| To better understand the atrial repolarization process, an electrode array capable of recording monophasic action potentials (MAP) from up to sixteen opposing sites from the atrial epicardium and endocardium was designed and built.; The mapping array consists of two opposing cylindrical plastic heads that contain non-polarizable sintered Ag/AgCl electrodes. The heads were designed so that each epicardial element registers exactly with its opposing endocardial pair to provide the necessary counter pressure to record stable and long-term MAPs.; The array was tested on nine anesthetized, open chest pigs. Atrial recordings exhibited triangular MAP morphologies, with amplitudes ranging from 5 to 10 mV, smooth repolarization phases and stable baselines for up to 90 minutes. The array was also tested in the ventricular tissue where the recordings exhibited MAP waveforms with well defined plateau phases, amplitudes ranging from 15 to 40 mV, smooth repolarization phases and stable baselines.; Using this technique, the three-dimensional nature of atrial repolarization was investigated by measuring MAPs on opposing sites of the atrial epicardium and endocardium.; During sinus and paced rhythms, repolarization times were similar on endocardial and epicardial surfaces in some sites, but others showed significant differences.; Two interventions were performed to dissociate the electrophysiologic characteristics of the atrial epicardium and endocardium: Cooling of the epicardial surface using cold saline infusions and intravenous injections of adenosine.; Cooling of the atrial epicardium generated a temperature gradient across the atrial wall and produced MAP duration lengthening in both surfaces. Intravenous infusion of adenosine caused MAP duration shortening in both surfaces. Some sites exhibited differences in MAP duration across epicardial and endocardial sites that persisted during both interventions.; These findings suggest that atrial repolarization has three-dimensional characteristics, perhaps due to the presence of pectinate musculature on the endocardial surface.; 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 and the inherent difficulties in obtaining multiple MAPs from the beating heart. |
