Local activation time sampling density for atrial tachycardia contact mapping: how much is enough?

Abstract

Aims: Local activation time (LAT) mapping forms the cornerstone of atrial tachycardia diagnosis. Although anatomic and positional accuracy of electroanatomic mapping (EAM) systems have been validated, the effect of electrode sampling density on LAT map reconstruction is not known. Here, we study the effect of chamber geometry and activation complexity on optimal LAT sampling density using a combined in silico and in vivo approach.

Methods and results: In vivo 21 atrial tachycardia maps were studied in three groups: (1) focal activation, (2) macro-re-entry, and (3) localized re-entry. In silico activation was simulated on a 4×4cm atrial monolayer, sampled randomly at 0.25-10 points/cm2 and used to re-interpolate LAT maps. Activation patterns were studied in the geometrically simple porcine right atrium (RA) and complex human left atrium (LA). Activation complexity was introduced into the porcine RA by incomplete inter-caval linear ablation. In all cases, optimal sampling density was defined as the highest density resulting in minimal further error reduction in the re-interpolated maps. Optimal sampling densities for LA tachycardias were 0.67 ± 0.17 points/cm2 (focal activation), 1.05 ± 0.32 points/cm2 (macro-re-entry) and 1.23 ± 0.26 points/cm2 (localized re-entry), P = 0.0031. Increasing activation complexity was associated with increased optimal sampling density both in silico (focal activation 1.09 ± 0.14 points/cm2; re-entry 1.44 ± 0.49 points/cm2; spiral-wave 1.50 ± 0.34 points/cm2, P < 0.0001) and in vivo (porcine RA pre-ablation 0.45 ± 0.13 vs. post-ablation 0.78 ± 0.17 points/cm2, P = 0.0008). Increasing chamber geometry was also associated with increased optimal sampling density (0.61 ± 0.22 points/cm2 vs. 1.0 ± 0.34 points/cm2, P = 0.0015).

Conclusion: Optimal sampling densities can be identified to maximize diagnostic yield of LAT maps. Greater sampling density is required to correctly reveal complex activation and represent activation across complex geometries. Overall, the optimal sampling density for LAT map interpolation defined in this study was ∼1.0-1.5 points/cm2.

Keywords: Atrial arrhythmias; Electroanatomic mapping systems; Local activation time mapping; Sampling density.

Figure 1

Optimal LAT sampling densities. Calculated optimal LAT sampling densities are shown for simulated activation patterns (A) and in vivo LA activation patterns (B). FO, focal origin; MA, macro re-entry; MI, micro (localised) re-entry.

Figure 2

The process used for determination of optimal LAT sampling density. (A) The process is shown for a focal tachycardia in a 4×4 cm monolayer with fiber orientation of 18° to the x-axis. (B) Activation times are re-sampled at increasing sampling density and regional activation is re-interpolated to give the resulting ‘down-sampled’ activation maps. Sampling densities (points/cm²) are given above each example map. (C) Mean normalized LAT map error at each sampling density is calculated by comparing activation times at each node with the original activation times in A. (D) Taking the first-derivative of the curve in ‘C’ indicates the sampling density at which minimal further improvement in map accuracy is generated.

Figure 3

Clinical isochronal local activation time maps. Local activation time (LAT) maps for example clinical tachycardias are shown. Tachycardia mechanisms (confirmed by response to entrainment manoeuvres and to ablation) are given as headings in each column. (A) focal activation in low posterior LA; (B) perimitral macro-re-entry; (C) localized anterior re-entry. Anterior-posterior and posterior-anterior projections are shown (top and bottom row respectively). Left-most maps of each pair are the original isochronal maps produced at the time of the clinical procedure with purple dots representing sampled LAT point locations. Right-most maps of each pair are single examples of re-interpolated maps generated at the calculated optimal densities with black dots representing the re-sampled point locations. MV indicates the mitral valve annulus; * indicates the site of focal activation.

Figure 4

Porcine right atrial LAT maps. (A) Pre-ablation LAT shows uniform activation across the chamber from coronary sinus towards the right atrial appendage. (B) Post-ablation LAT shows a new activation detour (asterisk) via the mid-chamber gap in the ablation line. Ablation points are shown with red tags and catheter positions during ablation with pink dots using the Visitag Carto3 module. (C) Comparison between optimal LAT sampling density for pre- and post-ablation LAT maps.

Figure 5

Initiation of activation patterns in the atrial monolayer. (A) Linear activation; (B) focal activation; (C) re-entrant activation; and (D) spiral wave activation. Stimulated regions are shown in white in the left-most column of each row.

Figure 6

Simulated isochronal local activation time maps. (A) Linear activation; (B) focal activation; (C) re-entrant activation; and (D) spiral wave activation. Reference LAT maps are shown in the left most column. In A and B, local activation time is taken as the first activation of each node. In C and D, a window of interest (WOI) incorporating 100% of the tachycardia cycle length (TCL) was specified. Grey colour represents tissue that is never activated during the WOI—either non-conducting (C) or functionally refractory (D).