A visualized left‐sided accessory pathway away from the mitral annulus using open window mapping with the early meets late algorithm

A 70yearold woman who presented with intermittent palpitation symptoms for the past few years. There was no preexcitation during sinus rhythm on 12lead surface ECG and a Holter ECG showed supraventricular tachycardia (SVT) (Figure 1A). After informed consent was obtained, catheter ablation was performed. Early atrial excitation during right ventricular (RV) apex pacing was recorded in the left posterolateral wall (Figure 1B), showing an intermittent block and no decremental property. SVT was induced by an atrial doublecoupled extra stimulus with a cycle length of 270 ms, and early atrial excitation was identical to that during RV pacing (Figure 1B,C). Because of nonsustained status, electrophysiologic studies during tachycardia were not available, but based on other findings, SVT was diagnosed as orthodromic reciprocating tachycardia (ORT) via a concealed left posterolateral AP. To identify the location of the intermittent retrograde AP conduction, the open window mapping (OWM) during RV apex pacing was performed via a transseptal approach by using a multipolar catheter and threedimensional mapping system (Pentaray, CARTO3; Biosense Webster, Inc, Irvine, CA). The reference was set to the pacing spike, and the window of interest was set from +20 ms to +200 ms to include ventricular to atrial potentials. Local ventricular and atrial potentials around the posterolateral wall of the mitral annulus (MA) were acquired using Pentaray. These potentials are annotated on the wavefront where the distal electrode's steepest unipolar negative dV/dt coincides with the bipolar downslope. Early Meets Late (EML) displays a white line when there is a timephase difference between any two adjacent points showing the activation delay between the ventricle and the atrium, which could be regarded as an atrioventricular annulus. The lower threshold was adjusted to 30% to match the propagation map. A typical AP location is shown as a white line gap where the ventricular and atrial potentials are continuous. However, there was no white line defect, and the earliest atrial activation site (EAAS) was located 2 cm above the MA (Figure 2A). The propagation map showed that after the ventricular excitation by RV pacing conducted to the MA, the excitation temporarily disappeared, and propagated as if it was springing from the left atrial posterolateral wall (Figure 3, Supplemental Movie S1). Atrial excitation on the MA was apparently delayed and no AP potential was observed. Radiofrequency applications to the EAAS area were performed. The power output was 30 W and the average contact force was 11– 15 g. The effective sites where intermittent AP conduction blockade was achieved, and the successful site required over 5– 10 s of radiofrequency application. Each application continued for 30– 50 s. The EAAS subtly sifted to the adjacent region after effective applications and then multiple times ablation to the wider area was required to eliminate the AP on the epicardial side (Figure 2B). SVT has not recurred for more than 1 year. OWM is a useful mapping technique that reduces annotation errors and facilitates AP location because the nearfield potentials are

A 70-year-old woman who presented with intermittent palpitation symptoms for the past few years.There was no pre-excitation during sinus rhythm on 12-lead surface ECG and a Holter ECG showed supraventricular tachycardia (SVT) (Figure 1A).After informed consent was obtained, catheter ablation was performed.
Early atrial excitation during right ventricular (RV) apex pacing was recorded in the left posterolateral wall (Figure 1B), showing an intermittent block and no decremental property.SVT was induced by an atrial double-coupled extra stimulus with a cycle length of 270 ms, and early atrial excitation was identical to that during RV pacing (Figure 1B,C).Because of non-sustained status, electrophysiologic studies during tachycardia were not available, but based on other findings, SVT was diagnosed as orthodromic reciprocating tachycardia (ORT) via a concealed left posterolateral AP.
To identify the location of the intermittent retrograde AP conduction, the open window mapping (OWM) during RV apex pacing was performed via a trans-septal approach by using a multipolar catheter and three-dimensional mapping system (Pentaray, CARTO3; Biosense Webster, Inc, Irvine, CA).The reference was set to the pacing spike, and the window of interest was set from +20 ms to +200 ms to include ventricular to atrial potentials.Local ventricular and atrial potentials around the posterolateral wall of the mitral annulus (MA) were acquired using Pentaray.These potentials are annotated on the wavefront where the distal electrode's steepest unipolar negative dV/dt coincides with the bipolar downslope.Early Meets Late (EML) displays a white line when there is a time-phase difference between any two adjacent points showing the activation delay between the ventricle and the atrium, which could be regarded as an atrioventricular annulus.The lower threshold was adjusted to 30% to match the propagation map.
A typical AP location is shown as a white line gap where the ventricular and atrial potentials are continuous.However, there was no white line defect, and the earliest atrial activation site (EAAS) was located 2 cm above the MA (Figure 2A).The propagation map showed that after the ventricular excitation by RV pacing conducted to the MA, the excitation temporarily disappeared, and propagated as if it was springing from the left atrial posterolateral wall (Figure 3, Supplemental Movie S1).Atrial excitation on the MA was apparently delayed and no AP potential was observed.Radiofrequency applications to the EAAS area were performed.The power output was 30 W and the average contact force was 11-15 g.The effective sites where intermittent AP conduction blockade was achieved, and the successful site required over 5-10 s of radiofrequency application.
Each application continued for 30-50 s.The EAAS subtly sifted to the adjacent region after effective applications and then multiple times ablation to the wider area was required to eliminate the AP on the epicardial side (Figure 2B).SVT has not recurred for more than 1 year.F I G U R E 2 A: Open window mapping with Early Meets Late (EML) during RVa pacing from the left posterolateral view.Local ventricular and atrial potentials around the posterolateral wall of the mitral annulus (MA) were acquired using Pentaray via a transseptal approach.The potentials are annotated on the wavefront where the steepest unipolar -dV/dt of the distal electrode coincides with the bipolar downslope.EML was set by 30% of the lower threshold and 90% of the upper threshold to match the propagation map, showing a white line that indicates the MA.Notably, there was no white line gap, and the activation map showed that the earliest atrial activation site (EAAS) was located 2 cm above the white line.The intracardiac electrogram showed that atrial excitation in CS5-6 was apparently delayed from the EAAS corresponding to 11-12 poles of Pentaray (yellow square) at which no ventricular potential was observed.B: Ablation sites to the EAAS area.Tags in a yellow frame showed effective sites leading to an intermittent retrograde accessory pathway (AP) conduction block during RVa pacing.A green tag showed the successful site requiring a radiofrequency application for more than 10 s to eliminate atrial attachment of the AP on the epicardial side.Others are unsuccessful or additional ablation sites.White tags indicate ablation index values lower than 400, light red tags indicate above 400, and dark red tags above 450.The area of effective and successful sites was approximately 0.7 cm 2 .CS, coronary sinus; LA, left atrium; LV, left ventricle; RVa, right ventricular apex.

OWM is a useful mapping technique that reduces annotation er-
F I G U R E 3 Propagation map during right ventricular apex pacing showed that after the ventricular excitation conducted to the mitral annulus (MA), the excitation temporarily disappeared and propagated as if it was springing from the left atrial posterolateral wall 2 cm above the MA.
rors and facilitates AP location because the near-field potentials are This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.© 2023 The Authors.Journal of Arrhythmia published by John Wiley & Sons Australia, Ltd on behalf of the Japanese Heart Rhythm Society.

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I G U R E 1 A: 12-lead ECG before ablation showed sinus rhythm and right bundle branch block without antegrade pre-excitation.Intracardiac electrograms during RVa pacing in B, and SVT in C. Early atrial excitation during RVa pacing was recorded in CS5-6, identical to that during SVT.D: Catheter position at the successful ablation site in RAO and LAO views.CS, coronary sinus; HIS, His bundle; LAO, left anterior oblique; RAO, right anterior oblique; RVa, right ventricular apex; SVT, supraventricular tachycardia.