Ischemia detection using a heart sound sensor

A system comprising:

• an implantable medical device (IMD) comprising:
• an implantable heart sound sensor operable to produce an electrical signal representative of at least one heart sound, the heart sound associated with mechanical activity of a patient's heart;
• a heart sound sensor interface circuit coupled to the heart sound sensor to produce a heart sound signal;
• at least one implantable cardiac signal sensing circuit operable to produce an electrical cardiac signal representative of cardiac activity of the patient;
• and
• a signal analyzer circuit coupled to the heart sound sensor interface circuit and the cardiac signal sensing circuit, wherein the signal analyzer circuit is configured to:
• measure a heart sound signal in association with the electrical cardiac activity signal;
• measure a baseline value of a characteristic of at least one of an S3 or S4 heart sound in the heart sound signal;
• assign a first weight to the measured subsequent change in the heart sound signal from the established baseline heart sound signal and a second weight to the measured change in the electrical cardiac signal from an established baseline electrical cardiac signal;
• and
• deem that an ischemic event occurred using a measured change in the electrical cardiac signal from an established baseline electrical cardiac signal, a measured subsequent change in the heart sound characteristic from the established baseline value of the characteristic, and the assigned weights.