Background: Different algorithms of estimating local activation time (LAT) can be usedduring the mapping of focal atrial tachycardia (FAT).
Objective: The impact of these algorithms on the reproducibility of LAT measurementand the location of the focus.
Methods: Fifteen patients (48 ± 17 yrs) with FAT were studied. Three independentobservers reviewed 1438 bipolar electrograms and successively assigned the LAT on thepeak amplitude (Bi-peak), the steepest downslope (Bi-dslope), and the onset (Bi-on) ofthe electrograms. The reproducibility of LAT measurement was estimated.
Results: The mean interobserver absolute differences in LAT for the three algorithmswere 1.47 ± 2.75 ms (Bi-peak) vs. 2.15 ± 3.89 ms (Bi-dslope) vs. 2.87 ± 3.47 (Bi-on) (p <0.0001). The corresponding intraobserver differences were 2.29 ± 3.74 ms (Bi-peak) vs2.47 ± 4.17 ms (Bi-dslope) vs 3.16 ± 4.49 ms (Bi-on) (p < 0.0001). The interobserverdifferences in the location of the focus were 3.57 ± 3.81 mm (Bi-peak) vs 5.47 ± 4.98mm (Bi-dslope) vs 6.57 ± 6.94 mm (Bi-on) (p = 0.03), with differences of up to 13 mm(Bi-peak), 16 mm (Bi-dslope), and 25 mm (Bi-on). However, regardless of the method ofLAT determination, the foci computed by the three observers clustered within regions oflow-amplitude fractionated electrograms.
Conclusions: Significant observer variability exists among the three algorithms, whichtend to compute different LAT and foci with different locations. However, the foci aresituated in regions of low voltage fractionated electrograms.