An implantable medical device including at least one electrode line having an electrode pole, an electrode feed line, a counter electrode to the at least one electrode line, and an insulation sleeve. The insulation sleeve surrounds the electrode feed line and provides insulation between the electrode feed line and an electrolyte formed by bodily fluid. The electrode feed line and the electrode pole(s) include different materials, wherein the materials are different based on electrochemical series. The implantable medical device includes an insulation test unit having a DC voltage detector arranged between the electrode pole and the counter electrode, in order to detect an electrochemical voltage produced in the event of an insulation fault of the insulation sleeve due to defective contact between the electrolyte and the electrode feed line.