Prevalence of retrograde accessory pathway conduction during atrial fibrillation.

INTRODUCTION

Although atrial fibrillation occurs frequently in patients with the preexcitation syndrome, its pathogenesis remains controversial. The purpose of this study was to test the hypothesis that retrograde conduction over the accessory pathway occurs during atrial fibrillation and can serve as an important source of new wavefronts in atrial fibrillation.

METHODS AND RESULTS

Eight patients undergoing surgical division of their accessory pathway(s) were studied. A plaque electrode array containing 56 (7 x 8) bipolar electrodes (5-mm resolution) was placed epicardially at the AV junction over the accessory pathway and atrial fibrillation was electrically induced. Excluding one patient who had only preexcited QRS complexes during atrial fibrillation and another whose accessory pathway was outside the mapped region, 4 of the 6 patients studied showed retrograde conduction over the accessory pathway during atrial fibrillation (mean atrial cycle length 157 +/- 59 msec). In these patients, 186 atrial wavefronts near the accessory pathway were analyzed. Among 67 wavefronts immediately following nonpreexcited QRS complexes, 17 originated from retrograde conduction. This constituted 9% (17/186) of total atrial wavefronts near the accessory pathway. Estimated atrial refractory period during atrial fibrillation ranged from 81 to 165 msec.

CONCLUSIONS

(1) In patients with the preexcitation syndrome and atrial fibrillation, retrograde conduction over the accessory pathway contributed up to 9% of total atrial wavefronts near the accessory pathway. (2) The presence of an excitable gap in human atrial fibrillation was suggested by atrial preexcitation during retrograde conduction.