valve or via the septum; we identified 3 types. Type 1: BiAT with a reentrant circuit around the mitral and tricuspid annuli, using 2 interatrial connections without the septa being involved in the critical circuit. Propagation on both septa showed either collision or block. Type 2: BiAT with a reentrant circuit around the mitral annulus and the RA septum with wavefront collision or block in the LA septum. This is, to the best of our knowledge, the first description of each septum propagating separately, with conduction on one side and conduction block on the other. Type 3: BiAT with a reentrant circuit ran around the LA septum and RA septum, with passive activation around both AV valves. We did not observe activation around the tricuspid annulus and LA septum, without RA septal involvement, but such a circuit may, theoretically, be possible as type 4. Classification of BiAT in this manner highlights the importance of prior linear lesions in the maintenance of these tachycardias. All except type 3 are dependent on conduction in the mitral or tricuspid isthmuses and, therefore, on gaps in lines of block, should these have been ablated previously.
Finally, in terms of surface ECG analysis, the ECGs of BiAT 2, 3, and 8, identified atrial activities of low amplitude, which probably reflected a certain amount of damaged tissue in both atria. In addition, it is known that interpretation of the surface ECG post–LA ablation has major limitations that hinder its use.7 At this time, we think it is challenging to diagnose BiAT based on the surface ECG characteristics.
Electric Interatrial Connection
BiAT are dependent on there being 2 separate interatrial electric connections,1–4 as seen in all patients in the present study, despite extensive prior ablation. In keeping with previously described details of interatrial connection,8–16 interatrial connection via Bachmann’s bundle was intact in all cases in our series. The other limb of the circuit was the CS (7/9, 77.8%) or anterior septum (2/9, 22.2%). Interatrial connections are anatomically robust, with complex insertions over a wide area and epicardial connections,12–17 which may explain the persistence of such connections despite widespread ablation and the difficulty in achieving interatrial conduction block.17 This may make the interatrial connections an unattractive target for ablation of BiAT, and ablation at a critical isthmus distant to the interatrial connection may have greater success.
Where Is the First Ablation Target?
Complete understanding of the AT circuit allowed identification of the appropriate target in most patients. In circuits dependent on an AV valve annulus, that is, types 1 and 2, the preferred target is a classic anatomic isthmus (cavotricuspid isthmus or mitral isthmus line). In type 3, septal lesions can be more challenging because of the risk of AV block possibly resulting from direct AV node ablation. Thus, a minimal line or point ablation may be safer. For all types, when delivering RF energy for septal or interatrial connections, it should be realized that this may lead to more extensive intra-atrial conduction delay or AV block (possibly because of the direct effect on the compact AV node). In addition, in type 1 or type 2 BiAT, conduction delay to left atrial appendage may occur, but the electric connection via Bachmann bundle will still be preserved.
In this case series, entrainment in both atria was not performed in all BiATs. However, mapping of each of the atria separately did not identify a reentrant circuit, and parts of the CL were missing in each chamber. In addition, other possible types of biatrial circuits may be possible—for example, BiAT using the tricuspid annulus and the LA septum (the missing type 4) or any subtypes of type 1 or type 2, such as those using the vein of Marshall or the carina of the left pulmonary veins. We used the Rhythmia system in the present study to provide case series with uniform mapping; however, we think it would be entirely possible to diagnose 3 types of BiAT if a sufficient number of mapping points were correctly annotated using any mapping system. Furthermore, even using a high-density mapping system with a mini-basket multipolar catheter, we may have annotated far-field signals from the opposite septum when mapping either septum. In addition, the follow-up period was relatively short to determine the long-term efficacy of our ablation strategy for BiAT. Finally, the number of patients is still limited.
All patients who developed BiAT had an electric obstacle on the septum, most commonly with prior anteroseptal LA ablation. In patients with this type of previous ablation, mapping of both atria should be considered during mapping of macroreentrant AT. Because 3 types of single-loop BiATs were observed, ablation strategies should be adjusted to the type of BiAT circuit.
Takeshi Kitamura, MD et al
Takeshi Kitamura, MD; Ruairidh Martin,
Claire A. Martin,
Nora Al Jefairi,
We wish to thank Stefano Capellino, BE, and Jean-Rodolphe Roux, BE, for their contribution. In addition, we would like to thank Dr Takigawa for the part of information from the database. We would like to thank Xavier Pillois for the statistical analysis.
Sources of Funding
Dr Kitamura is supported by a Japan Heart Rhythm Society–European Heart Rhythm Association fellowship program 2016–2017. Dr Martin is supported by a Travel Fellowship (FS/16/71/32487) from the British Heart Foundation.
Drs Denis, Derval, Jaïs, and Sacher received speaking honoraria and consulting fees from Boston Scientific. Dr Takigawa is a temporary consultant of the Rhythmia system for Boston Scientific Japan. The other authors report no conflicts.
The full author list is available on page 10.
The Data Supplement is available at http://circep.ahajournals.org/lookup/suppl/doi:10.1161/CIRCEP.117.005558/-/DC1.
Circ Arrhythm Electrophysiol is available at http://circep.ahajournals.org.
- Received August 22, 2017.
- Accepted December 18, 2017.
- © 2018 American Heart Association, Inc.
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