Methods for Determining the Refractory Period and Excitable Gap During Persistent Atrial Fibrillation in the Goat

Abstract

Background — Recently, the temporal excitable gap during atrial fibrillation (AF) has been identified as a vulnerable parameter for cardioversion of AF. In this study, we evaluated 5 methods to measure the refractory period (RP AF ) and the excitable period (EP AF ) during persistent AF. Methods and Results — In 11 goats instrumented with 83 epicardial atrial electrodes, persistent AF (43±34 days) was induced with a median AF cycle length (CL) of 98±14 ms. To measure RP AF , premature stimuli were applied to the center of the electrode array on the right or left atrium. The RP AF measured by mapping of premature stimuli was 70±12 ms (“gold standard”). The RP AF determined during entrainment of AF was 77±17 ms ( R 2 =0.88, P <0.01). Statistical analysis of the effects of synchronized stimuli (each coupling interval ×100) on the AFCL histogram yielded an RP AF of 70±13 ms ( R 2 =0.94, P <0.01). A further simplification was to apply slow fixed-rate pacing (1 Hz) during AF. For each stimulus (n=250 to 500), the paced AFCL was plotted against its coupling interval, and capture was determined by statistical shortening of the AFCL (RP AF 71±17 ms, R 2 =0.84, P <0.01). The 5th percentile of the AFCL histogram as an index of RP AF was 77±12 ms ( R 2 =0.90, P <0.01). Conclusions — During persistent AF with an AFCL of 98±14 ms, the RP AF determined by mapping of synchronized premature stimuli (gold standard) was 70±12 ms, with an excitable period of 28±8 ms. Although the indirect methods to measure RP AF all correlated well with the gold standard, slow fixed-rate pacing seems to be the most attractive technique because of the ease of acquiring the data and the clear graphic result.