Regional and functional factors determining induction and maintenance of atrial fibrillation in dogs.

The present study was designed to determine the factors governing the ability of premature beats at various atrial sites to initiate atrial fibrillation (AF) and the determinants of the duration of AF in dogs at 1-10 Hz. The site of atrial extrasystoles determined their ability to induce AF. Regional differences in AF inducibility were due to differences in local refractoriness. Premature beats initiated AF by blocking in regions of greater refractoriness, causing macroreentrant activation with subsequent disorganization producing fibrillation. The atrial refractory period and wavelength during rapid 1:1 atrial pacing were weak predictors of AF duration (r = 0.24 and 0.23, respectively), which depended strongly on variability in regional refractoriness measured by the standard deviation in local refractory periods (r = 0.80, P < 0.001) and on the heterogeneity of activation during AF (r = 0.74, P < 0.001). Thus, premature beats cause AF by initiating a single macroreentrant cycle that degenerates into multiple wavefronts, regional refractoriness is the primary determinant of AF induction by premature beats, and variability in refractoriness may be an important determinant of the ability of AF to sustain itself.