DYNAMIC ELECTROPHYSIOLOGICAL BEHAVIOR OF HUMAN ATRIA DURING PAROXYSMAL ATRIAL-FIBRILLATION

Background The aims of our study were to investigate the meaning of lo cal atrial activation and its behavior during paroxysmal atrial fibril lation and to study the effect of overdrive pacing on local atrial act ivity. Methods and Results Twenty-five patients with lone paroxysmal a trial fibrillation underwent electrophysiological study. Functional an d effective atrial refractoriness was determined. Mean and fifth perce ntile values of 100 consecutive atrial fibrillation intervals (FF) wer e evaluated at three atrial sites either at arrhythmia onset or at sel f-termination (or at minute 5). A high-voltage burst pacing was perfor med after 6 minutes of stable atrial fibrillation in 10 patients. Mean FF intervals were evaluated 5 seconds before and after atrial pacing. Forty-nine atrial fibrillation episodes were induced: 39 self-termina ting within 5 minutes and 10 long-lasting. A significant correlation w as found between mean FF and atrial functional refractory period (r=.7 3, P<.001) and between fifth percentile FF and atrial effective refrac tory period (r=.57, P<.005). Atrial fibrillation self-termination was associated with significant mean FF prolongation, whereas long-lasting fibrillation behaved the opposite. In 10 patients, burst pacing resul ted in significant shortening of the mean FF at the stimulation site; no changes were observed in the two distant recording sites. Conclusio ns The analysis of the FF intervals demonstrates a strict correlation with atrial functional refractoriness. The self-termination of atrial fibrillation is related to a prolongation of the functional refractori ness (mean FF), whereas a shortening of both functional and effective refractoriness (fifth percentile) is associated with atrial fibrillati on persistence. The provoked shortening of the mean FF at the stimulat ion site is consistent with the presence of a gap of excitability duri ng atrial fibrillation in the human atria.