Implantable medical device for monitoring congestive heart failure

Abstract

An implantable stimulator and monitor measures a group of heart failure parameters indicative of the state of heart failure employing EGM signals, measures of blood pressure including absolute pressure P, developed pressure (DP=systolic P−diastolic P), and/or dP/dt, and measures of heart chamber volume (V) over one or more cardiac cycles. These parameters include: (1) relaxation or contraction time constant tau (&tgr;); (2) mechanical restitution (MR), i.e., the mechanical response of a heart chamber to premature stimuli applied to the heart chamber; (3) recirculation fraction (RF), i.e., the rate of decay of PESP effects over a series of heart cycles; and (4) end systolic elastance (E ), i.e., the ratios of end systolic blood pressure P to volume V. These heart failure parameters are determined periodically regardless of patient posture and activity level. However, certain of the parameters are only measured or certain of the data are only stored when the patient heart rate is regular and within a normal sinus range between programmed lower and upper heart rates. The parameter data is associated with a date and time stamp and with other patient data, e.g., patient activity level, and the associated parameter data is stored in IMD memory for retrieval at a later date employing conventional telemetry systems. Incremental changes in the parameter data over time, taking any associated time of day and patient data into account, provide a measure of the degree of change in the heart failure state of the heart.