Subthreshold lead impedance measurement for subcutaneous device

An implantable medical system, comprising:

• a housing;
• a lead coupled to the housing;
• a first electrode coupled at a distal end of the lead;
• a second electrode;
• an operational circuitry disposed within the housing, the operational circuitry including:
• an energy source;
• a switch electrically coupled to the energy source at a first terminal;
• an output circuit arrayed having a high side and a low side and including four interconnected legs, the high side having a first leg and a third leg and the low side having a second leg and a fourth leg, wherein the first leg is coupled between a second terminal of the diode and the first electrode and the fourth leg is coupled to the second electrode;
• an impedance testing leg coupled to the output circuit;
• and
• a control circuit configured to control monitoring of a voltage between the first electrode and the second electrode.