Patent ID: 8840563

Claim:
An implantable medical system, comprising: a sensing circuit configured to sense at least one electrogram; a cardiac event detector coupled to the sensing circuit and configured to produce a cardiac signal using the at least one electrogram, the cardiac signal indicative of heart beats; an acoustic sensor configured to sense an acoustic signal indicative of third heart sounds (S3); and a heart sound analyzer circuit coupled to the acoustic sensor and the cardiac event detector, the heart sound analyzer including: an S3 index calculator configured to calculate an S3 index including a ratio of a number of S3 beats detected during a predetermined time period to a number of the heart beats detected during the predetermined time period; and an S3 trend generator configured to generate a trend of S3 index using a plurality of S3 indices calculated over a plurality of measurement periods; and a heart failure event detector configured to detect heart failure using the trend of S3 index.