A high density in vitro extracellular electrode array: description and implementation.

The detailed activation sequence in myocardium provides information critical to the understanding of the mechanisms of cardiac arrhythmias and the influence of interventions. Despite the pivotal role of activation mapping, the interpretation of isochronic maps and the correlation to detailed tissue morphology may be limited when the interelectrode distances are large with respect to cell dimensions. Additionally, dynamic beat-to-beat variations in the activation pattern or the effect of interventions such as single extra stimuli cannot be assessed adequately without recording from all sites simultaneously. To surmount these limitations, we have fabricated and tested an extracellular recording array consisting of 224 bipolar tungsten wire electrodes with a 350-microns interelectrode distance (140 microns edge-to-edge distance), and used signal processing equipment to record from all electrodes simultaneously at a 2-kHz sample rate. Stimulation can be performed sequentially from 12 different sites at 30 degree angles around the periphery of the recording array. Transarray bipoles can be recorded from any combination of eight radially oriented sites. Activation maps recorded in normal tissue after programmed stimulation and activation maps from an area of fixed anatomic block in the epicardial border zone of infarcted tissue are presented. The results demonstrate a lack of influence of the recording array on the electrophysiological properties of the tissue as verified with transmembrane action potential recordings and sequential extracellular maps. This electrode permits precise assessment of transient details of the activation sequence with unparalleled anatomic resolution.