Line Of Block Research Articles

Sinoatrial node function and the role of sinoatrial conduction in the typical atrial flutter substrate

BackgroundSinoatrial node (SAN) activation and sinoatrial conduction pathways (SACPs) have been assessed in animals but not in humans. ObjectivesWe used ultrahigh-density mapping and simulated models to characterize the SAN and to investigate whether slowed SAN conduction may contribute to the atrial flutter (AFL) substrate. MethodsTwenty-seven patients undergoing electrophysiologic procedures had right atrial mapping. SAN activation patterns and conduction block were analyzed. The interaction between the SAN and the intercaval line of block (LOB) was analyzed, and right atrial simulations with different degrees of block were created to investigate arrhythmia mechanisms. ResultsFifteen AFL patients and 12 reference patients were enrolled. SACPs were identified in all patients with sinus rhythm maps. An SAN-adjacent LOB was observed in AFL patients. SAN conduction velocity was slower in AFL vs reference (0.60 m/s [0.56–0.78 m/s] vs 1.13 m/s [1.00–1.21 m/s]; P = .0021). Coronary sinus paced maps displayed an intercaval LOB in AFL patients but not in reference patients, which was completed superiorly by the SAN-adjacent LOB. Corrected sinus node recovery time was longer in AFL patients (552.3 ± 182.9 ms vs 325.4 ± 138.3 ms; P < .006) and correlated with degree of intercaval block (r = 0.7236; P = .0003). Computer modeling supported an important role of SAN-associated block in the flutter substrate. ConclusionUltrahigh-density mapping accurately identifies SAN activation and SACPs. The LOB important for typical AFL was longer in AFL patients, and when partial, it was always present inferiorly and completed superiorly because of slowed conduction across the SAN. Corrected sinus node recovery time correlated with intercaval block, suggesting a role for SAN disease in the genesis of the typical AFL substrate.

Activation pattern within Koch's triangle during sinus rhythm in patients with and without atrioventricular nodal reentrant tachycardia.

Several studies have visualized the slow pathway during sinus rhythm using high-density mapping of Koch's triangle (KT) in patients with atrioventricular nodal reentrant tachycardia (AVNRT). However, it is unclear whether the slow pathway can be visualized in all people. Therefore, we evaluated the activation pattern within KT during sinus rhythm in patients with and without AVNRT. High-density mapping using the Advisor HD Grid mapping catheter (Abbott) within KT during sinus rhythm was created in 10 patients with slow-fast AVNRT and 30 patients without AVNRT. In 8 (80%) patients with AVNRT, the activation pattern pivoting around a block line (BL) within KT was observed. In 12 (40%) patients without AVNRT, similar activation pattern pivoting around BL was observed, but jump was observed in 11 (92%) of these patients. In all patients, the activation pattern pivoting around BL was observed in 17 (85%) of 20 patients with jump, but only 3 (15%) of 20 patients without jump (p < 0.0001). During jump, there was a long period of no potential from the last atrial potential within KT to the His bundle potential, suggesting the slow pathway conduction through the rightward inferior extension that cannot be visualized. A linear ablation between the pivot point and the septal tricuspid annulus was successful for slow-fast AVNRT. Although the slow pathway could not be visualized using high-density mapping during sinus rhythm, the activation pattern pivoting around BL within KT was observed in most patients with the dual pathway physiology, with or without AVNRT.

Reducing Line-of-Block Artifacts in Cardiac Activation Maps Estimated Using ECG Imaging: A Comparison of Source Models and Estimation Methods.

To investigatecardiac activation maps estimated using electrocardiographic imaging and to find methods reducing line-of-block (LoB) artifacts, while preserving real LoBs. Body surface potentials were computed for 137 simulated ventricular excitations. Subsequently, the inverse problem was solved to obtain extracellular potentials (EP) and transmembrane voltages (TMV). From these, activation times (AT) were estimated using four methods and compared to the ground truth. This process was evaluated with two cardiac mesh resolutions. Factors contributing to LoB artifacts were identified by analyzing the impact of spatial and temporal smoothing on the morphology of source signals. AT estimation using a spatiotemporal derivative performed better than using a temporal derivative. Compared to deflection-based AT estimation, correlation-based methods were less prone to LoB artifacts but performed worse in identifying real LoBs. Temporal smoothing could eliminate artifacts for TMVs but not for EPs, which could be linked to their temporal morphology. TMVs led to more accurate ATs on the septum than EPs. Mesh resolution had anegligible effect on inverse reconstructions, but small distances were important for cross-correlation-based estimation of AT delays. LoB artifacts are mainly caused by the inherent spatial smoothing effect of the inverse reconstruction. Among the configurations evaluated, only deflection-based AT estimation in combination with TMVs and strong temporal smoothing can prevent LoB artifacts, while preserving real LoBs. Regions of slow conduction are of considerable clinical interest and LoB artifacts observed in non-invasive ATs can lead to misinterpretations. We addressed this problem by identifying factors causing such artifacts.

Physiology of slow pathway conduction during sinus rhythm: evidence from high density mapping within the triangle of Koch.

To evaluate nature of AV nodal activation in patients with AVNRT using high density electro-anatomic mapping (HD-EAM). HD-EAM was created in 30 patients with AVNRT from the triangle of Koch (ToK) in sinus rhythm (SR). Isochronal late activation maps (ILAM) were created. EAMs were analyzed for slow pathway (SPW) and fast pathway (FPW) activation. A pivot point (PP) was defined where FPW and SPW collided and pivoted back to the AV node (AVN). Conduction was assessed with programmed extrastimulus (PES) in 9 patients until FPW refractory period (ERP). The change in PP distance from the HIS (ΔPP) was measured in SR and PES. The ΔPP was compared to ΔAH. The PP was ablated and SR re-mapped. The FPW activates the His and moves inferiorly toward the coronary sinus (CS). Activation also enters the ToK near the CS and collides with the FPW which then pivots around a functional line of block (LOB) within the ToK and moves superiorly along the septal tricuspid annulus. PP electrograms are fractionated, low amplitude, and consistent with SPW potentials (Haissaguerre et al. in Circulation 85:2162-2175, 1992). During PES the PP moved superiorly until FPW ERP when only SPW activation occurs. Normalized ΔAH and ΔPR vs ΔPP was highly correlated p < 0.0001. Ablation at the PP was successful and associated with loss of SPW fusion and pivot. We conclude HD-EAM/ILAM provide a novel method for localizing the SPW in SR. This study provides further understanding of dual AV nodal physiology and may aid in targeting the SPW for ablation of AVNRT.

The nature of fast and slow pathway interaction during premature pacing: evaluation with high density mapping

Abstract Background Dual AV Nodal (AVN) inputs are associated with the fast pathway (FPW) superiorly, while the SPW activates inferiorly. In the present study, we evaluate the impact of PES on dual antegrade conduction. Objective To Define Antegrade Conduction Properties of the AV Node during PES Methods High density mapping (Orion, Rhythmia) was performed and analyzed in SR and S2 PES in 12 pts. The FPW activates the AVN and travels inferiorly, there is a point where the activation pivots toward the SPW and travels superiorly along the TV. The distance from the pivot point was measured to the HIS location in sinus rhythm and for each coupling interval. Both the distance and prematurity of the S2 coupling was normalized to the BCL during sinus rhythm. The coupling interval was then plotted vs the HIS-Collision distance. A regression analysis was used to compare data sets with significance defined a &amp;lt;0.05. Results Data was obtained in all 12 patients. In all patients, as pre-maturity of S2 increased, the pivot point moved superiorly until there was block in the FPW and activation to the AV node was entirely from the SPW. There is a functional line of block (LOB) between the FPW and SPW. Comparing normalized data decrement vs change in pivot point: R=0.8 p&amp;lt;0.0001 Conclusion During PES, the F/SPW interaction changes: increasing prematurity causes pivot point to move superiorly until the FPW blocks and AVN activates via the SPW. Decremental antegrade conduction occurs within FPW and is associated with the superior pivot shift toward the AVN suggesting a functional LOB. This relationship is linear. Funding Acknowledgement Type of funding source: None

Electrogram signature of specific activation patterns: Analysis of atrial tachycardias at high-density endocardial mapping

The significance of fractionated electrograms (EGMs) is object of debate, with multiple mechanisms described. Using Rhythmia, a high-density mapping system, we sought to investigate the relationship between specific electrophysiological phenomena and EGM characteristics at those sites. Twenty-five consecutive patients underwent high-density atrial mapping during atrial tachycardias. Bipolar EGMs were recorded with a 64-electrode basket catheter. The following atrial phenomena were identified: slow conduction (SC) areas, lines of block (LB), wavefront collisions (WFC), pivot sites (PS), and gaps. EGMs collected at these predefined areas were analyzed in terms of amplitude, duration, and morphology. Twenty-five atrial maps with 195 sites of interest (1755 EGMs) were object of our analysis. Thirty-five percent were sites of SC: fractionation had low amplitude (0.16 ± 0.07 mV) and long duration (87.8 ± 10.7 ms); wavefront collisions were seen in 38% of sites with EGMs shorter in duration (46.5 ± 4.5 ms) and higher in voltage (0.58 ± 0.13 mV); 17% were lines of block, never responsible for fractionation (0.13 ± 0.05 mV; 122.4 ms ± 24.8 ms); 9% were PS with a high degree of fractionation (0.55 ± 0.15 mV; 85.8 ± 7.9 ms). Two gaps were identified (1%) with a low degree of fractionation. Specific EGM characteristics in atrial tachycardia can be reproducibly linked to electrophysiological mechanisms. High-voltage and short-duration EGMs are associated with collision sites and PS that are unlikely to form critical sites for ablation; long-duration, low-voltage EGMs are associated with SC. However, not all SC regions will lie within the critical circuit and identification by only EGM characteristics cannot guide ablation.

Fixed intercaval block in the setting of atrial fibrillation promotes the development of atrial flutter

In the canine sterile pericarditis model, typically only atrial fibrillation (AF) is inducible on postoperative day 2. In this model, we tested the hypothesis that on postoperative day 2, placing a fixed line of block (LoB) between the vena cavae critically alters the atrial substrate, favoring the induction of sustained atrial flutter (AFL) instead of AF. In 6 sterile pericarditis dogs, sustained AF was induced by rapid atrial pacing. After terminating AF, a fixed LoB between the vena cavae was created (cryoablation), and AF reinduction was attempted. Simultaneous mapping from 400 to 420 electrodes on the right and left atrial epicardium and the interatrial atrial septum was performed during all studies. Before creation of the LoB, in all 6 dogs, rapid atrial pacing induced sustained AF because of a rapid (mean cycle length [CL] 110 +/- 10 ms), regular, left atrial reentrant driver, which caused fibrillatory conduction. After creation of the LoB, in 5 dogs, rapid atrial pacing now induced sustained AFL (mean CL 167 +/- 13 ms). In the 6th dog, AFL failed to develop because the left atrial driver that was induced before the LoB was still reproducibly induced despite the LoB. In this model of sustained AF, altering the substrate to create a fixed LoB between the vena cavae creates a substrate favoring the induction of AFL.

Atrial Fibrillation–Atrial Flutter Interactions

An appreciation of the article by Moreira et al in the current issue of Circulation 1 requires an understanding of the close interrelationship between atrial fibrillation (AF) and atrial flutter (AFL). These authors have understood this interrelationship and applied it to their data to advance the approach to both AF and AFL ablation. Key to this understanding is the recognition that cavotricuspid isthmus (CTI)–dependent AFL almost always develops from antecedent AF of variable duration.2–5 This is because in almost all instances, it is during the AF that a functional line of block (LoB) necessary for the development of AFL forms between the superior and inferior vena cavae. This LoB acts as a critical lateral boundary that prevents short-circuiting of the AFL reentrant circuit. Thus, in the vast majority of instances, without preceding AF, there can be no AFL. The most recent additional support of this concept comes from the report by Ellis et al,6 which found that of 363 patients who presented with only CTI-dependent AFL and who underwent CTI ablation, long-term follow-up (mean of 39±11 months) demonstrated newly recognized AF in 82%. It also should be noted that, as Moreira et al1 recognize, in some patients, a LoB between the vena cavae may be fixed (ie, anatomic) rather than functional. In such patients, AF may not be required for AFL to develop. Article p 2786 As Moreira et al1 further recognize, their report does not answer all the questions about the interrelationships of AF and AFL as they relate to AF ablation, …

Tachycardia Circuit in Typical Atrial Flutter: The Role of a Posterolateral Line of Block in the Perpetuation of the Tachycardia

The essential boundaries in typical atrial flutter (AF) are unknown. To examine the role of the tricuspid annulus (TA) and posterolateral line of block (LB) in maintaining AF, single extrastimuli were delivered during AF both around the LB and the TA in 29 patients. Single extrastimuli were delivered from the superior, middle, and inferior third of the anterior LB, superior, middle, and inferior third of the posterior LB, and the superior, lateral, inferior, and septal portions of the TA. The longest coupling interval (LCI) of single extrastimuli that reset AF and subsequent return cycle (RC) were analyzed. The resetting response showed two patterns (groups 1 and 2). The differences between the AF cycle length (AFCL) and the LCI (AFCL-LCI) at the superior, lateral, inferior, and septal portions of the TA were the shortest, and were significantly shorter than those at the other sites (P < 0.0001) in group 1. However, the AFCL-LCI at the superior, middle, and inferior third of the anterior LB, and the superior, lateral, inferior, and septal portions of the TA were the shortest, and were significantly shorter than those at the other sites (P < 0.0001) in group 2. The difference between the RC and the AFCL exhibited the same two patterns, similar to the AFCL-LCI. In group 1, a single extrastimulus produced an artificial conduction across the LB, but AF was not reset. Two types of reentry circuits exist in AF; one has its essential reentry circuit confined to the TA and thus the LB acts as a bystander, while the LB and the TA are essential boundaries in the other one.

AB36-3: Iso-duration mapping during ventricular pacing as a tool to ablate unmappable ventricular tachycardia after remote myocardial infarction

VT after MI is usually due to reentry through a protected isthmus bounded by functional lines of block (LoB). When VT is not inducible or not tolerated (unmappable VT) there is a need to unmask the isthmus by sinus mapping or pacing maneuvers. Experimental data suggest that sinus rhythm electrograms (EGM) along the central common pathway have a short duration compared to longer EGMs along LoBs. Using Carto® we aimed at identifying these isthmus-related LoBs by mapping the EGM duration during RV pacing.

A New and Simple Method for Distinguishing Complete from Incomplete Block Through the Cavotricuspid Isthmus

A complete line of block (CLOB) in the cavotricuspid isthmus (CTI) is the endpoint of typical atrial flutter ablation. Before CTI block is obtained, a progressive CTI conduction delay due to an incomplete line of block (InLOB) can be difficult to distinguish from CLOB. The purpose of this study was to assess a new simple approach based on the changes in atrio-ventricular (AV) conduction delays during septal and lateral right atrial pacing, to distinguish a CLOB from an InLOB during typical atrial flutter (AFL) ablation. Forty patients who presented an InLOB before a CLOB, and a stable (AV) conduction delay at 600 ms cycle length pacing (when in sinus rhythm), during AFL ablation were included in this study. A 24-pole mapping catheter was positioned so that 2 adjacent dipoles bracketed the targeted CTI line of block (LOB), with proximal dipoles lateral to the LOB and distal dipoles in the coronary sinus. Two pacing sites were lateral (position L1 and L2) and one was septal (position S) to the LOB, with locations L1 and S closest to the LOB. During L1, L2 and S site pacing, the delay between the pacing artefact and the peak of the R wave in a surface ECG (lead II) was measured. We measured the following conduction delays (mean +/- SD in ms), during InLOB versus CLOB: (L1 to R) 320.5 +/- 68.0 versus 367.0 +/- 62.0, p = 0.001; (L2 to R) 333.0 +/- 59.0 versus 338.0 +/- 62.0, p = 0.663, (S to R) 259.4 +/- 51.5 versus 247.1 +/- 55.5, p = 0.987. We calculated the following data during an InLOB versus a CLOB: (L1R-L2R) -12.3 +/- 7 versus 20.2 +/- 12.7, p = 0.001; (L1R-SR) 51.1 +/- 21.5 versus 120.1 +/- 16.6, p < 0.05. The sensitivity, specificity, positive and negative predictive values for CLOB with (L1R-SR > 94 ms) and with (L1R-L2R > 0 ms) were respectively; 100%, 98%, 98% and 100%. This study establishes that lateral versus septal right atrial pacing sites combined with the measure of AV conduction delay on a surface ECG can be useful to distinguish a CLOB from an InLOB during AFL ablation.

Cavotricuspid Isthmus Mapping to Assess Bidirectional Block During Common Atrial Flutter Radiofrequency Ablation

We sought to compare published methods to an alternative approach ascertaining cavotricuspid isthmus (CTI) block during atrial flutter ablation. In 39 consecutive patients who underwent an atrial flutter ablation procedure, a 24-pole mapping catheter was positioned so that 2 adjacent dipoles were bracketing the targeted CTI line of block (LOB), with proximal dipoles lateral to the LOB and distal dipoles in the coronary sinus. Two pacing sites were lateral (positions A and B) and 2 were septal (positions C and D) to the LOB, with locations A and D closest to the LOB. A resulting CTI block was accepted when 3 criteria were fulfilled: (1) complete reversal of the right atrial depolarization on the 24-pole catheter when pacing in the coronary sinus, (2) conduction delays from A to D greater than from B to D, and (3) conduction delays from D to A greater than from C to A. A successful CTI block was obtained in all patients. Before CTI block was obtained, a progressive CTI conduction delay was observed in 11 patients (28.2%). During the procedure, the 3 criteria defined above were either all present or all absent. This study establishes that reversal of the atrial depolarization sequence up to the LOB is a definitive and mandatory criteria of successful atrial flutter ablation.

Gyrotropic propagation of vertical Bloch lines

Vertical Block line (BL) gyrotropic propagation was studied experimentally. Single BLs nucleated in an as-grown (YSmBi)/sub 3/(FeGa)/sub 5/O/sub 12/ garnet film were viewed directly using the PADO (polarized anisotropic dark-field observation) technique. Gyrotropic force was provided by an asymmetrical triangular-shaped bias field pulse. A short-risetime pulse moved the line of a straight wall in one direction, whereas a large-risetime pulse moved it backward. This gyrotropic propagation phenomenon is reproducible for varying bias field; however, some scatter is observed in BL displacement. Block wall response to the bias field pulses is also considered. The range of effective drive field inducing good gyrotropic propagation is discussed. >