A system analyzes and characterizes cardiac electrophysiological signals by determining instantaneous signal entropy for identifying and characterizing cardiac disorders, differentiating cardiac arrhythmias, determining pathological severity and predicting life-threatening events. The grid electrodes are mounted to the mounting ring with slots and fastening pins that allow sliding thermal expansion and contraction between the grid electrodes and mounting ring while substantially maintaining alignment of grid openings and spacing between the grid electrodes. The members are moveable relative to each other. Metadata objects for the specified named entities are fetched. The copyright and trademark owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but reserves all other copyright and trademark rights whatsoever. In one embodiment, each amplifier includes a transistor connected in series with R1 which conducts current IR1; these currents are coupled to the input and output terminals of a current mirror, preferably via respective virtual ground nodes such that the IA requires only one current mirror, to produce the IA’s output voltage.