Impact of Low Voltage Threshold Adjustment on Activation Mapping Interpretation for Atrial Tachycardia in Low-Voltage Left Atrium

Figures

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  Fig. 1.. The impact of low voltage threshold adjustment (LVTA) on low voltage zone (LVZ) in the same map. As the low voltage threshold (LVT) was adjusted from 0.03 mV (A) to 0.02 mV (B) and 0.01 mV (C), the area of the LVZ on left atrial (LA) anterior wall gradually decreased. Consequently, more points in this area were assigned colors and were subsequently included in activation mapping. The white dots were used to outline the LVZ areas (represented in grey), and these areas were manually measured by the mapping system.

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  Fig. 2.. An example of Type 1.1 mechanism re-identification. Panel A depicts the scenario at the default LVT of 0.03 mV, where activation mapping suggested a single-loop AT. In this configuration, the wavefront circumnavigated the LVZ at the LA roof, activating both atria centrifugally. Panel B shows that after LVTA (0.01 mV), activation mapping suggested biAT. Furthermore, the wavefront was activated in the LA septum (in an areal pattern), ran around the block line at LA anterior wall, proceeded towards the LA roof, and jumped to right atrium via Bachmann’s bundle. The Solid lines with arrows, the AT circuit as suggested by activation mapping; jagged lines, the wavefront passing through the slow conduction area; dashed red/yellow lines, passive activation propagation; dotted lines, inter-atrial bypasses or epicardial conduction propagation; circle, the origin of focal AT; dashed white lines, conduction block lines; grey dots: planned ablation strategy before LVTA; red dots: effective ablation strategy after LVTA (similarly hereinafter). Abbreviations: AT, atrial tachycardia; biAT, bi-atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment;…

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  Fig. 3.. An example of Type 1.2 mechanism re-identification. In panel A, at the default LVT of 0.03 mV, activation mapping indicated epiAT and the wavefront circulated around the MA clockwise before jumping across the LVZ at the MI via an epicardial connection. In panel B, following LVTA (LVT adjustment to 0.01 mV), activation mapping suggested clockwise peri-mitral AT passing MI via both endocardium and epicardial connections simultaneously. White arrows indicated simultaneous endocardial and epicardial connections. Abbreviations: AT, atrial tachycardia; epiAT, epicardium-mediated atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone; MA, mitral annulus; MI, mitral isthmus.

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  Fig. 4.. An example of Type 1.3 mechanism re-identification. In panel A, at the default LVT of 0.03 mV, activation mapping suggested a bi-loop AT, where the activation wavefront circulated around both the MA and LVZ at LA anterior wall simultaneously, utilizing a shared corridor between the MA and LVZ. In Panel B, following LVTA (0.01 mV), a complete conduction block line across LA anterior wall was revealed within LVZ. Activation mapping suggested single-loop counter-clockwise peri-mitral AT. Abbreviations: AT, atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone; MA, mitral annulus.

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  Fig. 5.. An example of Type 1.4 mechanism re-identification. Panel A shows that at the default LVT of 0.03 mV, the LVZ was identified at the left pulmonary ridge. Activation mapping suggested focal AT originating from the left pulmonary ridge. In Panel B, after LVTA (0.01 mV), the activation mapping suggested single-loop reentrant AT, facilitated via two conduction gaps on the pre-ablation line. Abbreviations: AT, atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone.

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  Fig. 6.. An example of Type 2 mechanism re-identification. Panel A shows that at the default LVT of 0.03 mV, the activation mapping suggested counter-clockwise peri-mitral AT. The wavefront crossed the conduction gap within the LVZ, extending from the right superior pulmonary vein to MA. In Panel B, following LVTA (0.01 mV), the AT mechanism remained as a counter-clockwise peri-mitral AT. However, another conduction gap within LVZ was revealed after LVTA, and the wavefront transversed the two conduction gaps almost simultaneously. The dashed red lines indicated AT circuit behind the atrial structure. Abbreviations: AT, atrial tachycardia; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone; MA, mitral annulus.

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  Fig. 7.. An example of Type 3 mechanism re-identification. Panel A shows that at the default LVT of 0.03 mV, activation mapping suggested focal AT originating from LA inferior wall. Panel B shows that after LVTA (0.01 mV), the AT mechanism remained unchanged. However, a conduction gap within the LVZ was revealed following LVTA, through which activation wavefront propagated to activate LA anterior wall. Subsequently, additional ablation was performed to target the conduction gap in the LA anterior wall. Abbreviations: AT, atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone.

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  Fig. 8.. An example of Type 4.1 mechanism re-identification. Panel A shows the default LVT (0.03 mV) where activation mapping suggested the wavefront moved counter-clockwise around the LVZ located at LA anterior wall with the LVZ being inside AT circuit. Panel B shows that after LVTA (0.01 mV), the AT circuit remained unchanged. The LVZ was still inside AT circuit and continued to block conduction. Abbreviations: AT, atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone.

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  Fig. 9.. An example of Type 4.2 mechanism re-identification. Panel A illustrates that with the default LVT (0.03 mV), activation mapping suggested the wavefront activated the LA ridge in an areal pattern, moved around the base of the LA appendage, following the LA ridge toward the MI. The wavefront then proceeded to activate the LA ridge, possibly through the ligament of Marshall. In this case, the LVZs were not part of AT circuit. Panel B shows that after LVTA (0.01 mV), the AT circuit remained unchanged, but there was a significant decrease in the LVZ in the right area. Abbreviations: AT, atrial tachycardia; LA, left atrium; LVT, low voltage threshold; LVTA, low voltage threshold adjustment; LVZ, low voltage zone; MI, mitral isthmus.