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(Circulation. 2001;104:957.)
© 2001 American Heart Association, Inc.

Basic Science Reports

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

Mattias Duytschaever, MD; Frans Mast, PhD; Matthijs Killian, PhD; Yuri Blaauw, MD; Maurits Wijffels, MD, PhD; Maurits Allessie, MD, PhD

From the Department of Physiology, Maastricht University, Maastricht, the Netherlands.

Correspondence to Prof M.A. Allessie, Department of Physiology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands.

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 (R²=0.88, P<0.01). Statistical analysis of the effects of synchronized stimuli (each coupling interval x100) on the AFCL histogram yielded an RP_AF of 70±13 ms (R²=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, R²=0.84, P<0.01). The 5th percentile of the AFCL histogram as an index of RP_AF was 77±12 ms (R²=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.

Key Words: fibrillation • electrophysiology • excitation

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