RESUMO
INTRODUCTION: Rapid atrial pacing alters atrial electrophysiology, promoting initiation and maintenance of atrial fibrillation (AF). The aim of this study was to assess differences in the electrophysiologic properties of atrial tissue between patients with and without AF episodes and to determine whether electrophysiologic properties can predict the clinical efficacy of antiarrhythmic agents. METHODS AND RESULTS: Sixty patients were studied, 33 with documented episodes of paroxysmal atrial fibrillation (PAF) and 27 control patients. Atrial effective refractory period (AERP), atrial vulnerability, and intra-atrial conduction time were measured at baseline and after rapid constant atrial pacing for 5 minutes at rates of 130, 150, 170, and 190 beats/min. The clinical efficacy of antiarrhythmic agents for PAF prophylaxis was assessed over 14 months with an antiarrhythmic agent identical to that administered intravenously, and the antiarrhythmic agent effects on AERP, atrial vulnerability, and intra-atrial conduction time were assessed. AERP shortening and atrial vulnerability increase were significantly larger in the PAF group. Antiarrhythmic agents that were clinically effective in suppressing PAF significantly attenuated AERP shortening, but antiarrhythmic agents that were clinically ineffective did not. CONCLUSION: Changes in AERP and atrial vulnerability observed after rapid atrial pacing are considered indicative of the electrophysiologic substrate of PAF. Attenuation of AERP and atrial vulnerability by antiarrhythmic agents might be useful in predicting their clinical efficacy.