Medical devices are described for performing mapping, ablating, pacing, andor defibrillating procedures on one or more layers of the cardiac wall via an epicardial or extra-pericardial approach in a minimally invasive surgical procedure. First and second LPFs convert the pulse density signals into multi-bit signals. zH2O, where: M2+ is one or more of Mg2+, Ca2+, Fe2+, Ni2+, and Zn2+; M3+ is one or more of Al3+, Fe3+, and Cr3+; and An\u2212 is one or more of OH\u2212, CO32\u2212, Cl\u2212, and 2\u2212. A link contents detection part detects the link contents.