To investigate the mechanism of atrial fibrillation (AF), monophasic action potentials (MAPs) from the atrial myocardium were studied in 7 patients with paroxysmal AF (PAF) and in 7 control individuals. The MAPs were recorded using a contact catheter during sinus rhythm and continuous pacing at the high right atrium (HRA) with pacing cycle lengths of 600, 500 and 400 ms. MAPs were obtained from 6 sites in each participant. The MAPD
90 was measured from onset to 90% of MAP repolarization. Average, maximal and minimal MAPD
90 (avMAPD
90, maxMAPD
90 and minMAPD
90) were obtained from all participants. The dispersion of MAPD
90 (dispMAPD
90) was defined as the difference between maxMAPD
90 and minMAPD
90. The width of each atrial potential (WAP) and the wavelength index (WLI = MAPD
90 / WAP) were determined. Average, maximal and minimal WLI (avWLI, maxWLI and minWLI) were obtained from all participants. The avMAPD
90 and maxMAPD
90 did not significantly differ between the 2 groups. The minMAPD
90 in the PAF group was significantly smaller than that in the control group at HRA pacing with cycle lengths of 500 and 400 ms (210±18 ms vs 245±14 ms, p<0.05; 207±23 ms vs 238±20 ms, p<0.05; respectively). The dispMAPD
90 was significantly longer in the PAF group than in the control group during sinus and HRA pacing. The WAP value did not differ between the 2 groups. The minWLI in the PAF group was significantly smaller than that in the control group at HRA pacing with cycle lengths of 500 and 400 ms (3.3±0.5 vs 3.8±0.3, p<0.05; 3.2±0.4 vs 3.7±0.3, p<0.02). A shortened and widened dispersion of atrial refractoriness may play an important role in the genesis of AF. Furthermore, smaller wavelengths may form in the atrium of patients with PAF. (
Jpn Circ J 2001;
65: 893 - 896)
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