An insert has a plurality of pieces and a pair of coupling portions. An embodiment of one method in accordance with the invention includes delivering sufficient electrical energy for initiation of cardiac activation to a plurality of different test locations at the heart of a patient, and determining hemodynamic responses in reaction to that the stimulus delivered to the different test locations. Termination rings formed of ring-shaped trenches containing floating polysilicon plugs surrounds and terminates the device active area. Auxiliary grip holes are provided at the anchoring portion to enable disengagement of said anchoring portion even in case of breaking of the intermediate neck ; finally, a push rod is removably connected with an end of the anchoring portion itself. The mixture ratio is varied to achieve desired floating or sinking characteristics of the resultant blend.