an implantable medical device having at least one elongated electrical function conductor and an electrode pole connected to the at least one elongated function conductor . the at least one elongated function conductor transmits therapeutic signals or diagnostic signals or both . the electrode pole delivers electrical current or field or sense electrical potentials , or both , in surrounding tissue during use . the implantable medical device includes a sensing device connected to a field - generating electrode pole , a potential - sensing electrode pole , and a reference pole . the sensing device detects generated electrical potentials via the potential - sensing electrode pole in relation to the reference pole , and generates an output signal that represents a detected electrical potential . the implantable medical device includes a control device connected to the sensing device to evaluate an output signal generated by the sensing device , and to control the medical device as a function of the potential detected by the sensing device .