Adaptive cardiac resynchronization therapy

1. A system for delivering cardiac resynchronization therapy, the system comprising:

a pacing device configured for implantation within a patient, the pacing device comprising:

a plurality of electrodes;

signal generation circuitry configured to deliver ventricular pacing via the plurality of electrodes; and

a sensor configured to produce a signal that indicates mechanical activity of the heart; and

processing circuitry configured to:

identify one or more features of a cardiac contraction within the signal;

determine whether the cardiac contraction is a fusion beat based on the one or more features; and

control a timing interval for delivery of the ventricular pacing based on the determination; and

wherein the system further comprises another implantable medical device, wherein the other implantable medical device is configured to:

detect the at least one of an atrial event or a ventricular event; and

transmit a signal to the pacing device to control the pacing device to deliver the ventricular pacing pulse in response to the detection of the at least one of the atrial event or the ventricular event.

2. The system of claim 1 , wherein the pacing device comprises a housing configured for implantation on or within the heart, wherein at least one of the signal generation circuitry and the sensor are within the housing.

3. The system of claim 1 , wherein the sensor comprises a three-dimensional accelerometer.

4. The system of claim 1 , wherein the processing circuitry comprises processing circuitry of the other implantable medical device.

5. The system of claim 1 , wherein the other implantable medical device is configured to detect atrial fibrillation, and the processing circuitry is, in response to the detection of atrial fibrillation, configured to: identify the one or more features of the cardiac contraction, determine whether the cardiac contraction is a fusion beat based on the one or more features, and control the timing interval for delivery of the ventricular pacing.

6. The system of claim 1 , wherein the processing circuitry comprises processing circuitry within the pacing device.

7. A method for delivering cardiac resynchronization therapy by a pacing device, the method comprising, by processing circuitry of a medical device system comprising the pacing device:

receiving a signal from a sensor of the pacing device, the signal indicating mechanical activity of a heart;

identifying one or more features of a cardiac contraction within the signal;

determining whether the cardiac contraction is a fusion beat based on the one or more features; and

controlling a timing interval for delivery of ventricular pacing by the pacing device based on the determination;

wherein the method further employs another implantable medical device and wherein the other implantable medical device detects at least one of an atrial event or a ventricular event and transmits a signal to the pacing device to control the pacing device to deliver the ventricular pacing pulse in response to the detection of the at least one of the atrial event or the ventricular event.

8. The method of claim 7 , wherein the sensor comprises a three-dimensional accelerometer.

9. The method of claim 7 , wherein the processing circuitry of the medical device system comprises processing circuitry within the other device.

10. The method of claim 7 , wherein the other implantable medical device is configured to detect atrial fibrillation, and wherein steps to identify the one or more features of the cardiac contraction, to determine whether the cardiac contraction is a fusion beat based on the one or more features, and to control the timing interval for delivery of the ventricular pacing are performed in response to the detection of atrial fibrillation.

11. The method of claim 7 , wherein the processing circuitry of the medical device system comprises processing circuitry within the pacing device.