Implantable cardiac stimulation device and method for self-regulating sampling of measured parameters

• US 6,366,812 B1
• Filed: 03/24/2000
• Issued: 04/02/2002
• Est. Priority Date: 12/14/1998
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Levine, Paul A., Weinberg, Lisa P.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US09/534,958
• Time in Patent Office: 739 Days
• Field of Search: 607/27, 607/28, 607/9, 607/5
• US Class Current: 607/27
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold
• CPC Class Codes: G16H 40/67 for remote operation

Abstract

An implantable cardiac device, such as a pacemaker or an implantable cardioverter-defibrillator that has a control unit which is adapted to sample a time-varying parameter relating to either the patient'"'"'s changing physiological condition or to the delivery of therapeutic electrical stimulation pulse to the heart at a sampling frequency. The control unit is adapted to increase the sampling frequency when the variation between successive measurements of the parameter exceed a preselected value. The control unit is further adapted to decrease the sampling frequency when the variation between successive measurements of the parameter are less than a preselected value. In alternate embodiments, the parameter to be sampled is capture threshold, sensing threshold, lead-tissue impedance, and battery performance.

Claims

1. An implantable cardiac stimulation device having pulse generating means for delivering stimulation pulses to the heart of a patient, the device comprising:

measuring means for measuring a parameter having a volatile value which varies over time relating to the delivery of therapeutic electrical stimulation, and for providing an output signal representative thereof; and

processing means for triggering the measuring means to measure the output signals at a variable rate, wherein the processing means determines the variable rate based on a comparison between a current output signal and a previous output signal so that the output signal is measured at a greater frequency when the parameter value is volatile and at a lesser frequency when the parameter value remains stable.

2. The device of claim 1, wherein the processing means comprises:

means for increasing the measuring rate when the difference between the magnitude of a current output signal and a previous output signal is greater than a preselected value.

3. The device of claim 2, wherein the processing means comprises:

means for decreasing the measuring rate when the difference between the magnitude of a current output signal and a previous output signal is less than the preselected value.

4. The device of claim 1, further comprising:

storage means for storing the measured output signals at the variable rate so that the output signal is stored at a greater frequency when the parameter value is volatile and at a lesser frequency when the parameter value remains stable; and

telemetry means for transferring the stored output signals from the storage means to an external programmer having a display screen capable of displaying the output signals as a function of time.

5. The device of claim 1, wherein the processing means comprises:

means for triggering the measuring means to measure the output signals at a first predetermined frequency when the parameter value is volatile, and at a frequency less than the first predetermined frequency when the difference between the current output signal and the previous output signal is less than a preselected amount.

6. The device of claim 1, wherein the processing means comprises:

means for triggering the measuring means to measure the output signals at a first predetermined frequency when the parameter value is stable, and at a frequency greater than the first predetermined frequency when the difference between the current output signal and the previous output signal is greater than a preselected amount.

7. The device of claim 1, further comprising impedance measuring means coupled to the pulse generating means, the device being coupled to an implantable lead which delivers the stimulation pulses to the heart, wherein:

the parameter comprises a lead-tissue impedance of the patient'"'"'s heart;

the processor comprises means for triggering the impedance measuring means to measure at least one of voltage or current delivered to the lead during a stimulation pulse, and for computing the impedance thereof; and

the output signal comprises the value of the computed impedance.

8. The device of claim 1, further comprising a battery which powers the device, and battery measuring means for measuring battery capacity of the battery, wherein:

the parameter comprises a battery capacity;

the processor comprises means for triggering the battery measuring means to measure at least one of voltage, current, or impedance of the battery, and for computing the battery capacity thereof; and

the output signal comprises at least one of the voltage, current, impedance, or the value of the computed battery capacity.

9. The device of claim 1, further comprising sensing means having programmable sensitivities, wherein:

the parameter comprises a sensing threshold of the patient'"'"'s cardiac signal;

the processor comprises means for triggering the sensing means to sequentially decrease the sensitivity of the sensing means until sensing of the cardiac signal is lost; and

the output signal comprises the lowest sensitivity that detects the patient'"'"'s cardiac signal.

10. The device of claim 1, wherein:

the parameter comprises capture threshold of the patient'"'"'s heart;

the processor comprises means for triggering the pulse generating means to provide a series of stimulation pulses of decreasing magnitude to the heart until capture is lost; and

the output signal comprises the smallest magnitude of stimulation pulse delivered to the patient'"'"'s heart that evoked capture.

11. An implantable cardiac stimulation device for delivering stimulation pulses to the heart of a patient, the device comprising:

a sensor which senses a first parameter having a volatile value which varies over time relating to at least one of the patient'"'"'s physiologic condition or the delivery of stimulation pulses, and provides an output signal indicative thereof;

a memory adapted to store data corresponding to the output signal provided by the sensor; and

a processor which triggers the memory to store the output signal according to an adjustable recordation frequency, wherein the processor adjusts the recordation frequency based upon the volatility of the first parameter.

12. The device of claim 11, wherein the processor compares a first signal received from the sensor to a second signal that was previously received from the sensor to adjust the recordation frequency based upon the volatility of the first parameter.

13. The device of claim 12, wherein the processor increases the recordation frequency when the difference between the first signal and the second signal exceed a preselected value.

14. The device of claim 13, wherein the processor decreases the recordation frequency when the difference between the first signal and the second signal is less than the preselected value.

15. The device of claim 14, wherein the processor triggers the memory to record data corresponding to the output signal at a first frequency.

16. The device of claim 15, wherein the processor is further adapted to trigger the memory to record additional output signals at a second frequency when the additional output signals change more than a preselected amount from a first value.

17. The device of claim 11, wherein:

the first parameter comprises at least one of lead-tissue impedance of the patient'"'"'s heart, a capture threshold, a sensing threshold, battery capacity, and the need for an automatic test to be performed.

18. A method of recording data in a memory of an implantable cardiac device, the method comprising:

measuring a time-varying parameter representative of a parameter having a volatile value which varies over an extended period of time and relating to at least one of the patient'"'"'s physiologic condition or the delivery of stimulation pulses;

sampling the measured signal at a sampling frequency; and

adjusting the sampling frequency based upon the volatility of the signal so that the parameter is sampled at a greater frequency when the parameter is volatile and at a lesser frequency when the parameter remains stable.

19. The method of claim 18, wherein the step of adjusting the sampling frequency based upon the volatility of the parameter comprises the step of:

comparing a current measured signal with a previously measured signal; and

increasing the sampling frequency when the difference between the current measured signal and the previously measured signal exceeds a preselected value.

20. The method of claim 19, wherein the step of adjusting the sampling frequency based upon the volatility of the parameter further comprises the step of:

decreasing the sampling frequency when the difference between the current measured signal and the previously measured signal is less than the preselected value.

21. The method of claim 20, further comprising the step of:

recording data corresponding to the measured signals that are stable into the memory at a first frequency; and

recording data corresponding to the measured signals that are volatile in the memory at a frequency greater than the first frequency when the difference between a current measured signal and a previously measured signal is greater than a preselected amount.

22. The method of claim 20, further comprising the step of:

recording data corresponding to the measured signals that are volatile into the memory at a first frequency; and

recording data corresponding to the measured signals that are stable in the memory at a frequency less than the first frequency when the difference between a current measured signal and a previously measured signal is less than a preselected amount.

23. The method of claim 19, further comprising the step of:

recording data corresponding to the measured signals in the memory at the adjusted sampling frequency.

24. The method of claim 23, further comprising the step of:

providing the data recorded in the memory to an external source for subsequent display of the data as a function of time.