Patent ID: 8630700

Claim:
An implantable heart monitoring system comprising: a control unit comprising a control circuit; a memory in communication with said control circuit; a plurality of electrode surfaces adapted for positioning to measure an impedance across at least a part of an atrium of the heart to generate an impedance signal that varies as a function of a change in volume of said atrium; cardiac sensing circuitry in communication with at least some of said electrode surfaces to sense cardiac events in at least one chamber of the heart; said control circuit being configured to determine a first value indicating the rate of change of the measured impedance signal during at least a portion of a first cardiac cycle, and to store the first value in said memory; and said control circuit being configured to determine a second value indicating the rate of change of the measured impedance signal during at least a portion of a second cardiac cycle and to store the second value in said memory, to produce, in said memory, a record of stored values having a variation that is related to variation of a speed with which the atrium is filled with blood during atrial diastole, wherein said control circuit is configured to determine whether said impedance signal decreases within a time interval following detection of a QRS signal by the cardiac sensing circuitry to determine whether the measured impedance indicates an inverse of an amount of blood in the atrium.