Rate adaptive pacemaker controlled by ejection fraction

Claim 2

A rate adaptive cardiac pacemaker comprising, in combination: (a) a pulse generator having timing means for establishing the rate at which cardiac stimulating pulses are produced; (b) means for applying said stimulating pulses to cardiac tissue; (c) means for developing a control signal proportional to at least one of residual fraction and ejection fraction of the heart; and (d) means for applying said control signal to said timing means for varying the rate at which said cardiac stimulating pulses are produced as a function of the heart's contractility.

Claim 3

The rate adaptive cardiac pacemaker as in claim 1 wherein said means for developing a control signal proportional to the ejection fraction of the heart comprises: (a) means for developing a first signal proportional to the stroke volume of the heart; (b) means for developing a second signal proportional to the end-diastolic volume of the heart; and (c) means for producing said control signal as the ratio of said first signal to said second signal; (d) means for compensation of non linearity between changes of end-diastolic volumes and end-systolic volumes when metabolic demand is stable.

Claim 4

The rate adaptive cardiac pacemaker as in claim 2 wherein said means for developing said first and second signals includes intracardiac impedance sensing means.

Claim 5

The rate adaptive cardiac pacemaker as in claim 3 wherein said intracardiac impedance sensing means includes: (a) means for applying an alternating current carrier voltage of a predetermined frequency between two spaced points in the heart; and (b) means for sensing instantaneous changes in amplitude of said alternating current carrier voltage due to systolic activity of the heart.

Claim 6

The rate adaptive cardiac pacemaker as in claim 4 wherein said means for developing said first signal includes: (a) means for computing the difference between the maximum and minimum amplitude excursions of said alternating current carrier voltage.

Claim 7

The rate adaptive cardiac pacemaker as in claim 4 wherein said means for developing said second signal includes: (a) means for measuring the minimum amplitude excursions of said alternating current carrier voltage.

Claim 8

The rate adaptive cardiac pacemaker as in claim 1 wherein said means for developing a control signal proportional to residual fraction includes: (a) means for developing a first signal proportional to end-systolic volume of the heart; (b) means for developing a second signal proportional to the end-diastolic volume of the heart; and (c) means for dividing said first signal by said second signal.

Claim 9

A rate adaptive pacemaker comprising, in combination: (a) an electronic pulse generator having variable timing means for determining the rate at which cardiac stimulating pulses are produced; (b) means for applying said pulses to the heart; (c) means for sensing intracardiac impedance variations occasioned by systolic events; (d) means responsive to said means for sensing intracardiac impedance for computing the ejection fraction of the heart; and (e) means for adjusting said timing means in relation to the computed ejection fraction.

Claim 10

A rate adaptive pacemaker comprising, in combination: (a) an electronic pulse generator having variable timing means for determining the rate at which cardiac stimulating pulses are produced; (b) means for applying said pulses to the heart; (c) means for sensing intracardiac impedance variations occasioned by systolic events; (d) means responsive to said means for sensing intracardiac impedance for computing the ejection fraction of the heart; and (e) means for adjusting said timing means in relation to the computed ejection fraction.

Claim 11

The rate adaptive pacemaker as in claim 8 wherein said means for computing ejection fraction comprises: (a) means for sampling the amplitude of the intracardiac impedance upon the occurrence of an R-wave or a cardiac stimulating pulse in the absence of an R-wave to establish end-diastolic volume (EDV); (b) means for at least temporarily storing a EDV value proportional to the sampled amplitude; (c) means for sampling the amplitude of the intracardiac impedance at a predetermined time following the occurrence of the R-wave or cardiac stimulating pulse to establish an end-systolic volume value (ESV); (d) means for subtracting the ESV value from the stored value to determine stroke volume value (SV); and (e) means for dividing the SV value by the EDV value.

Claim 12

The rate adaptive pacemaker as in claim 8 wherein said means for computing ejection fraction comprises: (a) means for sampling the minimum excursion of said intracardiac impedance variation to establish end-diastolic value (EDV); (b) means for temporarily storing the EDV value; (c) means for sampling the maximum excursion of said intracardiac impedance variation to establish an end-systolic volume value (ESV); (d) means for temporarily storing the ESV value; and (e) means for computing the ratio (ESV - EDV)/EDV.