Multi-site dual surface monophasic action potential mapping of atrial repolarization in vivo: Is atrial repolarization a two- or three-dimensional process?

Although the atrial free wall is a thin structure, atrial depolarization ha s been shown to have aspects of three-dimensionality. This study asks wheth er the same is true for atrial repolarization. By using a multi-element dua l-surface probe, monophasic action potentials (MAPs) were recorded simultan eously at several opposing sites on the right atrial endocardial and epicar dial surfaces in six open-chest pigs. The times of depolarization and repol arization were marked in recordings during sinus, paced rhythms, and during infusions of cold saline to the epicardial surface, which generated a temp erature gradient across the atrial wall. Repolarization times were similar on endocardial and epicardial surfaces in some sites, but others showed sig nificant differences during sinus and paced rhythms. Cold saline infusion p roduced a significant lengthening of MAP duration, and this was more pronou nced on the atrial endocardial sites than on the epicardial sites. The obse rved differences in endocardial and epicardial repolarization times ma) be due to the presence of atrial pectinate muscles on the endocardial surface. These results suggest that in some regions atrial repolarization is a thre e-dimensional process. Possible limitations of this study include the fact that the depth of view of MAPs recorded from the atrial wall may extend to the opposing surface.