US Patent 7682316 Implantable heart sound sensor with noise cancellation

An implantable medical device system senses a first signal using a first acoustical sensor adapted to be operatively positioned in a first internal body location for sensing heart sounds in a patient. The system includes a second acoustical sensor adapted to be operatively positioned in a second internal body location for sensing sounds in the patient and generate a second signal that is less responsive to the heart sounds than the first acoustical signal. An implantable medical device including a housing and a processor enclosed in the housing receives the first signal and the second signal and generates a corrected first signal by canceling non-cardiac signals in the first signal using the second signal.