Quantitative analysis of localized sources identified by focal impulse and rotor modulation mapping in atrial fibrillation

Abstract

Background: New approaches to ablation of atrial fibrillation (AF) include focal impulse and rotor modulation (FIRM) mapping, and initial results reported with this technique have been favorable. We sought to independently evaluate the approach by analyzing quantitative characteristics of atrial electrograms used to identify rotors and describe acute procedural outcomes of FIRM-guided ablation.

Methods and results: All FIRM-guided ablation procedures (n=24; 50% paroxysmal) at University of California, Los Angeles Medical Center were included for analysis. During AF, unipolar atrial electrograms collected from a 64-pole basket catheter were used to construct phase maps and identify putative AF sources. These sites were targeted for ablation, in conjunction with pulmonary vein isolation in most patients (n=19; 79%). All patients had rotors identified (mean, 2.3±0.9 per patient; 72% in left atrium). Prespecified acute procedural end point was achieved in 12 of 24 (50%) patients: AF termination (n=1), organization (n=3), or >10% slowing of AF cycle length (n=8). Basket electrodes were within 1 cm of 54% of left atrial surface area, and a mean of 31 electrodes per patient showed interpretable atrial electrograms. Offline analysis revealed no differences between rotor and distant sites in dominant frequency or Shannon entropy. Electroanatomic mapping showed no rotational activation at FIRM-identified rotor sites in 23 of 24 patients (96%).

Conclusions: FIRM-identified rotor sites did not exhibit quantitative atrial electrogram characteristics expected from rotors and did not differ quantitatively from surrounding tissue. Catheter ablation at these sites, in conjunction with pulmonary vein isolation, resulted in AF termination or organization in a minority of patients (4/24; 17%). Further validation of this approach is necessary.

Keywords: atrial fibrillation; catheter ablation; electrophysiology.

Figure 1

Left atrial basket catheter position and recordings. A, Fluoroscopic image of 64-pole Constellation basket catheter in left atrium (LA) with good chamber coverage and equidistant splines. B, Basket catheter with compressed splines, resulting in inadequate coverage of posterior and septal LA. C, Basket catheter with bunched splines, resulting in large areas of unsampled LA endocardium. D, Example of 64 unipolar electrograms recorded simultaneously during atrial fibrillation.

Figure 2

Analysis of basket catheter coverage. A, Electroanatomic map created with Ensite NAVX system. Left atrial (LA) surface was segmented to calculate total surface area outside pulmonary veins (outlined in white), and then 1-cm fill threshold was set to calculate the surface area near any basket electrode (colored area). B, Example of mapped and unmapped LA endocardial areas plotted on electroanatomic map.

Figure 3

Quantitative analysis of atrial unipolar electrograms. A, Raw unipolar signal from single electrode on a basket catheter, with red arrows indicating QRS complexes to be filtered out. B, QRS waveforms are plotted simultaneously to create an aggregated QRS–T complex. C, Remainder signal after QRS–T subtraction shows pure atrial electric activity.

Figure 4

Example of frequency domain and entropy analysis. Both panels are 8×8 grids representing each electrode of the 64-channel basket catheter from a single patient. Top, Dominant frequency (DF) of each atrial unipolar signal is shown in a color map. Insets, Representative Fourier transforms illustrating similar DF at a focal impulse and rotor modulation (FIRM)–identified rotor site, and elsewhere in the atrium. Bottom, Similar Shannon entropy (ShEn) in a FIRM-identified rotor region and the rest of the left atrium.

Figure 5

Detailed results of frequency domain and entropy analysis. A, Histogram of dominant frequency at all rotor and nonrotor sites shows similar frequency distribution. B, Histogram of Shannon entropy (ShEn) at all rotor and nonrotor sites shows similar frequency distribution.

Figure 6

Atrial electrogram analysis: local activation time. A, Top, Surface ECG lead II. Bottom, Local electrogram (EGM) from a rotor site recorded by using a basket catheter. Only ventricular activation can be seen on the local tracing. B, On this unipolar recording with a voltage of 0.06 mV, low-amplitude atrial EGM can be seen, but activation time cannot be accurately annotated. C, On this unipolar recording with a voltage of 0.28 mV, atrial EGM is decipherable and shows variable cycle length.

Figure 7

Electroanatomic mapping. A, Sequential activation isochrone maps show disorganized activity with no rotation. B, Rotational activity seen, with change in chirality in sequential activation sequences.