A sensor array apparatus for monitoring medical signals includes a flexible substrate adapted to generally conform to a topography of a skin surface. The flexible substrate includes a central portion arranged about a central focal point and a plurality of finger-like projections extending radially outwardly from the central portion. At least one reference electrode is disposed on the central portion of the flexible substrate. A medical electrode is disposed on at least one of the finger-like projections, preferably, each of the finger-like projections. Connector, in electrical communication with the medical electrode, is adapted to connect to an electronic system. The flexible substrate defines at least two reference apertures for accommodating a body structure. The apertures permit the conductor to interface with the electrical system from either side of patient tissue.