Pacemaker and method for ventricular rate limit operation and termination of pacemaker mediated tachycardia

• US 4,712,556 A
• Filed: 09/25/1985
• Issued: 12/15/1987
• Est. Priority Date: 11/22/1982
• Status: Expired due to Term

• Current Assignee: Intermedics Incorporated
• Original Assignee: Intermedics Incorporated
• Inventors: Baker, Ross G. Jr.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/780,702
• Time in Patent Office: 811 Days
• Field of Search: 128/419 PG, 128/419 PT
• US Class Current: 607/14
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions

Abstract

A microprocessor-controlled pacemaker is programmed to extend an atrial refractory interval in response to the detection of events which could initiate a pacer sustained tachycardia. The extended atrial refractory interval ensures that a spurious atrial event resulting from retrograde conduction of a ventricle event will not cause a pace of the ventricle. The pacer is also programmed to break out of a pacer sustained tachycardia by inhibiting a ventricular pace when a predefined number of previous successive ventricular paces have occurred at the ventricular rate limit. The pacer is further programmed so that in response to a high atrial rate, the ventricle is paced at either a predefined ventricular upper rate limit value or at a rate limit value that is decremented to a fallback rate limit value. The pacer further increases the VA interval when the ventricle is paced at the ventricular rate limit. The pacer is also programmed to show Wenckebach behavior and thereby occasionally drop a ventricular pace in response to an atrial rate that exceeds the ventricular rate limit. The pacer resets the defined ventricular rate limit to an upper rate limit value when two successive ventricular paces are provided at a rate less than the defined ventricular rate limit. A nonphysiological interval is defined after an atrial pace. If a ventricular event is detected during the nonphysiological interval, the ventricle is paced at a predefined time period following the initiating atrial event.

Claims

1. A heart pacemaker, comprising:

means for sensing electrical events that occur in the atrium of a heart;

means for sensing electrical events that occur in the ventricle of the heart;

means for selecting an atrial refractory period;

means for timing said atrial refractory period from detected electrical events of the ventricle;

means for pacing the ventricle of the heart in synchronism with atrial events detected outside said atrial refractory period;

means for selecting a value of a ventricular rate limit that defines the maximum rate at which the ventricle can be paced;

said means for pacing the ventricle including means for pacing the ventricle at a rate that does not exceed said value of the ventricular rate limit;

means for counting a preselected number of successive atrial synchronous paces of the ventricle at the ventricular rate limit; and

means for preventing a pace of the ventricle in response to an atrial event sensed outside said atrial refractory period and after said preselected number of successive atrial synchronous paces of the ventricle is counted.

2. The pacemaker of claim 1, wherein said means for selecting a value for a ventricular rate limit includes:

means for selecting an upper rate limit value for a pacing rate;

means for selecting a fallback rate limit value for a pacing rate, the pacing rate defined by the fallback value being less than the pacing rate defined by the upper rate limit value;

means for setting the ventricular rate limit equal to the upper rate limit value; and

means for decrementing the ventricular rate limit thus defined to the fallback rate limit value by a predefined amount after each ventricular pace which occurs at the then defined ventricular rate limit.

3. The pacemaker of claim 2, including means for setting the ventricular rate limit equal to the upper rate limit value when at least two successive ventricular paces or sense events occur at a rate less than the then defined ventricular rate limit.

4. The pacemaker of claim 1, wherein said preselected number is equal to 15.

5. The pacemaker of claim 1, further including:

means for preventing a pace of the ventricle in response to an atrial event occurring during the atrial refractory period, so that a ventricular pace is periodically dropped;

means for selecting a VA time period;

means for timing the VA time period from a sensed or paced ventricular event;

means for pacing the atrium at the end of said VA time period if an atrial event is not sensed within said VA time period; and

means for increasing the VA time period by a predefined amount when the ventricle is paced at said ventricular rate limit to increase the chance of detecting an atrial event following said periodically dropped ventricular pace.

6. The pacemaker of claim 5, wherein said predefined amount is 300 milliseconds.

7. The pacemaker of claim 1, further including:

means for selecting an artifact sensing interval;

means for timing the interval from a predetermined time after an electrical event is sensed in the atrium;

said means for pacing including means for pacing the ventricle in response to at least one electrical event sensed in the ventricle during the artifact sensing interval.

8. The pacemaker of claim 7, wherein said means for pacing includes means for pacing the ventricle at the end of said artifact sensing interval, when at least one ventricular event is sensed during the interval.

9. The pacemaker of claim 7, wherein said means for pacing includes means for pacing the ventricle at a predefined time after the end of the artifact sensing interval when at least one ventricular event is sensed during the interval.

10. The pacemaker of claim 1, further including:

means for preventing a ventricular pace in response to electrical events occurring in the atrium during the atrial refractory period, so that a ventricular pace is periodically dropped.

11. The pacemaker of claim 10, wherein said means for selecting a value of a ventricular rate limit includes:

means for selecting an upper rate limit value for a pacing rate;

means for selecting a fallback rate limit value for a pacing rate, the pacing rate defined by the fallback value being less than the pacing rate defined by the upper rate limit value;

means for setting the ventricular rate limit equal to the upper rate limit value; and

means for decrementing the ventricular rate limit thus defined to the fallback rate limit value by a predefined amount after each ventricular pace which occurs at the then defined ventricular rate limit.

12. A heart pacemaker, comprising:

means for detecting electrical events in the atrium of a heart;

means for selecting a ventricular rate limit;

means for pacing the ventricle of the heart in synchronism with detected atrial events at a rate that does not exceed said ventricular rate limit;

means for defining a preselected VA interval when said ventricle is paced at a rate less than said ventricular rate limit;

means for defining an increased VA interval when said ventricle is paced at said ventricular rate limit; and

means for timing the VA interval following each pace of the ventricle.

13. The pacemaker of claim 12, further including:

means for counting successive paces of the ventricle at the ventricular rate limit; and

means for inhibiting a pace of the ventricle when the number of successive ventricular paces at the ventricular rate limit is equal to a predefined value.

14. The pacemaker of claim 12, further including:

means for selecting an artifact sensing interval;

means for timing the interval from a predetermined time after an electrical event is sensed in the atrium; and

means for sensing electrical events in the ventricle of the heart during said artifact sensing interval;

said means for pacing including means for pacing the ventricle when at least one electrical event is sensed in the ventricle during the artifact sensing interval.

15. The pacemaker of claim 14, wherein said means for pacing includes means for pacing the ventricle at the end of said artifact sensing interval, when at least one ventricular event is sensed during the interval.

16. The pacemaker of claim 14, wherein said means for pacing includes means for pacing the ventricle at a predefined time after the end of the artifact sensing interval when at least one ventricular signal is sensed during the interval.

17. A method for operating a pacemaker to avoid pacemaker sustained tachycardia, comprising the steps of:

selecting an atrial refractory interval;

sensing electrical events in the ventricle of the heart;

timing the atrial refractory interval from sensed ventricular events;

selecting an AV delay interval;

sensing an electrical event in the atrium of the heart outside said atrial refractory interval;

timing out said AV delay interval from the sensed atrial event;

selecting a value for a ventricular rate limit;

pacing the ventricle at the end of the AV delay interval if no ventricular event is sensed during the AV delay interval and if the pace will not exceed the defined ventricular rate limit;

pacing the ventricle at the ventricular rate limit if a pace at the end of the AV delay interval would exceed the ventricular rate limit;

counting successive paces of the ventricle at the ventricular rate limit;

identifying a pacemaker sustained tachycardia condition by detecting a predefined number of successive ventricular paces at the ventricular rate limit; and

inhibiting a pace of the ventricle and thereby terminating the pacemaker sustained tachycardia when the pacemaker sustained tachycardia condition is detected.

18. The method of claim 17, wherein said step of selecting an AV delay interval includes the steps of:

selecting a blanking period;

selecting an artifact sensing period; and

selecting a ventricular pacing period;

said step of timing the AV delay interval includes the steps of;

timing said blanking period when an electrical event is sensed in the atrium outside said atrial refractory interval;

timing said artifact sensing period from the end of said blanking period;

timing said ventricular pacing period from the end of said artifact sensing period; and

pacing the ventricle at the end of the ventricular pacing period if an event is sensed in the ventricle during the artifact sensing period.

25. The pacemaker of claim 18, including means for setting said preselected number equal to fifteen.

19. A method for operating a pacemaker to avoid a pacemaker sustained tachycardia, comprising the steps of:

selecting a value for a ventricular rate limit;

sensing electrical events in the ventricle of the heart;

sensing electrical events in the atrium of the heart;

timing out a predefined AV delay interval from each sensed atrial event;

pacing the ventricle at the end of the AV delay interval if no ventricular event is sensed during the AV delay interval and if the pace will not exceed the defined ventricular rate limit;

pacing the ventricle at the ventricular rate limit if a pace at the end of the AV delay interval would exceed the ventricular rate limit;

selecting a VA time period when the ventricle is paced at less than the ventricular rate limit;

increasing the VA time period by a preselected amount when the ventricle is paced at the ventricular rate limit;

timing the VA time period from a sensed or paced ventricular event; and

pacing the atrium if an atrial event is not sensed within the VA time period.

20. The method of claim 19, further including the steps of:

selecting an upper rate limit value for a pacing rate;

setting the ventricular rate limit equal to the selected upper rate limit value;

reducing the ventricular rate limit by a predefined amount each time that a pace of the ventricle occurs at the then defined ventricular rate limit; and

setting the ventricular rate limit equal to the upper rate limit value when at least two successive ventricular pace or sense events occur at a rate less than the then defined ventricular rate limit.

21. A pacemaker for sensing electrical events in the atrium and ventricle of a heart and pacing the heart, comprising:

means for sensing electrical events in the atrium;

means for sensing electrical events in the ventricle;

means for selecting an artifact sensing interval;

means for timing the interval from a predetermined start time after an electrical event is sensed in the atrium; and

means for pacing the ventricle at a predefined time after the end of the artifact sensing interval when at least one ventricular event is sensed during the artifact sensing interval.

22. The pacemaker of claim 21, including means for defining a blanking interval immediately following a sensed atrial event and for preventing the sensing of ventricular events during the blanking interval, the end of the blanking interval defining said start time for timing the artifact sensing interval.

23. A method for operating a pacemaker, comprising the steps of:

sensing atrial and ventricular events;

timing at least one predefined blanking interval from a sensed atrial event;

preventing the sensing of ventricular events during the timing of the blanking interval;

timing a predefined artifact sensing interval from the end of the blanking interval; and

pacing the ventricle at a predefined time after the end of the artifact sensing interval when at least one ventricular event is sensed during the artifact sensing interval.

24. A pacemaker for preventing a pacemaker sustained tachycardia, comprising:

means for sensing electrical signals of the ventricle of a heart;

means for timing a preselected atrial refractory interval after sensing a ventricular signal;

means for sensing electrical signals of the atrium of the heart;

means for pacing the ventricle in synchronism with atrial signals that occur outside said atrial refractory interval;

means for detecting a condition indicative of a pacemaker sustained tachycardia; and

means for inhibiting a pace of the ventricle to terminate the detected pacemaker sustained tachycardia.

26. The pacemaker of claim 24, further including means for selecting a value of a ventricular rate limit which defines the maximum rate at which the ventricle can be paced, said means for pacing including means for preventing an atrial synchronous pace of the ventricle and instead pacing the ventricle at a rate equal to the ventricular rate limit if an atrial synchronous pace would exceed said ventricular rate limit.

27. The pacemaker of claim 26, wherein said means for detecting includes means for counting a preselected number of successive paces of the ventricle that occur at said ventricular rate limit.

28. The pacemaker of claim 26, wherein said means for selecting a value of a ventricular rate limit includes:

means for selecting an upper rate limit value for a pacing rate;

means for selecting a fallback rate limit value for a pacing rate, the pacing rate defined by the fallback value being less than the pacing rate defined by the upper rate limit value;

means for setting the ventricular rate limit equal to the upper rate limit value; and

means for decrementing the ventricular rate limit thus defined by a predefined amount after each ventricular pace that occurs at the then defined ventricular rate limit.

29. The pacemaker of claim 28, including means for setting the ventricular rate limit equal to the upper rate limit value when at least two successive ventricular paces or sensed ventricular signals occur at a rate less than the then defined ventricular rate limit.

30. The pacemaker of claim 26, further including means for selecting a nominal value for a VA time period;

means for timing the nominal VA time period from ventricular events that occur at less than the ventricular rate limit; and

means for increasing the VA time period by a predefined amount when the ventricle is paced at said ventricular rate limit;

said means for timing including means for timing the increased VA interval from the ventricular pace at the ventricular rate limit.

31. The pacemaker of claim 30, wherein said predefined amount is 300 milliseconds.

32. The pacemaker of claim 24, further including:

means for selecting an artifact sensing interval;

means for timing the interval from a predetermined time after an atrial signal is sensed;

said means for pacing including means for pacing the ventricle in response to at least one ventricular signal sensed during the artifact sensing interval.

33. The pacemaker of claim 32, wherein said pacing means includes means for pacing the ventricle at the end of said artifact sensing interval, when a ventricular signal is sensed during the interval.

34. The pacemaker of claim 32, wherein said pacing means includes means for pacing the ventricle at a predefined time after the end of the artifact sensing interval when at least one ventricular signal is sensed during the artifact sensing interval.

35. The pacemaker of claim 24, wherein said means for detecting includes means for defining a pacemaker sustained tachycardia recognition rate and means for counting a preselected number of successive paces of the ventricle that occur at a rate that is at least equal to said pacemaker sustained tachycardia recognition rate.

36. A heart pacemaker, comprising:

means for detecting electrical events that occur in the atrium of a heart;

means for detecting electrical events that occur in the ventricle of the heart;

means for selecting an atrial refractory period;

means for timing said atrial refractory period from detected electrical events of the ventricle;

means for pacing the ventricle of the heart in synchronism with atrial events detected outside said atrial refractory period;

means for selecting a value of a ventricular rate limit that defines the maximum rate at which the ventricle can be paced;

said means for pacing the ventricle including means for pacing the ventricle at a rate that does not exceed said value of the ventricular rate limit;

means for selecting a VA time period when the ventricle is paced at a rate less than the ventricular rate limit;

means for increasing the VA time period by a predefined amount when the ventricle is paced at said ventricular rate limit;

means for timing the VA time period from detected ventricular events; and

means for pacing the atrium at the end of said VA time period if an atrial event is not detected within said VA time period.

37. A heart pacemaker, comprising:

means for detecting electrical events that occur in the atrium of a heart;

means for detecting electrical events that occur in the ventricle of the heart;

means for selecting an atrial refractory period;

means for timing said atrial refractory period from detected electrical events of the ventricle;

means for pacing the ventricle of the heart in synchronism with atrial events detected outside said atrial refractory period;

means for selecting a value of a ventricular rate limit that defines the maximum rate at which the ventricle can be paced;

said means for pacing the ventricle including means for pacing the ventricle at a rate that does not exceed said value of the ventricular rate limit;

means for counting a preselected number of successive atrial synchronous paces of the ventricle at the ventricular rate limit;

means for preventing a pace of the ventricle in response to an atrial event detected outside said atrial refractory period and after said preselected number of successive atrial synchronous paces of the ventricle is counted;

means for selecting a VA time period when the ventricle is paced at a rate less than the ventricular rate limit;

means for increasing the VA time period by a predefined amount when the ventricle is paced at said ventricular rate limit;

means for timing the VA time period from detected ventricular events; and

means for pacing the atrium at the end of said VA time period if an atrial event is not detected within said VA time period.

38. A method for operating a heart pacemaker, comprising the steps of:

sensing electrical events in the atrium of a heart;

selecting a blanking period;

selecting an artifact sensing period;

successively timing said blanking period and artifact sensing period after sensing an electrical event in the atrium;

sensing electrical events in the ventricle of the heart during said artifact sensing period; and

pacing the ventricle at a predefined time after the end of said artifact sensing period if at least one event is sensed in the ventricle during the artifact sensing period.