Leadless pacemaker system

1. A system comprising:

a ventricular pacing device configured for implantation entirely within a ventricle of a heart, the ventricular pacing device configured to sense intrinsic ventricular depolarizations and one of:

inhibit delivery of pacing pulses responsive to sensed intrinsic ventricular depolarizations; or

deliver pacing pulses to the ventricle responsive to an absence of sensed intrinsic ventricular depolarizations; and

an atrial pacing device configured for implantation entirely within an atrium of the heart, the atrial pacing device being operable without receiving communication from the ventricular pacing device and being configured to:

detect ventricular activation events; and

deliver pacing pulses to the atrium, each pacing pulse of the pacing pulses being timed based on when respective ventricular activation events are detected by the atrial pacing device.

2. The system of claim 1 , wherein the ventricular activation event arises due to one of an intrinsic ventricular depolarization or a paced ventricular event.

3. The system of claim 1 , wherein the atrial pacing device is operable without a communication link between the atrial pacing device and the ventricular pacing device.

4. A system comprising:

a ventricular pacing device configured for implantation within a ventricle of a heart, the ventricular pacing device configured to sense intrinsic ventricular depolarizations and one of:

inhibit delivery of pacing pulses responsive to sensed intrinsic ventricular depolarizations; or

deliver pacing pulses to the ventricle responsive to an absence of sensed intrinsic ventricular depolarizations; and

an atrial pacing device configured for implantation within an atrium of the heart, the atrial pacing device being operable without receiving communication from the ventricular pacing device and being configured to:

detect ventricular activation events; and

deliver pacing pulses to the atrium, each pacing pulse of the pacing pulses being timed based on when respective ventricular activation events are detected by the atrial pacing device;

wherein the atrial pacing device is configured to deliver pacing pulses at an atrial pacing rate, and wherein the ventricular pacing device is configured to deliver pacing pulses at a ventricular pacing rate that is less than the atrial pacing rate.

5. The system of claim 4 , wherein the ventricular pacing device is configured to detect intrinsic ventricular depolarizations and inhibit the delivery of a pacing pulse to the ventricle upon detection of an intrinsic ventricular depolarization, wherein the ventricular pacing rate is set such that the ventricular pacing device delivers pacing pulses to the ventricle when atrioventricular (AV) block in the heart prevents intrinsic ventricular depolarizations being precipitated by atrial depolarizations.

6. A system comprising:

a ventricular pacing device configured for implantation within a ventricle of a heart, the ventricular pacing device configured to sense intrinsic ventricular depolarizations and one of:

inhibit delivery of pacing pulses responsive to sensed intrinsic ventricular depolarizations; or

deliver pacing pulses to the ventricle responsive to an absence of sensed intrinsic ventricular depolarizations; and

an atrial pacing device configured for implantation within an atrium of the heart, the atrial pacing device being operable without receiving communication from the ventricular pacing device and being configured to:

detect ventricular activation events; and

deliver pacing pulses to the atrium, each pacing pulse of the pacing pulses being timed based on when respective ventricular activation events are detected by the atrial pacing device;

wherein the atrial pacing device is configured to:

determine a length of an interval between a ventricular activation event of the ventricular activation events and a respective previous atrial event;

schedule a time at which to deliver a pacing pulse of the pacing pulses to the atrium based on the length of the interval; and

control the delivery of the pacing pulse of the pacing pulses at the scheduled time.

7. The system of claim 6 , wherein the atrial pacing device is configured to:

sense ventricular electrical activity; and

detect the ventricular activation events by detecting the ventricular electrical activity.

8. The system of claim 7 , wherein the ventricular electrical activity comprises a far-field R-wave.

9. The system of claim 6 , wherein the atrial pacing device includes a sensor that generates signals that indicate mechanical cardiac characteristics, and wherein the atrial pacing device is configured to detect contraction of the ventricle based on the generated signals.

10. A method comprising:

sensing intrinsic ventricular depolarizations of a ventricle of a heart using a ventricular pacing device configured for implantation within the ventricle;

delivering pacing pulses to the ventricle of the heart using the ventricular pacing device responsive to an absence of the sensed intrinsic ventricular depolarizations;

detecting ventricular activation events using an atrial pacing device that is operable without receiving communication from the ventricular pacing device and configured for implantation entirely within an atrium of the heart; and

delivering, by the atrial pacing device, pacing pulses to the atrium, each pacing pulse of the pacing pulses being timed based on when respective ventricular activation events are detected by the atrial pacing device.

11. The method of claim 10 , wherein the ventricular activation events arise due to one of respective intrinsic ventricular depolarizations or respective paced ventricular events.

12. The method of claim 10 , wherein the atrial pacing device is operable without a communication link between the atrial pacing device and the ventricular pacing device.

13. A method comprising:

sensing intrinsic ventricular depolarizations of a ventricle of a heart using a ventricular pacing device configured for implantation within the ventricle;

delivering pacing pulses to the ventricle of the heart using the ventricular pacing device;

detecting ventricular activation events using an atrial pacing device that is operable without receiving communication from the ventricular pacing device and configured for implantation within an atrium of the heart;

delivering, by the atrial pacing device, pacing pulses to the atrium, each pacing pulse of the pacing pulses being timed based on when respective ventricular activation events are detected by the atrial pacing device;

delivering pacing pulses at an atrial pacing rate using the atrial pacing device; and

delivering pacing pulses at a ventricular pacing rate that is less than the atrial pacing rate using the ventricular pacing device.

14. The method of claim 13 , further comprising inhibiting the delivery of a pacing pulse to the ventricle upon detection of an intrinsic ventricular depolarization, wherein the ventricular pacing rate is set such that pacing pulses are delivered to the ventricle when atrioventricular (AV) block in the heart prevents intrinsic ventricular depolarizations being precipitated by atrial depolarizations.

15. A method comprising:

sensing intrinsic ventricular depolarizations of a ventricle of a heart using a ventricular pacing device configured for implantation within the ventricle;

delivering pacing pulses to the ventricle of the heart using the ventricular pacing device;

detecting ventricular activation events using an atrial pacing device that is operable without receiving communication from the ventricular pacing device and configured for implantation within an atrium of the heart;

delivering, by the atrial pacing device, pacing pulses to the atrium, each pacing pulse of the pacing pulses being timed based on when the ventricular activation events are detected by the atrial pacing device;

delivering pacing pulses at an atrial pacing rate using the atrial pacing device;

delivering pacing pulses at a ventricular pacing rate that is less than the atrial pacing rate using the ventricular pacing device;

determining a length of an interval between a ventricular activation event of the ventricular activation events and a respective previous atrial event;

scheduling a time at which to deliver a pacing pulse of the pacing pulses to the atrium based on the length of the interval; and

controlling the delivery of the pacing pulse of the pacing pulses at the scheduled time.

16. The method of claim 15 , further comprising:

sensing ventricular electrical activity; and

detecting the ventricular activation events by detecting the ventricular electrical activity.

17. The method of claim 16 , wherein the ventricular electrical activity comprises a far-field R-wave.

18. The method of claim 15 , further comprising:

generating signals that indicate mechanical cardiac characteristics; and

detecting contraction of the ventricle based on the generated signals.

19. A system comprising:

a first pacing device configured for implantation entirely within a first chamber of a heart, the first pacing device configured to sense intrinsic depolarizations of the first chamber of the heart and one of:

inhibit delivery of pacing pulses responsive to sensed intrinsic depolarizations of the heart; or

deliver pacing pulses to the heart responsive to an absence of sensed intrinsic depolarizations of the heart; and

a second pacing device configured for implantation entirely within a second chamber of the heart, the second pacing device being operable without a communication link between the first pacing device and the second pacing device, wherein the second pacing device is configured to deliver pacing pulses to the heart timed based on when respective events, from a chamber of the heart different from the second chamber, are detected by the second pacing device.

20. The system of claim 19 , wherein the second pacing device is configured to deliver pacing pulses at a second pacing rate, and wherein the first pacing device is configured to deliver pacing pulses at a first pacing rate that is less than the second pacing rate.

21. The system of claim 20 , wherein the first pacing device is configured to detect intrinsic ventricular depolarizations and inhibit the delivery of a pacing pulse to the ventricle upon detection of an intrinsic ventricular depolarization, wherein the first pacing rate is set such that the first pacing device delivers pacing pulses to the ventricle when atrioventricular (AV) block in the heart prevents intrinsic ventricular depolarizations being precipitated by atrial depolarizations.

22. The system of claim 19 , wherein the second pacing device is configured to:

determine a length of an interval between an event of the respective events detected from the chamber different from the second chamber of the heart and a respective previous event detected from the second chamber of the heart;

schedule a time at which to deliver a pacing pulse to the second chamber based on the length of the interval; and

control the delivery of the pacing pulse of the pacing pulses at the scheduled time.

23. The system of claim 22 , wherein the second pacing device is configured to:

sense ventricular electrical activity; and

detect the respective events from the chamber different from the second chamber by detecting the ventricular electrical activity.

24. The system of claim 23 , wherein the ventricular electrical activity comprises a far-field R-wave.

25. The system of claim 19 , wherein:

the first chamber of the heart comprises a ventricle of the heart,

the second chamber of the heart comprises an atrium of the heart, the first pacing device is a ventricular pacing device configured for implantation within the ventricle of the heart, and the second pacing device is configured for implantation within the atrium of the heart.