System and method of AV interval selection in an implantable medical device

• US 20070093872A1
• Filed: 10/25/2005
• Published: 04/26/2007
• Est. Priority Date: 10/25/2005
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Chirife, Raul, Lundstrom, Russell, Combs, William
• Granted Patent: US 7,769,449 B2
• Time in Patent Office: Days
• US Class Current: 607/9
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371

Abstract

An implantable medical device provides ventricular pacing capabilities and optimizes AV intervals for multiple purposes. In general, intrinsic conduction is promoted by determining when electromechanical systole (EMS) ends and setting an AV interval accordingly. EMS is determined utilizing various data including QT interval, sensor input, and algorithmic calculations.

Claims

1. An implantable medical device (IMD) comprising:

a processor;

a memory coupled with the processor;

means for generating pacing stimuli;

means for computing a current electromechanical systole (EMS) value from an algorithm that proportionally reduces a resting EMS (EMSr) value stored in the memory based upon a current cycle length (CL); and

means for determining an AV value equal to a current cycle length minus the current EMS value.

2. The IMD of claim 1, wherein the current EMS value is equal to:

EMSr−

(CLr−

CL)×

P), where CLr is a resting cycle length and P is a correction factor.

3. The IMD of claim 2, wherein P is a value between 0.2 and 0.25.

4. The IMD of claim 2, wherein P equals 0.22.

5. The IMD of claim 2, wherein the means for computing utilizes the EMS value for sensed ventricular events and uses an EMSp value for paced ventricular events, wherein EMSP is equal to the EMS+IVD, where IVD is a value for interventricular conduction delay.

6. The IMD of claim 5, wherein the means for determining the AV value determines a SAV value when atrial events are sensed and a PAV value when atrial pacing occurs.

7. The IMD of claim 6, wherein the SAV=CL−

EMS+IAEMDs−

PSO, where the IAEMDs is a value for interatrial electromechanical conduction delay resulting from sensed atrial events and the PSO is a value for a P wave sense offset and the PAV=CL−

EMSp+IAEMDP, where IAEMDP is a value for interatrial electromechanical conduction delay resulting from paced atrial events.

8. The IMD of claim 7, further comprising:

means for comparing the CL to an Activities of Daily Living (ADL) rate; and

means for providing a normalized AV interval that is less than the SAV or PAV when the CL is greater than the ADL rate.

9. The IMD of claim 8, wherein the normalized AV interval includes a SAVnorm value for sensed atrial events, the SAVnorm equals IAEMDs−

PSO−

IVD+MNV, wherein MNV is a mean normal value for left side mechanical AV intervals, and PAVnorm for paced atrial events, the PAVnorm=MNV+IAEMDp−

IVD.

10. The IMD of claim 9, wherein the MNV equals is a value between 65 and 105 ms.

11. A method comprising:

measuring a resting electromechanical systole (EMSr) value at a resting heart rate (CLr);

calculating a current EMS value (EMSs) based upon a reduction from the EMSr of a proportional value of a difference between the CLr and a current heart rate (CL); and

setting a current AV interval in an implantable medical device having pacing capabilities, wherein the AV interval is equal to the Cl−

EMSs.

12. The method of claim 11, further comprising calculating a current EMS value for ventricular pacing events (EMSp), wherein EMSp=EMSs+IVD where IVD is a value for interventricular conduction delay.

13. The method of claim 12, wherein the current AV interval includes a SAV value when atrial events are sensed and a PAV value when atrial pacing occurs and the SAV=CL−

EMSs+IAEMDs−

PSO, where IAEMDs is a value for interatrial electromechanical delay for sensed atrial events and PSO is a value for a P wave sense offset and the PAV=CL−

EMSp+IAEMDp where the IAEMDp is a value for interatrial electromechanical conduction delay for paced events.

14. The method of claim 11 wherein the proportional value is 0.22

15. A method for setting operating parameters for an implantable medical device (IMD) having pacing capabilities, the method comprising:

initializing a set of parameters, the parameters including;

a current heart rate (CL)

a resting heart rate (CLr);

a measured resting electromechanical systole (EMSr);

sensed electromechanical systole (EMSs), where EMSs=EMSr−

((CLr−

CL)×

P) where P is a proportionality constant;

paced electromechanical systole (EMSp), where EMSp=EMSs+IVD where IVD is the interventricular conduction delay;

a non encroaching AV interval for cardiac cycles having sensed atrial events (SAVmax), where SAVmax=CL−

EMSs+IAEMDs−

PSO where IAEMDs is a value for interatrial electromechanical conduction delay for intrinsic atrial events and PSO is a value for a P wave sense offset;

a non-encroaching AV interval for cardiac cycles having paced atrial events (PAVmax), where PAVmax=CL−

EMSP+IAEMDp where IAEMDp is a value for interatrial electromechanical conduction delay for paced atrial events;

setting an AV interval of the IMD to SAVmax for cardiac cycles having sensed atrial events and PAVmax for cardiac cycles having paced atrial events;

initiating the AV interval with occurrence of an atrial event;

sensing for ventricular activity during the AV interval;

delivering ventricular pacing upon the expiration of the AV interval absent sensed ventricular activity;

updating the value for CL based upon current heart rate; and

recalculating EMSs, EMSP, SAVmax, and PAVmax for a subsequent cardiac cycle based upon the updated CL.

16. The method of claim 15, further comprising:

initializing a SAVnorm parameter having a duration less than SAVmax and a PAVnorm parameter having a duration less than PAVmax;

determining if the CL is greater than an activities of daily living (ADL) rate, wherein the ADL rate is a value between a lower rate of the device and an upper rate of the device; and

setting the AV interval to SAVnorm and PAVnorm if the CL is greater than the ADL rate.

17. The method of claim 16, further comprising setting the AV interval to SAVmax and PAVmax if the CL is equal to or less than the ADL rate.

18. The method of claim 16, wherein determining if the CL is greater than the ADL rate only occurs in a given cardiac cycle if a ventricular pace is delivered.

19. The method of claim 15, wherein SAVnorm=MNV+IAEMDs−

PSO−

IVD and PAV norm=MNV+IAEMDp−

IVD were MNV is a mean normal value for left side mechanical delay.

20. The method of claim 19, wherein P is about 0.22 and MNV is about 85 ms.

21. The method of claim 16, further comprising:

performing an intrinsic conduction check at periodic intervals while the CL is greater than then ADL rate by setting the AV interval to SAVmax and PAVmax from SAVnorm and PAVnorm for at least one cardiac cycle.

22. The method of claim 21, wherein the periodic intervals between conduction check increase in duration between subsequent conduction checks.