Inhomogeneity of Cellular Refractoriness in Human Atrium: Factor of Arrhythmia?

Spatial inhomogeneity of refractory periods, as measured during clinical electrophysiological studies, is a known predisposing factor of arrhythmia. We studied effective refractory periods (ERP) and action potential duration (ADP90) on isolated human atrium. Twelve samples of right atrium obtained during cardiac surgery from patients with (n = 6) and without (n = 6) atrial fibrillation (AF) were studied by microelectrode technique. For each preparation, ERP were measured at basic cycle lengths (BCL) of 1,600, 1,200, 800, and 400 msec in five different cells located around (0.8 mm) the stimulating electrode. Dispersion of ERP was significantly greater in the AF group (96.7 +/- 9 versus 70.9 +/- 9 msec, p = 0.01). In the non-AF group, we observed a positive linear correlation between ERP and BCL (r = 0.86) ADP90 and BCL (r = 0.93). On the contrary, in the AF group this correlation was absent between ERP and BCL (r = 0.28), poor between ADP90 and BCL (r = 0.62). These results suggest that nonhomogeneous recovery of excitability (dispersion and poor adaptation) may be an important factor of arrhythmia. This inhomogeneity is present at the cellular level as well as in the entire heart.