Alterations in atrial electrophysiology associated with chronic atrial fibrillation in man

Background The purpose of this study was to determine the changes in atrial electrophysiology associated with chronic persistent atrial fibrillation i n man. Methods and Results Atrial monophasic action potential duration at 90% repo larization and the effective refractory period were measured in 13 patients with chronic persistent atrial fibrillation after low-energy endocardial c ardioversion, and compared to eight controls without a history of atrial fi brillation. Measurements were made at the right atrial appendage and midlat eral right atrial wall at basic, 600 ms and 400 ms drive cycle lengths. In control patients, the effective refractory periods were significantly longe r at the atrial appendage than the lateral wall at 600 ms (right atrial app endage 265 ms, midlateral right atrial wall 228 ms, P<0.05), and 400 ms cyc le lengths (right atrial appendage 270 ms, midlateral right atrial wall 218 ms, P<0.05), but this was not evident in patients with atrial fibrillation . The monophasic action potentials and effective refractory periods at both atrial sites were shorter in the atrial fibrillation patients compared to controls; however, only the effective refractory periods at atrial appendag e at 600 ms (atrial fibrillation 210 ms, controls 265 ms, P<0.001), and 400 ms cycle lengths (atrial fibrillation 100 ms, controls 270 ms. P>0.001) re ached statistical significance. Effective refractory period dispersion was significantly greater in controls than in patients with atrial fibrillation (cycle length 600 ms: controls 36, atrial fibrillation 13, P=0.01; cycle l ength 400 ms: controls 54, atrial fibrillation 18, P<0.01). Conclusions In patients without a history of atrial fibrillation, the refra ctory period at the right atrial appendage is significantly longer than at the midlateral right atrial wall. This 'normal' pattern of atrial refractor y dispersion is lost in patients with chronic persistent atrial fibrillatio n, with marked shortening of the effective refractory period at the right a trial appendage. This may explain the high risk of recurrence of atrial fib rillation following successful electrical cardioversion.