Implantable medical device system having implantable cardioverter-defibrillator (icd) system and substernal leadless pacing device

An implantable cardiac system comprising:

• an implantable cardioverter-defibrillator (ICD) system comprising:
• an ICD configured to be implanted subcutaneously in a patient;
• and
• an implantable defibrillation lead having a proximal portion coupled to the ICD and a distal portion having a defibrillation electrode configured to deliver a defibrillation shock to a heart of the patient and at least one pace/sense electrode configured to deliver one or more pacing pulses to the heart of the patient;
• and
• an implantable leadless pacing device communicatively coupled to the ICD, the leadless pacing device including:
• a housing;
• a first electrode on the housing;
• a second electrode on the housing;
• and
• a sensing module within the housing and electrically coupled to the first electrode and the second electrode,
• wherein the housing is configured to be implanted substantially within an anterior mediastinum of the patient and the sensing module is configured to sense electrical signals of the heart of the patient via a sensing vector formed between the first and second electrodes.