Accelerometer-based rate-adaptive cardiac pacing with second generation signal processing

• US 5,649,968 A
• Filed: 11/14/1995
• Issued: 07/22/1997
• Est. Priority Date: 11/14/1995
• Status: Expired due to Term

• Current Assignee: Eckhard Alt
• Original Assignee: Intermedics Incorporated (Boston Scientific Corporation)
• Inventors: Schmidt, Matthias, Alt, Eckhard, Stotts, Lawrence J.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Evanisku, George R.
• Application Number:
  US08/557,204
• Time in Patent Office: 616 Days
• Field of Search: 607/4, 607/9, 607/17-19, 607/14, 607/25
• US Class Current: 607/19
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration

Abstract

A variable rate cardiac pacemaker is adapted to be implanted in a human patient for automatically adapting pacing rate to metabolic need of the patient when the patient is walking in an ascending path, a descending path, or on a level plane. An accelerometer senses the activity of the patient walking, and produces an electrical sensor signal representative of the activity. The accelerometer signal has variable parameters indicative of morphology, including amplitude, of the sensor signal according to status of activity of the patient and to the upward, downward, or horizontal direction of the patient'"'"'s walking. A pulse generator generates pacing pulses at a variable rate according to an applied control signal to electrically stimulate the patient'"'"'s heart at a pacing rate which varies according to patient activity. A processing and control circuit of the pacemaker processes the sensor signal for detecting differences in the signal morphology attributable to whether the patient is walking on an ascending path, a descending path, or a level path, irrespective of the presence or absence of disparity in the amplitude of the sensor signal resulting from walking along the respective path. The latter circuit also develops the control signal to dictate a basic pacing rate from the amplitude of the sensor signal, and an enhanced rate more appropriate to the metabolic need of the patient from the detected differences in morphology of the sensor signal, for application to the pulse generator.

Claims

1. A variable rate cardiac pacemaker adapted to be implanted in a human patient, for pacing the patient'"'"'s heart at a rate according to metabolic need of the patient when walking on a grade, the pacemaker comprising:

sensor means responsive to patient walking to produce an electrical sensor signal representative of activity of the patient during the walking, said sensor signal having variable signal parameters indicative of morphology of the sensor signal, said parameters including amplitude of the sensor signal, said morphology being representative of current state of activity of the patient and inclination of a grade on which the patient is walking corresponding respectively to an ascending, descending, or level path;

control means responsive to said sensor signal for processing thereof to detect amplitude of said sensor signal and differences in the morphology of said sensor signal attributable to the respective grade on which the patient is walking, to produce a control signal therefrom dictating a pacing rate representative of amplitude of the sensor signal modified according to any said difference detected in the morphology of the sensor signal;

said control means including

content means for establishing a baseline level for the sensor signal and weighting the sensor signal according to signal morphology differences attributable to the patient walking on said respective grades by measuring predetermined characteristics of content of the sensor signal above and below said baseline level; and

pulse generator means responsive to said control signal for generating pacing pulses at a variable rate according to patient activity, including differences in activity attributable to the patient walking on respective different grades, to be used for application to and electrical stimulation of the patient'"'"'s heart.

2. The rate adaptive cardiac pacemaker of claim 1, in which:

said sensor means is an accelerometer.

3. The rate adaptive cardiac peacemaker of claim 1, in which:

said baseline level is electrical zero.

4. The rate adaptive cardiac pacemaker of claim 1, in which:

said content means includes means for measuring and calculating a ratio of said predetermined characteristics of signal content above and below said baseline level.

5. The rate adaptive cardiac pacemaker of claim 1, in which:

said characteristics of content comprise respective areas beneath a curve of sensor signal excursions above and below said baseline level, and said content means includes means for determining and comparing said respective areas above and below said predetermined baseline level as said morphology differences indicative of said differences in activity attributable to the patient walking on respective different grades.

6. The rate adaptive cardiac pacemaker of claim 1, in which:

said characteristics of content comprise respective integrals of a curve of said sensor signal lying above and below said baseline level, and said content means includes means for integrating and comparing said integrals of the sensor signal above and below said predetermined baseline level as said morphology differences indicative of said differences in activity attributable to the patient walking on respective different grades.

7. The rate adaptive cardiac pacemaker of claim 1, in which:

said characteristics of content comprise respective amplitudes of said sensor signal above and below said baseline level, and said content means includes means for detecting and comparing respective amplitude of the sensor signal above and below said predetermined baseline level as said morphology differences indicative of said differences in activity attributable to the patient walking on respective different grades.

8. The rate adaptive cardiac pacemaker of claim 1, in which:

said characteristics of content comprise respective time intervals of said sensor signal successively above and below said baseline level, and said content means includes means for detecting and comparing successive time intervals during which the sensor signal remains above and below said predetermined baseline level as said morphology differences indicative of said differences in activity attributable to the patient walking on respective different grades.

9. The rate adaptive cardiac pacemaker of claim 1, in which:

said characteristics of content comprise zero crossings of said sensor signal relative to said baseline level, and said content means includes means for detecting successive zero crossings of the sensor signal relative to said predetermined baseline level as said morphology differences indicative of said differences in activity attributable to the patient walking on respective different grades.

10. The rate adaptive cardiac pacemaker of claim 9, in which:

said content means further includes means for detecting and calculating a ratio of time duration of said successive zero crossings in a positive direction and in a negative direction relative to said predetermined baseline level.

11. The rate adaptive cardiac pacemaker of claim 10, in which:

said content means includes means for calculating a quotient of the detected respective positive and negative zero crossings as said ratio.

12. A device-implemented method for rate-responsive pacing of a human patient'"'"'s heart to meet the metabolic needs of the patient when the patient is walking on a grade with an inclination constituting an ascending, descending, or level path, using a variable rate cardiac pacemaker adapted to be implanted in the patient, the method comprising the steps of:

sensing patient walking activity and responding thereto by producing an electrical sensor signal representative of such activity, said sensor signal having a pattern with variable parameters, including amplitude of the sensor signal, based on extent of patient activity including activity attributable to inclination of a grade on which the patient is walking;

generating pacing pulses at a controllably variable rate to electrically stimulate the patient'"'"'s heart at a pacing rate based on patient activity; and

processing said sensor signal to detect amplitude and pattern thereof and differences in the signal pattern attributable to extent of inclination of the respective grade on which the patient is walking, and controlling the rate of generation of the pacing pulses by establishing a basic pacing rate based on detected amplitude of the sensor signal, and deviating from said basic rate to provide a rate more appropriate to the metabolic needs of the patient based on detected differences in said signal pattern by establishing a baseline level and weighting the sensor signal according to a predetermined characteristic of content of said sensor signal above and below said baseline level as indicative of pacing rate variations required to accommodate activity level of the patient attributable to inclination of the grade on which the patient is walking.

13. The method of claim 12, in which:

said sensing of patient activity and responding thereto is performed by an accelerometer.

14. The method of claim 12, including:

establishing said baseline level as electrical zero.

15. A method of pacing the heart of a human patient using an implanted pacemaker device to automatically vary pacing rate according to whether the patient is engaged in types of activity characterized by walking up stairs, walking down stairs, or walking on a level surface, irrespective that intensity of the walking activity may be identical for all of said types of activity, comprising the device-implemented steps of:

sensing patient walking activity and producing an electrical sensor signal having an amplitude indicative of intensity thereof and a morphology that varies in at least one signal characteristic capable of distinguishing different ones among said types of the walking activity in which the patient is engaged;

establishing a baseline level of said sensor signal, and detecting variation of said at least one signal characteristic of the sensor signal morphology relative to said baseline level as indicating a specific one of said types of the patient'"'"'s walking activity;

generating pacing pulses at a variable rate for use in electrically stimulating the patient'"'"'s heart at a pacing rate that reflects metabolic need of the patient arising from walking activity; and

providing a base pacing rate at which said pacing pulses are generated in response to the amplitude of said sensor signal and modifying the base pacing rate by weighting the sensor signal wording to the variation of said at least one signal characteristic of the sensor signal morphology above and below said baseline level to generate pacing pulses at a rate which is appropriate for said specific one of said types of walking activity in which the patient is engaged.

16. The method of claim 15, in which:

said step of sensing patient activity is performed by an accelerometer.

17. The method of claim 15, in which:

said baseline level is electrical zero.