Methods for determining the refractory period and excitable gap during persistent atrial fibrillation in the goat

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 (EPAF) during persistent AF. Methods and Results-In I I goats instrumented with 83 epicardial atrial ele ctrodes, persistent A-F (43 +/- 34 days) was induced with a median AF cycle length (CL) of 98 +/- 14 ms. To measure RPAF, premature stimuli were appli ed 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 standar d"). The RPAF 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 X 100) on the AFCL histogram yielded an RPAF of 70 +/- 13 ms (R-2 = 0.94, P < 0.01). A further simplification was to apply sl ow fixed-rate pacing (I Hz) during A-F. 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 (RPAF 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 +/- 2 ms (R-2 = 0.90, P < 0.01). Conclusions-During persistent AF with an AFCL of 98 14 ins, the RPAF determ ined by mapping of synchronized premature stimuli (gold standard) was 70 +/ - 12 ms, with an excitable period of 28 +/- 8 ins. Although the indirect me thods to measure RPAF all correlated well with the gold standard, slow fixe d-rate pacing seems to be the most attractive technique because of the ease of acquiring the data and the clear graphic result.