A simultaneous multichannel monophasic action potential electrode array for in vivo epicardial repolarization mapping

While the recording of extracellular monophasic action potentials (MAPs) fr om single epicardial or endocardial sites has been performed for over a cen tury, we are unaware of any previous successful attempt to record MAPs simu ltaneously from a large number of sites in vivo. We report here the design and validation of an array of MAP electrodes which records both depolarizat ion and repolarization simultaneously at up to 16 epicardial sites in a squ are array on the heart in vivo. The array consists of 16 sintered Ag-AgCl e lectrodes mounted in a common housing with individual suspensions allowing each electrode to exert a controlled pressure on the epicardial surface. Th e electrodes are arranged in a square array, with each quadrant of four hav ing an additional recessed sintered Ag-AgCl reference electrode at its cent er. A saline-soaked sponge establishes ionic contact between the reference electrodes and the tissue. The array was tested on six anesthetized open-ch ested pigs. Simultaneous diagnostic-quality MAP recordings were obtained from up to 13 out of 16 ventricular sites. Ventricular MAPs had amplitudes of 10-40 mV wi th uniform morphologies and stable baselines for up to 30 min. MAP duration at 90% repolarization was measured and shown to vary as expected with cycl e length during sustained pacing. The relationship between MAP duration and effective refractory period was also confirmed, The ability of the array t o detect local differences in repolarization was tested in two ways. Placem ent of the array straddling the atrioventricular (AV) junction yielded simu ltaneous atrial or ventricular recordings at corresponding sites during 1:1 and 2:1 AV conduction. Localized ischemia via constriction of a coronary a rtery branch resulted in shortening of the repolarization phase at the isch emic, but not the nonischemic, sites. In conclusion, these results indicate that the simultaneous multichannel MA P electrode array is a viable method for in vivo epicardial repolarization mapping. The array has the potential to be expanded to increase the number of sites and spatial resolution.