Electrode assemblies and associated fixation members for implantable medical devices

An electrode assembly for an implantable medical device, the assembly comprising a longitudinal axis, a helical structure coupled to a distal portion of the device and extending distally from the distal portion and around the longitudinal axis, a first electrode surface formed on the helical structure, and a second electrode surface electrically isolated from the first electrode surface, the helical structure including a piercing distal tip located adjacent to the first electrode surface;

• and an improvement to the assembly comprising:
• a pair of fixation members, wherein each fixation member of the pair comprises:
• a fixed end coupled to the distal portion of the device;
• and
• a tissue engaging portion terminated by a piercing distal tip, each tissue engaging portion extending from the corresponding distal tip to the corresponding fixed end along a circular path, the helical structure being located within a perimeter of the circular path;
• and
• wherein both tissue engaging portions extend from the corresponding piercing distal tip thereof in a direction along the circular path that is the same as that in which the helical structure extends from the piercing distal tip thereof, either clockwise or counter-clockwise.