Fault-tolerant elective replacement indication for implantable medical device

• US 5,370,668 A
• Filed: 06/22/1993
• Issued: 12/06/1994
• Est. Priority Date: 06/22/1993
• Status: Expired due to Term

• Current Assignee: GADSON, GREGORY P., MS 301
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Schmidt, Craig L., Markowitz, H. Toby, Shelton, Michael B., Starkson, Ross O.
• Primary Examiner(s): MANUEL, GEORGE C
• Application Number:
  US08/081,746
• Time in Patent Office: 532 Days
• Field of Search: 607/27, 607/29, 607/34, 324/430
• US Class Current: 607/29
• CPC Class Codes: A61N 1/3708 for power depletion
• CPC Class Codes: A61N 1/378 Electrical supply
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

A pacemaker having a fault-tolerant elective replacement indicator (ERI) triggering scheme in which transient excursions of parameters used as criteria for triggering ERI are rejected as triggering events. Periodic assessments of certain indicia of battery depletion are made, and subjected to a long-term low-pass filtering operation in order to reduce the effects of transient excursions of the indicia which result from non-ERI conditions. Over a long period of time (e.g., a day) predetermined threshold values of the indicia of interest must be exceeded a predetermined number of times in order for the device to issue an ERI. In one disclosed embodiment of the invention, the battery'"'"'s loaded terminal voltage and internal impedance are used as indicators of the battery'"'"'s depletion level. Periodically, these values are measured and converted to digital values. The digital values are subjected to a low-pass filtering operation to prevent temporary or transient excursions of the impedance and voltage curves from causing ERI to be triggered. In another disclosed embodiment of the invention, a long term fading average of periodically measured values is maintained. When the measured values are found to fulfill the ERI criteria, assessment of the parameters of interest is performed at an increased rate. While assessments are performed at the increased rate, the continuously updated fading average value must fulfill the ERI triggering criteria at least a predetermined number of times before ERI is triggered. If the fading average fails to fulfill the ERI triggering criteria the required number of times, assessments are resumed at the first, slower periodic rate.

Claims

1. An implantable medical device, comprising:

a battery;

a monitoring circuit coupled to said battery and adapted to, at each predetermined test time during a predefined test period, assess a condition of said battery indicative of said battery'"'"'s depletion level and to periodically generate at least one signal reflecting said depletion level;

a comparison circuit, coupled to said monitoring circuit and responsive to said at least one signal to assert a comparison signal when said depletion level reflected by said at least one signal is less than a predetermined threshold level;

an accumulator circuit, coupled to said comparison circuit and responsive to assertion of said comparison signal to increment an accumulator value representing the number of times during each test period that said depletion level is less than said predetermined threshold level; and

a depletion indicator circuit, coupled to said accumulator circuit and adapted to assert a depletion indicator signal when said accumulator value exceeds a predetermined maximum, said depletion indicator circuit further adapted to periodically reset said accumulator value.

2. An implantable medical device in accordance with claim 1, wherein said condition indicative of said battery'"'"'s depletion level is said battery'"'"'s loaded terminal voltage.

3. An implantable medical device in accordance with claim 2, wherein said at least one signal comprises a binary digital value corresponding to said battery'"'"'s loaded terminal voltage.

4. An implantable medical device in accordance with claim 2, wherein said at least one signal comprises an analog voltage having a level corresponding to said battery'"'"'s loaded terminal voltage, and wherein said comparison circuit comprises an analog comparator.

5. An implantable medical device in accordance with claim 1, wherein said condition indicative of said battery'"'"'s depletion level is said battery'"'"'s internal impedance.