A catheter has a cooling distal section for freezing tissue to sub-zerotemperatures with oneor more miniature reverse thermoelectric or Peltier elements, also referred toherein as micro-Peltiercooling (MPC) units or electrodes. The MPC units may be on outer surface of aninflatableor balloon member or a tip electrode shell wall that has a fluid-containinginterior cavity acting as aheat sink. Each MPC unit has a hot junction and a cold junction whosetemperatures are regulatedby the heat sink, and a voltage/current applied to the MPC units. Atemperature differential ofabout 70 degrees Celsius may be achieved between the hot and cold junctionsfor extreme cooling,especially where the MPC units include semiconductor materials with highPeltier co-efflcients.An outer coating of thermally-conductive but electrically-insulative materialseals the MPC units toprevent unintended current paths through the MPC units.
