Capture window in human atrial fibrillation: Evidence of an excitable gap

Capture Window in Human AF. Introduction: Local capture of atrial fibrillat ion (AF) was shown in animal experiments for a wide range of pacing rates, thus demonstrating the existence of an excitable gap. The aim of this study was to assess the existence of an excitable gap in human AF by studying th e mechanism bf local control and acceleration of AF over a wide range of pa cing rates and by evaluating the time window of capture. Methods and Results: Recording and stimulation of electrical activity in th e right atrium during AF was performed by a monophasic action potential (MA P) contact electrode catheter in 17 patients with lone AF during electrophy siologic study. Stimulation was started at pacing intervals close to the me an AF interval, and the time window of capture was estimated by lengthening or shortening the pacing interval until capture was lost. Pacing intervals shorter than the minimum cycle length for capture were also tested. Beat-t o-beat measurements of AF intervals during pacing were performed. Atrial MA P signal showed rapid irregular activity with an average AF interval of 151 .3 +/- 16.1 msec and SD of 21.3 +/- 5.2 msec, Rapid pacing with a cycle len gth slightly shorter or longer than the mean AF interval resulted in local capture of AF. The width of time window of capture ranged from 22 to 36 mse c, with a mean value of 28.8 +/- 4.9 msec, The average minimum pacing inter val of stable capture was 129.2 +/- 19.5 msec, while the maximum was 158.1 +/- 18.7 msec, corresponding to 85% and 104% of mean AF cycle length, respe ctively. Pacing too rapidly resulted in a transient acceleration of AF, wit h an average shortening of fibrillation interval from 149.8 +/- 16.6 to 123 .2 +/- 15.1 msec (P < 0.01). Conclusion: Local capture is feasible during AF in humans over a wide range of pacing rates, indicating the possibility of regional control of the fib rillatory process. This result demonstrates the presence of an excitable ga p during AF in human atria.