Capture threshold measurement for selection of pacing vector

1. A method for facilitating selection of a vector from among a plurality of pacing vectors for pacing a first chamber of a heart, the method comprising:

delivering a pacing pulse to capture a first heart chamber using a combination of electrodes comprising at least a first electrode and a second electrode of the plurality of pacing vectors;

determining a first time interval between the pacing pulse and a sensed event in a second heart chamber;

determining a capture detection window in response to the determined first time interval;

iteratively decreasing a pacing pulse magnitude delivered in the first heart chamber until an event in the second heart chamber is not sensed during the determined capture detection window;

lengthening the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window; and

detecting a change in capturing electrodes of the combination of electrodes in response to sensing an event in the second heart chamber during the lengthened capture detection window after not sensing an event in the second heart chamber during the determined capture detection window.

2. The method of claim 1 , further comprising lengthening the capture detection window by starting the lengthened capture detection window earlier than the determined capture detection window.

3. The method of claim 2 , further comprising:

responsive to sensing the event in the second heart chamber during the lengthened capture detection window, determining a second time interval between a pacing pulse delivered to the first heart chamber and the sensed event in the second heart chamber;

determining a second capture detection window in response to the second determined time interval, the second capture detection window spanning a different time interval than the first capture detection interval; and

iteratively decreasing a pacing pulse magnitude until an event in the second heart chamber is not sensed during the second capture detection window.

4. The method of claim 1 , further comprising:

determining a cardiac interval between a first event other than the pacing pulse delivered to capture the first heart chamber and an intrinsic event sensed in the second heart chamber;

determining an expected intrinsic event time interval in response to the sensed intrinsic event; and

determining a pacing interval for delivering pacing pulses in the first heart chamber in response to the determined first time interval between the pacing pulse and a sensed event in a second heart chamber and the expected intrinsic event time interval.

5. The method of claim 4 , further comprising lengthening the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window.

6. The method of claim 5 , wherein lengthening the capture detection window comprises decreasing the determined pacing interval to a second pacing interval shorter than the first pacing interval.

7. The method of claim 1 , wherein iteratively decreasing the pacing pulse magnitude comprises delivering pacing pulses in the first heart chamber at a ventricular overdrive pacing interval.

8. The method of claim 7 further comprising determining a maximum ventricular overdrive pacing interval that allows the capture detection window to expire prior to an expected intrinsic event in the second heart chamber.

9. The method of claim 1 , wherein iteratively decreasing the pacing pulse magnitude comprises delivering pacing pulses in the first heart chamber at an atrial-ventricular pacing interval.

10. The method of claim 1 , further comprising:

lengthening the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window;

determining a second capture detection window in response to sensing a depolarization of the second heart chamber during the lengthened capture detection window; and

recording a capture threshold for each of the plurality of pacing vectors corresponding to a minimum pacing pulse magnitude resulting in a depolarization of the second heart chamber being sensed in one of the first capture detection window and the second capture detection window.

11. The method of claim 1 , wherein the detected change in capturing electrodes is detected as the pacing pulse magnitude is iteratively decreased and comprises a loss of capture at one of the first electrode and the second electrode and capture at the other of the first electrode and the second electrode.

12. A medical device for facilitating selection of a pacing vector from among a plurality of pacing vectors for pacing a first chamber of a heart, the device comprising:

a plurality of electrodes;

a signal generator coupled to the plurality of electrodes for delivering pacing pulses to a patient's heart;

a sensing module coupled to the plurality of electrodes for sensing cardiac event signals; and

a capture detection module coupled to the signal generator and the sensing module and configured to:

control the signal generator to deliver a pacing pulse to capture a first heart chamber using a combination of electrodes comprising at least a first electrode and a second electrode of the plurality of pacing vectors;

determine a first time interval between the pacing pulse and a sensed event in a second heart chamber;

determine a capture detection window in response to the determined first time interval;

iteratively decrease a pacing pulse magnitude delivered in the first heart chamber until an event in the second heart chamber is not sensed during the determined capture detection window;

lengthening the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window; and

detecting a change in capturing electrodes of the combination of electrodes in response to sensing an event in the second heart chamber during the lengthened capture detection window after not sensing an event in the second heart chamber during the determined capture detection window.

13. The device of claim 12 , wherein the capture detection module is further configured to lengthen the capture detection window by starting the lengthened capture detection window earlier than the determined capture detection window.

14. The device of claim 13 , wherein the capture detection module is further configured to:

responsive to sensing the event in the second heart chamber during the lengthened capture detection window, determine a second time interval between a pacing pulse delivered to the first heart chamber and the sensed event in the second heart chamber;

determine a second capture detection window in response to the second determined time interval, the second capture detection window spanning a different time interval than the first capture detection interval; and

iteratively decrease a pacing pulse magnitude until an event in the second heart chamber is not sensed during the second capture detection window.

15. The device of claim 12 , wherein the capture detection module is further configured to:

determine a cardiac interval between a first event other than the pacing pulse delivered to capture the first heart chamber and an intrinsic event sensed in the second heart chamber;

determine an expected intrinsic event time interval in response to the sensed intrinsic event; and

determine a pacing interval for delivering pacing pulses in the first heart chamber in response to the determined first time interval between the pacing pulse and a sensed event in a second heart chamber and the expected intrinsic event time interval.

16. The device of claim 15 , wherein the capture detection module is further configured to lengthen the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window.

17. The device of claim 16 wherein lengthening the capture detection window comprises decreasing the determined pacing interval to a second pacing interval shorter than the first pacing interval.

18. The device of claim 12 , wherein the capture detection module is further configured to iteratively decrease the pacing pulse magnitude in the first heart chamber at a ventricular overdrive pacing interval.

19. The device of claim 18 , wherein the capture detection module is further configured to determine a maximum ventricular overdrive pacing interval that allows the capture detection window to expire prior to an expected intrinsic event in the second heart chamber.

20. The device of claim 12 , wherein the capture detection module is further configured to iteratively decrease the pacing pulse magnitude in the first heart chamber at an atrial-ventricular pacing interval.

21. The device of claim 12 , wherein the capture detection module is further configured to:

lengthen the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window;

determine a second capture detection window in response to sensing a depolarization of the second heart chamber during the lengthened capture detection window; and

record a capture threshold for each of the plurality of pacing vectors corresponding to a minimum pacing pulse magnitude resulting in a depolarization of the second heart chamber being sensed in one of the first capture detection window and the second capture detection window.

22. A non-transitory, computer-readable storage medium comprising instructions that, when executed by a processor, cause the processor to:

control a signal generator to deliver a pacing pulse to capture a first heart chamber using a combination of electrodes comprising at least a first electrode and a second electrode of a plurality of pacing vectors;

determine a first time interval between the pacing pulse and a sensed event in a second heart chamber;

determine a capture detection window in response to the determined first time interval; and

enable a capture detection module to iteratively decrease a pacing pulse magnitude delivered in the first heart chamber until an event in the second heart chamber is not sensed during the determined capture detection window;

lengthen the capture detection window in response to a depolarization of the second heart chamber not being sensed during the determined capture detection window; and

detect a change in capturing electrodes of the combination of electrodes in response to sensing an event in the second heart chamber during the lengthened capture detection window after not sensing an event in the second heart chamber during the capture detection window.