Double figure-of-eight reentry during atrial tachycardia using 4 critical boundaries: A unique topological finding.

Reentry (macro or localized) is historically described as multiple pathways that are separated by barriers (either anatomic or functional) and involve active and passive loops (identified by electro-anatomic and entrainment mapping, EAM/ETM). Some reentrant atrial tachycardia (AT) cases are characterized by challenging activation patterns and unexpected ablation responses. A recent translational study, focusing on topology and the role of boundaries, suggests that thinking topology within EAM/ETM might offer extra control during mapping and ablation of reentrant AT. We aimed to propose and prospectively validate a workflow (EAM/ETM+TOP) in which we integrate topological thinking within an EAM/ETM workflow for mapping and ablation of left-sided (left atrium) AT. The integrated workflow was performed in 88 left atrium reentrant AT cases. After EAM/ETM, the number of loops and potential ablation strategy were verified against the number of critical and noncritical boundaries (critical boundary [CB], non-CB). Linear radiofrequency lesions were deployed to connect both CBs, preferably by one direct CB-CB line. EAM/ETM+TOP-based mapping was feasible in all cases and led to a diagnosis of a 2B topology with single-loop activation in 33 cases and a≥3B topology with dual-loop activation in 55 cases. In 87 out of 88 cases, subsequent ablation via a direct CB-CB approach (n=75), an indirect CB-non-CB-CB (n=9), or an indirect CB-non-CB-non-CB-CB approach (n=3) led to successful termination of AT. No unexpected changes in tachycardia cycle length occurred. After a median FU of 356 (IQR, 228-537) days, 16 patients experienced recurrence of AT (18%). Thinking topology within an EAM/ETM workflow may offer extra control during mapping and ablation of left-sided reentrant AT.

IntroductionIn the latest research on topology in cardiac arrhythmia, it was demonstrated through a fundamental mathematical principle called the index theorem that reentry based atrial tachycardias (AT) are maintained by pairs of counter-rotating waves that are either complete or near-complete rotations. Each wave is centered around a different anatomical object that exhibits a non-zero index/topological charge, called a critical boundary. Interconnecting both critical boundaries with an ablation line terminates the tachycardia.MethodsThis research focuses on the specific algorithms for calculating the index/topological charge of each anatomical boundary, called DGM-TOP. The algorithm used analyzes the electroanatomical map of the patient, extracting the nodes at each boundary. The index is then calculated for each boundary by sequentially summing the differences in local activation time and normalizing by the cycle length. Boundaries with a non-zero index are identified as critical boundaries.Results and discussionUsing this method, pairs of critical boundaries were consistently detected in 100% of the 578 in silico and 100% of the 24 clinical ATs. Adhering to the previously described index theorem. Additionally, ablation results in both datasets show that termination of AT is only possible by interconnecting both critical boundaries. This outcome highlights the importance of detecting the critical boundaries before deciding on the correct ablation line, as any ablation line that does not connect both critical boundaries is unable to terminate the AT. Moreover, in the case of incorrect ablation, the BCL-algorithm was proposed to estimate the increase in tachycardia cycle length. However, only moderate correlation is observed for simulations, indicating a refinement of this BCL-algorithm is necessary in addition to a larger clinical dataset.

IntroductionIn previous research on reentrant atrial tachycardia (AT), the index theorem has proven instrumental in uncovering consistent paired counter-rotating anatomical reentry (either complete or near-complete), driving the arrhythmia rotating around critical boundaries (CB). Furthermore, interconnecting each CB-pair with an ablation line has been shown to terminate the AT. In this study, we extend this approach to scar-related ventricular tachycardia (VT), complicating the calculations as VT is inherently a 3-dimensional problem. We propose that scar-related VT can be topologically simplified to one or more of four basic physiologically distinct scar-types: transmural (I-shaped), epicardially connected or endocardially connected (U-shaped) or intramural (O-shaped).MethodsSix simulations of scar-related VT were created, each featuring a distinct critical scar configuration. From each simulation, three transmural layers (endocardium, mid-myocardium and epicardium) were extracted to create 2-dimensional surfaces, which were analyzed with the index theorem, using the software package Directed Graph Mapping (DGM) extended with novel algorithms to detect the CBs.ResultsOn each layer, either no CBs were found or pairs of counter-rotating CBs were found, each CB had an opposite sign, adhering to the index theorem. Ablation was performed by connecting each pair of counter-rotating CBs on each layer to form a continuous ablation surface, bounded by scar tissue, the endocardial surface, or the epicardial surface. This ablation strategy consistently terminated all simulations, supporting the applicability of our topology-based approach to VT.ConclusionThe index theorem remains valid for scar-related VT. Successful ablation on VT should include, connecting the CB-pairs in each 2 dimensional surface. Any other type of ablation does not terminate the VT.

Macroreentry stands as the predominant mechanism of typical and atypical flutter. Despite advances in mapping, many aspects of macroreentrant atrial tachycardia remain unsolved. In this translational study, we applied principles of topology to understand the activation patterns, entrainment characteristics, and ablation responses in a large clinical macroreentrant atrial tachycardia database. Because the atrium can be topologically seen as a closed sphere with holes, we used a computational fixed spherical mesh model with a finite number of holes to induce and analyze macroreentrant atrial tachycardia. The ensuing insights were used to interpret high-density activation maps, postpacing interval-tachycardia cycle length values (difference between postpacing interval and tachycardia cycle length), and ablation response in 131 cases of typical and atypical flutter (n=106 left atrium, n=25 right atrium). Modeling of macroreentrant atrial tachycardia revealed that reentry on closed surfaces consistently manifests itself as paired rotation and that an odd number of critical boundaries is mathematically impossible. Together with mathematical confirmation by the index theorem, this led to a unifying construct that could explain the number of loops, difference between postpacing interval and tachycardia cycle length values, and ablation outcomes (termination, no change, or prolongation in tachycardia cycle length) in all 131 cases. Combining topology with the index theorem offers a novel and cohesive framework for understanding and managing typical and atypical flutter.