Rate responsive cardiac pacemaker and method for work-modulating pacing rate deceleration

• US 5,312,453 A
• Filed: 05/11/1992
• Issued: 05/17/1994
• Est. Priority Date: 05/11/1992
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Tollinger, Michael R., Combs, William J., Bennett, Tommy D., Shelton, Michael B., Riff, Kenneth M.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): Parker, Marianne
• Application Number:
  US07/880,877
• Time in Patent Office: 736 Days
• Field of Search: 128/419 PG, 607/19-26
• US Class Current: 607/19
• CPC Class Codes: A61N 1/36514 controlled by a physiological quantity other than heart potential, e.g. blood pressure controlled by two or more physical parameters A61N1/36585

Abstract

A rate-responsive cardiac pacemaker in which deceleration of the pacing rate is modulated according to recent patient activity or "work". Based on signals provided from an activity sensor in the pacemaker, the pacemaker maintains and periodically recomputes a work value corresponding to the amount of patient activity detected over time. In response to a decrease in or cessation of detected patient activity, the pacemaker reduces the pacing rate, first at a more rapid deceleration rate, then at a lower deceleration rate, and then once again at a more rapid deceleration rate. The length of time during which the pacing rate is reduced at the lower deceleration rate is modulated according to the work value maintained by the pacemaker. The work-modulated pacing rate deceleration occurs only if certain achievement criteria are met, the achievement criteria being specified in terms of the amount of time the pacemaker'"'"'s target pacing rate exceeds a predetermines rest value, and the difference between the target rate and the rest rate.

Claims

1. A method of operating a rate-responsive cardiac pacemaker, wherein said pacemaker is responsive to a change in a patient'"'"'s level of activity to vary a pacing delivery rate, comprising the steps of:

(a) detecting when said patient'"'"'s level of activity over time exceeds a predetermined level;

(b) quantifying said excess of detected patient level of activity;

(c) associating at least one work value with said quantification;

(d) increasing the pacing delivery rate in response to said work value;

(e) detecting when said patient'"'"'s level of activity returns to said predetermined level; and

(f) decreasing the pacing delivery rate along a deceleration curve that is modulated according to said at least one work value.

2. A rate responsive cardiac pacemaker comprising:

an activity sensor producing an activity signal indicative of detected levels of a patient'"'"'s activity;

processing means, coupled to the activity sensor, responsive to said activity signal to compute a pacing rate and a work value, said work value comprising a quantification of the patient'"'"'s activity over time;

a pulse generator, coupled to said processing means, for producing stimulating pulses at said computed pacing rate;

a pacing lead means, coupled to said pulse generator, for delivering said stimulating pulses to a patient'"'"'s heart; and

means for modulating deceleration of said pacing rate according to said work value.

3. An implantable, rate-responsive cardiac pacemaker, comprising:

a pulse generator, for generating cardiac stimulating pulses;

a pacing lead, coupled to said pulse generator and adapted to convey said stimulating pulses to a patient'"'"'s heart;

a piezoelectric activity sensor, adapted to be coupled to a patient and responsive to patient motion to produce an activity signal;

an activity circuit, coupled to said activity sensor and said pulse generator, and responsive to said activity signal to produce a stream of activity pulses;

an activity pulse counting circuit, coupled to said activity circuit and adapted to periodically compute an activity count value corresponding to a number of activity pulses produced by said activity circuit during a predetermined time interval;

a target rate computing circuit, coupled to said counting circuit and adapted to periodically compute a target pacing rate value proportional to said activity count value;

a work computing circuit, coupled to said rate computing circuit and adapted to periodically compute a work value that is proportional to excesses of previously computed target pacing rate values over a predetermined threshold value; and

a pacing rate computing circuit, coupled to said target rate computing circuit and to said work computing circuit, and adapted to periodically derive a pacing rate value from said target rate value and said work value;

wherein said pacing rate computing circuit is adapted to vary a rate of decrease in said pacing rate value in an inversely proportional relationship to said work value.

4. A method of controlling a pacing rate of a cardiac pacemaker comprising the steps of:

(a) setting said pacing rate to an initial rate;

(b) increasing said pacing rate from said initial rate to a first target rate along a predetermined acceleration curve;

(c) associating a work value with said increase in pacing rate; and

(d) decreasing said pacing rate from said first target rate along a deceleration curve having a plurality of phases with different deceleration rates, at least one of said plurality of phases having a duration modulated by said work value.

5. The method of claim 4, wherein the step of associating includes associating the work value such that said work value is proportional to a time interval during which said first target rate exceeds a predetermined rest rate, and proportional to a margin between said pacing rate and said predetermined rest rate during said time interval.