Distinct restitution properties in vagally mediated atrial fibrillation and six-hour rapid pacing-induced atrial fibrillation

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The atrial potential duration (APD) restitution has been suggested to play an important role in ventricular fibrillation; however, its role in atrial fibrillation (AF) has not been determined. This study sought to investigate the APD restitution properties in two different AF models: vagally mediated AF and 6-h rapid atrial pacing-induced AF. Twenty anaesthetized open-chest dogs were assigned to Group I, vagally mediated AF (n= 8) or Group II, 6-h rapid atrial pacing-induced AF (n= 12). In both groups, the monophasic APD was subsequently recorded at multiple pulmonary vein and atrial sites. The APD restitution curve was constructed using a dynamic pacing protocol and determined by plotting each APD(90) against the preceding diastolic interval at incremental atrial pacing rates at eight sites. In Group I, vagal stimulation significantly shortened the APD(90), flattened the APD restitution curve (slopes <1), and suppressed the APD alternans at each site, while increasing the AF inducibility and duration (P<0.05 for all). In Group II, 6-h rapid pacing-induced APD shortening steepened the restitution curves (slopes >1), facilitated the APD alternans, and also increased the incidence and duration of AF (P< 0.05 for all). The spatial dispersion of APD restitution was significantly increased in both groups. This study showed distinct atrial APD restitution properties in vagally mediated AF and 6-h rapid pacing-induced AF, indicating specific restitution kinetics in different mechanisms of AF.