Identification and Characterization of Sites Where Persistent Atrial Fibrillation Is Terminated by Localized Ablation

Abstract

Background: The mechanisms by which persistent atrial fibrillation (AF) terminates via localized ablation are not well understood. To address the hypothesis that sites where localized ablation terminates persistent AF have characteristics identifiable with activation mapping during AF, we systematically examined activation patterns acquired only in cases of unequivocal termination by ablation.

Methods and results: We recruited 57 patients with persistent AF undergoing ablation, in whom localized ablation terminated AF to sinus rhythm or organized tachycardia. For each site, we performed an offline analysis of unprocessed unipolar electrograms collected during AF from multipolar basket catheters using the maximum -dV/dt assignment to construct isochronal activation maps for multiple cycles. Additional computational modeling and phase analysis were used to study mechanisms of map variability. At all sites of AF termination, localized repetitive activation patterns were observed. Partial rotational circuits were observed in 26 of 57 (46%) cases, focal patterns in 19 of 57 (33%), and complete rotational activity in 12 of 57 (21%) cases. In computer simulations, incomplete segments of partial rotations coincided with areas of slow conduction characterized by complex, multicomponent electrograms, and variations in assigning activation times at such sites substantially altered mapped mechanisms.

Conclusions: Local activation mapping at sites of termination of persistent AF showed repetitive patterns of rotational or focal activity. In computer simulations, complete rotational activation sequence was observed but was sensitive to assignment of activation timing particularly in segments of slow conduction. The observed phenomena of repetitive localized activation and the mechanism by which local ablation terminates putative AF drivers require further investigation.

Keywords: atrial fibrillation; catheter ablation; computer simulation; humans; tachycardia.

© 2018 American Heart Association, Inc.

Figures

Figure 1. Acute termination in patients with persistent AF by ablation at sites marked (*)

A) Acute termination of AF in a 60-year-old man to sinus rhythm by ablation, depicted on the electroanatomic right atrial shell (i). B) Acute termination of AF in a 61-year-old with the first ablation lesion applied in the left atrium (ii). This study was designed to investigate these scenarios.

Figure 2. Consecutive isochronal maps at sites of AF termination

A) Partial rotational circuit with a termination site near the left pulmonary vein carina. B) Repetitive focal activity from site of termination on the LA roof. C) Complete rotational circuit with a termination site near the mitral valve. Isochronal maps (iia, iib, iic) are shown for three consecutive cycles of AF.

Figure 3. Complete rotational circuits at sites of termination of persistent AF

A) Three cycles of AF in a 66-year-old man, with unipolar electrograms spanning 100% of the AF cycle length (160ms). Dashed line shows the first derivative (-dv/dt), with red vertical lines indicating activation at each AF cycle (maximum –dv/dt). Blue boxes highlight a 50ms window used to detect local activation. Numbered traces on left atrial isochrones (i) show rotational circuits with head-meets-tail interaction. B) Three cycles of AF in a 54-year-old man with persistent AF annotated using blue vertical lines (local peak-to-peak amplitude). Coronary sinus recording confirms AF. (ii) Isochronal activation map shows rotational activation in right atrium.

Figure 3. Complete rotational circuits at sites of termination of persistent AF

A) Three cycles of AF in a 66-year-old man, with unipolar electrograms spanning 100% of the AF cycle length (160ms). Dashed line shows the first derivative (-dv/dt), with red vertical lines indicating activation at each AF cycle (maximum –dv/dt). Blue boxes highlight a 50ms window used to detect local activation. Numbered traces on left atrial isochrones (i) show rotational circuits with head-meets-tail interaction. B) Three cycles of AF in a 54-year-old man with persistent AF annotated using blue vertical lines (local peak-to-peak amplitude). Coronary sinus recording confirms AF. (ii) Isochronal activation map shows rotational activation in right atrium.

Figure 4. Phase mapping and isochronal mapping of AF

(A) Snapshot of a computer simulation of a spiral wave with period 180ms and a meandering tip trajectory in red. (B) Isochronal map using the activation times at the 8×8 grid shown in yellow in (A), identifying the spiral wave. (C) As in (B) but now with variations of the relative timing of each electrode chosen at random between ±20ms (± 10% of cycle length 180ms). Altered activation times alter the spiral wave in the isochronal map. (D) Sequence of phase maps spanning the time interval of (B). Phase singularities reveal a counter-clockwise rotation at these same activation times. See supplementary materials for phase methods.

Figure 5. Importance of timing assignment in multiple component electrograms in AF

A) Persistent AF in a 54-year-old man, with electrode D3 indicating 3 possible deflections. Annotating the first (minimum dv/dt; red lines) portrays a focal source at the termination site (i). Annotating the middle deflection (green) indicates a partial rotation (green box, ii). Annotating the third deflection (blue) gives a complete rotational circuit (blue box, iii). B) Termination of AF with ablation at D3.

Figure 6. Importance of selection of time window for analysis in computer simulation

(A) Snapshot of a computer simulation of a spiral wave and a meandering tip trajectory in red. Tissue is heterogeneous with a larger (smaller) conductivity above (below) the dashed line. Membrane potential is indicated using a gray scale with activated/deactivated tissue shown in white/black. (B) Isochronal map using activation times on the 8×8 grid shown in yellow in (A). No rotation is seen. (C) As in (B) using a time window shifted by 50ms. Rotation is identified. (D) Phase maps spanning the time interval of (B) using the activation times of the grid, with phase singularities shown as black (clockwise rotations) or white (counter-clockwise rotations) symbols.

Figure 7. Clinical Impact of timing window on AF maps

A) Three consecutive cycles of AF are shown in a 70-year-old female, as voltages and –dv/dt. The blue box represents one AF cycle (190ms), with electrograms spanning 100% of the AF cycle in all channels in a rotational circuit (i). Moving this box 15ms earlier (orange box) now shows focal activity (starting with F6) with activity spanning only 140ms (ii). Morphology (qS) did not indicate focal activity (cycles 2 and 3). Ablation at FG34 (from blue window) acutely terminated AF.